Why Rotating Wheel Weight Doesn't Matter: A Real World Cycling Experiment
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- Опубликовано: 20 янв 2025
- Rotating weight on a bike's wheels, does it actually matter? Last year we made a video looking into the science behind heavy and light wheels for cycling, and it caused a bit of disagreement. Lots of fellow cyclists will tell you that you need lighter wheels because rotating weight is worth more than the static weight of the rest of your road bike. Ollie has come up with a simple real world test to see whether that is really the case.
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What do you think? Does rotating weight matter?
If there is any positive effect, it's surely got to be on pedal stroke...?
Rotating weight must surely slow acceleration under pedal power more than static weight as you've got to increase the rotational inertia more then on a lighter wheel to get to the same linear speed, but on the other hand, that inertia is going to carry you through top/bottom dead centre with less loss of speed, isn't it...?
Pre-workout teddy grahams are all that matter. 😤
It pulls our legs anyway...
Taking this idea to the next level create a test using weight and rotational weight with a power meter in a more real world situation. Have a short TT flat section and a hilly section and hold the same speed and see the differences in power needed to maintain speed with different arrangements of weight.
No it doesn't matter, the only things that matter are those that convert pedalling energy into heat by friction (bearings, rolling resistance, braking) or movement of something other that the bike (air, soft ground).
Same as weight of the bike doesn't matter as long as you never brake or only race up hill.
Of course wheel weight and bike weight make a difference to the way the bike feels and in a way that matters.
The difference is in aceleration. Weight to the wheels means rotational inertia that is multiplied by speed and diameter sqare of the wheel. Weight to the frame is just normal inertia. Weight to the wheel affects aceleration way more, but it helps to keep top speed when you reach it
I experienced this and not a pro cyclist. And if they throw in the other factors like tubeless, tubular, latex and butyl tubes. Speed going downhill should increase slightly and the extra force in speed with less rolling resistance should get a greater distance.
Before I got my aero wheels, my bike review mentioned would not be as fast as others going downhill. I truly think if can go tubeless in theory my rolling resistance should decrease and should be able to go farther due to more speed forcing the bike to go farther without peddling.
Love it when ollie "drops" some knowledge.
Just a casual PhD in chemistry!
lol
7:30 - pee into the water bottle, there will be no weight loss :)
😂 That's a risky option...
@@gcntech especially if you forget momentarily that you’ve done it 🤣🤣🤣
Bear grills style
🤣👌🏽
Potential energy remains in the body . And when reached the lowest point, dispose it, by m1V1=m2V2 velocity should increase In theory
I think seeing the difference in acceleration would be more interesting. It would be cool if you could test two bikes that weigh the same i.e. a Canyon Ultimate Cf Sl with light wheels compared to a Ultimate CFR with deep wheels. If both bikes have the same geometry and weigh the same, only difference being the wheels, that would be interesting results.
You can just do some basic maths to calculate it. Simple angular momentum and acceleration. Basically it's bugger all
Then the acceleration is the same, that's basic physics
The inertia of the wheel with more weight using the formula for a hoop since most the weight is along the outside is I=MR^2 . Inertia is the resistance to motion, so if we add weight to the outside the resistance to motion increases. Therefor more weight on the outside of the wheel will mean the wheel accelerates slower with the same amount of power applied. NOOOW if we moved to a full disk wheel the formula changes to I= 1/2 MR^2 so if the wheel was the same mass as the one that was a hoop it would accelerate faster. That is assuming the mass is evenly spread across the wheel. This experiment primarily covered potential energy and energy conservation since they didn't apply any power themselves. (energy conservation = no outside forces). In short, It would be better to see them try this for acceleration but I also think human nature makes that hard to duplicate so we would almost want to see it with a motor applying 200 watts for x amount of seconds to get a real answer.
@@6speedtib again, you don't need to physically test it. The formulas say what it is
@@supernoodles908 no. Formulas don't tell it all. Just like the theory (and even testing in a wind tunnel) with aero frames and wheels; real world testing does not derive the same results. After 200,000 km's of riding, I can assure you, rotational wheel weight makes a difference. It makes a difference in the overall feel of the bike, and can change how quickly you can accelerate and attack hills.
I found it quite clever to choose Ollie for a video that doesn't require any physical effort.
