if manufacturers were to drop their BS, they'd still manufacture both light and heavy wheels and market each for their respective uses: lighter wheels for rides that consist of a lot of ac/decelerations (in crits and MTB) and heavier wheels for rides that need maintaining constant speeds (time trials, velodromes, downhills).
To isolate the aerodynamic effects, and test the effects of different rotational inertias, you need to compare various weights with the same aerodynamic section, i.e. add weight to an aero wheel and evaluate. I suspect a lot of the acceleration effects were ignored, for example when climbing the angular velocity of the crankset varies depending on the grade and cadence through the pedal stroke. Likewise angular acceleration in cornering was probably ignored. Higher rotational mass also results in greater friction losses in bearings and rolling resistance between the tire and pavement.
Engineer here: I love the explanation, the flywheel storing energy is exactly why the 'total system' does not change, but the feel could be different. (also, see KERS system in F1) But to be honest, this comment section is going to be more entertaining than the video in the long run. Cheers for trying to bring science to a group of stubborn cyclists!
Engineer here too! He's entirely correct, rotating vs static mass makes no differences at all. The change in energy is the same. I'm not sure why so many people are struggling to accept it.
@@benstanden8784 In a lab, a computermodel or a TT on a velodrome this is correct and easy to accept but in the real world of cycling a lighter pair of rims and tires makes a noticeable difference ( and no it's not just a placebo-effect ).
@@benstanden8784 MacDonalds drive thru guy here with an associates degree in applied water color art....I too can't believe people are struggling with a physics concept explained only using words by an engineer! Come on. I'm not sure either one of you engineers said anything that would help people understand. A lighter wheel is going to require less energy to get up to speed after every corner which will be easier on the rider. What would be the ideal application of light wheels? Cyclocross, lots of heavy braking and hard accelerations.
It absolutely makes sense. You can easily feel when the lighter wheel is easier to accelerate from the start, but it's nearly impossible to FEEL when the wheel maintain momentum better. Thus riders demand lighter wheels, and the industry just responds to this.
Looks like science is getting in the way of common sense! Marketeers are having a field day convincing people they've got the wrong equipment and should buy the latest expensive fad products.
Did the same. I wasn't an overweight guy, well within the normal bmi window, but still could loose almost 9 kilograms (84.6->75.4 and still counting), and streched for months to be able to get a spacer lower at the cockpit. Same bike, total different experience. I spend money on very high quality food and consume it responsibly, than put my money on x percent stiffer, x percent more aero bullshit. On long TT like strava segments, climbs, short sprint segments, everywhere I am faster by quite a margin. Previous best FTP was for me 3,84 w/kg, now 4.05 and I really feel I could achieve around 4.2 with winter training. Ohh and I was really into buying some Swissside wheels, but this guy talked so much BS, they lost me as customer.
He is actually correct for the most part. Unless the ride requires constant changes of speed, no energy is lost, but the bike is less responsive.. and you need higher spikes of energy to keep up with constant changes of speed. And that is key. Over broken terrain with suspension it is crucial that the suspended weight is as low as possible (not the case here). I think he is being sincere, dt swiss interest would be in saying that rotating speed is crucial.
I'd love to see this analysis applied to the typical cross-town excursion where you are constantly accelerating and decelerating. It's obviously negligible on an uphill ride with no stops, but I still assume that rotational mass has a very significant effect on a typical bike commute.
They explored that scenario with the criterium: 0.7 seconds over 1h race, that is your answer (12:00). On a bike commute across a town I don't know how much more you brake to make it "very significant"
XC and Enduro mountainbiking are probably the best examples of constant acceleration and deceleration combined with steep gradients. Lightweight wheels are valued there, but nobody goes overboard with their wheels. With both mountainbiking and commuting, comfort and durability seem far more important to me.
@@StefanoLinguanotto The crit models a closed course where braking only occurs 2% of the time. They're probably not coming to a full stop during any of that braking either. Wouldn't be surprised if typical city riding involves braking 20+% of the time with 100+% more energy loss per braking event.
I work in numerical simulation of complex systems. There's a saying "...all simulations are wrong, some are useful". I think that although the math may say there's zero point to lightweight wheels unless you're going uphill, I bet almost everyone notices the extra work to get up to speed with heavy wheels. Light wheels will help you perform better even though it does not matter to the wheel!
Light wheels accelerate faster, but do not help you stay there as well as heavier wheels. Light wheels spin down faster (i.e. lose inertia faster), as he addressed. Most people don't pay attention to that side of it. Said another way - you have to keep reapplying energy to the system in both cases, with light wheels it must be bursty, with heavier wheels it is more consistent. The energy quantity is the same, but the latter is easier to sustain.
I'd love to see a blind test. I agree on the statement on simulations, but something that can be trusted even less is trusting the feeling of people. 300g of wheel weight matters as much as 600g of the frame or rider (or less, depending on where on the wheel the weight is added), but you rarely hear: "My bike feels so much faster without the bottles", while "wow, the lighter wheels really help" seems common..
The point made in this video seems to have been missed by a loud minority. The argument is that if you buy a heavier, more aero wheel to replace a lighter, less aero wheel you'll go faster in almost all ride and race situations. Which has been demonstrated by real world data AND sophisticated models. Models which are valid. If they weren't your racing team looks like Ferrari, and not Mercedes. A heavier wheel ALL ELSE BEING EQUAL is slower in almost all situations. Yes. But a wheel that is heavier BECAUSE its 60 mm deeper, will only be faster because AEROGAINZ beats WEIGHTWEENIEZ by a large margin. And as a general point to those saying "the bike industry is pseudoscience and all BS": you can ride that 1980s steel bike with box section rims if you want, they look cool, but times change, technology improves, the rest of us will go faster, more comfortably and mug you off with out trying. Some things the industry may get wrong, or go down a particular route and find some success (weight), only to find another route offers more gains (aero) that have a bigger effect that may counter the first route. That's how research goes. There has been a huge focus on weight, now people are realising how damn important aero is.
@Paul Wieringa He has literally done the maths. These points were addressed in the video. Enve 7.8s or Mavic Open Pros. Every criterium rider is choosing the 7.8s even though they're heavier. The time saved from the aero efficiency outweighs the extra weight. I will always listen to one qualified guy who is a genuine expert and who has worked for 14 years as a lead engineer and done the maths on it, and has a validated model over a group who think they know better with next to no experience. Though you all have a large amount of confidence, your position on the Dunning-Kruger curve is almost certainly on the left, not the right. Take up his invitation, go out and try for yourself. Do an experiment. You may be surprised.
I think you make perfect sense. But if the video wants to claim what you are saying, then the title of the video and other aspects of rhetoric are completely misleading. You have two important factors (assuming all else are equal) -- aero and rotational mass. In many settings, the former is simply MORE important WITHIN LIGHTEST CARBON RIM wheel category. "Rotational mass does not matter" to describe this is a worst possible pseudoscientific propaganda I can think of. It sounds similar to justifying your business saying the cost is zero, when in fact your sales barely exceeded the large cost. They should have said rotational mass does not matter "as much as you have thought it would".
So lighter wheels are easier to pedal up to speed, but heavier wheels carry the inertia longer, so they don't slow down as fast? I love the feel of responsive acceleration though, so I'm keeping my lightweight wheels.
The problem in their experiment is that they've traded weight benefits for aero benefits. That isn't isolating the weight difference. The proper experiment would have been done using two alloy box rims where one was a lightweight race wheel with a really light rim, and the other one was a heavy wheel with a heavy rim....no aero benefits. This would give a better measure of whether rotating weight made any difference.
This begs the question on whether to achieve "the most responsive acceleration" you would be better off spending a couple thousand $ on lighter wheels or spending the same money achieving greater weight loss on other (non-rotating) bike components?
@@kingonthehill7 When accelerating on the flats, saving weight from the rim/tyres has twice the effect of saving weight from elsewhere. Buying 100 g lighter *rims* (or tyres) is better value than saving 150 g from the groupset. But ONLY in accelerations on flat roads. For climbing and even riding along at a steady speed on a flat road, saving 150 g anywhere is better than saving 100 g from wheels. Moreover, the difference in acceleration from rotating weight is *absolutely tiny*. You could have any number of bike journalists doing 'blind' tests with a wheelset that's 500 g heavier, and they wouldn't be able to guess any better than random chance.
@@chrisgilligan4968 They make that distinction in their time saving measurements. Isolating just the inertial time savings vs. just the aero time savings.
A heavier wheel (or flywheel) will require more energy to accelerate it to a given speed in an equal time, if you then allow that flywheel to spin down to zero, the energy conserved and time it takes will have a direct correlation to the energy put into the system at the beginning, so a heavier flywheel will spin longer after being accelerated to a given rotational speed.However, his example of only being on the brakes in a crit for 2% of the time implies that it is the time spent braking relative to the rest that matters, which is not the important part. Its the amount of energy you lose in the braking, a heavier flywheel will require more braking force to go from 100 rpm to 50 rpm, or 40 to 20 km/h, more braking equals more energy lost. You will then have to reintroduce that energy back into the system to accelerate to 40 km/h again, starting the cycle again.
He also assumes a perfect stroke, which is far from true. Fluctuations in energy disposed into the wheel differ a lot. And that hack picked triangle shaped wheels to gauge against aero profile ones to supposedly make a point about weight…
Well yes, but the overall picture won't actually be much different. Certainly not to swing a circa 20 second difference. No offence but this guy has worked for Sauber F1, I think I'll take his thoughts over yours (genuinely, no offence intended).
Steering is also largely affected by a heavier mass. I used to have a shop customer hold a heavier then a lighter wheel by the axle while I gave em a spin, then try and steer them. Priceless😉
I was about to make a similar comment; I rode lightweight shallow AL wheels for 5 years then finally upgraded to a set of 55cm carbon wheels. on paper they weighed basically the same, but the carbon wheels felt really skittish on fast descents. Something i had to get used to. Not sure if having more of the weight brought closer to the center of the wheel caused this, or something else. But it definitely felt less stable on fast descents compared to my old shallow AL wheels.
Yes but in real life you are not steering by the axle, which is like 12 cm, but by the handlebars, which is 44 cm. So the question is - would the customer be able to tell the difference if you let him steer by the handlebars? Probably not.
It would be cool to see gcn make a video actually comparing adding weights of the wheels versus adding weights to the whole system on non-rotating weights.
Agreed - and also make both sets box alloy rims...one with heavier rims, and one with lighter rims...ideally on exactly the same hubs if we're totally trying to isolate the effect of rotating weight.
@@chrisgilligan4968 Totally agree, test it. Use the same wheels and tyres. Add weight to one set of wheels, this can be as simple as changing the inner tube with slime filled and test the wheels using a power meter. Do different tests, acceleration, braking, TT, hill climb, race, crits, commuting in traffic, road, gravel MTB. You can use different levels of riders. Love to know the results.
xseamusmcx have you tried spinning your wheels and then leaving them to slow down on their own - where does the valve end up? Always at the bottom! Apparently some wheels try to balance the valve, but suspect most don’t. You can find videos that show the oscillation effect of the imbalance too
Those engineers have apparently never ridden a 10 lap crit race with 5 sharp corners where you have to slow down to 20 km/h and accelerate again to 50 km/h 5 times a lap! In the second half of the race you'll have a lot of trouble of closing the gap each time to the opponent whose rims and tires ( rotational weight ) are 400 grams lighter than yours. Your legs will blow up after 25 accelerations and you'll "loose the wheel" of the last rider of the peloton, game over! A bike with a set of light ( tubular ) tires and rims will feel much livelier than deep section alu rims for example which you will benefit from on a climb as well. Just like my sportscar is a lot more enjoyable to drive with the lighter summer wheels ( and a lightweight flywheel ). I agree with the theory for a time trial but reality differs a lot from the mathematics in the lab. So I suggest you compare two 8 kg bikes with 40 mm deep rims ( one alu, one carbon ) in a blind test and ask a few dozen experienced riders their opinion about the one they would prefer and why they would prefer it. That's practical and useful science imo.
I completely agree with you. I was so stunned at the performance of lighter wheels on my road bike that I - like you - went further, and specifically bought same-diameter, but nearly 10-pounds lighter per wheel, wheels for my truck. 0 to 35 MPH, only someone who knew the truck really well would notice the difference. 40 to 60 MPH - the difference was obvious and large. 60 to 90 MPH the difference was huge - much faster / better acceleration, and I was saving gas to boot (when driving sanely).
I was thinking about those > 40km/h corners where you don't have to brake, totally have to rely on your tire grip and can't peddle for multiple seconds. (90% of crit corners). Heavier wheels means higher exit speed, because of the stored energy and therefore less acceleration is needed.
@@sebastiaansiemensma I don't consider this corners but just a bend in the course. In Belgium most laps of a 65 km race contain at least 4 corners each lap where even the frontriders have to slow down to 25 km/h. After the turn they speed up to 50 km/h to make the other riders suffer. And on the straight you often need to accelerate suddenly to be sure to get in the breakaway.
@@sebastiaansiemensma Do they mean a higher exit speed? I could be wrong, but it seems that the entry speed seems limited by tire grip for how hard one is able to go in to the corner. Tire grip being a limitation, it means one has to slow for the corner to (what I believe) would be the same speed for a lighter or heavier wheel, but then the lighter wheel will win out when it comes to bumping that speed back up from that given traction-limit-speed for the given corner.
I can see the benefit of heavier wheels on rolling terrain where the inertia effect means you can maintain a constant speed with less acceleration. Acceleration is where the energy is expended. With more inertia you put in the effect at the start to spin up the flywheel, then recover and maintain a constant speed with little acceleration. But if you must decelerate and lose that inertia then you will expend more energy when you have to accelerate again. Pretty soon you are over your threshold and slow right down. I've done a few accelerate, brake, accelerate crits and it takes it out of you. If you have heavier wheels and cannot accelerate to stay on someones wheel then your aero really suffers - far more than the difference between deep and shallow rims. If you drop off the back you are done for.
Constant speed and zero acceleration is the fallacy that needs to be kicked into touch. If you can read power meter data and understand how power meters work you will realise that the wheel is constantly being accelerated
@@MP48 I suppose there is always wind resistance and gradients to overcome. And rolling resistance, bearing friction. And you pointed out power delivery during the pedal stroke. I notice when climbing steep gradients on light wheels it is like climbing stairs. Left foot down I move forward then stop, right foot down forward and stop. Better technique would help but if the gradient is very steep then it's out of the saddle and I don't know how you would smooth the pedal stroke when out of the saddle.
That was my thinking..the drafting effect didnt seem to be part of the calculation that you can do or not do with lighter/heavier wheels..if you can or cant follow someones wheel..
Makes 0 practical difference. The inertia contained in a rotating bike wheel is essentially 0 when compared to system mass and energy requirements. Go ahead and spin a wheel up to 40KPH on the work stand, then just grab it with your hand- it will stop almost instantly (wear a glove).
Rotational weight is affecting due to change of inertia and thus the added difficulty in the change of angular momentum the acceleration. For that reason it's harder to accelerate fast and may be fatigueing over the course of race with lot's of sprints. It's also very important to take into to account that the rotational weight of a aero wheel is distributed closer to the centre and thus the inertia of a the aero wheel will be smaller in comparison to a low rim profile wheel with the same weight. All of this has to do with the torque, witch the rider has to apply. In a race with lot's of accelerations it can be very power demanding to keep up with riders with lighter wheels. But it's very clear that aerodynamic advantages are more important over the whole course. And taking into account that the weight defences are very little (400gr) it's clear that the impact will be minor.
Nikolas Patelis Agree. I think a good way of thinking on this is race vs recreational: most of us, most of the time, are beginning and ending our rides at the same geographical position, ridning mostly on roads with curves designed for cars at around 50-70kmph. So, most time is spent in a pretty straight-ish line, keeping the speed somewhat constant (depending of course on your specific area, hilly or flat) resulting in the slower climbing will be almost nullified when speed is easier to maintain with that flywheel effect of the heavier wheel (a heavier rider such as myself has a similar experience when rolling besides his fitter and slimmer mattes 😃). The aero is playing the main role over 20-22kmph regarding rolling resistance and I would think it also dominates regarding regular rides in most cases. Races and such are different, geography, acceleration and climbs may, when combined, start to make weight a but more important factor.
If ever you lose a wheel because you could not accelerate in time to maintain the much bigger areo advantage of staying behind someone or the pack, then you only get to use that areo advantage in then wasted every to chase the pack or person that dropped you.
This is incredible. The fundamental premise here is that if you don't accelerate weight in the wheels doesn't matter. You have to constantly accelerate on a bike. Your bike is naturally decelerating all the time if you do nothing. Ride on the flat, don't pedal, you will eventually stop (due to wind resistance and mechanical friction). Ride up a hill, don't pedal, you will stop, usually a bit quicker (due to air resistance, mechanical friction and gravity). The watts you put into the bike are a force of acceleration against the deceleration forces of air, friction and gravity. Put in more watts you will speed up until you equal wind resistance, friction and gravity, put in less watts you will slow down until you equal wind resistance, friction and gravity, put in zero watts and you stop. More energy (watts) is required to accelerate 1 gram at the rim of a wheel compared to 1 gram on the frame due the laws of angular momentum, more easily descibed as leverage. Like a see-saw the further from the pivot point you are the harder it is to move you. So rotating weight is more important than non rotating weight. Notice how all Jean-Paul Ballard's comments are about his models. There is no real world data here and I am sure his models are basically wrong. And so is he along with the title of this video.
Whats interesting is that in crit racing or any racing, there are 2 big scenarios where it matters and where it would be nice to see the difference. First obviously are finish line sprints. Second is, whats not to be forgotten, is when someone attemps a breakaway you have to stay on his wheel to be in the slipstream. The slower you accelerate the more likely it is you loose the slipstream and thus cannot follow or loose too much energy for catching up into the slipstream.
I feel they also used a fixed crit as the example and fixed crits have a much more consistent speed than other crits as no one can brake and have to go into a corner slower so there would be less “braking” therefore less energy lost.
@@joeadlam-cook2769 judging by the video, they used a circuit race at a motor racing track around an old airfield. I’ve raced there too - it’s fast, wide and you should never have to brake. The only things that slow you down are the bloody headwinds and the occasional crash.
Yes. It's about the gaps--either accelerating to create one and force the person behind you to overcome all the air resistance themselves, or accelerating to prevent yourself from being gapped. Everything he's saying about the flywheel effect is true, but it's not the only consideration in the crit scenario.
Exactly! In addition to your settings, you can very easily drop out of the peloton not being responsive enough. I can understand how a "F1" engineer not too familiar with cycling comes up with an armchair theory. However, I have absolutely no idea how Ollie simply nods to the absurd explanation by Jean and even goes onto making another video about a stupid experiment on this theme...
You're absolutely right, but even then, simulations show a very low difference in required watts between 200gr on the rims versus 200gr on the frame. The fact remains that both the relative weight of rims versus total system weight and the speeds reached are relatively low. Compare steel versus magnesium rims on a 300kph race car and the results are very different.
Something that is also interesting is that heavier wheels will be harder to lean into a corner. Just take a wheel and spin it in your hand, see how hard it is to turn/lean. Physics teachers (myself included) do this every year, if you decrease the weight or speed it will make it easier to lean which means less arm fatigue which most cyclists should avoid...
This is the type of video that should be on the tech channel...diving deep into the engineering and technical aspect of cycling and giving the viewers a good insight about what is actually happening...this advanced level stuff is really appreciated (at least by me)...for example on the technical side...rather than explaining again and again about how to adjust brakes and gears that are covered in previous videos...new video can be about the effect of b tension screw or derailleur tension spring on gear shifting and how it can be tuned to perfection using that...there must be much more than just a barrel adjuster in indexing of gears on the advance level... please make videos like these...and I love Ollie's presentation of the techy things( obviously jon as well)....
You should check out the Park Tool channel for that sort of thing. Calvin Jones is a particularly good presenter on their channel - especially on derailleurs.
Going uphill requires constant acceleration in order to counter constant deceleration due to gravity and elevation gain. Even moving on level ground requires acceleration to overcome friction. Also, rotating mass is always in acceleration because of the constant change in direction (centrifugal forces is mass x acceleration which is taken at tangent to the wheel). If you were not accelerating then no need to pedal. You pedal you accelerate, you don't pedal you decelerate. It is the weight or mass of the wheel that you are pushing to rotate.
Same applies to the overall weight of the bike. Again the energy is only wasted when you use the brakes. Light bikes are overrated unless you only climb steep hills quickly. Where weight really matters is in a constant start stop scenario such as city riding.
Yeah, Gravitational potential energy = mass x force of gravity x height so more mass means more energy either pushing you down a hill or making it harder for you to ride up a hill
I am wondering if 1kg savings on your bike makes the same difference as 1 kg on someone's beerbelly. My knowledge of science tells me that spending thousands of Euro's on the bike for weight savings, you can better skip some McDonalds trips. With the money you save with that you can buy stuff for your bike
Its important to remember that the extra energy put in on a climb due to a heavier bike is only wasted if the brakes are used on the way back down. If only the uphill is timed then obviously light weight is important. A heavier bike when starting a hill climb will go further up the hill before reaching a lower terminal velocity determined by the available power output.
wjeurs once you are reasonably light, however, the bike is the last thing you can take weight from. I shaved 16 seconds off a 12 minute climb to poach a KOM by stashing my bidons in the bushes along a layby at the summit.
I've used heavy wheels and lighter wheels and I can really feel the difference when moving off, but once up to speed the heavier weight wheel does almost drags you up the hill, but I'm guessing that the breaking will impact on corners and that will slow you down overall.
I'll never forget the first time I rode uphill with carbon wheels. It felt almost effortless. Of ccourse it wasn't but that was the sensation, because it was much easier riding uphill than with heavier, alloy wheels (still is).
it's exactly the same with say car/bike engines and flywheels. a lightweight flywheel can make the engine feel revvy and zippy. but if you've got a low power engine you need a decent amount of flywheel mass to keep momentum between power pulses especially on a low cylinder count engine. 2cyl engine opposed crankshaft (same as riders legs) you don't want the flywheel to be so light that it looses speed so fast that engine can't get the piston to the next compression stroke on the other cyl, would make for a very lumpy ride with each power pulse kicking the motorbike.