Nice test.
I replaced my both winter tire 1200g to summer tyre both weight 540g. I felt a noticeable acceleration from stand point. The bike felt lighter and more nervous.
For me if one use light weight wheels this will help overall performance it changes the bike drastically.
I just changed my studded winter tires as well and it felt like a completely different bike - strava calculated the difference to 50W compared to a similar run. I think that rolling resistance also factors heavily in here though. But yea the best upgrade for your bike is definitely spring :)
@@The86rick But isn't this the same with a heavier frame? When you accelerate it, you have to apply more force, but it also has a higher momentum compared to a lighter frame at the same speed, so it will also retain its speed longer.
Agreed the rotating mass isn't so much an issue for more-or-less flat routes (with the exception of sprint/attack where lighter rotating mass is easier to accelerate); however, I would like to see an experiment to show just how much difference it makes for hill climbing...There should be a significant advantage for a lighter wheel (assuming aero qualities are the same) as climbing requires acceleration (varying with grade) to overcome the force of gravity. Many have commented on the physics of this already and it seems to me that this is at least an equally interesting and worthy experiment!
Rotating weight has more effect on the sudden accelerations and attacks than on slow run-outs.
in a race situation I can see the advantage of lower rotating mass to enable you to get into the back wheel of an attacking rider sooner and therefore get into the draft sooner, saving energy.
Add weight to wheelset without altering aerodynamics by adding latex sealant.
In that case my theory is that not all of the liquid would actually rotate :)
@@lasselyhne-hansen9338 Exactly, that is a problem with tubeless setup. You have to overcome the resistance of sealant flowing through a tyre. The sealant is probably non-newtonian fluid and combine it with the inner geometry of a tyre, roughness of its surface and heating during ride and you have problem which is analytically really shitty to solve. You would have to do simulations in Fluent etc and I would like to know, how many companies (Maxxis, Continental...) made those before their marketing department started their campaign.
One thing I learned is, that the deep section Zipp wheels are as aero as the shallow ones.
The perfect explaination 😂😂😂
Although, the weather conditions can affect as the sun was up during the aero wheels and hence increasing the temperature decreasing the density of air in turn affecting aerodynamics??? But this should mean that the shallow wheels are more aero😅
Exactly, or saying differently: the difference is negligable. One thing we learned here is that heavier bike descents better. That is something we all knew from skiing already. One needs to be heavy to go faster downhill...
Most of these types of wheels are tested at 40-60kph where the marginal aerodynamic gains are far more obvious, there is however of course are reason most of the Pro Peloton aren't seen on them, and that is due to them catching cross winds and only marginally better if at all in the real world for aerodynamics.
@@Alex-to8es exactly, you'd have to measure at peloton speed during a greater amount of time to get noticeable results
he won't be going fast enough for the aerodynamics to make a big effect, the deep wheels will only be about 10 watts faster at this speed so it won't make a noticeable difference in a test like this. If he was going at a decent pace, like 30mph average on this descent/short ascent, he will save 45 watts using the deep wheels which would be a noticeable difference. Especially if you were doing a strava segment, TT, race. I can do 30mph with about 280 watts using 80mms wheels for 5 minutes, my FTP is about 255, doing 320 watts with shallow wheels means I would only be able to hold 30mph for 3 minutes. That's a gigantic difference.
I replaced the stock OEM flywheel(22lbs) on my 92 MX-5 with a lighter chrome moly flywheel 7lbs. Blipping on the down shifts was so much fun.
Two orders of magnitude difference in weight
@@Shadowboost Umm, I think the new flywheel would need to be 0.22lbs to be 2 orders of magnitude lighter
On a peleton I think weight kinda matters, it can be a difference between responding to an attack and grabbing their wheel early or not being able to grabe their wheel early and have to chase them down
there are a couple of problems I see in real-world applications
- this only works at marginal weight increases, because the power required to accelerate a wheel that weighs, for exaggerative purposes, 5kg more will substantially affect the rider's long term endurance. this problem arises from the premise assuming humans have infinite power to accelerate the wheel, or are starting at the top of a hill. even most "heavy" wheels are fairly light, but if a rider is accelerating many times (as in a crit), this will add up over time
- the rolling resistance from the tire increases with mass, so doing the test with a much higher weight will increase friction (or again, add up the small increase over time for a very long track) and slow you down
oli 'science' bridgewood adds 600g of weights to a 600ml water bottle.. hmm water might of been a simpler alternative. :)
probably wouldnt matter for this experiment but using water adds an extra variable, whereas using the weights ensures you're adding the same mass to each run
You can't attach water to a wheel 😆
i just meant he probably had a full water bottle that he #dropped to fill with weights.