This has very little to do with cycling, unless you find a rider with an anomalously inefficient pedal stroke. In general, RPMs don't change much throughout a cyclist's pedal stroke. Very, very little throughout the pedal stroke of an experienced cyclist who has worked on high, smooth cadence. However, it does raise a point I was discussing with a tandem rider. The "drivetrain inertia" of a tandem team many feel leads to power output losses. Not sure I agree. However, in my experience, I have noticed that the inertia found in a tandem drivetrain does appear to sap my energy, I've found. When adding power to the pedals on a single (half) bike, the drivetrain responds and the rider and bicycle accelerate together. However, add power to a tandem drivetrain, and you have to overcome your partner's cadence, plus the added weight of the tandem. Result is greater fatigue fighting this increased inertia throughout an entire ride and thousands of pedal strokes.
Ollie, Yes, I've been waiting for this video, thanks! Throughout this discussion, no mention was made of the cyclic nature of power application to and through the pedals through each crank rotation. Maximum power transfer through the pedaling cycle only occurs while the rider is pushing DOWN on the pedals, somewhat augmented by pulling up on the back cycle with the opposite leg. Very little power is transmitted as the pedal(s) is(are) brought through the bottom and over the top. The result of this when climbing and/or riding into a stiff headwind is that EVERY down stroke on the pedals is an acceleration event, gravity and/or wind force counters and negates inertia effects. Observe your own pedaling while climbing @8:27 through 8:38 where each down stroke effort is a distinct effort event. Rolling hills are indeed a special case where, if enough speed can be built prior to the climb and maintained through the climb, inertia is indeed significant. Y'all at GCN are power meter nuts, I suggest you find some software that can record and display power generation peaks/surges and nulls through individual pedal cycles, see if there are or aren't corresponding bike+rider speed surges and lulls while climbing. I suspect you'll find an inertia benefit on gentle grades that diminishes from insignificant to detrimental as the grade increases.
Really interesting and informative. However, I would add that in a criterium the accelerations are crucial parts of the race. If you can accelerate quicker there is more chance of getting away or winning a sprint, it doesn't matter that you have that stored energy once you have crossed the finish line or once you have been caught. You have to put it into context, it isn't just a solo time trial with lots of accelerations in.
Completely agree, the difference might me tiny but the next thing I'd like to know is how much more power you'd have to apply during accelerating out of the corner with lighter (but equally aerodynamic) wheels. These are the most critical moments in a criterium where you potentially spend a lot of energy catching up to the rider in front of you. And I'd like to know how to use the stored energy in corners if you have heavier wheels. Would you ride differently? Would you start softpedaling earlier?
Great point and well put. I would love to see the simulation result on how big the gap difference is in a crit acceleration effort (with 400 gram wheel difference as discussed, not the straw-man 10+ kg some people want to pretend). Are we talking 1 meter plus or 1 cm?
In a criterium you should try to avoid having to accelerate a bunch except for the finish. I often see people grinding too big a gear out of corners, spin those legs
I took my touring bike with 36 spoke wheels for a 220k spin today. About 100k in, an unmarked crater in a forest section (couldn't see it in time to dodge). Must have been 4-5cm deep and 1m across. I was doing 36k an hour and hit it full on. Result? Wheels are as true as ever - no other damage either. This isn't the first time I've done this to these wheels and they have done about 15 thousand km.
@@orsations You call a 1.5 inch deep pothole a crater? ahahahahah what a good joke. Here in the city that's nothing, you can easily get ones that drop down 4-8 inches.
No. This would make the wheels more durable. This is not what the bike industry wants ;-) It prefers to sell you heavier wheels by just carbon fibre in useless places. And for your wheels to brake right after the warranty ended.
Something that wasn't explicitly said but seems relevant is this thought (if I understand it correctly). While you feel the difference (benefit) while you are accelerating (2% of the time or whatever), you don't notice the difference (penalty) spread out evenly over the 98% of the rest of the time when you are not paying attention to the extra work you are putting in to maintain your speed on a lightweight wheel. That would explain the counter-intuitive nature of these findings. Would love to hear any feedback if I misunderstood anything.
You couldn't describe it more precisely! And yes, you understood it 100% correctly, in contrast to everyone else here who says you'll have to pay more energy when you need to attack. That extra energy that you need to spend when accelerating your heavier tires for a sprint is exactly what you save when keeping that speed in contrast to your opponent with lighter tires. The necessary power is higher for accelerating and lower for keeping speed. Energy does not change, except resistance of wind and friction which are in both scenarios equal (given total bike mass is equal and the difference is only weight distribution on/off wheel).
Actually BS what i wrote. Keeping the speed doesn't cost you more or less energy. But you'll save your energy when you need to let your bike roll, e.g. corners, because you maintain your speed longer than with lighter wheels and your opponent with lighter wheel would have to paddle to keep up with your rolling speed.
@flo rian Another thing to keep in mind is that the rider's output is not stable. For non-race scenarios - touring, commuting, utility, etc. - over the course of a ride you gradually get more tired and modify your cadence to fit so you get where you need to go at all, in a reasonable time frame. In a race scenario speed is speed. So for your "average joe", a short 30 minute ride will "feel" better than the last 30 minutes of a 4+ hour ride. With heavier wheels, when the going gets tough you can theoretically optimize yourself by slowing your cadence, making your pedal stroke worse, and not lose as much speed. Reducing your power output while maintaining a higher level of air-cooling! With lighter wheels you'll find that you start slowing considerably, which may make it feel worse and force you to choose between looking for the next hill that will let you coast and stopping for a break. Of course on the flipside, if you have to constantly stop at lights and signs and so on then the heavier wheels will burn you out and make you considerably slower, so it depends on the actual route taken. As well as it not being a simple wheel swap - heavier wheels should mean a lighter frame and so on, which can impact other aspects of ride quality, cost, and durability. If you just swap to heavier wheels from lighter it will make everything harder - hills especially.
Two points come to mind: 1) If you choose the wheels that weigh 400 grams less, you're not adding 400g of static weight somewhere else on the bike. So the lighter wheels in this case DO make a difference. Certainly more than removing your bar tape or sanding the paint off your frame (right Ollie?). 2) Responsiveness during acceleration is important. So it's not just discarding energy through braking that you need to worry about, it's any time there is an increase in speed - especially during attacks, chases, sprints, etc.. Here's an idea for Ollie and @GCN Tech to test in the lab: How much power/energy does it take to accelerate 1) bike with 1600 g wheels, 2) same bike with 1200 g wheels, and 3) same bike with 1200 g wheels + 400g static weight added
Thats a good idea Kent, we should do that test. Although in terms of responsiveness to attacks you balance it out via the benefits of aerodynamics and the rotational momentum elsewhere
Ok so understand the science & math ( I think), but it seems to matter to me! I did the "light" vs "heavy" comparison test a few months ago Mavic Ksyrium SL vs Cosmic Carbon Pro. Whilst the overall time for my "fixed" route was about the same there were areas of decernable differences. On the steep climbs the Ksyriums were quicker, on the flat and especially the long descents the Cosmics were quicker. I also detected the "flywheel" effect of the Cosmics on the undulations of the road (not enough to call a climb!). So the question is why the Ksyriums are faster on climbs ... my thinking is that because I don't produce great power numbers and my cadence will drop on a 14% + climb, that with each pedal stroke I'm having to re-accelerate "the system" and that's hard work for me with "heavy" rims.
It matters when you take into account the sponsor, this years marketing agenda for said sponsor, and the test designed to achieve the desired marketable results. Then it all makes sense. It seems to me that the goal of the cycling industry at the moment is to make everything non-compatible so that the brand you pick (the brand that spent the most on marketing) is the one you're stuck with when it comes to replacing worn parts or upgrading. It's really sad to see. If you want to be the fastest guy on a group-ride get a recumbent. Forget all these arbitrary rules that professional cycling has placed on the simple sport of beating your friends racing down the street. Cycling might as well be Formula1. Just let the teams with the most money make the rules that allow the products that teams have already developed and tested. What's the argument for disc brakes on road bikes if rotational mass doesn't really matter? Sorry...I had to let out a rant. I feel better now.
To do this test correctly the bike must weight the same with both wheel sets. If you only change to a lighter wheel set so the "system weight" is going down, the bike will be faster uphill. The video was about if it is better to loose wight on a pair of wheels instead of elsewhere on the bike, not about if less weight is better than more weight
You misunderstood the video. In your last paragraph you say re accelerating the wheel on climbs is hard work. You're mistaken. If you're not braking, your wheels are not robbing you of energy. All the work you put in into accelerating the wheel gets stored as kinetic energy in the spinning wheel, which is expended by the wheel rolling up the hill. For example: if you had a bike with extremely heavy wheels and got it up to 30km/h, and then got to the start of a steep climb, and stopped pedaling, the heavy wheels would carry you up the hill with their inertia. Again, unless you're braking, no energy is lost.
The energy argument (if wheels are heavy, you put more energy into the wheels, you don't lose it) is correct in physics terms but does not tell the whole story for several reasons. One is that acceleration time matters: you could pull a trailer with your bike (yes, GCN tried!) and all the energy you put in goes into the trailer moving. Does it mean you will be "fast"? No, because it will take longer to accelerate up to speed, and also longer to slow down (e.g. before a corner). The energy is there, but the time it takes to get up to a certain speed matters in most scenarios of cycling (except steady-speed time trial on flat terrain). The other reason is that every time energy is converted into another form (say, from your body, to the rotational speed of the wheels), some is dissipated. Hence, it is better to minimise the energy converted into anything that is not linear speed of the bike. This is also true for KERS in cars: KERS converts kinetic energy into rotational energy of a flywheel, and then back into the car liner kinetic energy, but a bit of it is lost in the process (twice).
The point being that saving rotational weight isn't any better than saving ANY weight at all. So if it's 2000 Euro's to save 400 grams on wheels, or 200 Euro's to save 400 grams on a saddle, ten times over go for the saddle first. Well all that being accurate for competitive cycling. On a commute with stop lights that might be entirely out the window.
But you're missing the point about pedal phases. If the wheels store more energy, you can put a higher amount or energy into the rotational system at the most efficient phase of your pedal stroke and not rely so much on effort during the least efficient phase to prevent the loss of rotational velocity. Keeping the wheel turning during top/bottom dead centre means a more stable overall velocity -- stable velocity = less deceleration and acceleration = less energy lost. Reduce it to one factor and you don't get the full story.
I think you are on to something. The effect might be small, but it is not 0. Using myself for calculations, if we take 200 grams from my body and add it to the rims of my wheels this would result in accelerations requiring ~1% more effort despite the weight of the total system being the same. That is small because [like has already been stressed] this is only during acceleration. However in a Crit you would totally feel this!!! A simple way to look at this is 400 grams extra at my rims is equal to 890 grams or 1.96lbs of body weight. I will concede aero-gains are king, but don't belittle wheel weight. I think people forget just how much you need to be able to accelerate in races, adds up fast. Also what is crazy is this effect becomes even worse the lighter you are.
@@SeanBlader When coasting you are right, but every acceleration, the weight ar the rims has more than twice the momentum effect than static weight. So it could mean you loose the sprint at the end of the race.
I have watched the video a bunch of times since you first released it. I find myself returning to it at key moments in my life--precisely when I am obsessing about how much my bike weighs and when I am thinking about a new wheel set. It is a powerful example of how myths are generated and perpetuated. And, why it is so hard for the science to actually crush the myth. I understand the science and I still find myself believing the myth. This video is a reality check.
Science have debunked everything, everything is written down in some paper somewhere The way i see it is basically, everyone is just trying to sell snake oil, GCN, Shimano, the aero wheels salesman, etc And what is the answer about what is the best wheel? As always it depends on what you want to do And the course you are riding on Weight is always important, more weight means more energy you have to spend to accelerate to a certain speed, and the more energy you need to acend a slope Hardly irrelevant for long flat sections Aero is always important to and exponentially so The more coeficient of drag your bike (and you as a system) have, the less top speed, small changes in aero can bring huge watt savings at the top speed and will make much easier going against the wind Now going with heavier aero wheels will mean 2 things You will get more top speed on the flats but also it might be harder to go over not so smooth terrain because when you hit a bump your wheel has to move out of the way, which means you have to spend some energy into moving the wheel away from the bump, and that energy is taken from your foward momentum so the bumpier and heavier the more the speed toll you take Shallower and lighter wheels will accelerate faster and be more nimble and controllable in cross winds, as well as less energy taken from going over bumps, but they are draggy and drag is exponential so in the flats where you must be at top speed most of the time its not ideal, and front wind will be way more painful Tldr: for TT in perfect indoor condition and surfaces, use high pressure full aero wheels For courses with mild but mostly flat terrain without many climbs and mild winds, use 50-80mm deep wheels For less than ideal terrain use low pressure and lighter wheel combo, it will be faster
Loads of factors here. See some people trying to defend lightweight wheels for their lives, but all in all, I don't see much point in splashing out the cash for a little lighter wheels if the engine is crap. One thing that not discussed here is that rotating inertia is not the complete mass of the wheel being placed at the maximum radius of the wheel - the distribution of that mass affects inertia. Where Inertia = Mass * radius^2, you don't put r as a constant and simply vary the M. M being closer or further from the axle plays a big part. Simply put, a heavier aero wheel may very well have a much better distribution of weight near the axle, giving rise to the minimal results observed.
Interesting piece. I wonder what impact the tyres have. I know when I take my carbon tubs off and put on Fulcrum 5s with schwalbe marathons the local bunch ride gets about 10X harder!
13:49 offers a sneaky clue. From the point of the observer, we are biased towards only perceiving the effort of acceleration. And so the deceleration effect of light or heavy wheels are often discounted from the experience.
Because tyres can change rolling resistance and that difference can be quite big. You might be able to push 250W but struggle doing 256W needed when fitting worse tyres on. Other than that, weight is again not really the issue.
Tires can also impact aerodynamics. A wide tire presents a bigger frontal area to the air flow and if it the tire is significantly wider than the rim, the air flow separates at the bead and creates drag.
Many of these "scientific" explanations run simulations as if human cycling power is constant and dependable. It's neither. It is not constant like a motor, but pulsed, driven by contracting muscles that put power out often in two different power curves for each leg. And it's not dependable--it depends on one's motivational state. This psychological factor is never taken into account. Human's are not robots or motors that put out unconditional power. We have to believe the power we are putting out is effective. For instance, in a headwind, my morale is low and I might put out 180 watts average because I don't think it's much use to work hard, since putting out more wattage doesn't seem to affect my speed much. In a tailwind or in a group ride, morale is high and I feel the effect of putting out more power, motivating me to put out an average of say, 250+ watts average. The same can happen with heavy wheels, like gravel bike wheels, on a hill. Putting out 300 watts up a hill on those wheels seems like a fools errand, as their extra rotational and gravitational weight is felt acutely during the micro accelerations while pedaling up a hill, so psychologically I think it's useless to put that kind of power out using those wheels, so I back off to a lesser effort of say, 180 watts, like the headwind. I've been psychologically beat by the heavy wheels. When using lighter wheels however, as a climber, I feel a big difference on how much better they micro-accelerate with each pedal stroke up the hill, motivating me to put out 300+ watts for the endurance of the hill. Psychologically, the lighter wheels motivate me to work harder. This means if something like lighter wheels motivate you to work harder, you will go faster than with heavy wheels. Maybe not because lighter wheels perform better, but because YOU perform better using them.
@@sc9160 100% it DOES matter. I've recently gone from a 15kg MTB to a 9kg road bike and the difference in acceleration is huge. I now actually try harder because I am actively rewarded for the extra effort; the difference in acceleration is hugely noticeable.
@@sc9160 Using that logic, doing a hilly ride that starts and ends in the same place is no more difficult because of energy conservation. Or someone pulsing on a gas pedal of a car is going to get the same mileage that someone using constant pedal pressure does, which we know is not true. I'm with Dave. When they start using real models of how people cycle, rather than idealized ones, I'll put more faith in the results they arrive at.
The point is...your heavier wheels feel slow and heavy because they are, but you would feel just as slow and heavy with your light wheels on and an extra kilo of water in your cage or tools in your seat bag. The fact that the weight is rotational doesn't matter...the fact that heavy wheels are HEAVIER does matter. A subtle difference, but a difference nonetheless!
Hello, I agree with the video and former remarks. BUT!!! The results are fine and true in lab, but you should have added, what is the watt diferrence the heavier rim cyclist must make in order to accelerate from 20kmh to 45 khm, how many meters I loose when accelerating with the same watts from 20 km/h to 45 khm with 500watts with different wheelsets, etc? You are a racer and you must know that there is a difference when racing between two scenarios: First, when you hold a steady tempo 300W over one hour, and second, when you hold 200W over half an hour and 400W over the other half hour. The average (and total) power is the same but one is achievable and the other not (unless a pro rider). So, you should not repeat all over again that the power is lost only when braking, but try to explain in more depth the actual differences. That is where your video fails. Also, the name of the video is about rotating weight, not aero effects. Although it is helpful to see the effects of aero wheels, you can compare light/heavy aero and light/heavy non aero. comparing heavy aero and light non aero tells only half the story. In my opinion, the intention was perfect but the performance very poor. Also, I would like to see the course of the crit. There are crits when you do not need to break to less than 40, then there are city crits where you must brake to 20km/h and accelerate to 45 km/h. So, maybe the result should be: "all in all, you exert almost the same total power nonwithstanding the weight of the wheelset, but it feels very diferrently in some of the crits and it may loose you a crit if you do not manage to accelerate that quickly with heavy weight rims..." Is that correct or did I miss something? And last remark: During a race, there is 30 procent of time when you ride on the limit and 70 procent when you pedal easy... It is the 30 procent of time when on the limit when the power differences are important. It does not matter whether you must extend 220W with lighter rims when compared to 210W with heavier rims when just coasting... It matters whether you must extend 400W with heavier rims over 390W with lighter rims when actually racing (going into breaks, covering breaks, etc.). If you could dig deep into these questions, THAT WOULD BE HELPFUL! Thanks for the content, carry on and please dig deeper!
I think I agree with almost all of your points and dislike much of Jean's argument. I also think that your comment should be divided into paragraphs to ease reading however. You had too many good things to say in a single paragraph. It is a pity that your comment only has five upvotes.
Bokaj Grummel this isn’t actually very “heavy” on science at this point. First, it’s an incredibly small sample size. One rider on 3 courses. Second, it hasn’t been peer reviewed. To determine if the methodology is flawed or not, we need other people to replicate the results independently. One day it might turn out to be proved correct but for now it’s not rigorous enough to put a lot of “weight” into it.
@@sportbikejesus did you not hear him say that basically every engineer that they talked to said the same thing? No this isn't a scientific study, but it never set out to be. It's an informative video using science to explain a common misconception.
But the main topic this video is talking about is the rotating weight, so what you should do is use same rim profile but different weight. In that way, you're truly comparing rotating weight
This. I hate it when a light weight low profile rim is compared to a heavier, aero wheel. What i would like to know is how much is the difference between a cheaper and safer 2kg 50 mm alloy carbon wheelset and a 1,5kg 50 mm pure carbon wheelset. I know, aero is the most important.
It does not matter in terms of mathematic calculation. You have to difference weight and height ( which is aiming for different effect. Aerodynamics dont care about mass. It cares only for shape)
Agree with physics part of the assessment in terms of energy added and stored. However, weight does matter in real life because it’s all about the acceleration in the fastest amount of time to stick with the draft of the rider in front. If you have to put in more energy over a longer period of time riding heavier wheels, you will lose the draft of the person in front of you and therefore use more energy to keep same amount of speed. Lighter wheels help you quickly accelerate to stay in draft even if you have less inertia stored in the wheels. You can’t have scientists who don’t ride tell us what’s faster in real life. You need to understand not just what’s faster over an hr but when fast matters in a hr race.
you miss the point of inertia here. With a heavier wheel you spend more energy spinning it up but less keeping the speed. So you donˋt "put in more energy over a longer period of time" - you put it in differently though. My personal take on it is that you can only feel in the legs the acceleration bit, the rest is not something you can manage to sense or feel. You can see it on the time though. Also Iˋm a engineer but Iˋm not an expert in this particular field and through my actul work experience I have come to realise that for any field of complex physics simulation it is a highly specialised competency done by specialists and there is a 1000 ways that one could miss some small points actually making a difference. Hence I fully support the last bit about going out testing it in real life. Also to anyone not beeing such a specialised professional in this field to actually think you know better or more on this by genetics or practical experience is just arrogant and that is something I have witnessed to cause horrible failures in real life. Do doubt the specialised professional, like the heart surgeon prior to a open hart procedure - or do you trust him/here more than your own gut feeling in that situation? A lot of people largely overestimate their own knowledge based on nothing way too often. Get too know your actual competancies and let others del with the rest. We will all be better off with that.
I feel sorry that popular videos like this tend to have overlapping comments, since we all have no time to read all the comments (I am an exception escaping from reality). Yours and mine and several others all refer to peloton drafting effect completely ignored by the video. The similar comments each gain only very small number of upvotes and thus are not shown on the top of the comments. And so-called "engineers" look down upon the opposing folks as stubborn cyclists, not reaching the most scientific comments like yours. What a pity... I only hope that Google will find a better way of organizing too many comments in the future than simply using upvotes.
I live in Switzerland and have met JP and even bought his deep section 800 Swissside wheels for my TT bike. You might think I am biased.. however, ....I can honestly say my PBs instantly improved on fixed, flat courses both in and out of the wind. I was consistently faster and they are 500g heavier than my lightweight wheels. But, because I actually have only a meagre 175W FTP my climbing creates another interesting dynamic. When I climb anything above 5-6% my pedal stroke is noticeably exaggerating the lack of power delivery. Therefore, I actually do change speed marginally during the pedal stroke. I notice that my wheels are constantly "re-accelerating" because I can hear the whirr noise change in volume in tune with the irregular rhythm of my pedal stroke. I have several minutes difference in my PBs between these two wheels sets over a regular 20min climb I use. I think I need to change out my cassette for a lower 32T and check again. I think that would be interesting to isolate my pedal stroke deficiencies. I do believe though, that if I had a 300W FTP and a better pedal stroke I am sure I would get closer to seeing only a 4 secs difference. For me, two vastly different wheel-sets are a much needed compliment to my cycling armoury given my particular circumstances.