What if one filled the wheels with water, and then pump air in to fill it out and get it up to pressure.
@@lexistential not if you use a scale, 600g is 600g
Would be a Nice test to do the same wattage on a climb with the different weigh locations
When I moved from Mavic Askium to Campy Bora One 35, I felt like the bearings made more of a performance change than the pure weight of the wheel. Yes the wheels were stiffer for more efficient power transfer and more aero but they also hold speed much better than the Askium, even with less stored kinetic energy due to weight. There are certainly point of diminishing returns for any modification. Would be interesting to see some focus on stock wheel and BB bearings versus different cost upgrades. Where is the inflection point point between cost and improvement.
It would be interesting if you did this experiment going uphill..
Probably screwed any result by having different levels of tuck on each run, CdA bigger variable than the slight weight added.
This was my first thought. They didn't control for variables at all.
he got more and more aero each time lol
@@future62 They NEVER do
There is the issue of unsprung energy, meaning the heavy wheel is not as responsive to directional changes. Perhaps I'm showing my fondness for suspension
Even less valid than the first video...How about try adding weight to wheels in a crit race?
Basic physics. The velocity and acceleration are two different thing. Lighter wheels will acceleration faster going up.
@Alright Alright Alright agree. Got my industrial operations engineering degree at U of M. Aka the best in the country. Leave it to me to do the math
I'd be interested to find out if it took less time to get to the same place with the 808s than the shallower wheels.
No, not less time, more. The wheels are heavier, and since Ollie didn't pee, make up a bigger percentage of the mass of the system. So percentage wise a bigger part of gravitation is needed to spin up the wheels. So this causes less accelaration going downhill, but also less deceleration going up. So hé covers the same distance, but at lower pace.
Actually, this video proofs that rotating weight does make a sight difference. The more aero bike made it exactly as far as the non-aero bike, even though they were equally heavy. Of course, this test probably isn’t representative for every situation, like you said, but it is quite interesting still
I think the major effect of wheel weight is on "feel". The rotating wheel has a gyroscopic effect and once set in motion doesn't want to change direction. Try removing a front wheel from your bike, spin it up and then try to change the direction the wheel is pointing in. The effect is quite remarkable. I think this is why people like lightweight wheels - particularly when climbing out of the saddle, lighter wheels just feel so much better, and effort isn't wasted changing the direction of travel of the wheel - just have a look at the amount of deviation the front wheel makes when Nibali is on a steep climb - the wheels snake all over the road.
Yes of course it does...people that quote the small differences...don't count the HUGE number of rotations that take place....these small differences ADD UP
On a normal ride there's likely to be some braking on downhills and for junctions which will negate of the recovery of energy due to the flywheel effect and also some of the kinetic energy gained when ascending. Every time we brake energy is dissipated as heat due to friction. Also if you're using heavier bike and/or wheels you'll go slightly faster on downhills which will cause a greater aerodynamic drag. Although each instance of going faster downhill and braking will make a minimal difference, added up over a longer ride it must all count. Also, and more importantly, the lighter the bike and wheels the greater the feeling of 'nimbleness' which feels sooooo good. So it's a light frame and wheels for me (HUNT 3650 Carbon Wide Aero Wheelset).
Oh and I forgot about the up and down movement caused by aberrations in the road surface. As you and your bike travel over every little bump the weight is lifted, again dissipating energy* reducing forward speed. More weight means more energy lost. Doesn't sound like much but added up over a longer ride it must make a difference. (*This is why softer, tubeless tyres roll noticeably faster.)
Remember that when you stand up on a climb, each pedal stroke is a tiny acceleration. Also worth mentioning is that when I have taken steps to lighten my wheels, even when adding a second water bottle, the bike just plain feels better. Not the most scientific, but true nevertheless. Interesting vid though. Keep 'em coming.