When you are commuting through a city, you have constant stop-starts as you go from one traffic light or road crossing to the next. It may be as many as 5-10 full stops and accelerations per each km travelled. In addition, you very rarely reach the sort of speeds where aero of the wheel starts to make a difference before you have to stop again. It would be insanity to claim that the weight of a wheelset makes little difference to your commute speed and fatigue under these conditions. Clearly lighter is better for anyone interested in getting across urban areas fast. It’s up to the consumer to decide whether they want a heavy flywheel that reduces drag at constant high speeds, or a lighter one that bleeds less energy out of the brakes over repeated full stop - reacceleration cycles.
But urban commuting _isn't_ a competitive sport. And if you really needed to go so fast as to buy expensive wheelsets, you'd might as well get a moped, or even a second-hand car with that money instead.
I'm looking for testing that shows how much time a lighter wheel would save me in a commuting situation. If spending $1,000 on a new set of lighter (and possible more fragile) wheels saves me 30 seconds on my 5 mile commute then it clearly isn't worth the money to me.
@@francoisgenerau7250 then you could use the cash to plant trees or donate it to an organisation of your choice. Unless somehow not buying a set of carbon wheels magically means the guaranteed destruction of life on earth as we know it.
@@randompheidoleminor3011 Unless you care about carbon emissions, fuel costs, parking costs, sitting in traffic etc. But yeah, most people don't tend to spend at the "diminishing returns" end of the scale to get 1200g wheels for a city commute.
This is EXACTLY what I found out for myself empirically 27 years ago, when I bought my first lightweight bike, which weighed 10.5 kilos as opposed to the usual 14 kilos. Within the first 100 yards, I could FEEL that you had to make continued effort to maintain speed because the effect of inertia was diminished, however so slightly. Kind of like throwing a pingpong ball as opposed to a golf ball. I'm still riding that bike...
Without having seen the video, it's pretty obvious that due to conservation of angular momentum the energy that's used to get a heavier wheel spinning isn't wasted but stored. And thus the only effect a heavier wheel has is that acceleration will be slower.
Yeah but thats the point, we want to know exactly how much is the difference. Thats the big point. How much slows 500 g on similar wheels slow you down when accelerating. Do you loose a wheel length? A bike length? More? Thats whats interesting because that can matter.
@@satrioesar7151 "Yea pretty much the thing that change is the bike weight" No. They are comparing the same total weight: This video answer to the question: Is it better spent money to save 0.4 kg in the wheels or in the rest of the bike? In other words: 500 € to save 0.4 kg to the rest of your bike is better than 1000€ spent to save 0.4 in your wheels, as there is NO TIME advantage in saving the "rotational weight", other than a faster acceleration. The only difference, is that will be easier to change the direction of the bike, having the weel a less inerzia rotazionale and harder to stay on the wheels of somebody trying to escape from the peloton, which can allow him to escape.
@Click Bait yes, can i please have a weightless wheel with no air resistance, both parallel and perpendicular to the plane of the wheel? no, in a real world, bike wheel designers have to tradeoff between weight and air resistance. if what you wrote was the case, then pursuit track cyclists would use the lightest wheels possible with aerodynamic characteristics being of secondary importance. but they don't, they use disc wheels. this is because i) above ~40km/h the wheel's aerodynamic resistance is greater than rotating resistance due to increased weight, and ii) disc wheels are stiffer, and thus they have smaller energy losses due to wheel deformation.
I have a 8 kg racer with carbonwheels (23-28mm tyres)and a 10,4 kg cyclocross with sturdy mavicwheels and 32 mm tyres. It is actually difficult to measure significant timedifferences on tarmac. Other variables such as fitness for the day and wind matters.
Real life examle: (Yes, i know - it is road bike channel but, this can be a good point of view) Few years ago I switched my MTB bike from 26" to 29". So much more rotating mass! And - results: on gravel roads and tarmac sections - my speed and time instantly improved by 10% (average). New bike has slower acceleration, but running better at constant speed (bigger wheels has less rolling friction as well) When it is worse? At technical tracks, when lots of braking and accelerating happens - but bigger wheels are better at roots and stones.
Bigger wheels mean you go up and down less as you go over bumps and holes. This means several things: 1) Less flexion of the tires, so less heat generation, so less energy wasted. 2) Every time you have to go up, even an extra mm, to climb over a bump or out of a hole is an extra mm you have had to climb, even if your GPS doesn't count it. In a long climb, that is a lot of extra, hidden, mm that you have had to climb. Some may say that you recover that energy expenditure when you go back down into the next hole. But I suspect almost all of that is lost via #1 when you hit the bottom of said hole. 3) Every bump requires your body to expend muscle energy as it acts as a shock-absorber for your brain. That is energy that could have gone into climbing the hill.
Agree, I too just switch from 27.5 to 27.5+ bike, 2.1 before and now 2.8. To my surprise, it's wasn't any slower on the road which connect me to the trail.
My take out from this is that saving rotational weight compared to non-rotational weight creates very little difference which is new knowledge for me. But saving 400g is saving 400g and as another commenter (lost the comment for now, sorry) has already stated, you're always accelerating on a bike - all the time you are introducing force you are accelerating, even if it is to overcome gravity, air or rolling resistance, as force is proportional to acceleration (F=ma as I recall, and mass wouldn't be in there if it didn't matter). So point 1 - rotational weight isn't more important than non-rotational weight Point 2 - aerodynamic advantage is crucial to cyclists but even more crucial to people that make and sell aerodynamic wheels Point 3 - to call it science, there would need to be some sort of peer review, and throwing in a suggestion that the simulation of the crit was at 52kph (oh, he meant 40.2kph) leaves me a little worried about what was actually plugged into the simulation in the first place. I'll stick to my weight efficient strategy of always having a poo before I go for a ride.
Applying force to maintain your speed and actually accelerating, like increasing your speed are really two different things. You just can't say it's the same.
"you're always accelerating on a bike - all the time you are introducing force you are accelerating" No you aren't. He's even talking about it in the video. You're only accelerating when the speed indicated by your GPS changes. Yes, F=ma, but it's more like F_pedaling - F_aero - F_rolling_resistance - F_drivetrain - F_gravity = ma. And if you're plodding along at a fixed speed, a is 0, therefore all the forces cancel each other out. Obviously your speed is never actually fixed, if you want to be pedantic. With lighter wheels, your speed will fluctuate more with your pedal stroke (faster to accelerate, faster to decelerate). With heavier wheels your speed will be more static. Actually, if hour record bikes had a high minimum weight limit, it would be better to have added weight at the wheels, since your speed would fluctuate less, and drag increases very quickly with higher speed.
Del In strict physics, you ARE always accelerating on a bike. This is because there are always forces acting against your direction of motion (wind, rolling resistance, centrifugal force etc). In order to overcome these perpetual decelerations you need to perpetually accelerate: EVEN TO STAY THE SAME “SPEED” on your head unit.
First, not sure how much I’m going to trust anyone who worked at Sauber sheesh, but anyway he better go do some new calculations. A climb is nothing but thousands or more micro accelerations, one for every time you put a power stroke down on the pedals. It’s not a steady torque from an electric motor accelerating up, its pulses of power from legs on pedals.
Wrong. Your bike remains at a relative constant speed up the climb (assuming gradient and power remain constant). The video and physics don't show that weight doesn't matter, they show that rotating weight is the same as non-rotating weight.
That’s just it, with a person pedaling, power isn’t constant. As I said, it’s a series of micro accelerations (and decelerations) that at times aren’t so micro depending on the incline and rider weight.
@@christopherbeattie263 wheel speed constantly fluctuates while you cycle , ascending and descending changes the way gravity interacts with a bikes velocity . Going up hill gravity works as a deceleration force , so a rider must fight that extra force . Where does rotational weight come in ? The higher the rotational weight the more energy is required to accelerate a wheel to a set speed . Once up to speed energy consumption is the same , but seeing how on a climb gravity is decelerating the whole of the rider + bike the wheel now needs to be constantly accelerated to maintain a given speed to counter the deceleration of the whole body . With lighter wheels less energy is consumed to keep up the constant acceleration to counter the deceleration force of gravity . So the joules consumed by the rider will be less on a bike with a lighter wheelset than a heavy wheelset .
_Weight_ matters. Rotating weight DEFINITELY matters when braking, and _unsprung_ weight is the holy grail of handling when you have a suspension... hard frame road bike? Reduce overall weight if you want a lighter bike - it's that easy.
I wouldn’t disagree with JP’s essential conclusion. Nevertheless, the characteristic feel of light wheels may be due to reduced gyroscopic “precession”. This gyroscopic force means that when you try to turn a spinning wheel it will try to flip on its side and, conversely, if you try to tilt it, it tries to turn. The effect is very noticeable when you hold the axle of a spinning wheel in your hands, but it could also have a noticeable effect on bike handling.
@@andrewdeck7945 Well, yeah. Every bike frame is designed to create certain handling characteristics. The easiest thing you can change (to affect handling) after the bike is built is the front wheel.
I haven’t read all 1800 comments, but it seems like nobody is looking at this from a bio mechanical point of view. Tension on a muscle has an exponential cost, which explains why lighter wheels feel faster and why Mavic made the Comet+/- disc wheel with weights that can be added. If you are constantly changing speeds the peak tension on the muscles is lower with a lighter wheel. On the flip side, if you want to maintain a constant speed with hills and winds, a wheel with more inertia will allow the rider to avoid the highest muscle tension. Conservation of momentum works better on a blackboard than it does on a bike.
As a guy with an engineering background I’ve just quietly smiled and nodded then turned and walked away when people went on and on about how superior their light wheels were to the “heavy” aero wheels. It’s nice that now I can point them to a video for reference. Thanks for the good work.
Aero wheels will be beneficial when the aero losses outweigh the accelerational margin to be gained by light wheels. The problem is, the interviewee does not make this argument. He makes the argument that the total system energy is what matters, and that therefore the energy a rider puts into spinning heavier wheels is not in vain. There are obvious problems with this line of reasoning. First: the total system weight still matters and heavier wheels will impact climbing performance: but we all know that already. Second; heavy wheels force the rider to expend the effort spinning the heavy wheels “ahead of time”. As soon as the rider touches the brakes (eg for a corner) this extra stored effort is wasted as heat. With lighter wheels, you minimise this wastage by using only the minimum of effort in any given acceleration. In a time trial, heavy aero wheels probably make sense. In a twisty criterion, less so.
Ben Aston that would have to be an historically twisty criterion. But if you’ve got some real situation and the math to back it up. I’m sure we’d all be delighted to hear about it.
Brian Gardner It’s not just corners. Losing a wheel is another pertinent scenario. If a breakaway happens, if you’re on a heavier bike thanks to your aero wheels, you are more likely to be out-accelerated and fall out of the draft. So you have the aero gains of your heavier wheels, but that has to be subtracted from a significant efficiency loss from having to subsequently bridge the gap.
Ben Aston Although I understand your concerns, neither the math or the data I’ve seen supports that hypothesis. Please point to some research. Even my anecdotal experience disagrees with your claim. I used to have an old 2014 S-Works Roubaix with Zipp 303 wheels. Even though I was 30 pounds overweight and had a heavier bike, once I got above 14MPH my improved aerodynamic efficiency would start to leave people with lighter bikes and slimmer bodies behind. Over 18MPH, if they didn’t have extremely strong legs or an equally aero bike there was no contest. I can take a pretty twisty road at 14 to 18 miles per hour on a pair of 303s with a good set of 28 tires.
Considering the gap you have to close everytime someone in front of you leave you in the dust the amount of watts required you're working harder overtime to the sprint you're also going to loose due to a slow acceleration.
Like in every scientific experience it all comes to the boundary conditions: 1) Not every normal rider climb Sa Paobla averaging 18km/h with Oli's form weight: If you fight against gravity at 6-10km/h kicking the wheel to keep it in motion at each single pedal stroke, I empiricaly believe that Inertia holds you way more than Aero. 2) [Extension of topic => For your next video Olie!] Isn't Inertia more important than Aero once the wheel rpm comes to be lower than the crank rpm? -> I can imagine they calculate the potential gains backward based strictly on Olie's Power data (and weight), but how are the effects of stroke rpm and their uneveness considered here? And the corresponding torque/muscular fatigue? ->I feel that uphill, keeping your wheel spining at 8-11km/h cost you more fatigue, entertaining its inertia with a limited amount of crank rpm (39 chain ring) vs a higher rpm velocity from a "compact" crank (34 or 36). There I would state that adding more intertia on the wheel, accentuates the driver fatigue more than helps keeping speed (which is TBH frankly oscillating at each pedal stroke) , and finally be contra-productive ?! => Please a Debunk video on this one, for poor fitness rider!
Correct. I suspect the simulation assumes that the rider is pedaling perfect circles. In reality, on a steep climb, you are accellerating the wheel a little with every pedal stroke.
You're also decelerating between pedal strokes. A heavier wheel will decelerate slower than a lighter wheel. Thus, the effects on acceleration and deceleration cancel out - unless you hit the brakes, of course.@@bumbykitty
The falicy is that there is zero acceleration/deceleration on hill climbs.. And conservation of momentum you don't seem to be considering efficiencies in pedaling during micro accelerations/ deceleration while hill climbing.. I'm not buying it that rotating weigh is a null issue.
Conservation of momentum is exactly the key detail when considering the effect of micro-accelerations from pedaling...a wheel that is easy to accelerate is also fast to decelerate. Over the span of more than one complete pedal stroke the total effect of changes in inertia is zero.
It is not fallacy. The energy you put into the rotating mass every pedal stroke is stored, not dissipated, that is the point. Then it releases itself to fight gravity. The mass weight is however loss of energy as you carry that mass up the hill. He never said lighter wheels are not better for climbing, he said any saved weight is better be it rotating or not.
How about backing this up with some maths? Let's assume you want to speed up at the end of a criterium, e.g. from 10m/s (e.g. 36km/h) to 17m/s (e.g. approx 61km/h). Those are reasonable speeds for amateure sprinters. For simplification let's assume 250g safed per wheel, evenly distributed across the wheelset, so a total of 500g safed (surely on the higher end of the spectrum, but close to leightweight vs swiss side). This equates to a rotational inertia of approx 0.244kgm^2 for both wheels combined. The added kinetic energy stored in the wheels equates to about 23J for the rotational energy and about 47J for the extra translational energy of the 500g heavier wheels, aka an additional 70Watts if the acceleration takes place over one second, 35Watts if over two seconds. I don't know about you, but if, over the course of a surgy race, I have to do just 2s of 30W more for a 100 times, I will be severely more cooked than otherwise. Hence, rotational certainly is not the cheapest or even most cost effective way to save energy (think wheight, position, fitness,...), but for a fit individual with competitive aspirations it seems quite legit to put a few bucks into better wheels (not saying they have to be 4k leightwheight ones :D)
“If you’re riding at a constant speed, there’s no change in inertia… “ I wish I could also climb with a perfect pedal stroke and no rocking of the wheels/bike!!
The best weight saving and performance upgrade and relatively cheap for me without doubt has been tyres. Just switching to GP4000sii seemed like having a lighter wheelset as rolled quicker without forking out 100s.
I upgraded my wheelset from a stock Trek wheel to a nice Hunt alloy, saving about 530 grams. Can't say I noticed a big difference. Then replaced my stock Bontragers with the Continental GP 5000, instantly noticed more lively acceleration, less work to maintain cruising speed and added comfort.
Awesome video Ollie, I'm a huge F1 fan(one of the few American fans)so having an F1 engineer on your show was cool as well as informative. Honesty the "flywheel" reference thats when it clicked for me, lighter spins up to speed faster while heavier loses its energy slower. Two yrs ago when I installed Stan's No tube road bike wheels(Avion) , they were easier to start spinning and easier to slow down, compared to OEM alloy wheels. Also how cool is it the have so many F1 teams in your back your, if you live in that area(or is it Shire? I don't know I'm American)?
Eternal Optimist The historic counties of England are areas that were established for administration by the Normans, in many cases based on earlier kingdoms and shires created by the Anglo-Saxons and others. They are alternatively known as ancient counties, traditional counties, former counties or simply as counties. Modern Counties are administrative areas and many retain the ancient county names. I live in Warwickshire and I’m not a hobbit 😂
The statement (at 6:29 in the video) that "there is no acceleration on the climb" is flat out wrong. "No acceleration" only occurs when speed is exactly constant; this has never been my experience in climbing - speed changes with grade, effort and on a small scale with every pedal stroke. So, all of the modeling results based on this "no acceleration when climbing" assumption are wrong and highly misleading.
Always be wary of anyone talking about 'the physics' without showing any kind of actual working proof. There is no argument here other than 'we said it makes no difference'. Here's an article with actual calculations and citations as to where they got their information from. www.wheelfanatyk.com/blog/rotating-weight/
Great video Ollie! After being served and drinking the Kool-Aid as a bike mechanic years ago, the flywheel analogy makes sense - I don’t know why it took 30 years for that lightbulb to come on. It makes me think too that, along with aero and rolling resistance, frictional losses on bearing surfaces might play a bigger role than weight too. However my mind is possibly too blown at the moment to think straight. I need a coffee...
Same for HEV dish-like wheels. HEV can store energy in battery so gain benefit at start-stop situation, but no benefit in constant high speed. So they(manufacturer) use aero-wheels for HEVs which is benefitial in constant hight-speed situation.
The problem is that having fast acceleration is much more important than having slow deceleration. You will probably be dropped easier even if you don't loose any energy by having heavier wheels. The difference is probably not very big, but I still think that's an important factor that haven't been considered in this analysis.
I agree, there are times when the pace on a race picks up and the difference between getting on a wheel and not is a huge amount of energy spent. and that little bit less effort to get on a wheel is greatly appreciated, even if you are spending a bit more energy once on the wheel.
@@MicheasHerman I agree with you both. I would like to know, How is it than no one considers the wattage output required to get a heavy wheel up to a given speed at a given time compered to a light wheel? Also how many watts required to maintain a required speed compared to a lighter wheel? In MHO, it takes less watts to accelerate a lighter wheel. In the case where it is said that a heavier wheel rolls longer or further due to rotational mass, when that energy is spent, i believe it will take a greater amount of energy to maintain your speed as compared to a lighter wheel which may lose its rolling energy before the heavier wheel. Final point, Does rotational mass affects the overall weight of the bike? In other words, if i weigh a bike while it's wheels are spinning, will the bike weigh more, less or same as if it was weighed without spinning wheels? If the answer is same or more( cause i can't see it being less) then this follows the same principle that causes us to make our bikes lighter by upgrades etc Heavier bike vs lighter bike. Our performance improves with lighter bikes i think.
@@howardmarcelle2165 Yes it takes less watts to accelerate a light wheel How many watts are required to maintain speed: Going to be the same for both if the ground is level. Otherwise more watts to lift heavier wheel, less watts going down on a heavier wheel since it had more stored potential. Does rotational mass affects overall weight of the bike? (weigh bike with wheels spinning): Not really but technically yes because potential energy actually does add weight. A spring that is compressed actually weighs some fraction more then the same spring uncompressed. But you wont be able to measure that difference its way too small for a normal scale to pick up. Some good physics videos around that will explain this. To the OP: I agree, and acceleration is the point where your already dumping a ton of energy - if your putting put 500 watts and you need to put out 550 to get the same accelerating on heavier wheels thats much harder then later putting out 100 instead of 50 because the bike is slowing down faster.
You're viewing things incorrectly. Acceleration is instantaneously met with corresponding rotational inertia, therefore, "having fast acceleration" is equally important to "having slow deceleration". You don't "lose any energy by having heavier wheels" and won't be dropped any easier because the energy you put into them is the same regardless of how heavy they are (assuming overall system weight is the same). Theoretically, there is an extremely rare scenario where the lighter wheels could win in a sprint, but it's equally likely that the heavier wheels would win, because it depends on where in the pedal stroke the person is relative to a hypothetical constant-torque motor (if it were in the dead spot of the pedal stroke, the heavier wheels would win, if it were in the 3 o'clock position of the pedal stroke, the lighter wheels would win). None of this is to say that lighter wheels/bikes aren't faster, because they are in most scenarios. The argument is that there's no difference between lighter wheels and an equivalently lighter frame/components/body.
@@squiresuzuki this thing is complex, guess it's down to the placebo effect. In my own non scientific experiment, a lighter pair of wheels gives me a faster time with less hurt in my legs.🤷♂️
As a youth, I did some experiments along this line. Of course carrying mass up a hill takes kinetic energy. Any mass in this case (seat bolt, latecomer tub) takes more energy up the hill, and gives most back on the downhill. But if you use your brakes, you throw it away, As the analysis below shows rotating mass is more important. I mounted a training clincher wheel into my mechanism, which had a fan blowing on it. I cranked them up to the same speed with a drill and let them coast to a stop. I recorded the time. Then did it with a tubular training wheel with less than half the rotating mass. I then carefully covered the wheel with a “disk” of carefully folded and taped to the wheel. Results 1- tubular. Shortest “coast” by far - indicating the lowest kinetic energy. 2- clincher. Longer coast, indicating higher kinetic energy. 3- dissed clincher. Coasted forever. Summary. Rotating mass does require more kinetic energy (acceleration). A disc, or perhaps bladed spokes are more important.
I think it matters a lot for commutes. Starting from 0 feels so much better with my light wheels and you stop a lot if you ride in the city. I'd love to see the numbers, how much energy it takes to go from 0 - 30km/h with heavy vs. light wheels.
Easy math to do as an estimation: Weight added at the outside of the wheel "counts twice" for kinetic energy (that's the worst case, if you add the weight closer to the hub it's less). So riding with wheels that are 500g heavier total is roughly the same as adding 1kg to the frame. So yes, it sort of matters quite a bit more there, but (especially in the commute scenario), it's still not really all that much considering the full system weight.
Almost everybody can do a simple experiment to demonstrate that the wheels' rotational inertia is small compared to the total linear inertia. Put your bike into a turbo trainer, with no resistance, and the bike in top gear. Sprint as hard as you can and see how long it takes you to get to 20kph - then double it to account for both wheels. Now take your bike out onto the road, again with it in top gear. Sprint and see how long it takes you to get to 20 kph. There will be a huge difference in the times. I suggested 20 kph to eliminate as far as possible aerodynamic influence. Terry
@@decidrophobBeen there, off the back, many times. Much better off concentrating on aerodynamics, slipstreaming and tactics first and then worry about the small stuff.
Another flywheel comment here - On the several dirt bikes (with motors) I have run, we change the flywheel on the motor to increase traction on slower woods enduro courses because we don't need the wheel spinning punch that is fine for the MX course, and it lowered that chance of a stalled motor. Same motor different feel, it can also be used as a crutch for a peaky torque curve or just to make the bike feel more controllable. The flywheel effect kept the motor turning and it slowed the initial punch but it was recognized that this also decreases your potential hit off the line if you can control the hook up. Totally different reason for a flywheel, heavy or lighter because the power from the motor was not the limiting factor. We always had too much power when compared to traction. Not even in the same ballpark of what we deal with on a human powered bicycle. We never added or sought heavier wheels because an increase in unsprung weight is detrimental to the ability of the suspension to follow the terrain. I would guess the idea of unsprung weight negatively impacting the suspension performance applies to road cars as well but I have zero knowledge there. All that said was to point out that weight and flywheels have a place in motorsports racing and on motors for that matter but not on my bicycle wheels. Outside of the Hour Record, Go Ollie! and even then it does not seem conclusive because different attempts have used different equipment. Yes Aero wheels will equal gains but at what expense to the initial and constant inertia changes in the real world? The quick 5 second effort when the pack looks like a slinky because you are not in the front. No matter what your specialty, everybody is driving toward lightness. The only hold outs seem to be the time trials/triathlon where you really are attempting for a steady state effort. Look at this years TDF where riders switched bikes from the aero bike to their road bike for the final climb. Im sure they didn't ask for the heavy wheels!
disabled man I guess if you're doing that much braking in a city, you're probably commuting to work rather than training so the marginal benefit just delivers you into the hands of the greedy capitalist half a second earlier. Stop being a sheep and join a union, bro.
@@deskelly9313 > i need lighter wheels because I don't like fighting my rim's inertia >You need to join a union wat? How are those in any way, shape or form related to each other?
@@disabledman8697 Waiting for someone to explain this joke. Whoever said that explaining a joke doesn't make it funnier was wrong... It just makes it funnier in a different way. Waiting...
As a mountain biker this is pretty interesting, from the point that the whole bike is what matters. For a mountain bike, especially for enduro, the rotating mass matter's even less, as you want durability, which comes with cost of weight, but as it's a dynamic sport, every component matters and quite often you can ascend just as fast on an enduro bike than on an XC bike, due to better grip and geometry suited for climbing.
Wheres the revelation here?! We've known this for years. The wheels are not heavy enough to be effective flywheels. What he seems to not talk about is that the wheels are constantly being accelerated because power delivery is not constant. So I guess he's trying to sell some wheels
"What he seems to not talk about is that the wheels are constantly being accelerated because power delivery is not constant." They're constantly being accelerated... and decelerated. Heavier wheels will decelerate less, therefore keeping speed more static. Overall, very little difference.
Del Heavier wheels will decelerate “less” only because the rider (you!) had to exert more effort spinning them up to the same speed. There is no free lunch. The difference is that with heavier wheels the effort must be expended ahead of time, whereas with lighter wheels it can be reserved to be used at a future more useful time.
I'm using a singlespeed bike for shopping and stuff. At first, I had installed 25mm tyres, I changed them to 32mm tyres (~400g heavier incl. tubes). I changed them back quickly. If you have to accelerate over and over again at traffic lights and you are always in the same relatively big gear, you definitely can feel the difference. So, for city riding on a singlespeed bike, rotational weight DOES matter :-)
All I know is that after putting lighter wheels on the bike, my times on Strava segments are faster and I am less fatigued after a long ride. But I was not using aero wheels before if that is the difference. So many variables in this sort of analysis makes me doubt the conclusion.
To clarify the title, rotating weight is still weight, so if you have much climbing on a ride, saving weight on your wheels will make your rides a little easier. Exactly as much as saving weight anywhere else on your bike (or your kit, or your body).
The question asked was about rotational vs static mass. Comparing different system weights and aerodynamics changes the whole situation. He also emphasized the importance of aerodynamics, confirming your experience with your new aero wheels. Buy the same aero wheels with 200gr more weight at the rims, but a 200gr lighter hub, and the difference on time (not feel!) should be negligible.
Where having a lighter wheel should be really noticeable is if you're not staying in the saddle but stand on your pedals and rock the bike rapidly side to side, having a low angular mass gives less gyroscopic forces which will be felt as a force resisting your attempt to alter the orientation of the wheel.
Old story, and may already be some follow-ups to this, but I'd be curious to see this (I think the conclusion is sound, but I'm sure there are doubters still), presented differently. Using pedal power-meters, to keep everything as "equal" as possible, ride the same bike, on the same course under the same conditions (as best as possible, and/or on a velodrome indoors for example), with aero vs non-aero wheels, ignore completely making a choice by the weight other than "reasonably similar market range" wheels, then do the test criteria by maintaining an average speed of "x" over the course for a time of "y" and record the results via the power meter. With a few runs of each to get a solid data set, that should clearly result in a distinct "savings/cost" difference in watts. So for example, 2 miles, starting at 0 and maintaining after the initial acceleration, an average speed of 25.0mph (proper magnet wheel measurement, not GPS, to eliminate variability, and to not have to be concerned about measuring the actual course, the "2 miles" is per the measured wheel, so it should be extremely consistent and immune to slight variability in the riding line, etc...) My guess is it'll be probably a double-digit savings on the aero wheels on any course that isn't a steady-, very steep climb (where the system weight penalty, and reduction in aero benefits due to lower speeds, may cross). Anyhow, food for thought, since this was 2 years ago I didn't read the near-2000 comments to see if it's been suggested already, if so my apologies.
well i can tell you i got strava personal records on my 7kg carbon wheeled road bike, as well as on my 12kg all steel 50mm schwalbe marathon touring tire gravel bike for the same routes. a bit of wind change is enough to make one bike faster than the other. there is very little (a bit more than 1kph) in average speed difference over longer flat rides with both bikes. the gravel bike (specially in touring mode with those heavy tires) is far from fealing lively and direct though. it takes a while to pick up speed and it just plows along without wanting to turn. the road bike is like a little buzzing bee in comparision. so totaly different characters. so yes, wheight does matter. more for feel than for average speed though. thats also the reason i always would go for a semi aero wheelset on the road bike that is still light and feels zippy. dont care if i could be marginaly faster on an all-out deep aero set when ithe rims are 400grams+ heavier and make the ride more sluggish.
Try it on something that isn't perfectly flat. Also, account for position on the bike. You are taking one hacky example for heaviness in aero wheels, and turning it into an example of weight not mattering between bikes despite of inherent aero conditions.
@@cccpkingu Or he's making the obvious point that there are a bunch of variables at play and when you're dealing with minute gains, any hoped for benefit can be wiped out by an inopportune fart.
Yeah my Cervelo RS XS with 650c wheels is now my washoo kicker bike because the widest performance tires is 25mm. Now that I am riding 650b Babyshoe Pass 42 mm tires on my gravel bike, I'm never going back. For shorter/smaller riders(I'm 5'2"/105lbs), I recommend a 650B wheel gravel bike with road-like geometry like the Salsa Warroad, Norco Search XR, etc.
I still ride a 650C Litespeed with 23mm schwalbe 1 tyres . Nothing is as easy to accelerate on or chuck around as a super light tiny mavic alloy wheel and a tiny little lightweight tube and tyre . Definitely not aero but my best strava short sprint sector’s out of corners were all on the old 9 speed Litespeed and I have a Cippolini with 11 speed campy eps and deep dish zipp and euros climbing rims and neither get close in acceleration or ease of climbing. Good luck Joey I disagree the enves will cook you in the surges and climbs amd sprints in the crits
Agreed with everything until he said "I could understand why you'd add weight to your wheel for a TT race." - Then I knew why Sauber were always back of the pack. Nah. Dude is obviously a clever guy and 1000x more intelligent than me. Fair play. Keep on keeping on. Internet fist bump to that guy.
One area not covered is the change of direction comparison between the two, where weight saving might be more significant. Which is in courses with lots of consecutive bends for example. Hopefully in a follow up video :)
I'm perfectly happy for lots of people to believe this video and buy heavy wheels. The more people that do, the more I can drop on the climbs. Thanks GCN, I owe you :-D
I don't think you understood the explanation. Weight only wins aero in long and steep climbs. This is just physics. You can or can not believe it but it doesn't mean it is wrong...
The video was about rotating weight vs. weight on any other part of the bike, not about heavy bike vs. light bike. Seems like your brain is more aero than your wheels.
In the late 90s/00s British Cycling developed a set of track wheels that had weights on a spring system inside the wheels so as you sped up the weights moved to the out aide of the wheel to keep up the speed! Maybe try and find a pair of those for testing as well.
Really very interesting video. I want to buy my first pair of carbon wheels, i have a gravel bike that i mainly use on the road and in the choice I was giving lot of importance to weight (like all poor beginners like me…). Since the wheels I have selected are in the range of 1420-1580 gr, from this video I understand that i would probably feel no difference, and therefore i can choose based on the aesthetics… right?!
the video concludes that for performance gain, aero profile is key. however, for personal satisfaction of such an expensive (relative to the overall bike) purchase, personal aesthetic preference is most definitely a key factor. at least for me, if i'm being honest. where they intersect is, for instance, the depth of a carbon wheel; deeper for better aero but more poor for cross-wind situations. thankfully, i like the looks of a 40-45mm wheel, which seems to be the sweet-spot for most of us riding in mixed terrain and often windy conditions.
As a physicist I can say absolutely that the rotating weight has no extra effect when climbing hills. But it has double the effect of static mass when accelerating the bike such as in a sprint. If your wheels had 2 kg at the periphery ( put together) it is equivalent to adding 4kg mass to the bike under acceleration. If it was possible to get the wheels down to half this then it is equivalent to removing 2kg from the mass of the bike under acceleration. This might make a difference if two riders start next to each other and are in a sprint to the finish.
it looks like some reasonable assumptuons were made. but if we consider the simple power to weight ratio a lighter wheelset will be faster for the same energy put into the system as there is overall less to move. if we then treat aero dynamics as an opposing force. the aero wheels will provide less opposition than the non-aero wheels. so you have an two opposing forces and tyre friction. additionally the rider position will vary between the models used as examples different bikes and different system weights too many variables to make a solid analysis. Surely the better test would be to ride the same bike in each scenario with either wheelset (6 runs) and make it very achievable for the rider ideally with the same tyres. its all marginal/edge case gains at the end of the day. Everyone feels faster on their new toys. whilst its difficult to put a figure on it you cant ignore outright enthusiasm of a rider who feels the decks are now stacked better in their favour. Lab Models are great and produce a set of results kn a controlled environment. i used best bike split to calculate a time on zwift it got it within seconds of the time i set a few days before hand. But on the roads, in a gentle wind, with the sun out i was no where near it. If its one set of wheels for one bike for you to ride the nicest set of 30-40mm rims you can afford will deal with everything you will ever need:-)
Engineer here … the video is overcomplicating things. lets say you accelerate a fictional bike that has 1-kilo-weights attached to various spots, then accelerating these 1kg-spots from standstill to 1 meter/sec takes the following energies: - bike frame: 1 Newton - bottom of wheel: 0 Newton - back of wheel: 1 Newton - top of wheel: 2 Newton - front of wheel: 1 Newton wheel average: 1 Newton. In other words: the molecules in a bike wheel have the identical speed (averaged over the entire wheel) than frame, saddle & your belly, and hence there is also no difference to acceleration force & energy. Interestingly, this only holds true for wheels that are physically connected to the ground - which means: rotational energy IS a thing for cranks, chain, legs & pedals. Just not the wheels.
Unit of energy is Nm, Ws or kgm²/s². Newton is force...? What do you want to engineer? My 50 mm road wheels on 27,5" MTB are much harder to accelerate then the same in 28 mm on road bike (both Conti contact speed). After some sprints it's easy to feel the difference in the legs.
This analysis seems suspect for a few reasons. 1. When comparing aero wheels to box sections, more weight is closer to the axis of rotation, this reduces the moment of inertia which will make it easier to rotate. A heavier aero wheel could "feel" lighter because it might have a lower momentum of inertia. 2. For the climbing test it seems as though it is assumed that the wheels are maintaining a relatively constant angular velocity, but on really steep climbs, its quite evident that during/between strokes the wheel will accelerate and decelerate throughout the pedal stroke. Now you might argue that the bigger one would have more inertia, which is correct, but gravity will also have a greater force on it. So essentially during a climb, on each pedal stroke you will have to accelerate the angular velocity of the wheel. That is where a lighter wheel will be felt on the legs and the clock. 3. During the crit, the amount of time spent braking is borderline irrelevant. The important thing is the time spent accelerating, which is A LOT more than 2% of the time. Also, the heavier wheel will have a higher gyroscopic effect. This means it will resist changing direction. To feel this, take your front wheel off and hold on to the QR skewer and spin the wheel fast. Then try to turn it simulating turning your bike. It will resist your movement. The heavier the wheel, the more it will resist this change in direction. 4. This test took into account aero gains from the wheels which was not the point. This wasn't supposed to a test of weight vs aero. The point was to test weights. ie a light box section vs a heavy box section or a light aero wheel vs a heavy aero wheel.
On point 1, the difference in rotational inertia is very very small. The "fairing" part of a deep rim is very thin and has little mass, not a whole lot different than the sum of the extra 50mm of 24 steel spokes. On point 2, each acceleration from the dead zone of the pedal stroke is reduced when the wheels carry more energy through that dead zone. I agree with point 3: snapping onto the jump of that guy ahead of you matters a lot, and slower acceleration in that critical case is vastly more important than it seems to a non-rider. Centimeters matter. Very small fractions of second matter. And in a criterium, that critical case happens constantly. In a road race like Flanders, it still happens a lot, very dramatically on every sharp turn in a narrow road (which is pretty much all of the roads). I'd like to see numbers computed for how many centimeters difference the wheels make when trying to regain shelter from mid-accordion position in a turn that slows you to 20 km/hr when sprinting at 1,000 W for a few seconds to get back up to 55 km/hr. The guys in front know exactly what they're doing, and intentionally drive the speeds way above the average coming out of those sharp corners.
It matters greatly in technical MTB,specially on natural trails with loads of big rocks and roots.Why? Because of multiple short high power acceleration on technical sections followed by big decelerations.On the other hand, for Enduro or Downhill,where times downhill are the only accounted, heavier wheels are better (due to the increase inertia).
@@nowaynowayvideo the material isn't the issue . Aluminium rims for MTB are pretty light . Eg the DT Swiss E540 rim is erm.....540g . Its called and enduro rim but many DH riders (in the UK scene at least) will run them or something similar weight wise . XC rims tend to be from 300g up (Ryde rims are some of the lightest at 210g each) . There is a compromise situation with DH , light , strong , cheap . The DH wheelsets on pro or semi pro riders are only marginally heavier than XC wheels . Even then that xtra weight is mostly found in the hub not the rim . For example the lightest xc rim by dt swiss is 355g and the lightest Enduro rim is 473g the profile of the rim (for tyre size and tyre profile ) is the biggest cause of that difference of weight . The ex475 being 4mm wider and deeper in profile to the XR331 . Both of these weights are for 29er rims . All mountainbikers apart from dirt jumpers and maybe street trials riders want lighter wheels . Its why compaction trials riders drill out their rims . Its why so many DH riders went all in for tubless (no need for heavy DH specific inner tubes that weigh almost 700g each ) . Heavy wheels did used to be desired around 15 years ago to help with roots ect . But the growth of 29er and 27.5 in enduro and DH have ment that heavy wheels are no longer needed to help stabilise a bike or keep inertia for a rider . Slacker head angles , longer wheel base and bigger wheels have ment a shift to much lighter wheels in all mountain bike disciplines. Gone are the days of DH wheels like the Halo Combats wheel sets coming in at 2.7kg being considered relatively light . DH bikes were often in excess of 50lb in weight . Now most are just around the 30lb mark and some even getting sub 30lb , same weight as some trail bikes .
And I thought I was a really bad rider not being able to feel any difference beetween my "light wheels" on my Canyon Ultimate and my 62mm aero wheel on my Canyon Aeroad.
The question is whether rotating weight makes more difference than the weight of a component that is not rotating. So, does 100 grammes on your rims, tyres, tubes make MORE difference than 100 grammes on your frame or seat? I get it about the flywheel effect and I have experienced it. A heavy wheel may roll over uneven ground or hold its speed into a gust of wind better than a light wheel. Extra weight on the bike anywhere affects you when climbing, accelerating or braking. Extra weight on the circumference of the wheel means more stored energy if you're maintaining a fairly steady speed. The circumference of a wheel moves further, and therefore faster, than any other part of the bike. Therefore, it takes more energy to get 100g of wheel rim up to speed than 100g of frame. Therefore it will affect acceleration. However, like most things on bikes, we are dealing with such small numbers that it is barely measurable. A weight weenie who saves 50g here or there on his bike is making a negligible difference if he weighs 80,000g himself.
When your wheel spins you are moving as much up as down so it is costing you literally nothing. You lose energy from friction though so it can be very misleading as you could have much much more friction with a very wide tire for example. But it is mainly the tire you need to worry about.
Wonder if this has anything to do with disc brakes and heavier aero wheels.. anyone who rides a lot knows lightweight wheels transform a bike...so much marketing BS...
So what my wife says is true: "First, loose 5kg on your belly before you spent 2000 Euros an a wheelset"... :(
Sorry Bernd, your wife *might* be right, but you can buy the wheels if they make you happy
@@gcntech are you happy for no real gain?
Complicating the situation are your wife's ulterior motives! (Can't blame her :)
That's not the answer when you weigh 55 kilos.
@@dmitrykiselev8087
Amputate legs for carbon fiber PTS.
I can already see the adverts from wheel manufacturers: "Now, 7% heavier than our competitor!"
going to fill in lead instead of air next time. once they're spinning I can go around the world without pedaling ;-)
if manufacturers were to drop their BS, they'd still manufacture both light and heavy wheels and market each for their respective uses: lighter wheels for rides that consist of a lot of ac/decelerations (in crits and MTB) and heavier wheels for rides that need maintaining constant speeds (time trials, velodromes, downhills).
*M'eh, I don't trust this guy. Until Hambini says it, just a rumor.*
To isolate the aerodynamic effects, and test the effects of different rotational inertias, you need to compare various weights with the same aerodynamic section, i.e. add weight to an aero wheel and evaluate.
I suspect a lot of the acceleration effects were ignored, for example when climbing the angular velocity of the crankset varies depending on the grade and cadence through the pedal stroke. Likewise angular acceleration in cornering was probably ignored. Higher rotational mass also results in greater friction losses in bearings and rolling resistance between the tire and pavement.
there used to be be disc wheels with moving weights inside them to exacerbate the fly wheel effect.
Engineer here: I love the explanation, the flywheel storing energy is exactly why the 'total system' does not change, but the feel could be different. (also, see KERS system in F1)
But to be honest, this comment section is going to be more entertaining than the video in the long run. Cheers for trying to bring science to a group of stubborn cyclists!
🤣 🍿
Engineer here too! He's entirely correct, rotating vs static mass makes no differences at all. The change in energy is the same. I'm not sure why so many people are struggling to accept it.
@@benstanden8784 In a lab, a computermodel or a TT on a velodrome this is correct and easy to accept but in the real world of cycling a lighter pair of rims and tires makes a noticeable difference ( and no it's not just a placebo-effect ).
@@benstanden8784 MacDonalds drive thru guy here with an associates degree in applied water color art....I too can't believe people are struggling with a physics concept explained only using words by an engineer! Come on. I'm not sure either one of you engineers said anything that would help people understand. A lighter wheel is going to require less energy to get up to speed after every corner which will be easier on the rider. What would be the ideal application of light wheels? Cyclocross, lots of heavy braking and hard accelerations.
Lolz, how can you take this seriously when his model for a 10km, 700m climb with about 15 hairpins has no acceleration?
Laughable.
It absolutely makes sense. You can easily feel when the lighter wheel is easier to accelerate from the start, but it's nearly impossible to FEEL when the wheel maintain momentum better. Thus riders demand lighter wheels, and the industry just responds to this.
Now that's why my Fatbike is so fast. I store a lot of energy in the wheels and then hide in my front wheel's slipstream.
Ha ha 😅
I need a wheel thats the width of an armchair to keep up with you
Hilarious
Looks like science is getting in the way of common sense! Marketeers are having a field day convincing people they've got the wrong equipment and should buy the latest expensive fad products.
Lose 10 kg, get low, put some nice steel bearings in and clean the chain. That's the best bang for the buck.
Yup the hybrid ceramic bearings are a joke . Bocca used to make awesome full ceramic bearings but boy were they pain to install .
@@edmundscycles1 Train your legs with weights/deadlifts. Not longer rides.
@@Welther47 Train yourself to squat 3x your body weight for reps and overtake cars uphill 🤣 (powerlifter who comute on bike)
Put good low resistance tires and inflate them properly - this does a lot more than “bearings”.
Did the same. I wasn't an overweight guy, well within the normal bmi window, but still could loose almost 9 kilograms (84.6->75.4 and still counting), and streched for months to be able to get a spacer lower at the cockpit. Same bike, total different experience. I spend money on very high quality food and consume it responsibly, than put my money on x percent stiffer, x percent more aero bullshit. On long TT like strava segments, climbs, short sprint segments, everywhere I am faster by quite a margin. Previous best FTP was for me 3,84 w/kg, now 4.05 and I really feel I could achieve around 4.2 with winter training.
Ohh and I was really into buying some Swissside wheels, but this guy talked so much BS, they lost me as customer.
the psuedoscience and marketing nonsense in the cycling industry is only rivaled by the supplement industry
"We measured with our simulation tool" what a fraud.