You could also try adding 300ml of sealant per wheel to distribute the weight more evenly :)
not really, approximately 250ml of that sealant would be sitting happily on the bottom of the tire for the whole ride, being a static mass with some extra friction.
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.
It only matters if you don’t want two heavy gyroscopes correcting any sort of wobbles/leaning you do.
What this experiment also shows, is that it's often worth pedalling downhill.
Yep, adding more inertia by the added mass of my post Covid body weight looks like an advantage (up to a point.....)
When you put the weights on the non-aero wheels it takes longer to get up to speed. The aero wheels might take as long to to get up to speed, but they'll travel further just on the basis of the aerodynamics.
10:16 I like that the dogs wear jackets that match their handlers.
Starting and climbing mountains with heavier wheels (I’m talking like a pound or two more) will be much harder than with lighter wheels
How do you know the added aero benefit of the deeper wheel didn't offset the data (i.e. increase the distance)? You didn't mention this benefit even though you mentioned a potential aero penalty with the wheel weights
It went the same distance as the weight in the bottle with the shallower, less aero wheels. Therefore, aero didn't matter in this situation of two different depth aero wheels rolling down hill. Weight was more important here because you are increasing the potential energy into the system and that's why they went further than the shallower wheels with no weight. I suspect the coefficient of drag for the deeper section wheels was very similar to the shallower wheels in this situation, but the coefficient of drag for the shallower wheels with the weights stuck on was significantly higher. Hence, the bike didn't go as far.
Once the wheel is up to speed then it effectively disappears (as in vacuum). It is no longer a factor, even up a hill. (Unless the whole bike is heavier) If your speed is accelerating and decellerating as in a complicated course, with many conners then it will affect things.
Conners? Conor does seem like he could affect things with his size. I’m not sure what many of them would do or look like?
Since we are splitting an already split hair here... There is a slight asymmetry, I believe: the aero drag and gravitation add up against you on an ascent only. On a descent gravitation is your ally against a wind...
BTW, shouldn't Ollie hide a bottle in a pocket at his back?
Its satisfying when science finally works in the real world. Cool experiment. I have done similar to test Crr of tubolito vs latex, but I had to keep speeds low to get aero issues out of the equation.
The problem is not downhill, it's uphill. Uphill speed is not constant. The bike is repeatedly accelerated by a pedal downstroke, then slows before the next. The kinetic energy of the bike has two parts: the weight of the bike x velocity, and the rotational energy of the wheels and to a much lesser extent the crank, measured as 1/2 x moment of inertia x angular velocity squared. The moment of inertia of a wheel is increased most by weight at the rim/tire, not so much by the hub. Each downstroke has to accelerate the weight of the bike and the rotational energy of the wheels. The lighter the rim/tire, the less energy is expended per stroke. Rolling downhill, the bike gains speed in a smooth fashion and is less affected by the moment of inertia.
plot twist, their whole test was just one giant acceleration (downhill) and deceleration (uphill). so if you'd claim climbing contains of very short bursts of pedal stroke causing acceleration and decelerating on the dead spot - there you have it. it's all the same.
@@GrzegorzGlowaty. They were not pedaling uphill which is what you normally do, they were rolling, so the repetitive energy loss was not experienced.
@@67daltonknox imagine it was just all one giant pedal stroke. Makes sense?
@@GrzegorzGlowaty. You are missing the point. If a bike travels at a constant speed, then the energy required is equal to the various forms of resistance plus the change in potential energy. Pedaling up hill is not done at constant speed. The bike is repeatedly accelerated and slowed which is why the "test" is not equal to uphill riding.
@@67daltonknox you don't understand my metaphore, but it doesn't matter
Because nobody ever uses their brakes to slow down which would waste all that stored energy you've paid for when getting them spun up. ;)
Hi Team nice Experiment. I just want to mention that in theory rotating weight should result is less kinetic energy therefore the less travel is explained. You need to consider that the potential energy you have on a hill is transferred into kinnetic energy plus the rotation energy of the wheel and this rotation energy is dependent on the weight. Just try this experiment use a hollow zylinder and a full zylinder with same weight and diameter and let it roll down a slope you will find that one is faster than the other due to the fact that the rotation energy changes by placing the weight all on the outside.