@@factotum6245 you mean tool?
Only if you say "Ammh" 400 times in one video...
He is actually correct for the most part. Unless the ride requires constant changes of speed, no energy is lost, but the bike is less responsive.. and you need higher spikes of energy to keep up with constant changes of speed. And that is key.
Over broken terrain with suspension it is crucial that the suspended weight is as low as possible (not the case here).
I think he is being sincere, dt swiss interest would be in saying that rotating speed is crucial.
I know, right? Ha ha! :P
I'd love to see this analysis applied to the typical cross-town excursion where you are constantly accelerating and decelerating. It's obviously negligible on an uphill ride with no stops, but I still assume that rotational mass has a very significant effect on a typical bike commute.
it's impossible for mere mortals like me to keep consistent speed be it on climbs or flats
They explored that scenario with the criterium: 0.7 seconds over 1h race, that is your answer (12:00). On a bike commute across a town I don't know how much more you brake to make it "very significant"
@@naufalap It is not about perfect constant speed, it is about braking. Only when you brake you lose the energy that is stored in that wheel
XC and Enduro mountainbiking are probably the best examples of constant acceleration and deceleration combined with steep gradients. Lightweight wheels are valued there, but nobody goes overboard with their wheels.
With both mountainbiking and commuting, comfort and durability seem far more important to me.
@@StefanoLinguanotto The crit models a closed course where braking only occurs 2% of the time. They're probably not coming to a full stop during any of that braking either. Wouldn't be surprised if typical city riding involves braking 20+% of the time with 100+% more energy loss per braking event.
I work in numerical simulation of complex systems. There's a saying "...all simulations are wrong, some are useful". I think that although the math may say there's zero point to lightweight wheels unless you're going uphill, I bet almost everyone notices the extra work to get up to speed with heavy wheels. Light wheels will help you perform better even though it does not matter to the wheel!
Light wheels accelerate faster, but do not help you stay there as well as heavier wheels. Light wheels spin down faster (i.e. lose inertia faster), as he addressed. Most people don't pay attention to that side of it. Said another way - you have to keep reapplying energy to the system in both cases, with light wheels it must be bursty, with heavier wheels it is more consistent. The energy quantity is the same, but the latter is easier to sustain.
What do you do when the math gives you one number and the actual real world measurements give you another?
@@kalijasin Correct the math, but people often say that real world results are different without actually showing any objective measurements...
@@kalijasin Question whether your real world results are biased or not.
I'd love to see a blind test. I agree on the statement on simulations, but something that can be trusted even less is trusting the feeling of people. 300g of wheel weight matters as much as 600g of the frame or rider (or less, depending on where on the wheel the weight is added), but you rarely hear: "My bike feels so much faster without the bottles", while "wow, the lighter wheels really help" seems common..
The point made in this video seems to have been missed by a loud minority. The argument is that if you buy a heavier, more aero wheel to replace a lighter, less aero wheel you'll go faster in almost all ride and race situations. Which has been demonstrated by real world data AND sophisticated models. Models which are valid. If they weren't your racing team looks like Ferrari, and not Mercedes.
A heavier wheel ALL ELSE BEING EQUAL is slower in almost all situations. Yes. But a wheel that is heavier BECAUSE its 60 mm deeper, will only be faster because AEROGAINZ beats WEIGHTWEENIEZ by a large margin.
And as a general point to those saying "the bike industry is pseudoscience and all BS": you can ride that 1980s steel bike with box section rims if you want, they look cool, but times change, technology improves, the rest of us will go faster, more comfortably and mug you off with out trying. Some things the industry may get wrong, or go down a particular route and find some success (weight), only to find another route offers more gains (aero) that have a bigger effect that may counter the first route. That's how research goes. There has been a huge focus on weight, now people are realising how damn important aero is.
@Paul Wieringa He has literally done the maths. These points were addressed in the video. Enve 7.8s or Mavic Open Pros. Every criterium rider is choosing the 7.8s even though they're heavier. The time saved from the aero efficiency outweighs the extra weight.
I will always listen to one qualified guy who is a genuine expert and who has worked for 14 years as a lead engineer and done the maths on it, and has a validated model over a group who think they know better with next to no experience. Though you all have a large amount of confidence, your position on the Dunning-Kruger curve is almost certainly on the left, not the right.
Take up his invitation, go out and try for yourself. Do an experiment. You may be surprised.
I think you make perfect sense. But if the video wants to claim what you are saying, then the title of the video and other aspects of rhetoric are completely misleading. You have two important factors (assuming all else are equal) -- aero and rotational mass. In many settings, the former is simply MORE important WITHIN LIGHTEST CARBON RIM wheel category. "Rotational mass does not matter" to describe this is a worst possible pseudoscientific propaganda I can think of. It sounds similar to justifying your business saying the cost is zero, when in fact your sales barely exceeded the large cost.
They should have said rotational mass does not matter "as much as you have thought it would".
So lighter wheels are easier to pedal up to speed, but heavier wheels carry the inertia longer, so they don't slow down as fast? I love the feel of responsive acceleration though, so I'm keeping my lightweight wheels.
And whenever you use brakes you waste any energy which was stored in the wheels.
The problem in their experiment is that they've traded weight benefits for aero benefits. That isn't isolating the weight difference. The proper experiment would have been done using two alloy box rims where one was a lightweight race wheel with a really light rim, and the other one was a heavy wheel with a heavy rim....no aero benefits. This would give a better measure of whether rotating weight made any difference.
This begs the question on whether to achieve "the most responsive acceleration" you would be better off spending a couple thousand $ on lighter wheels or spending the same money achieving greater weight loss on other (non-rotating) bike components?
@@kingonthehill7 When accelerating on the flats, saving weight from the rim/tyres has twice the effect of saving weight from elsewhere. Buying 100 g lighter *rims* (or tyres) is better value than saving 150 g from the groupset. But ONLY in accelerations on flat roads.
For climbing and even riding along at a steady speed on a flat road, saving 150 g anywhere is better than saving 100 g from wheels.
Moreover, the difference in acceleration from rotating weight is *absolutely tiny*. You could have any number of bike journalists doing 'blind' tests with a wheelset that's 500 g heavier, and they wouldn't be able to guess any better than random chance.
@@chrisgilligan4968 They make that distinction in their time saving measurements. Isolating just the inertial time savings vs. just the aero time savings.
2:25 Lmao I see what the editor did there
Underrated comment
Good eye.
well spotted
A heavier wheel (or flywheel) will require more energy to accelerate it to a given speed in an equal time, if you then allow that flywheel to spin down to zero, the energy conserved and time it takes will have a direct correlation to the energy put into the system at the beginning, so a heavier flywheel will spin longer after being accelerated to a given rotational speed.However, his example of only being on the brakes in a crit for 2% of the time implies that it is the time spent braking relative to the rest that matters, which is not the important part. Its the amount of energy you lose in the braking, a heavier flywheel will require more braking force to go from 100 rpm to 50 rpm, or 40 to 20 km/h, more braking equals more energy lost. You will then have to reintroduce that energy back into the system to accelerate to 40 km/h again, starting the cycle again.
He also assumes a perfect stroke, which is far from true. Fluctuations in energy disposed into the wheel differ a lot. And that hack picked triangle shaped wheels to gauge against aero profile ones to supposedly make a point about weight…
Well yes, but the overall picture won't actually be much different. Certainly not to swing a circa 20 second difference. No offence but this guy has worked for Sauber F1, I think I'll take his thoughts over yours (genuinely, no offence intended).
Maybe we can add in freewheel time and energy recovery time to the picture. That would make things even more interesting.
Isn't it relative as long as you're in motion?
@@rossfripp4503 You can have both with a light aerodynamic wheel set
Steering is also largely affected by a heavier mass. I used to have a shop customer hold a heavier then a lighter wheel by the axle while I gave em a spin, then try and steer them. Priceless😉
that's a good point, I couldn't believe the handling difference after upgrading to a lighter set
I was about to make a similar comment; I rode lightweight shallow AL wheels for 5 years then finally upgraded to a set of 55cm carbon wheels. on paper they weighed basically the same, but the carbon wheels felt really skittish on fast descents. Something i had to get used to. Not sure if having more of the weight brought closer to the center of the wheel caused this, or something else. But it definitely felt less stable on fast descents compared to my old shallow AL wheels.
Yes but in real life you are not steering by the axle, which is like 12 cm, but by the handlebars, which is 44 cm. So the question is - would the customer be able to tell the difference if you let him steer by the handlebars? Probably not.
You also don't turn by "steering". You do it by leaning....
@@padmanabhaprasannasimha5385 Steering or leaning, both are changing the axis of rotation of the wheel, and the angular momentum resists that change.
It would be cool to see gcn make a video actually comparing adding weights of the wheels versus adding weights to the whole system on non-rotating weights.
Agreed - and also make both sets box alloy rims...one with heavier rims, and one with lighter rims...ideally on exactly the same hubs if we're totally trying to isolate the effect of rotating weight.
There's a shop that puts weights under the rim tape of clincher wheels opposite the valve hole to balance the wheels. So it can be done.
@@chrisgilligan4968
Totally agree, test it.
Use the same wheels and tyres. Add weight to one set of wheels, this can be as simple as changing the inner tube with slime filled and test the wheels using a power meter. Do different tests, acceleration, braking, TT, hill climb, race, crits, commuting in traffic, road, gravel MTB. You can use different levels of riders. Love to know the results.
@@earthstick doesn't the valve balance the wheel? it has seemed good enough for me for the last 30+ years
xseamusmcx have you tried spinning your wheels and then leaving them to slow down on their own - where does the valve end up? Always at the bottom! Apparently some wheels try to balance the valve, but suspect most don’t. You can find videos that show the oscillation effect of the imbalance too
Those engineers have apparently never ridden a 10 lap crit race with 5 sharp corners where you have to slow down to 20 km/h and accelerate again to 50 km/h 5 times a lap!
In the second half of the race you'll have a lot of trouble of closing the gap each time to the opponent whose rims and tires ( rotational weight ) are 400 grams lighter than yours. Your legs will blow up after 25 accelerations and you'll "loose the wheel" of the last rider of the peloton, game over!
A bike with a set of light ( tubular ) tires and rims will feel much livelier than deep section alu rims for example which you will benefit from on a climb as well.
Just like my sportscar is a lot more enjoyable to drive with the lighter summer wheels ( and a lightweight flywheel ).
I agree with the theory for a time trial but reality differs a lot from the mathematics in the lab.
So I suggest you compare two 8 kg bikes with 40 mm deep rims ( one alu, one carbon ) in a blind test and ask a few dozen experienced riders their opinion about the one they would prefer and why they would prefer it. That's practical and useful science imo.
I completely agree with you. I was so stunned at the performance of lighter wheels on my road bike that I - like you - went further, and specifically bought same-diameter, but nearly 10-pounds lighter per wheel, wheels for my truck. 0 to 35 MPH, only someone who knew the truck really well would notice the difference. 40 to 60 MPH - the difference was obvious and large. 60 to 90 MPH the difference was huge - much faster / better acceleration, and I was saving gas to boot (when driving sanely).
He does actually cover this in the video
I was thinking about those > 40km/h corners where you don't have to brake, totally have to rely on your tire grip and can't peddle for multiple seconds. (90% of crit corners). Heavier wheels means higher exit speed, because of the stored energy and therefore less acceleration is needed.
@@sebastiaansiemensma I don't consider this corners but just a bend in the course. In Belgium most laps of a 65 km race contain at least 4 corners each lap where even the frontriders have to slow down to 25 km/h. After the turn they speed up to 50 km/h to make the other riders suffer. And on the straight you often need to accelerate suddenly to be sure to get in the breakaway.
@@sebastiaansiemensma Do they mean a higher exit speed? I could be wrong, but it seems that the entry speed seems limited by tire grip for how hard one is able to go in to the corner. Tire grip being a limitation, it means one has to slow for the corner to (what I believe) would be the same speed for a lighter or heavier wheel, but then the lighter wheel will win out when it comes to bumping that speed back up from that given traction-limit-speed for the given corner.
I can see the benefit of heavier wheels on rolling terrain where the inertia effect means you can maintain a constant speed with less acceleration. Acceleration is where the energy is expended. With more inertia you put in the effect at the start to spin up the flywheel, then recover and maintain a constant speed with little acceleration. But if you must decelerate and lose that inertia then you will expend more energy when you have to accelerate again. Pretty soon you are over your threshold and slow right down. I've done a few accelerate, brake, accelerate crits and it takes it out of you. If you have heavier wheels and cannot accelerate to stay on someones wheel then your aero really suffers - far more than the difference between deep and shallow rims. If you drop off the back you are done for.
Constant speed and zero acceleration is the fallacy that needs to be kicked into touch. If you can read power meter data and understand how power meters work you will realise that the wheel is constantly being accelerated
@@MP48 I suppose there is always wind resistance and gradients to overcome. And rolling resistance, bearing friction. And you pointed out power delivery during the pedal stroke. I notice when climbing steep gradients on light wheels it is like climbing stairs. Left foot down I move forward then stop, right foot down forward and stop. Better technique would help but if the gradient is very steep then it's out of the saddle and I don't know how you would smooth the pedal stroke when out of the saddle.
@@MP48 Yes, this was my thought as well, you have to move the rotating weight just to maintain consistent speed...
That was my thinking..the drafting effect didnt seem to be part of the calculation that you can do or not do with lighter/heavier wheels..if you can or cant follow someones wheel..
Makes 0 practical difference. The inertia contained in a rotating bike wheel is essentially 0 when compared to system mass and energy requirements. Go ahead and spin a wheel up to 40KPH on the work stand, then just grab it with your hand- it will stop almost instantly (wear a glove).
So man who sells heavy aero wheels telling us to buy heavy aero wheels. Nice.
He must have told his Formula 1 team rotating mass doesn't matter too!
Rotational weight is affecting due to change of inertia and thus the added difficulty in the change of angular momentum the acceleration. For that reason it's harder to accelerate fast and may be fatigueing over the course of race with lot's of sprints. It's also very important to take into to account that the rotational weight of a aero wheel is distributed closer to the centre and thus the inertia of a the aero wheel will be smaller in comparison to a low rim profile wheel with the same weight. All of this has to do with the torque, witch the rider has to apply. In a race with lot's of accelerations it can be very power demanding to keep up with riders with lighter wheels. But it's very clear that aerodynamic advantages are more important over the whole course. And taking into account that the weight defences are very little (400gr) it's clear that the impact will be minor.
Nikolas Patelis Agree. I think a good way of thinking on this is race vs recreational: most of us, most of the time, are beginning and ending our rides at the same geographical position, ridning mostly on roads with curves designed for cars at around 50-70kmph. So, most time is spent in a pretty straight-ish line, keeping the speed somewhat constant (depending of course on your specific area, hilly or flat) resulting in the slower climbing will be almost nullified when speed is easier to maintain with that flywheel effect of the heavier wheel (a heavier rider such as myself has a similar experience when rolling besides his fitter and slimmer mattes 😃). The aero is playing the main role over 20-22kmph regarding rolling resistance and I would think it also dominates regarding regular rides in most cases. Races and such are different, geography, acceleration and climbs may, when combined, start to make weight a but more important factor.
so you say my 26" mtb is faster tgan my buddies 29" mtb. but my 30 kilo plus are the problem?😂
so you say my 26" mtb is faster than my buddies 29" mtb. but my 30 kilo plus are the problem?😂
If ever you lose a wheel because you could not accelerate in time to maintain the much bigger areo advantage of staying behind someone or the pack, then you only get to use that areo advantage in then wasted every to chase the pack or person that dropped you.
Agree when it comes to lots of sprints, or lots of slinky-ing within a group that is always pushing it.
This is incredible. The fundamental premise here is that if you don't accelerate weight in the wheels doesn't matter. You have to constantly accelerate on a bike. Your bike is naturally decelerating all the time if you do nothing. Ride on the flat, don't pedal, you will eventually stop (due to wind resistance and mechanical friction). Ride up a hill, don't pedal, you will stop, usually a bit quicker (due to air resistance, mechanical friction and gravity). The watts you put into the bike are a force of acceleration against the deceleration forces of air, friction and gravity. Put in more watts you will speed up until you equal wind resistance, friction and gravity, put in less watts you will slow down until you equal wind resistance, friction and gravity, put in zero watts and you stop.
More energy (watts) is required to accelerate 1 gram at the rim of a wheel compared to 1 gram on the frame due the laws of angular momentum, more easily descibed as leverage. Like a see-saw the further from the pivot point you are the harder it is to move you. So rotating weight is more important than non rotating weight.
Notice how all Jean-Paul Ballard's comments are about his models. There is no real world data here and I am sure his models are basically wrong.
And so is he along with the title of this video.
Whats interesting is that in crit racing or any racing, there are 2 big scenarios where it matters and where it would be nice to see the difference. First obviously are finish line sprints. Second is, whats not to be forgotten, is when someone attemps a breakaway you have to stay on his wheel to be in the slipstream. The slower you accelerate the more likely it is you loose the slipstream and thus cannot follow or loose too much energy for catching up into the slipstream.
I feel they also used a fixed crit as the example and fixed crits have a much more consistent speed than other crits as no one can brake and have to go into a corner slower so there would be less “braking” therefore less energy lost.
@@joeadlam-cook2769 judging by the video, they used a circuit race at a motor racing track around an old airfield. I’ve raced there too - it’s fast, wide and you should never have to brake. The only things that slow you down are the bloody headwinds and the occasional crash.
Yes. It's about the gaps--either accelerating to create one and force the person behind you to overcome all the air resistance themselves, or accelerating to prevent yourself from being gapped. Everything he's saying about the flywheel effect is true, but it's not the only consideration in the crit scenario.
Exactly! In addition to your settings, you can very easily drop out of the peloton not being responsive enough. I can understand how a "F1" engineer not too familiar with cycling comes up with an armchair theory. However, I have absolutely no idea how Ollie simply nods to the absurd explanation by Jean and even goes onto making another video about a stupid experiment on this theme...
You're absolutely right, but even then, simulations show a very low difference in required watts between 200gr on the rims versus 200gr on the frame. The fact remains that both the relative weight of rims versus total system weight and the speeds reached are relatively low. Compare steel versus magnesium rims on a 300kph race car and the results are very different.
Something that is also interesting is that heavier wheels will be harder to lean into a corner. Just take a wheel and spin it in your hand, see how hard it is to turn/lean. Physics teachers (myself included) do this every year, if you decrease the weight or speed it will make it easier to lean which means less arm fatigue which most cyclists should avoid...
This is the type of video that should be on the tech channel...diving deep into the engineering and technical aspect of cycling and giving the viewers a good insight about what is actually happening...this advanced level stuff is really appreciated (at least by me)...for example on the technical side...rather than explaining again and again about how to adjust brakes and gears that are covered in previous videos...new video can be about the effect of b tension screw or derailleur tension spring on gear shifting and how it can be tuned to perfection using that...there must be much more than just a barrel adjuster in indexing of gears on the advance level... please make videos like these...and I love Ollie's presentation of the techy things( obviously jon as well)....
You should check out the Park Tool channel for that sort of thing. Calvin Jones is a particularly good presenter on their channel - especially on derailleurs.
Hallelujah!
except they didn't dive into the engineering and the insights are cherry-picked.
Going uphill requires constant acceleration in order to counter constant deceleration due to gravity and elevation gain. Even moving on level ground requires acceleration to overcome friction. Also, rotating mass is always in acceleration because of the constant change in direction (centrifugal forces is mass x acceleration which is taken at tangent to the wheel). If you were not accelerating then no need to pedal. You pedal you accelerate, you don't pedal you decelerate. It is the weight or mass of the wheel that you are pushing to rotate.
Same applies to the overall weight of the bike. Again the energy is only wasted when you use the brakes.
Light bikes are overrated unless you only climb steep hills quickly.
Where weight really matters is in a constant start stop scenario such as city riding.
Yeah, Gravitational potential energy = mass x force of gravity x height
so more mass means more energy either pushing you down a hill or making it harder for you to ride up a hill
I am wondering if 1kg savings on your bike makes the same difference as 1 kg on someone's beerbelly. My knowledge of science tells me that spending thousands of Euro's on the bike for weight savings, you can better skip some McDonalds trips. With the money you save with that you can buy stuff for your bike
Its important to remember that the extra energy put in on a climb due to a heavier bike is only wasted if the brakes are used on the way back down.
If only the uphill is timed then obviously light weight is important.
A heavier bike when starting a hill climb will go further up the hill before reaching a lower terminal velocity determined by the available power output.
So... it's only affect weight, deceleration and accelaration? And handling I suppose but a fraction
wjeurs once you are reasonably light, however, the bike is the last thing you can take weight from. I shaved 16 seconds off a 12 minute climb to poach a KOM by stashing my bidons in the bushes along a layby at the summit.
I've used heavy wheels and lighter wheels and I can really feel the difference when moving off, but once up to speed the heavier weight wheel does almost drags you up the hill, but I'm guessing that the breaking will impact on corners and that will slow you down overall.
I'll never forget the first time I rode uphill with carbon wheels. It felt almost effortless. Of ccourse it wasn't but that was the sensation, because it was much easier riding uphill than with heavier, alloy wheels (still is).
it's exactly the same with say car/bike engines and flywheels. a lightweight flywheel can make the engine feel revvy and zippy. but if you've got a low power engine you need a decent amount of flywheel mass to keep momentum between power pulses especially on a low cylinder count engine. 2cyl engine opposed crankshaft (same as riders legs) you don't want the flywheel to be so light that it looses speed so fast that engine can't get the piston to the next compression stroke on the other cyl, would make for a very lumpy ride with each power pulse kicking the motorbike.
thanks for that
This has very little to do with cycling, unless you find a rider with an anomalously inefficient pedal stroke. In general, RPMs don't change much throughout a cyclist's pedal stroke. Very, very little throughout the pedal stroke of an experienced cyclist who has worked on high, smooth cadence.