The important question is-did you check that your disks weren’t rubbing when you changed to the 808’s??
I only ask as I always have to re-set my brakes on my gravel bike when I swap wheels......
I bet, if that was an issue, the difference would be dramatic. Also you might consider shimming the rotors to equal distances, RoJ has a nice and thorough video on that topic
It is called "moment of inertia" and it will not only require some energy to be stored in a conservative force but also effect the hysterisis curve of the wheel contact surface, i.e. the rolling resistance and tracktion. The effect is not too discernable for most modern wheels due to modern materials and design. It can easily be compamsated by changing air pressure and pattern.
Looks like you had fun. The reason rotating weight matters is generally ignored in all discussions of this subject. The main assumption is that things remain constant, even acceleration ( gravity in this case). The problem is when pedaling, we do not apply force to the pedals consistently throughout out one revolution. We are constantly accelerating and de-accelerating. The rotating mass, and its polar moment of inertia affect how quickly we accelerate or de-accelerate, especially as we try to change speeds. That’s why it matters, and why we all feel the difference in wheel weights.
Yes this is the point ... take a TDF - it will be massive gain to have lighter wheels.
Fun fact; Added weight makes you faster on downhills. If you only do rolling runs without pedaling, starting downhill, you are correct, weight doesn't matter. Whether it's on the wheels, bike or the rider. :)
Exactly correct. The theory posited is correct, assuming a constant velocity and applied force (or lack of in this case). A lighter flywheel spins up more quickly, yet loses speed faster, this is why physics says that it makes no difference overall. However we do not exactly pedal with consistant applied torque (or lack of it) as is mirrored here. Going downhill assists distance via MOMENTUM. This multiplies the difference added weight makes. Therefore a heavier bike that takes longer to "spin down" will travel further.
THE OPPOSITE is true going up a hill, given some variance in applied torque/accelation. So yes....Without the application of force, this experiment proves nothing and only shows you that the position of weight makes no difference coasting down a hill.
It is not a useful experiment and you can't learn anything from it that you wouldn't logically expect. It does not apply to real world cycling per se, aside from coasting down a hill. From a physics standpoint, acceleration over inclined sections of varied gradient does make a slight difference, however the difference is very little and the aerodynamic advantage of deeper heavier wheels is in comparison very significant.
Both the experiment and the use of it in order to to come to a conclusion is flawed. There are also too many variables that have not been accounted for.
I love Oli’s determination to the story! Holding a wee, for results accuracy? Splendid! 🙌 ...also, seems like Alex gave up half way through. 🤔 Anyway, keep it up Oli - back to the drawing board and more tests could be done on this topic! Cheers.
LOL. Alex just disappeared without mention.
You know who else disappeared without mention.... Tom Last!!! Where the heck did he go????!?!?!
I understand that rotating weight doesn't matter in the course of a whole ride, but I very much like my light wheels when accelerating or going uphill, both of which I am crap at. What I don't really feel is the conserved momentum when coasting downhill. And while aerodynamics always make a difference, that difference for me is small. I'm just not fast enough that aero is as big a factor for me as it is for some.
Even it doesn't explain anything, it was pure fun to watch this video!
Another botched GCN "experiment". You completely eliminated the advantage of light wheels... ACCELERATION!!
In the words of Scotty “Yuh cana change the laws of physics Captain”
It affects you when accelerating, starting off or climbing hills, its basic physics, if your wheels weighed one ton you would never get up a hill and accelerate very slowly. It still affects you on the flat but less noticeable.
If your frame weighed one tonne you wouldn't move it either...
Wheely feel better when their lighter, more springy. But in general weight differences on wheel or any part of the bike are identical in performance.
At the very end, Ollie points out it may matter in a hillclimb. Gee, why not do a hillclimb for a test?
Weight on the edge of the wheel counts exactly twice as much as non-rotating weight for acceleration. No difference in climbing performance.
If you do a distance test where you roll under gravity with no pedal input, the heavier wheels actually have a small theoretical advantage: they store the same kinetic energy while rolling slower, so less energy is lost to air friction. But we are talking negligible effects compared to bike + rider weight.