However, it does raise a point I was discussing with a tandem rider. The "drivetrain inertia" of a tandem team many feel leads to power output losses. Not sure I agree. However, in my experience, I have noticed that the inertia found in a tandem drivetrain does appear to sap my energy, I've found. When adding power to the pedals on a single (half) bike, the drivetrain responds and the rider and bicycle accelerate together. However, add power to a tandem drivetrain, and you have to overcome your partner's cadence, plus the added weight of the tandem. Result is greater fatigue fighting this increased inertia throughout an entire ride and thousands of pedal strokes.
Ollie,
Yes, I've been waiting for this video, thanks!
Throughout this discussion, no mention was made of the cyclic nature of power application to and through the pedals through each crank rotation.
Maximum power transfer through the pedaling cycle only occurs while the rider is pushing DOWN on the pedals, somewhat augmented by pulling up on the back cycle with the opposite leg.
Very little power is transmitted as the pedal(s) is(are) brought through the bottom and over the top.
The result of this when climbing and/or riding into a stiff headwind is that EVERY down stroke on the pedals is an acceleration event, gravity and/or wind force counters and negates inertia effects.
Observe your own pedaling while climbing @8:27 through 8:38 where each down stroke effort is a distinct effort event.
Rolling hills are indeed a special case where, if enough speed can be built prior to the climb and maintained through the climb, inertia is indeed significant.
Y'all at GCN are power meter nuts, I suggest you find some software that can record and display power generation peaks/surges and nulls through individual pedal cycles, see if there are or aren't corresponding bike+rider speed surges and lulls while climbing.
I suspect you'll find an inertia benefit on gentle grades that diminishes from insignificant to detrimental as the grade increases.
Really interesting and informative. However, I would add that in a criterium the accelerations are crucial parts of the race. If you can accelerate quicker there is more chance of getting away or winning a sprint, it doesn't matter that you have that stored energy once you have crossed the finish line or once you have been caught. You have to put it into context, it isn't just a solo time trial with lots of accelerations in.
Totally. these are the moments races are won or lost.
If you can't accelerate quick enough to stay on someones wheel then you aero suffers far more than the difference between deep and shallow wheels.
Completely agree, the difference might me tiny but the next thing I'd like to know is how much more power you'd have to apply during accelerating out of the corner with lighter (but equally aerodynamic) wheels. These are the most critical moments in a criterium where you potentially spend a lot of energy catching up to the rider in front of you. And I'd like to know how to use the stored energy in corners if you have heavier wheels. Would you ride differently? Would you start softpedaling earlier?
Great point and well put. I would love to see the simulation result on how big the gap difference is in a crit acceleration effort (with 400 gram wheel difference as discussed, not the straw-man 10+ kg some people want to pretend). Are we talking 1 meter plus or 1 cm?
In a criterium you should try to avoid having to accelerate a bunch except for the finish. I often see people grinding too big a gear out of corners, spin those legs
Utterly fascinating. I can see how having slightly heavier wheels in a time trial with rollers would help keep you in the sweet spot with your cadence
Does this mean manufacturers can start adding a few more spokes for durability?
I took my touring bike with 36 spoke wheels for a 220k spin today. About 100k in, an unmarked crater in a forest section (couldn't see it in time to dodge). Must have been 4-5cm deep and 1m across. I was doing 36k an hour and hit it full on. Result? Wheels are as true as ever - no other damage either. This isn't the first time I've done this to these wheels and they have done about 15 thousand km.
@@orsations You call a 1.5 inch deep pothole a crater? ahahahahah what a good joke. Here in the city that's nothing, you can easily get ones that drop down 4-8 inches.
Nah, low spoke counts are for aerodynamics.
Better ask their spokesman :)
No. This would make the wheels more durable. This is not what the bike industry wants ;-) It prefers to sell you heavier wheels by just carbon fibre in useless places. And for your wheels to brake right after the warranty ended.
Something that wasn't explicitly said but seems relevant is this thought (if I understand it correctly).
While you feel the difference (benefit) while you are accelerating (2% of the time or whatever), you don't notice the difference (penalty) spread out evenly over the 98% of the rest of the time when you are not paying attention to the extra work you are putting in to maintain your speed on a lightweight wheel.
That would explain the counter-intuitive nature of these findings.
Would love to hear any feedback if I misunderstood anything.
You couldn't describe it more precisely! And yes, you understood it 100% correctly, in contrast to everyone else here who says you'll have to pay more energy when you need to attack. That extra energy that you need to spend when accelerating your heavier tires for a sprint is exactly what you save when keeping that speed in contrast to your opponent with lighter tires. The necessary power is higher for accelerating and lower for keeping speed. Energy does not change, except resistance of wind and friction which are in both scenarios equal (given total bike mass is equal and the difference is only weight distribution on/off wheel).
Actually BS what i wrote. Keeping the speed doesn't cost you more or less energy. But you'll save your energy when you need to let your bike roll, e.g. corners, because you maintain your speed longer than with lighter wheels and your opponent with lighter wheel would have to paddle to keep up with your rolling speed.
@flo rian Another thing to keep in mind is that the rider's output is not stable. For non-race scenarios - touring, commuting, utility, etc. - over the course of a ride you gradually get more tired and modify your cadence to fit so you get where you need to go at all, in a reasonable time frame. In a race scenario speed is speed.
So for your "average joe", a short 30 minute ride will "feel" better than the last 30 minutes of a 4+ hour ride. With heavier wheels, when the going gets tough you can theoretically optimize yourself by slowing your cadence, making your pedal stroke worse, and not lose as much speed. Reducing your power output while maintaining a higher level of air-cooling! With lighter wheels you'll find that you start slowing considerably, which may make it feel worse and force you to choose between looking for the next hill that will let you coast and stopping for a break.
Of course on the flipside, if you have to constantly stop at lights and signs and so on then the heavier wheels will burn you out and make you considerably slower, so it depends on the actual route taken. As well as it not being a simple wheel swap - heavier wheels should mean a lighter frame and so on, which can impact other aspects of ride quality, cost, and durability. If you just swap to heavier wheels from lighter it will make everything harder - hills especially.
Boy, I am so glad I saw this. This is exactly what I needed to help me move into the top 100 of my local Wednesday night group ride
Two points come to mind:
1) If you choose the wheels that weigh 400 grams less, you're not adding 400g of static weight somewhere else on the bike. So the lighter wheels in this case DO make a difference. Certainly more than removing your bar tape or sanding the paint off your frame (right Ollie?).
2) Responsiveness during acceleration is important. So it's not just discarding energy through braking that you need to worry about, it's any time there is an increase in speed - especially during attacks, chases, sprints, etc..
Here's an idea for Ollie and @GCN Tech to test in the lab: How much power/energy does it take to accelerate 1) bike with 1600 g wheels, 2) same bike with 1200 g wheels, and 3) same bike with 1200 g wheels + 400g static weight added
Thats a good idea Kent, we should do that test. Although in terms of responsiveness to attacks you balance it out via the benefits of aerodynamics and the rotational momentum elsewhere
Ok so understand the science & math ( I think), but it seems to matter to me! I did the "light" vs "heavy" comparison test a few months ago Mavic Ksyrium SL vs Cosmic Carbon Pro. Whilst the overall time for my "fixed" route was about the same there were areas of decernable differences. On the steep climbs the Ksyriums were quicker, on the flat and especially the long descents the Cosmics were quicker. I also detected the "flywheel" effect of the Cosmics on the undulations of the road (not enough to call a climb!). So the question is why the Ksyriums are faster on climbs ... my thinking is that because I don't produce great power numbers and my cadence will drop on a 14% + climb, that with each pedal stroke I'm having to re-accelerate "the system" and that's hard work for me with "heavy" rims.
It matters when you take into account the sponsor, this years marketing agenda for said sponsor, and the test designed to achieve the desired marketable results. Then it all makes sense.
It seems to me that the goal of the cycling industry at the moment is to make everything non-compatible so that the brand you pick (the brand that spent the most on marketing) is the one you're stuck with when it comes to replacing worn parts or upgrading. It's really sad to see.
If you want to be the fastest guy on a group-ride get a recumbent. Forget all these arbitrary rules that professional cycling has placed on the simple sport of beating your friends racing down the street.
Cycling might as well be Formula1. Just let the teams with the most money make the rules that allow the products that teams have already developed and tested.
What's the argument for disc brakes on road bikes if rotational mass doesn't really matter?
Sorry...I had to let out a rant. I feel better now.
To do this test correctly the bike must weight the same with both wheel sets. If you only change to a lighter wheel set so the "system weight" is going down, the bike will be faster uphill. The video was about if it is better to loose wight on a pair of wheels instead of elsewhere on the bike, not about if less weight is better than more weight
@@AndreDargan Agreed!
You misunderstood the video. In your last paragraph you say re accelerating the wheel on climbs is hard work. You're mistaken. If you're not braking, your wheels are not robbing you of energy. All the work you put in into accelerating the wheel gets stored as kinetic energy in the spinning wheel, which is expended by the wheel rolling up the hill. For example: if you had a bike with extremely heavy wheels and got it up to 30km/h, and then got to the start of a steep climb, and stopped pedaling, the heavy wheels would carry you up the hill with their inertia. Again, unless you're braking, no energy is lost.
The energy argument (if wheels are heavy, you put more energy into the wheels, you don't lose it) is correct in physics terms but does not tell the whole story for several reasons. One is that acceleration time matters: you could pull a trailer with your bike (yes, GCN tried!) and all the energy you put in goes into the trailer moving. Does it mean you will be "fast"? No, because it will take longer to accelerate up to speed, and also longer to slow down (e.g. before a corner). The energy is there, but the time it takes to get up to a certain speed matters in most scenarios of cycling (except steady-speed time trial on flat terrain). The other reason is that every time energy is converted into another form (say, from your body, to the rotational speed of the wheels), some is dissipated. Hence, it is better to minimise the energy converted into anything that is not linear speed of the bike. This is also true for KERS in cars: KERS converts kinetic energy into rotational energy of a flywheel, and then back into the car liner kinetic energy, but a bit of it is lost in the process (twice).
Thanks just what i was looking for!
The point being that saving rotational weight isn't any better than saving ANY weight at all. So if it's 2000 Euro's to save 400 grams on wheels, or 200 Euro's to save 400 grams on a saddle, ten times over go for the saddle first. Well all that being accurate for competitive cycling. On a commute with stop lights that might be entirely out the window.
But you're missing the point about pedal phases. If the wheels store more energy, you can put a higher amount or energy into the rotational system at the most efficient phase of your pedal stroke and not rely so much on effort during the least efficient phase to prevent the loss of rotational velocity. Keeping the wheel turning during top/bottom dead centre means a more stable overall velocity -- stable velocity = less deceleration and acceleration = less energy lost.
Reduce it to one factor and you don't get the full story.
I think you are on to something. The effect might be small, but it is not 0. Using myself for calculations, if we take 200 grams from my body and add it to the rims of my wheels this would result in accelerations requiring ~1% more effort despite the weight of the total system being the same. That is small because [like has already been stressed] this is only during acceleration. However in a Crit you would totally feel this!!!
A simple way to look at this is 400 grams extra at my rims is equal to 890 grams or 1.96lbs of body weight.
I will concede aero-gains are king, but don't belittle wheel weight. I think people forget just how much you need to be able to accelerate in races, adds up fast.
Also what is crazy is this effect becomes even worse the lighter you are.
@@SeanBlader When coasting you are right, but every acceleration, the weight ar the rims has more than twice the momentum effect than static weight. So it could mean you loose the sprint at the end of the race.
I have watched the video a bunch of times since you first released it. I find myself returning to it at key moments in my life--precisely when I am obsessing about how much my bike weighs and when I am thinking about a new wheel set. It is a powerful example of how myths are generated and perpetuated. And, why it is so hard for the science to actually crush the myth. I understand the science and I still find myself believing the myth. This video is a reality check.
Science have debunked everything, everything is written down in some paper somewhere
The way i see it is basically, everyone is just trying to sell snake oil, GCN, Shimano, the aero wheels salesman, etc
And what is the answer about what is the best wheel? As always it depends on what you want to do
And the course you are riding on
Weight is always important, more weight means more energy you have to spend to accelerate to a certain speed, and the more energy you need to acend a slope
Hardly irrelevant for long flat sections
Aero is always important to and exponentially so
The more coeficient of drag your bike (and you as a system) have, the less top speed, small changes in aero can bring huge watt savings at the top speed and will make much easier going against the wind
Now going with heavier aero wheels will mean 2 things
You will get more top speed on the flats but also it might be harder to go over not so smooth terrain because when you hit a bump your wheel has to move out of the way, which means you have to spend some energy into moving the wheel away from the bump, and that energy is taken from your foward momentum so the bumpier and heavier the more the speed toll you take
Shallower and lighter wheels will accelerate faster and be more nimble and controllable in cross winds, as well as less energy taken from going over bumps, but they are draggy and drag is exponential so in the flats where you must be at top speed most of the time its not ideal, and front wind will be way more painful
Tldr: for TT in perfect indoor condition and surfaces, use high pressure full aero wheels
For courses with mild but mostly flat terrain without many climbs and mild winds, use 50-80mm deep wheels
For less than ideal terrain use low pressure and lighter wheel combo, it will be faster
Now wide tyres and heavy wheels are better for performance...
Must be why racers all use fat bikes?
Loads of factors here. See some people trying to defend lightweight wheels for their lives, but all in all, I don't see much point in splashing out the cash for a little lighter wheels if the engine is crap.
One thing that not discussed here is that rotating inertia is not the complete mass of the wheel being placed at the maximum radius of the wheel - the distribution of that mass affects inertia. Where Inertia = Mass * radius^2, you don't put r as a constant and simply vary the M. M being closer or further from the axle plays a big part. Simply put, a heavier aero wheel may very well have a much better distribution of weight near the axle, giving rise to the minimal results observed.
Interesting piece. I wonder what impact the tyres have. I know when I take my carbon tubs off and put on Fulcrum 5s with schwalbe marathons the local bunch ride gets about 10X harder!
13:49 offers a sneaky clue. From the point of the observer, we are biased towards only perceiving the effort of acceleration. And so the deceleration effect of light or heavy wheels are often discounted from the experience.
Because tyres can change rolling resistance and that difference can be quite big. You might be able to push 250W but struggle doing 256W needed when fitting worse tyres on. Other than that, weight is again not really the issue.
Tyres / tubes will potentially have a bigger impact than wheels and wheel weight.
that's because the rolling resistance of the tires is like 30 watts higher at 45 km/h, which applies regardless of whether you are in a draft or not.
Tires can also impact aerodynamics. A wide tire presents a bigger frontal area to the air flow and if it the tire is significantly wider than the rim, the air flow separates at the bead and creates drag.
Great!! So I guess it's time to order my 100Kg concrete rimmed wheel-set!!!
Many of these "scientific" explanations run simulations as if human cycling power is constant and dependable. It's neither. It is not constant like a motor, but pulsed, driven by contracting muscles that put power out often in two different power curves for each leg. And it's not dependable--it depends on one's motivational state.
This psychological factor is never taken into account. Human's are not robots or motors that put out unconditional power. We have to believe the power we are putting out is effective. For instance, in a headwind, my morale is low and I might put out 180 watts average because I don't think it's much use to work hard, since putting out more wattage doesn't seem to affect my speed much. In a tailwind or in a group ride, morale is high and I feel the effect of putting out more power, motivating me to put out an average of say, 250+ watts average. The same can happen with heavy wheels, like gravel bike wheels, on a hill. Putting out 300 watts up a hill on those wheels seems like a fools errand, as their extra rotational and gravitational weight is felt acutely during the micro accelerations while pedaling up a hill, so psychologically I think it's useless to put that kind of power out using those wheels, so I back off to a lesser effort of say, 180 watts, like the headwind. I've been psychologically beat by the heavy wheels. When using lighter wheels however, as a climber, I feel a big difference on how much better they micro-accelerate with each pedal stroke up the hill, motivating me to put out 300+ watts for the endurance of the hill. Psychologically, the lighter wheels motivate me to work harder.
This means if something like lighter wheels motivate you to work harder, you will go faster than with heavy wheels. Maybe not because lighter wheels perform better, but because YOU perform better using them.
@@sc9160 100% it DOES matter. I've recently gone from a 15kg MTB to a 9kg road bike and the difference in acceleration is huge. I now actually try harder because I am actively rewarded for the extra effort; the difference in acceleration is hugely noticeable.
@@sc9160 Using that logic, doing a hilly ride that starts and ends in the same place is no more difficult because of energy conservation. Or someone pulsing on a gas pedal of a car is going to get the same mileage that someone using constant pedal pressure does, which we know is not true.
I'm with Dave. When they start using real models of how people cycle, rather than idealized ones, I'll put more faith in the results they arrive at.
The point is...your heavier wheels feel slow and heavy because they are, but you would feel just as slow and heavy with your light wheels on and an extra kilo of water in your cage or tools in your seat bag. The fact that the weight is rotational doesn't matter...the fact that heavy wheels are HEAVIER does matter. A subtle difference, but a difference nonetheless!
Hello, I agree with the video and former remarks. BUT!!! The results are fine and true in lab, but you should have added, what is the watt diferrence the heavier rim cyclist must make in order to accelerate from 20kmh to 45 khm, how many meters I loose when accelerating with the same watts from 20 km/h to 45 khm with 500watts with different wheelsets, etc? You are a racer and you must know that there is a difference when racing between two scenarios: First, when you hold a steady tempo 300W over one hour, and second, when you hold 200W over half an hour and 400W over the other half hour. The average (and total) power is the same but one is achievable and the other not (unless a pro rider). So, you should not repeat all over again that the power is lost only when braking, but try to explain in more depth the actual differences. That is where your video fails. Also, the name of the video is about rotating weight, not aero effects. Although it is helpful to see the effects of aero wheels, you can compare light/heavy aero and light/heavy non aero. comparing heavy aero and light non aero tells only half the story. In my opinion, the intention was perfect but the performance very poor. Also, I would like to see the course of the crit. There are crits when you do not need to break to less than 40, then there are city crits where you must brake to 20km/h and accelerate to 45 km/h. So, maybe the result should be: "all in all, you exert almost the same total power nonwithstanding the weight of the wheelset, but it feels very diferrently in some of the crits and it may loose you a crit if you do not manage to accelerate that quickly with heavy weight rims..." Is that correct or did I miss something? And last remark: During a race, there is 30 procent of time when you ride on the limit and 70 procent when you pedal easy... It is the 30 procent of time when on the limit when the power differences are important. It does not matter whether you must extend 220W with lighter rims when compared to 210W with heavier rims when just coasting... It matters whether you must extend 400W with heavier rims over 390W with lighter rims when actually racing (going into breaks, covering breaks, etc.). If you could dig deep into these questions, THAT WOULD BE HELPFUL! Thanks for the content, carry on and please dig deeper!
I think I agree with almost all of your points and dislike much of Jean's argument.
I also think that your comment should be divided into paragraphs to ease reading however. You had too many good things to say in a single paragraph. It is a pity that your comment only has five upvotes.
I love your science videos! Wouldn't mind more of them
Bokaj Grummel this isn’t actually very “heavy” on science at this point. First, it’s an incredibly small sample size. One rider on 3 courses. Second, it hasn’t been peer reviewed. To determine if the methodology is flawed or not, we need other people to replicate the results independently. One day it might turn out to be proved correct but for now it’s not rigorous enough to put a lot of “weight” into it.
@@sportbikejesus did you not hear him say that basically every engineer that they talked to said the same thing? No this isn't a scientific study, but it never set out to be. It's an informative video using science to explain a common misconception.
@@sportbikejesus so.. more science videos, you agree, right? haha
this is surprising, but actually makes sense once you hear the reasons. great stuff! thanks!!!
But the main topic this video is talking about is the rotating weight, so what you should do is use same rim profile but different weight. In that way, you're truly comparing rotating weight
This. I hate it when a light weight low profile rim is compared to a heavier, aero wheel. What i would like to know is how much is the difference between a cheaper and safer 2kg 50 mm alloy carbon wheelset and a 1,5kg 50 mm pure carbon wheelset. I know, aero is the most important.
It does not matter in terms of mathematic calculation. You have to difference weight and height ( which is aiming for different effect. Aerodynamics dont care about mass. It cares only for shape)
Agree with physics part of the assessment in terms of energy added and stored. However, weight does matter in real life because it’s all about the acceleration in the fastest amount of time to stick with the draft of the rider in front. If you have to put in more energy over a longer period of time riding heavier wheels, you will lose the draft of the person in front of you and therefore use more energy to keep same amount of speed. Lighter wheels help you quickly accelerate to stay in draft even if you have less inertia stored in the wheels. You can’t have scientists who don’t ride tell us what’s faster in real life. You need to understand not just what’s faster over an hr but when fast matters in a hr race.
Bang on
you miss the point of inertia here. With a heavier wheel you spend more energy spinning it up but less keeping the speed. So you donˋt "put in more energy over a longer period of time" - you put it in differently though. My personal take on it is that you can only feel in the legs the acceleration bit, the rest is not something you can manage to sense or feel. You can see it on the time though. Also Iˋm a engineer but Iˋm not an expert in this particular field and through my actul work experience I have come to realise that for any field of complex physics simulation it is a highly specialised competency done by specialists and there is a 1000 ways that one could miss some small points actually making a difference. Hence I fully support the last bit about going out testing it in real life. Also to anyone not beeing such a specialised professional in this field to actually think you know better or more on this by genetics or practical experience is just arrogant and that is something I have witnessed to cause horrible failures in real life. Do doubt the specialised professional, like the heart surgeon prior to a open hart procedure - or do you trust him/here more than your own gut feeling in that situation? A lot of people largely overestimate their own knowledge based on nothing way too often. Get too know your actual competancies and let others del with the rest. We will all be better off with that.
Thanks Robin, but I am a Ph.D engineer and I can prove he is wrong with math. Kind of ironic that you questioned my knowledge with your comment. 🤣
But don’t you will coast longer with the greater inertia? You didn’t think about that.
I feel sorry that popular videos like this tend to have overlapping comments, since we all have no time to read all the comments (I am an exception escaping from reality). Yours and mine and several others all refer to peloton drafting effect completely ignored by the video. The similar comments each gain only very small number of upvotes and thus are not shown on the top of the comments. And so-called "engineers" look down upon the opposing folks as stubborn cyclists, not reaching the most scientific comments like yours. What a pity... I only hope that Google will find a better way of organizing too many comments in the future than simply using upvotes.