All the critiques notwithstanding, I think we should applaud Ollie for even attempting to bring an analytical approach to cycling issues. His various sciene-based videos on GCN, whether on wind tunnel tests, nutrition, etc. are the best there is. I look forward to more of the same.
But how often is that gained flywheel energy wasted by braking at junctions? All the time. It's very common for road layouts to have junctions at the bottom.
Great to see your dedication to this test. I don't think coasting is the right way to measure it though. It's the small accelerations and decelerations on every pedal stroke and from changes in terrain that make the difference. All you need to do is ride for a few minutes on rollers with alloy rims vs carbon and you will immediately feel the difference. The former will feel like you are riding through sand.
In the road world, where there is hardly any significant external variable such punchy incline and braking, the argument of why spend the money on fancy light wheels is more valid. But it is very significant in the MTB world, which I have experienced first hand the differences. Lighter wheels and tires netted me a 4 tooth difference in chainring size between bikes, 34 on my xc bike and 30 on the trail bike with more robust wheels and tires.
Light wheels won’t affect the speed in a downhill like that, because they are just like a flywheel on a motor as you said. But like a flywheel, a lighter one allow to accelerate faster, but will be less stable in its RPM due to decreased moment of inertia.
In a downhill the added weight increase you potential energy so you will go faster and travel further. That’s why aero bikes don’t care so much about the weight. The added weight will cause some added watts to keep the same speed, but the aero advantages will compensate and make the bike faster. In a way, like a supercharger on an engine. The added drag of the belt and rotors compressing air may cost you 40 or 50hp, but the increased admission pressure will make a 100 more hp. Overall you still have more power because the total gain is 50hp.
The benefit of lighter wheels is more in the agility part. Having less moment of inertia, the bike will be more nimble and peppy, and accelerate and slow down faster. In a crit or a race it can make all of the difference in the world.
It's called moment of inertia. It's where the weight is located that makes a difference in how quickly the wheel accelerates. The higher the percentage of the weight that's around the outer edges of the wheels will make the wheel harder to accelerate and vice versa if the weight is closer to the center. The test should be performed with the weights added to the edges vs added to the center, and then measure the time it takes at a given wattage to reach a certain speed. If you're rolling downhill, then measure the time it takes to get up to 50kph, for example. Theoretically, if the weight is distributed to the outer edges of the wheel, it should take longer to reach a specific speed when rolling downhill.
What about the tyre pressures between the two wheelsets?
The experiment to be run is: peddle about half way down the downhill and input and fixed amount of energy E=(Power)d(time) and see it the energy you but into the bike is better stored in the deep (80mm rim) or the shallow (30mm rim) rim. To keep the weight of the bike constant, add weight to the bottle when you put on the shallow rim.
I think a chap called Galileo beat you to it by over 400 years: en.wikipedia.org/wiki/Galileo%27s_Leaning_Tower_of_Pisa_experiment
But I applaud that you're actually coming up with simple real world tests for some of the myths of cycling. Good job, keep it up!
As a heavy rider (325lb system weight (147kg)), any difference in the rotating weight shouldn't make a difference.
However, I have found a difference in handling between my son's bike and mine.
We both have a RadMission but his is two years older. The tires are the same brand and model (Kenda Kontact) but his tread is about 3x deeper than mine.
I'm not sure how much all that extra rubber weighs, but I'm sure they are heavier than my tires.
I find when taking on a steep corner at high speeds, where you counter-steer and lean the bike in quite far and keep your body more upright, the gyroscopic effect by moving the rotating mass out of it's rotational plane, creates quite a different feel to the ground. Plus, the thicker rubber has a different deformation feel as it squashes as it rotates into the ground.
I'm not sure which I like better. His feels more like a pedal-assisted-electric-motorbike whereas mine more like a motor-assisted-electric-bicycle.
The one situation where rotational inertia counts is the sprint. That's where the kinetic energy is lost at the end when crossing the line, and quick reaction is paramount. If you were the type of rider who can profit from inertia stored in the system prior to launch of the sprint, you wouldn't be a sprinter; you'd try to win the race before.
Easier way to do this - add the weights on the spokes at different distances from the hub? You still get an aero disturbance but it's easier to control variables that way.