I live in Switzerland and have met JP and even bought his deep section 800 Swissside wheels for my TT bike. You might think I am biased.. however, ....I can honestly say my PBs instantly improved on fixed, flat courses both in and out of the wind. I was consistently faster and they are 500g heavier than my lightweight wheels. But, because I actually have only a meagre 175W FTP my climbing creates another interesting dynamic. When I climb anything above 5-6% my pedal stroke is noticeably exaggerating the lack of power delivery. Therefore, I actually do change speed marginally during the pedal stroke. I notice that my wheels are constantly "re-accelerating" because I can hear the whirr noise change in volume in tune with the irregular rhythm of my pedal stroke. I have several minutes difference in my PBs between these two wheels sets over a regular 20min climb I use. I think I need to change out my cassette for a lower 32T and check again. I think that would be interesting to isolate my pedal stroke deficiencies. I do believe though, that if I had a 300W FTP and a better pedal stroke I am sure I would get closer to seeing only a 4 secs difference. For me, two vastly different wheel-sets are a much needed compliment to my cycling armoury given my particular circumstances.
I think if you kept your cadence higher then you wouldn't feel those decelerations during the pedal stroke. Definitely get a 32 cassette!
One of the best episodes ever. By the way you are a wonderful presenter. Clear honest genuine and a true lover off the sport. Very good job.
When you are commuting through a city, you have constant stop-starts as you go from one traffic light or road crossing to the next. It may be as many as 5-10 full stops and accelerations per each km travelled. In addition, you very rarely reach the sort of speeds where aero of the wheel starts to make a difference before you have to stop again. It would be insanity to claim that the weight of a wheelset makes little difference to your commute speed and fatigue under these conditions. Clearly lighter is better for anyone interested in getting across urban areas fast. It’s up to the consumer to decide whether they want a heavy flywheel that reduces drag at constant high speeds, or a lighter one that bleeds less energy out of the brakes over repeated full stop - reacceleration cycles.
But urban commuting _isn't_ a competitive sport. And if you really needed to go so fast as to buy expensive wheelsets, you'd might as well get a moped, or even a second-hand car with that money instead.
I'm looking for testing that shows how much time a lighter wheel would save me in a commuting situation. If spending $1,000 on a new set of lighter (and possible more fragile) wheels saves me 30 seconds on my 5 mile commute then it clearly isn't worth the money to me.
@@randompheidoleminor3011 you heard about green house gases and climate change ?
@@francoisgenerau7250 then you could use the cash to plant trees or donate it to an organisation of your choice.
Unless somehow not buying a set of carbon wheels magically means the guaranteed destruction of life on earth as we know it.
@@randompheidoleminor3011 Unless you care about carbon emissions, fuel costs, parking costs, sitting in traffic etc. But yeah, most people don't tend to spend at the "diminishing returns" end of the scale to get 1200g wheels for a city commute.
This is EXACTLY what I found out for myself empirically 27 years ago, when I bought my first lightweight bike, which weighed 10.5 kilos as opposed to the usual 14 kilos. Within the first 100 yards, I could FEEL that you had to make continued effort to maintain speed because the effect of inertia was diminished, however so slightly. Kind of like throwing a pingpong ball as opposed to a golf ball.
I'm still riding that bike...
Without having seen the video, it's pretty obvious that due to conservation of angular momentum the energy that's used to get a heavier wheel spinning isn't wasted but stored. And thus the only effect a heavier wheel has is that acceleration will be slower.
Yea pretty much the thing that change is the bike weight
so will decceleration, and then you need to get it upto speed again
Yeah but thats the point, we want to know exactly how much is the difference. Thats the big point. How much slows 500 g on similar wheels slow you down when accelerating. Do you loose a wheel length? A bike length? More? Thats whats interesting because that can matter.
@@satrioesar7151
"Yea pretty much the thing that change is the bike weight"
No. They are comparing the same total weight: This video answer to the question: Is it better spent money to save 0.4 kg in the wheels or in the rest of the bike?
In other words: 500 € to save 0.4 kg to the rest of your bike is better than 1000€ spent to save 0.4 in your wheels, as there is NO TIME advantage in saving the "rotational weight", other than a faster acceleration.
The only difference, is that will be easier to change the direction of the bike, having the weel a less inerzia rotazionale and harder to stay on the wheels of somebody trying to escape from the peloton, which can allow him to escape.
@Click Bait yes, can i please have a weightless wheel with no air resistance, both parallel and perpendicular to the plane of the wheel? no, in a real world, bike wheel designers have to tradeoff between weight and air resistance. if what you wrote was the case, then pursuit track cyclists would use the lightest wheels possible with aerodynamic characteristics being of secondary importance. but they don't, they use disc wheels. this is because i) above ~40km/h the wheel's aerodynamic resistance is greater than rotating resistance due to increased weight, and ii) disc wheels are stiffer, and thus they have smaller energy losses due to wheel deformation.
I have a 8 kg racer with carbonwheels (23-28mm tyres)and a 10,4 kg cyclocross with sturdy mavicwheels and 32 mm tyres. It is actually difficult to measure significant timedifferences on tarmac. Other variables such as fitness for the day and wind matters.
Real life examle:
(Yes, i know - it is road bike channel but, this can be a good point of view)
Few years ago I switched my MTB bike from 26" to 29".
So much more rotating mass!
And - results: on gravel roads and tarmac sections - my speed and time instantly improved by 10% (average).
New bike has slower acceleration, but running better at constant speed (bigger wheels has less rolling friction as well)
When it is worse? At technical tracks, when lots of braking and accelerating happens - but bigger wheels are better at roots and stones.
Bigger wheels mean you go up and down less as you go over bumps and holes. This means several things:
1) Less flexion of the tires, so less heat generation, so less energy wasted.
2) Every time you have to go up, even an extra mm, to climb over a bump or out of a hole is an extra mm you have had to climb, even if your GPS doesn't count it. In a long climb, that is a lot of extra, hidden, mm that you have had to climb. Some may say that you recover that energy expenditure when you go back down into the next hole. But I suspect almost all of that is lost via #1 when you hit the bottom of said hole.
3) Every bump requires your body to expend muscle energy as it acts as a shock-absorber for your brain. That is energy that could have gone into climbing the hill.
I think you get more advantage from lightweight wheels when you have suspension. Less unsprung mass should make your suspension work better.
Agree, I too just switch from 27.5 to 27.5+ bike, 2.1 before and now 2.8. To my surprise, it's wasn't any slower on the road which connect me to the trail.
I'm thinkin of weight on the edge of my wheel
Are you sure you changed the wheel diameter measurement in your Garmin? 😉
My take out from this is that saving rotational weight compared to non-rotational weight creates very little difference which is new knowledge for me. But saving 400g is saving 400g and as another commenter (lost the comment for now, sorry) has already stated, you're always accelerating on a bike - all the time you are introducing force you are accelerating, even if it is to overcome gravity, air or rolling resistance, as force is proportional to acceleration (F=ma as I recall, and mass wouldn't be in there if it didn't matter).
So point 1 - rotational weight isn't more important than non-rotational weight
Point 2 - aerodynamic advantage is crucial to cyclists but even more crucial to people that make and sell aerodynamic wheels
Point 3 - to call it science, there would need to be some sort of peer review, and throwing in a suggestion that the simulation of the crit was at 52kph (oh, he meant 40.2kph) leaves me a little worried about what was actually plugged into the simulation in the first place.
I'll stick to my weight efficient strategy of always having a poo before I go for a ride.
Hahaha, espresso, then poo, then fly on your bike!
Applying force to maintain your speed and actually accelerating, like increasing your speed are really two different things. You just can't say it's the same.
"you're always accelerating on a bike - all the time you are introducing force you are accelerating"
No you aren't. He's even talking about it in the video. You're only accelerating when the speed indicated by your GPS changes.
Yes, F=ma, but it's more like F_pedaling - F_aero - F_rolling_resistance - F_drivetrain - F_gravity = ma. And if you're plodding along at a fixed speed, a is 0, therefore all the forces cancel each other out.
Obviously your speed is never actually fixed, if you want to be pedantic. With lighter wheels, your speed will fluctuate more with your pedal stroke (faster to accelerate, faster to decelerate). With heavier wheels your speed will be more static. Actually, if hour record bikes had a high minimum weight limit, it would be better to have added weight at the wheels, since your speed would fluctuate less, and drag increases very quickly with higher speed.
Del In strict physics, you ARE always accelerating on a bike. This is because there are always forces acting against your direction of motion (wind, rolling resistance, centrifugal force etc). In order to overcome these perpetual decelerations you need to perpetually accelerate: EVEN TO STAY THE SAME “SPEED” on your head unit.
First, not sure how much I’m going to trust anyone who worked at Sauber sheesh, but anyway he better go do some new calculations. A climb is nothing but thousands or more micro accelerations, one for every time you put a power stroke down on the pedals. It’s not a steady torque from an electric motor accelerating up, its pulses of power from legs on pedals.
Not just sauber , but sauber at their worst when it comes to their aero package .
Wrong. Your bike remains at a relative constant speed up the climb (assuming gradient and power remain constant). The video and physics don't show that weight doesn't matter, they show that rotating weight is the same as non-rotating weight.
That’s just it, with a person pedaling, power isn’t constant. As I said, it’s a series of micro accelerations (and decelerations) that at times aren’t so micro depending on the incline and rider weight.
@@GNX157 I don't think some people can grasp that less than 50% of a pedal stroke is power input .
@@christopherbeattie263 wheel speed constantly fluctuates while you cycle , ascending and descending changes the way gravity interacts with a bikes velocity . Going up hill gravity works as a deceleration force , so a rider must fight that extra force .
Where does rotational weight come in ? The higher the rotational weight the more energy is required to accelerate a wheel to a set speed . Once up to speed energy consumption is the same , but seeing how on a climb gravity is decelerating the whole of the rider + bike the wheel now needs to be constantly accelerated to maintain a given speed to counter the deceleration of the whole body .
With lighter wheels less energy is consumed to keep up the constant acceleration to counter the deceleration force of gravity . So the joules consumed by the rider will be less on a bike with a lighter wheelset than a heavy wheelset .
_Weight_ matters. Rotating weight DEFINITELY matters when braking, and _unsprung_ weight is the holy grail of handling when you have a suspension... hard frame road bike? Reduce overall weight if you want a lighter bike - it's that easy.
I wouldn’t disagree with JP’s essential conclusion. Nevertheless, the characteristic feel of light wheels may be due to reduced gyroscopic “precession”. This gyroscopic force means that when you try to turn a spinning wheel it will try to flip on its side and, conversely, if you try to tilt it, it tries to turn. The effect is very noticeable when you hold the axle of a spinning wheel in your hands, but it could also have a noticeable effect on bike handling.
I had not considered bike handling effects. Excellent perception!
Yeah he was selective in the data to be sure... Also forgets that the airflow isn't always face on...
@@andrewdeck7945 The spinning wheel flips because nature seeks balance or equilibrium. Bike fanatics aren't necessarily balanced!
@@andrewdeck7945
Well, yeah. Every bike frame is designed to create certain handling characteristics. The easiest thing you can change (to affect handling) after the bike is built is the front wheel.
I like a quick handling bike so lighter suits me well.
I haven’t read all 1800 comments, but it seems like nobody is looking at this from a bio mechanical point of view. Tension on a muscle has an exponential cost, which explains why lighter wheels feel faster and why Mavic made the Comet+/- disc wheel with weights that can be added. If you are constantly changing speeds the peak tension on the muscles is lower with a lighter wheel. On the flip side, if you want to maintain a constant speed with hills and winds, a wheel with more inertia will allow the rider to avoid the highest muscle tension. Conservation of momentum works better on a blackboard than it does on a bike.
As a guy with an engineering background I’ve just quietly smiled and nodded then turned and walked away when people went on and on about how superior their light wheels were to the “heavy” aero wheels. It’s nice that now I can point them to a video for reference. Thanks for the good work.
Aero wheels will be beneficial when the aero losses outweigh the accelerational margin to be gained by light wheels. The problem is, the interviewee does not make this argument. He makes the argument that the total system energy is what matters, and that therefore the energy a rider puts into spinning heavier wheels is not in vain. There are obvious problems with this line of reasoning. First: the total system weight still matters and heavier wheels will impact climbing performance: but we all know that already. Second; heavy wheels force the rider to expend the effort spinning the heavy wheels “ahead of time”. As soon as the rider touches the brakes (eg for a corner) this extra stored effort is wasted as heat. With lighter wheels, you minimise this wastage by using only the minimum of effort in any given acceleration. In a time trial, heavy aero wheels probably make sense. In a twisty criterion, less so.
Ben Aston that would have to be an historically twisty criterion. But if you’ve got some real situation and the math to back it up. I’m sure we’d all be delighted to hear about it.
Brian Gardner It’s not just corners. Losing a wheel is another pertinent scenario. If a breakaway happens, if you’re on a heavier bike thanks to your aero wheels, you are more likely to be out-accelerated and fall out of the draft. So you have the aero gains of your heavier wheels, but that has to be subtracted from a significant efficiency loss from having to subsequently bridge the gap.
Ben Aston Although I understand your concerns, neither the math or the data I’ve seen supports that hypothesis. Please point to some research. Even my anecdotal experience disagrees with your claim. I used to have an old 2014 S-Works Roubaix with Zipp 303 wheels. Even though I was 30 pounds overweight and had a heavier bike, once I got above 14MPH my improved aerodynamic efficiency would start to leave people with lighter bikes and slimmer bodies behind. Over 18MPH, if they didn’t have extremely strong legs or an equally aero bike there was no contest.
I can take a pretty twisty road at 14 to 18 miles per hour on a pair of 303s with a good set of 28 tires.
Considering the gap you have to close everytime someone in front of you leave you in the dust the amount of watts required you're working harder overtime to the sprint you're also going to loose due to a slow acceleration.
Like in every scientific experience it all comes to the boundary conditions:
1) Not every normal rider climb Sa Paobla averaging 18km/h with Oli's form weight: If you fight against gravity at 6-10km/h kicking the wheel to keep it in motion at each single pedal stroke, I empiricaly believe that Inertia holds you way more than Aero.
2) [Extension of topic => For your next video Olie!] Isn't Inertia more important than Aero once the wheel rpm comes to be lower than the crank rpm?
-> I can imagine they calculate the potential gains backward based strictly on Olie's Power data (and weight), but how are the effects of stroke rpm and their uneveness considered here? And the corresponding torque/muscular fatigue?
->I feel that uphill, keeping your wheel spining at 8-11km/h cost you more fatigue, entertaining its inertia with a limited amount of crank rpm (39 chain ring) vs a higher rpm velocity from a "compact" crank (34 or 36).
There I would state that adding more intertia on the wheel, accentuates the driver fatigue more than helps keeping speed (which is TBH frankly oscillating at each pedal stroke) , and finally be contra-productive ?! => Please a Debunk video on this one, for poor fitness rider!
Correct. I suspect the simulation assumes that the rider is pedaling perfect circles. In reality, on a steep climb, you are accellerating the wheel a little with every pedal stroke.
You're also decelerating between pedal strokes. A heavier wheel will decelerate slower than a lighter wheel. Thus, the effects on acceleration and deceleration cancel out - unless you hit the brakes, of course.@@bumbykitty
The falicy is that there is zero acceleration/deceleration on hill climbs.. And conservation of momentum you don't seem to be considering efficiencies in pedaling during micro accelerations/ deceleration while hill climbing.. I'm not buying it that rotating weigh is a null issue.
Conservation of momentum is exactly the key detail when considering the effect of micro-accelerations from pedaling...a wheel that is easy to accelerate is also fast to decelerate. Over the span of more than one complete pedal stroke the total effect of changes in inertia is zero.
It is not fallacy. The energy you put into the rotating mass every pedal stroke is stored, not dissipated, that is the point. Then it releases itself to fight gravity. The mass weight is however loss of energy as you carry that mass up the hill. He never said lighter wheels are not better for climbing, he said any saved weight is better be it rotating or not.
How about backing this up with some maths?
Let's assume you want to speed up at the end of a criterium, e.g. from 10m/s (e.g. 36km/h) to 17m/s (e.g. approx 61km/h). Those are reasonable speeds for amateure sprinters.
For simplification let's assume 250g safed per wheel, evenly distributed across the wheelset, so a total of 500g safed (surely on the higher end of the spectrum, but close to leightweight vs swiss side). This equates to a rotational inertia of approx 0.244kgm^2 for both wheels combined. The added kinetic energy stored in the wheels equates to about 23J for the rotational energy and about 47J for the extra translational energy of the 500g heavier wheels, aka an additional 70Watts if the acceleration takes place over one second, 35Watts if over two seconds.
I don't know about you, but if, over the course of a surgy race, I have to do just 2s of 30W more for a 100 times, I will be severely more cooked than otherwise. Hence, rotational certainly is not the cheapest or even most cost effective way to save energy (think wheight, position, fitness,...), but for a fit individual with competitive aspirations it seems quite legit to put a few bucks into better wheels (not saying they have to be 4k leightwheight ones :D)
“If you’re riding at a constant speed, there’s no change in inertia… “
I wish I could also climb with a perfect pedal stroke and no rocking of the wheels/bike!!
The best weight saving and performance upgrade and relatively cheap for me without doubt has been tyres. Just switching to GP4000sii seemed like having a lighter wheelset as rolled quicker without forking out 100s.
I upgraded my wheelset from a stock Trek wheel to a nice Hunt alloy, saving about 530 grams. Can't say I noticed a big difference. Then replaced my stock Bontragers with the Continental GP 5000, instantly noticed more lively acceleration, less work to maintain cruising speed and added comfort.
because tires are more about rolling resistance than saving weught
Olly - time for some concrete-filled disk wheels and some testing !
After you get to speed, there will be no difference in maintaining that speed(if the rolling resistance is the same).
@@aliancemd even so, I would still like to see them fill the wheels with concrete
Maus m Going to turn into a train, hard to get to speed, hard to stop. Need better brakes for that
Awesome video Ollie, I'm a huge F1 fan(one of the few American fans)so having an F1 engineer on your show was cool as well as informative. Honesty the "flywheel" reference thats when it clicked for me, lighter spins up to speed faster while heavier loses its energy slower. Two yrs ago when I installed Stan's No tube road bike wheels(Avion) , they were easier to start spinning and easier to slow down, compared to OEM alloy wheels. Also how cool is it the have so many F1 teams in your back your, if you live in that area(or is it Shire? I don't know I'm American)?
Gordon Murray is a good F1 engineer as well and he famously said making a car lighter improves it in every way.
Hobbits live in the Shire, in Britain we have counties (some of which have "shire" in the name, but it no longer has a particular meaning).
@@earthstick they are not disagreeing. he is talking the specifics of a road bike under certain conditions
Eternal Optimist The historic counties of England are areas that were established for administration by the Normans, in many cases based on earlier kingdoms and shires created by the Anglo-Saxons and others. They are alternatively known as ancient counties, traditional counties, former counties or simply as counties. Modern Counties are administrative areas and many retain the ancient county names. I live in Warwickshire and I’m not a hobbit 😂
@@trick700 We'll believe that when we see your feet!
The statement (at 6:29 in the video) that "there is no acceleration on the climb" is flat out wrong. "No acceleration" only occurs when speed is exactly constant; this has never been my experience in climbing - speed changes with grade, effort and on a small scale with every pedal stroke. So, all of the modeling results based on this "no acceleration when climbing" assumption are wrong and highly misleading.
Always be wary of anyone talking about 'the physics' without showing any kind of actual working proof.
There is no argument here other than 'we said it makes no difference'.
Here's an article with actual calculations and citations as to where they got their information from. www.wheelfanatyk.com/blog/rotating-weight/
Great video Ollie! After being served and drinking the Kool-Aid as a bike mechanic years ago, the flywheel analogy makes sense - I don’t know why it took 30 years for that lightbulb to come on. It makes me think too that, along with aero and rolling resistance, frictional losses on bearing surfaces might play a bigger role than weight too. However my mind is possibly too blown at the moment to think straight. I need a coffee...
Same for HEV dish-like wheels. HEV can store energy in battery so gain benefit at start-stop situation, but no benefit in constant high speed. So they(manufacturer) use aero-wheels for HEVs which is benefitial in constant hight-speed situation.
The problem is that having fast acceleration is much more important than having slow deceleration. You will probably be dropped easier even if you don't loose any energy by having heavier wheels. The difference is probably not very big, but I still think that's an important factor that haven't been considered in this analysis.
I agree, there are times when the pace on a race picks up and the difference between getting on a wheel and not is a huge amount of energy spent. and that little bit less effort to get on a wheel is greatly appreciated, even if you are spending a bit more energy once on the wheel.
@@MicheasHerman I agree with you both. I would like to know, How is it than no one considers the wattage output required to get a heavy wheel up to a given speed at a given time compered to a light wheel? Also how many watts required to maintain a required speed compared to a lighter wheel? In MHO, it takes less watts to accelerate a lighter wheel. In the case where it is said that a heavier wheel rolls longer or further due to rotational mass, when that energy is spent, i believe it will take a greater amount of energy to maintain your speed as compared to a lighter wheel which may lose its rolling energy before the heavier wheel. Final point, Does rotational mass affects the overall weight of the bike? In other words, if i weigh a bike while it's wheels are spinning, will the bike weigh more, less or same as if it was weighed without spinning wheels? If the answer is same or more( cause i can't see it being less) then this follows the same principle that causes us to make our bikes lighter by upgrades etc Heavier bike vs lighter bike. Our performance improves with lighter bikes i think.
@@howardmarcelle2165 Yes it takes less watts to accelerate a light wheel
How many watts are required to maintain speed: Going to be the same for both if the ground is level. Otherwise more watts to lift heavier wheel, less watts going down on a heavier wheel since it had more stored potential.