Rotating wheel weight isn't a major concern until the gradient rises. Right there and then a lightweight wheelset is a valuable asset to your training
Weight is less of a problem when falling, than when trying to fly.
It’s when accelerating, or pushing a bike up a hill, the weight becomes an issue.
I would hypothesize that a difference in the moment of inertia of the wheels makes the biggest difference not so much in hill climbing, which is dominated by the increase in potential energy, but in technical courses (e.g. crits), where you constantly have to accelerate and brake. 🤔
A few years ago, I thought a wheel upgrade would be great. I couldn't feel any performance difference between a nice (1550g) wheelset and the original (1900g) wheelset when riding. The nice wheelset had GP4000 tires compared to Open Sports and still if blindfolded, I couldn't tell a difference when riding. The only functional advantage was lifting the bike onto a bike rack was easier with the light wheels.
I just cracked my Bontrager Paradigm rim (second time) on my Domane. So, since I just serviced the freehub I'm gonna rebuild it w a DT Swiss RR 511 rim brake rim. Hope it lasts.
Another interesting video. Thanks Ollie and Alex 👏👍
Video actually starts at 10:51
Turn around and go up the hill, and/or take some turns going fast on the way down. Wheels are also a major contributor to overall bike weight, which is clearly important for speed and performance.
Wheel weight affects acceleration and deceleration of the wheels. As you pedal the ground undulates. There is subtle ups and downs. Added wheel mass will add force needed to overcome these accelerations and decelerations. Your test completely eliminates this effect. Wheel weight affects your power transfer to the ground. Added weight on the wheels decrease how much power you transfer to the ground through peddling. Try your experiment on a lumpy road holding a steady watts for a set period of time over distance. Even better use an e bike with a set watt output. Heavy wheels will travel a shorter distance. Add a few stop signs to make the difference more apparent.
There are two kinetic energies in a bike: the overall mass including the wheels, times the velocity *plus* the rotating kinetic energy of the wheels, which is proportional to their mass times the *square* of the angular velocity. The angular velocity is proportional to speed, so we can say the rotating kinetic energy of the wheels is proportional to the *square* of the velocity. So 300g of weight on the rims requires not only accelerating this extra mass forward, but *also* spinning it up, which for going from say 20 to 40 km/h is equivalent to accelerating a 1200g mass forward since it quadruples. Plus the 300g added to the total - so 300g of wheel weight acts like 1500g of weight elsewhere on the bike in terms of energy required to increase the speed. And 300g isn't much, just 150g per rim. It also tells us the faster you ride, the proportionally more of the overall kinetic energy is in the wheels in the form of angular kinetic energy. In addition, it further tells us the additional energy required to incrementally increase speed is dependent on the starting speed - the faster you ride, the more you have to work to increase the rotational speed. So while conservation of energy requires exactly the observations you made, and anything else would be due to things like aerodynamics or tire pressures or something else other than the mechanics, it's not a far stretch to say that a wheel that requires less effort to accelerate is for all practical purposes "faster". Of course, as you've observed, it also resists slowing down more, but that doesn't help one bit when you're about to get gapped! Another way to determine which is "faster" more closely related to this would be to instead compare the speeds reached at the bottom of the hill. Note that the potential energy is that of a 300g mass; that potential energy has to be split between overall forward kinetic energy and angular kinetic energy on the wheels. The greater the latter is as a proportion, the less will go into the former, and hence speed will suffer.
When someone is perfect at pacing, with a minimal variability, the rotating mass indeed does not matter. In the real world of traffic lights, amateur unskilled cyclists where one's speed changes constantly, rotating mass matters infinitely.
As always, very amusing to watch...but this particular video goes no further as it's scientific value is nil. :)
It matters as much as any other weight when you're climbing. If you are on flat ground and want to keep going the same speed, more mass should help maintain speed. A lighter wheel should help most if you must stop quickly and climb a lot. All the experiment shows is that momentum is conserved.
Awesome! You guys should/could have put the weights back in the water bottle with the last wheels to see if you were able to get a little further :)
yay! you just demonstrated energy conservation! bravo gcn! maybe you will consider accelerating and braking and understand that rotating weight does matter! the title is very misleading
plot twist, their whole test was just one giant acceleration (downhill) and deceleration (uphill). so if you'd claim climbing contains of very short bursts of pedal stroke causing acceleration and decelerating on the dead spot - there you have it. it's all the same.
@@GrzegorzGlowaty i thought maybe the video was an Aprils fools joke, i don’t think I can take this channel serious anymore
Did you record and compare the time of each run? The lighter wheels should spin up faster!
Interesting video, but I wonder if it could be missing a key point. My non-physicist self thinks that when you're pedaling, you aren't actually applying constant power evenly with each pedal stroke. Instead there must be slight variations in power with each revolution of the crank, meaning you slow down and speed up by incremental amount each stroke. So, even though it may feel like we're applying consistently smooth power, we're actually accelerating a wee bit each stroke to keep our speed constant. As this video suggests, accelerating is harder when a wheel weighs more. Ergo: Lighter wheels are faster -- when you're pedaling. But lighter and heavier wheels are about the same when just coasting.
Great video thanks guys. Can we please have same test please but only doing very steep a hill climb
Repeat the experiment with a box section wheel 32 spoke. There you can easily stick the weights to the rims in between the spokes. Will not negate the aero as much as on an aero wheel. However I would recommend to have the weighted rims balanced. Since an unbalanced mass on rotating wheels can add all sorts of vibrations and strange feelings.
However whenever you are braking a lot like on a switchback descent or in a tight crit. The inertia is lost on braking.... And who doesnt like the feeling of light wheels.
Just from ride experience, I think for a light rider having light wheels gives more response attacking on ramps and keeping form on extended steep sections
To increase rotating weight just use 600g of sealant in your tyres. That way you eliminate the aero variable and have a proper scientific result.
Or empty the water bottles into the tires.
Speed isn't what's affected most; it's handling. Not just acceleration and deceleration, but also cornering and stability. Lighter wheels respond a lot faster.
Interesting test, but... This point may have been mentioned but wouldn’t a better test have been against a set of stock/cheap wheels that bikes often come fitted with, rather than an expensive set of aero wheels? That would help answer the question about where money is best spent on upgrading a stock bike/cyclist - wheels, groupset, fasting clinic etc?
A better way to add weights to the wheels would have been to stick them on the inside of tubeless rims, possibly with an extra layer of rim tape so it does'nt come loose.
As for "not taking a leak" : next time, bring lead suppositories, or drink a pint (2nd option for me...).
This would be more interesting if you had the starting from stopped and hill climb elements, perhaps for another video?
Interesting experiment. What would be more applicable to the real world is testing it up a series of short, steep climbs with similar descents where you need to brake. This is usually the case with British hills and in this case I think the weight, and rotational weight especially, would hurt you more because you’re not gaining the benefit on the descent, just paying the penalty on the climb
Yes but it appears that that is due to the greater weight of the bike rather than where that weight is on the bike (or rider).
Spin a light wheel in your hands and try to turn it. Spin a heavy wheel and try to turn it. Now wonder if that experience will impact cornering.
Greater gyroscopic inertia might not be a bad thing for handling. You can market it as stability in cornering for example...
Rotating mass absolutely has an effect (unless it goes against disc brakes and fat tire marketing, lol). High performance race cars strive to lighten wheels & tires for better performance. Anytime the wheels accelerate or decelerate the change in weight can be felt.
So, a full bottle and a full bladder are crucial to optimum performance! Good hydration IS the key!
Would it not be a better experiment to get to a certain speed without weight and record the average power over a set distance once up to speed and then repeat with weight added and see whether the power required is less with the weighted wheels.
If you really want to test this correctly. You should use the same rim depth wheelset, but one set is alloy and the other set is carbon. That way aero doesnt play almost any role. And you have a significant difference in wheel weight
These slow mo are !!!SICK!!!
You should have change the tires from the 303s to the 808s.
Because rolling resistance etc.
The acceleration at the begining is the same for all, regardless of weight, as the accel is a component of gravity and the angle with the horizontal, i.e. a = g sin (theta) , where theta is the angle from the horizontal.
This experiment is essentially a verification of conservation of energy, and of course, does not examine what you had hoped. Polar moment, and angular acceleration are the quantities of interest, and quite importantly at higher speeds the polar moment will also effect the turn in of the bike. (due to angular momentum effects) On motorcycles this is extremely apparent and important.