Does rotational mass affects overall weight of the bike? (weigh bike with wheels spinning): Not really but technically yes because potential energy actually does add weight. A spring that is compressed actually weighs some fraction more then the same spring uncompressed. But you wont be able to measure that difference its way too small for a normal scale to pick up. Some good physics videos around that will explain this.
To the OP: I agree, and acceleration is the point where your already dumping a ton of energy - if your putting put 500 watts and you need to put out 550 to get the same accelerating on heavier wheels thats much harder then later putting out 100 instead of 50 because the bike is slowing down faster.
You're viewing things incorrectly. Acceleration is instantaneously met with corresponding rotational inertia, therefore, "having fast acceleration" is equally important to "having slow deceleration". You don't "lose any energy by having heavier wheels" and won't be dropped any easier because the energy you put into them is the same regardless of how heavy they are (assuming overall system weight is the same). Theoretically, there is an extremely rare scenario where the lighter wheels could win in a sprint, but it's equally likely that the heavier wheels would win, because it depends on where in the pedal stroke the person is relative to a hypothetical constant-torque motor (if it were in the dead spot of the pedal stroke, the heavier wheels would win, if it were in the 3 o'clock position of the pedal stroke, the lighter wheels would win).
None of this is to say that lighter wheels/bikes aren't faster, because they are in most scenarios. The argument is that there's no difference between lighter wheels and an equivalently lighter frame/components/body.
@@squiresuzuki this thing is complex, guess it's down to the placebo effect. In my own non scientific experiment, a lighter pair of wheels gives me a faster time with less hurt in my legs.🤷♂️
As a youth, I did some experiments along this line.
Of course carrying mass up a hill takes kinetic energy. Any mass in this case (seat bolt, latecomer tub) takes more energy up the hill, and gives most back on the downhill. But if you use your brakes, you throw it away,
As the analysis below shows rotating mass is more important.
I mounted a training clincher wheel into my mechanism, which had a fan blowing on it.
I cranked them up to the same speed with a drill and let them coast to a stop.
I recorded the time. Then did it with a tubular training wheel with less than half the rotating mass.
I then carefully covered the wheel with a “disk” of carefully folded and taped to the wheel.
Results
1- tubular. Shortest “coast” by far - indicating the lowest kinetic energy.
2- clincher. Longer coast, indicating higher kinetic energy.
3- dissed clincher. Coasted forever.
Summary.
Rotating mass does require more kinetic energy (acceleration).
A disc, or perhaps bladed spokes are more important.
I think it matters a lot for commutes. Starting from 0 feels so much better with my light wheels and you stop a lot if you ride in the city.
I'd love to see the numbers, how much energy it takes to go from 0 - 30km/h with heavy vs. light wheels.
Easy math to do as an estimation: Weight added at the outside of the wheel "counts twice" for kinetic energy (that's the worst case, if you add the weight closer to the hub it's less). So riding with wheels that are 500g heavier total is roughly the same as adding 1kg to the frame.
So yes, it sort of matters quite a bit more there, but (especially in the commute scenario), it's still not really all that much considering the full system weight.
Almost everybody can do a simple experiment to demonstrate that the wheels' rotational inertia is small compared to the total linear inertia. Put your bike into a turbo trainer, with no resistance, and the bike in top gear. Sprint as hard as you can and see how long it takes you to get to 20kph - then double it to account for both wheels. Now take your bike out onto the road, again with it in top gear. Sprint and see how long it takes you to get to 20 kph. There will be a huge difference in the times. I suggested 20 kph to eliminate as far as possible aerodynamic influence.
Terry
And we all know that this is what matters in peloton cycling. You do not want to drop out of the peloton.
@@decidrophobBeen there, off the back, many times. Much better off concentrating on aerodynamics, slipstreaming and tactics first and then worry about the small stuff.
Nice impartial science based video..... from a sponsored manufacturer of (heavy) aero wheels.
Another flywheel comment here - On the several dirt bikes (with motors) I have run, we change the flywheel on the motor to increase traction on slower woods enduro courses because we don't need the wheel spinning punch that is fine for the MX course, and it lowered that chance of a stalled motor. Same motor different feel, it can also be used as a crutch for a peaky torque curve or just to make the bike feel more controllable. The flywheel effect kept the motor turning and it slowed the initial punch but it was recognized that this also decreases your potential hit off the line if you can control the hook up. Totally different reason for a flywheel, heavy or lighter because the power from the motor was not the limiting factor. We always had too much power when compared to traction. Not even in the same ballpark of what we deal with on a human powered bicycle.
We never added or sought heavier wheels because an increase in unsprung weight is detrimental to the ability of the suspension to follow the terrain. I would guess the idea of unsprung weight negatively impacting the suspension performance applies to road cars as well but I have zero knowledge there.
All that said was to point out that weight and flywheels have a place in motorsports racing and on motors for that matter but not on my bicycle wheels. Outside of the Hour Record, Go Ollie! and even then it does not seem conclusive because different attempts have used different equipment. Yes Aero wheels will equal gains but at what expense to the initial and constant inertia changes in the real world? The quick 5 second effort when the pack looks like a slinky because you are not in the front. No matter what your specialty, everybody is driving toward lightness. The only hold outs seem to be the time trials/triathlon where you really are attempting for a steady state effort. Look at this years TDF where riders switched bikes from the aero bike to their road bike for the final climb. Im sure they didn't ask for the heavy wheels!
Somehow I don't see cyclists ditching their lightweight wheels.
If you're riding in a city, why would you? It's constant acceleration and deceleration. Lightweight is made for this.
disabled man I guess if you're doing that much braking in a city, you're probably commuting to work rather than training so the marginal benefit just delivers you into the hands of the greedy capitalist half a second earlier. Stop being a sheep and join a union, bro.
@@deskelly9313 hahaha
@@deskelly9313
> i need lighter wheels because I don't like fighting my rim's inertia
>You need to join a union
wat?
How are those in any way, shape or form related to each other?
@@disabledman8697 Waiting for someone to explain this joke. Whoever said that explaining a joke doesn't make it funnier was wrong... It just makes it funnier in a different way.
Waiting...
As a mountain biker this is pretty interesting, from the point that the whole bike is what matters. For a mountain bike, especially for enduro, the rotating mass matter's even less, as you want durability, which comes with cost of weight, but as it's a dynamic sport, every component matters and quite often you can ascend just as fast on an enduro bike than on an XC bike, due to better grip and geometry suited for climbing.
Wheres the revelation here?! We've known this for years. The wheels are not heavy enough to be effective flywheels. What he seems to not talk about is that the wheels are constantly being accelerated because power delivery is not constant. So I guess he's trying to sell some wheels
"What he seems to not talk about is that the wheels are constantly being accelerated because power delivery is not constant."
They're constantly being accelerated... and decelerated. Heavier wheels will decelerate less, therefore keeping speed more static. Overall, very little difference.
Del Heavier wheels will decelerate “less” only because the rider (you!) had to exert more effort spinning them up to the same speed. There is no free lunch. The difference is that with heavier wheels the effort must be expended ahead of time, whereas with lighter wheels it can be reserved to be used at a future more useful time.
I'm using a singlespeed bike for shopping and stuff. At first, I had installed 25mm tyres, I changed them to 32mm tyres (~400g heavier incl. tubes). I changed them back quickly. If you have to accelerate over and over again at traffic lights and you are always in the same relatively big gear, you definitely can feel the difference. So, for city riding on a singlespeed bike, rotational weight DOES matter :-)
All I know is that after putting lighter wheels on the bike, my times on Strava segments are faster and I am less fatigued after a long ride. But I was not using aero wheels before if that is the difference. So many variables in this sort of analysis makes me doubt the conclusion.
To clarify the title, rotating weight is still weight, so if you have much climbing on a ride, saving weight on your wheels will make your rides a little easier. Exactly as much as saving weight anywhere else on your bike (or your kit, or your body).
The question asked was about rotational vs static mass. Comparing different system weights and aerodynamics changes the whole situation. He also emphasized the importance of aerodynamics, confirming your experience with your new aero wheels. Buy the same aero wheels with 200gr more weight at the rims, but a 200gr lighter hub, and the difference on time (not feel!) should be negligible.
Where having a lighter wheel should be really noticeable is if you're not staying in the saddle but stand on your pedals and rock the bike rapidly side to side, having a low angular mass gives less gyroscopic forces which will be felt as a force resisting your attempt to alter the orientation of the wheel.
Fascinating! One question: At what point does the weight of the wheel starts to be detrimental to overall performance then ? More than 2 kg?
Old story, and may already be some follow-ups to this, but I'd be curious to see this (I think the conclusion is sound, but I'm sure there are doubters still), presented differently. Using pedal power-meters, to keep everything as "equal" as possible, ride the same bike, on the same course under the same conditions (as best as possible, and/or on a velodrome indoors for example), with aero vs non-aero wheels, ignore completely making a choice by the weight other than "reasonably similar market range" wheels, then do the test criteria by maintaining an average speed of "x" over the course for a time of "y" and record the results via the power meter. With a few runs of each to get a solid data set, that should clearly result in a distinct "savings/cost" difference in watts.
So for example, 2 miles, starting at 0 and maintaining after the initial acceleration, an average speed of 25.0mph (proper magnet wheel measurement, not GPS, to eliminate variability, and to not have to be concerned about measuring the actual course, the "2 miles" is per the measured wheel, so it should be extremely consistent and immune to slight variability in the riding line, etc...)
My guess is it'll be probably a double-digit savings on the aero wheels on any course that isn't a steady-, very steep climb (where the system weight penalty, and reduction in aero benefits due to lower speeds, may cross). Anyhow, food for thought, since this was 2 years ago I didn't read the near-2000 comments to see if it's been suggested already, if so my apologies.
well i can tell you i got strava personal records on my 7kg carbon wheeled road bike, as well as on my 12kg all steel 50mm schwalbe marathon touring tire gravel bike for the same routes. a bit of wind change is enough to make one bike faster than the other. there is very little (a bit more than 1kph) in average speed difference over longer flat rides with both bikes.
the gravel bike (specially in touring mode with those heavy tires) is far from fealing lively and direct though. it takes a while to pick up speed and it just plows along without wanting to turn. the road bike is like a little buzzing bee in comparision. so totaly different characters. so yes, wheight does matter. more for feel than for average speed though.
thats also the reason i always would go for a semi aero wheelset on the road bike that is still light and feels zippy. dont care if i could be marginaly faster on an all-out deep aero set when ithe rims are 400grams+ heavier and make the ride more sluggish.
Absolutely spot on I notice this all the time when riding my winter bike and racing bike!
So what’s Hambini’s take on this I wonder?
Try it on something that isn't perfectly flat. Also, account for position on the bike. You are taking one hacky example for heaviness in aero wheels, and turning it into an example of weight not mattering between bikes despite of inherent aero conditions.
@@cccpkingu Or he's making the obvious point that there are a bunch of variables at play and when you're dealing with minute gains, any hoped for benefit can be wiped out by an inopportune fart.
Get a set of Enve tubular disc 5.6s. Those rims are aero and light at around 400g per rim. Have your cake and eat it too.
I wish 650c wheels (and tire choices) were still widely available. Instant weight loss, and playing really well with shorter and female riders.
Yeah my Cervelo RS XS with 650c wheels is now my washoo kicker bike because the widest performance tires is 25mm. Now that I am riding 650b Babyshoe Pass 42 mm tires on my gravel bike, I'm never going back. For shorter/smaller riders(I'm 5'2"/105lbs), I recommend a 650B wheel gravel bike with road-like geometry like the Salsa Warroad, Norco Search XR, etc.
I still ride a 650C Litespeed with 23mm schwalbe 1 tyres . Nothing is as easy to accelerate on or chuck around as a super light tiny mavic alloy wheel and a tiny little lightweight tube and tyre . Definitely not aero but my best strava short sprint sector’s out of corners were all on the old 9 speed Litespeed and I have a Cippolini with 11 speed campy eps and deep dish zipp and euros climbing rims and neither get close in acceleration or ease of climbing. Good luck Joey I disagree the enves will cook you in the surges and climbs amd sprints in the crits
Agreed with everything until he said "I could understand why you'd add weight to your wheel for a TT race." - Then I knew why Sauber were always back of the pack. Nah. Dude is obviously a clever guy and 1000x more intelligent than me. Fair play. Keep on keeping on. Internet fist bump to that guy.
One area not covered is the change of direction comparison between the two, where weight saving might be more significant. Which is in courses with lots of consecutive bends for example.
Hopefully in a follow up video :)
I'm perfectly happy for lots of people to believe this video and buy heavy wheels. The more people that do, the more I can drop on the climbs. Thanks GCN, I owe you :-D
I don't think you understood the explanation. Weight only wins aero in long and steep climbs. This is just physics. You can or can not believe it but it doesn't mean it is wrong...
The video was about rotating weight vs. weight on any other part of the bike, not about heavy bike vs. light bike. Seems like your brain is more aero than your wheels.
@Paul Wieringa So you are disputing their findings, mkay. Maybe you should contact Swisside
In the late 90s/00s British Cycling developed a set of track wheels that had weights on a spring system inside the wheels so as you sped up the weights moved to the out aide of the wheel to keep up the speed! Maybe try and find a pair of those for testing as well.
Really very interesting video. I want to buy my first pair of carbon wheels, i have a gravel bike that i mainly use on the road and in the choice I was giving lot of importance to weight (like all poor beginners like me…). Since the wheels I have selected are in the range of 1420-1580 gr, from this video I understand that i would probably feel no difference, and therefore i can choose based on the aesthetics… right?!
the video concludes that for performance gain, aero profile is key. however, for personal satisfaction of such an expensive (relative to the overall bike) purchase, personal aesthetic preference is most definitely a key factor. at least for me, if i'm being honest. where they intersect is, for instance, the depth of a carbon wheel; deeper for better aero but more poor for cross-wind situations. thankfully, i like the looks of a 40-45mm wheel, which seems to be the sweet-spot for most of us riding in mixed terrain and often windy conditions.
As a physicist I can say absolutely that the rotating weight has no extra effect when climbing hills. But it has double the effect of static mass when accelerating the bike such as in a sprint. If your wheels had 2 kg at the periphery ( put together) it is equivalent to adding 4kg mass to the bike under acceleration. If it was possible to get the wheels down to half this then it is equivalent to removing 2kg from the mass of the bike under acceleration. This might make a difference if two riders start next to each other and are in a sprint to the finish.
it looks like some reasonable assumptuons were made. but if we consider the simple power to weight ratio a lighter wheelset will be faster for the same energy put into the system as there is overall less to move.
if we then treat aero dynamics as an opposing force. the aero wheels will provide less opposition than the non-aero wheels.
so you have an two opposing forces and tyre friction.
additionally the rider position will vary between the models used as examples
different bikes and different system weights
too many variables to make a solid analysis.
Surely the better test would be to ride the same bike in each scenario with either wheelset (6 runs) and make it very achievable for the rider ideally with the same tyres.
its all marginal/edge case gains at the end of the day. Everyone feels faster on their new toys. whilst its difficult to put a figure on it you cant ignore outright enthusiasm of a rider who feels the decks are now stacked better in their favour.
Lab Models are great and produce a set of results kn a controlled environment. i used best bike split to calculate a time on zwift it got it within seconds of the time i set a few days before hand. But on the roads, in a gentle wind, with the sun out i was no where near it.
If its one set of wheels for one bike for you to ride the nicest set of 30-40mm rims you can afford will deal with everything you will ever need:-)
Yeah 30-40mm semi aero rims are a great compromise . Especially if they have a 19mm internal diameter.
A lighter wheeler means faster acceleration and handling. Rotational inertia. Basic physics here.
Engineer here … the video is overcomplicating things. lets say you accelerate a fictional bike that has 1-kilo-weights attached to various spots, then accelerating these 1kg-spots from standstill to 1 meter/sec takes the following energies:
- bike frame: 1 Newton
- bottom of wheel: 0 Newton
- back of wheel: 1 Newton
- top of wheel: 2 Newton
- front of wheel: 1 Newton
wheel average: 1 Newton.
In other words: the molecules in a bike wheel have the identical speed (averaged over the entire wheel) than frame, saddle & your belly, and hence there is also no difference to acceleration force & energy.
Interestingly, this only holds true for wheels that are physically connected to the ground - which means: rotational energy IS a thing for cranks, chain, legs & pedals. Just not the wheels.
Unit of energy is Nm, Ws or kgm²/s². Newton is force...? What do you want to engineer? My 50 mm road wheels on 27,5" MTB are much harder to accelerate then the same in 28 mm on road bike (both Conti contact speed). After some sprints it's easy to feel the difference in the legs.
This analysis seems suspect for a few reasons. 1. When comparing aero wheels to box sections, more weight is closer to the axis of rotation, this reduces the moment of inertia which will make it easier to rotate. A heavier aero wheel could "feel" lighter because it might have a lower momentum of inertia. 2. For the climbing test it seems as though it is assumed that the wheels are maintaining a relatively constant angular velocity, but on really steep climbs, its quite evident that during/between strokes the wheel will accelerate and decelerate throughout the pedal stroke. Now you might argue that the bigger one would have more inertia, which is correct, but gravity will also have a greater force on it. So essentially during a climb, on each pedal stroke you will have to accelerate the angular velocity of the wheel. That is where a lighter wheel will be felt on the legs and the clock. 3. During the crit, the amount of time spent braking is borderline irrelevant. The important thing is the time spent accelerating, which is A LOT more than 2% of the time. Also, the heavier wheel will have a higher gyroscopic effect. This means it will resist changing direction. To feel this, take your front wheel off and hold on to the QR skewer and spin the wheel fast. Then try to turn it simulating turning your bike. It will resist your movement. The heavier the wheel, the more it will resist this change in direction. 4. This test took into account aero gains from the wheels which was not the point. This wasn't supposed to a test of weight vs aero. The point was to test weights. ie a light box section vs a heavy box section or a light aero wheel vs a heavy aero wheel.
On point 1, the difference in rotational inertia is very very small. The "fairing" part of a deep rim is very thin and has little mass, not a whole lot different than the sum of the extra 50mm of 24 steel spokes. On point 2, each acceleration from the dead zone of the pedal stroke is reduced when the wheels carry more energy through that dead zone. I agree with point 3: snapping onto the jump of that guy ahead of you matters a lot, and slower acceleration in that critical case is vastly more important than it seems to a non-rider. Centimeters matter. Very small fractions of second matter. And in a criterium, that critical case happens constantly. In a road race like Flanders, it still happens a lot, very dramatically on every sharp turn in a narrow road (which is pretty much all of the roads). I'd like to see numbers computed for how many centimeters difference the wheels make when trying to regain shelter from mid-accordion position in a turn that slows you to 20 km/hr when sprinting at 1,000 W for a few seconds to get back up to 55 km/hr. The guys in front know exactly what they're doing, and intentionally drive the speeds way above the average coming out of those sharp corners.
It matters greatly in technical MTB,specially on natural trails with loads of big rocks and roots.Why? Because of multiple short high power acceleration on technical sections followed by big decelerations.On the other hand, for Enduro or Downhill,where times downhill are the only accounted, heavier wheels are better (due to the increase inertia).
Except they aren't. Even DH riders want light wheels to aide cornering and acceleration. Light tyres , lighter rims ect.
@@edmundscycles1 just look at all EWS teams...they all go for aluminium for compliance,sturdiness and inertia.
@@nowaynowayvideo the material isn't the issue . Aluminium rims for MTB are pretty light . Eg the DT Swiss E540 rim is erm.....540g . Its called and enduro rim but many DH riders (in the UK scene at least) will run them or something similar weight wise . XC rims tend to be from 300g up (Ryde rims are some of the lightest at 210g each) . There is a compromise situation with DH , light , strong , cheap .
The DH wheelsets on pro or semi pro riders are only marginally heavier than XC wheels . Even then that xtra weight is mostly found in the hub not the rim .
For example the lightest xc rim by dt swiss is 355g and the lightest Enduro rim is 473g the profile of the rim (for tyre size and tyre profile ) is the biggest cause of that difference of weight . The ex475 being 4mm wider and deeper in profile to the XR331 .
Both of these weights are for 29er rims .
All mountainbikers apart from dirt jumpers and maybe street trials riders want lighter wheels . Its why compaction trials riders drill out their rims . Its why so many DH riders went all in for tubless (no need for heavy DH specific inner tubes that weigh almost 700g each ) .
Heavy wheels did used to be desired around 15 years ago to help with roots ect . But the growth of 29er and 27.5 in enduro and DH have ment that heavy wheels are no longer needed to help stabilise a bike or keep inertia for a rider .
Slacker head angles , longer wheel base and bigger wheels have ment a shift to much lighter wheels in all mountain bike disciplines.
Gone are the days of DH wheels like the Halo Combats wheel sets coming in at 2.7kg being considered relatively light . DH bikes were often in excess of 50lb in weight . Now most are just around the 30lb mark and some even getting sub 30lb , same weight as some trail bikes .
And I thought I was a really bad rider not being able to feel any difference beetween my "light wheels" on my Canyon Ultimate and my 62mm aero wheel on my Canyon Aeroad.
The question is whether rotating weight makes more difference than the weight of a component that is not rotating. So, does 100 grammes on your rims, tyres, tubes make MORE difference than 100 grammes on your frame or seat? I get it about the flywheel effect and I have experienced it. A heavy wheel may roll over uneven ground or hold its speed into a gust of wind better than a light wheel. Extra weight on the bike anywhere affects you when climbing, accelerating or braking. Extra weight on the circumference of the wheel means more stored energy if you're maintaining a fairly steady speed. The circumference of a wheel moves further, and therefore faster, than any other part of the bike. Therefore, it takes more energy to get 100g of wheel rim up to speed than 100g of frame. Therefore it will affect acceleration. However, like most things on bikes, we are dealing with such small numbers that it is barely measurable. A weight weenie who saves 50g here or there on his bike is making a negligible difference if he weighs 80,000g himself.
When your wheel spins you are moving as much up as down so it is costing you literally nothing. You lose energy from friction though so it can be very misleading as you could have much much more friction with a very wide tire for example. But it is mainly the tire you need to worry about.
Wonder if this has anything to do with disc brakes and heavier aero wheels.. anyone who rides a lot knows lightweight wheels transform a bike...so much marketing BS...