Do Heavier Riders REALLY Descend FASTER?
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- Опубликовано: 10 июл 2024
- Descending is one of the great joys of riding a bike, with some of the pros like Tom Piddcock hitting over 100km/h in the Grand Tours. What factors affect your speed downhill? Could carrying more weight be a positive when descending? Si and Conor test whether being heavier actually makes you faster downhill.
Check out our Strava route 👉 gcn.eu/descendingfastroute
00:00 Intro
02:44 Si's descent with a weighted vest
05:54 Conor's descent lightweight
06:33 Si's descent lightweight
08:50 Conor's descent with a weighted vest
09:15 Descent speed result
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Do you think heavier is faster when descending? 🧐
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Do you think heavier is faster when descending? 🧐
Yes, and no. Compact riders descend the quickest. Then the Clydesdales. Lightest ridesrs descend the slowest, naturally. But add in power on the drop and the lightest riders can pass the heaviest. All comes down to physics.
i was gonna say yes but then i remembered that being heavy also means you are probably wider which probably isn't aero so i dunno.
Absolutely. The problem is that the reverse is also true: heavier cyclists ascend slower, lol.
On A Related Note: Heavier bikes descend faster too. Bike shops love it when customers pick up a light bike and get excited. And with good reason, they're easier to get up the hill. BUT what nobody likes to tell customers is that yer gonna hafta push these lightweight bikes all the way down the hill to get any real speed out of 'em. It's just physics. 🤷♂️
In real world, heavier is faster, or my bike is just better riding downhill. I always pass lighter people in descents.
Please see Galilei Galileo who answered that long ago! From a simple physicist!
As a 110kg cyclist, I can confirm I'm rather quick when gravity is on my side. I'm also rather slow when gravity is fighting against me! 😢
Mate I'm 112kg ..I totally feel your pain..but don't take us big guys on descending...... I'm pretty bloody quick on a snowboard as well... love gravity....sometimes...😂😂
108kg yep, seem to accelerate past everyone downhill!!!!! If I want to maintain the same speed as others I need to sit fully upright and be a wind block!!!
Was in a similar boat but dropped down to 92 now and slowly dropping more, feels so much better up hills with being under 100kg. But miss the high speed downhills.
this is why i run 180mm rotors front and rear (also because i have 203mm rotors on my 170mm trail bike and hate the feeling of discrepency between the 2 bikes)
As a heavy cyclist, YES. Descending is the best part of cycling! The one before that (climbs) are the worst! 😅
What goes up... 😳
Me too
...must come down @@gcn
We once ascended Mt Samat for 3 hours to tackle a difficult 7 km ascent, only to blitz it for 15 mins at 60 km/h downhill. Oh ya, I'm heaviest at that time.
When cycling, what goes down, must come up... 😂
You guys need to do this with two riders that weigh different amounts and are used to the weight. Anyone who just suddenly throws on more weight will definitely be more cautious about the weight while on a ride, while someone who just weighs more and is used to going into corners and just riding in general will have no problem throwing the weight around and dealing with it..
the effects of air resistance would be completely different for both riders so their times cannot be compared because too many variables are being changed at once
There’s just too many variables so can just anecdotally test. Even tire pressure needs to be adjusted if it’s a single rider with an added vest. For example adding the vest would be similar to lowering your psi
Naturally heavier riders will also have a different weight distribution. It won’t be all gained in one area.
I agree, you are going to feel off your game suddenly wearing a 25kg vest. I know as a heavier rider, I always start passing folks in a group on the downhills without even trying, while they may still be working. Of course, the lighter riders will then kill me on the climbs, but there is definitely an advantage going down for me. Overall, it's MUCH better to be lighter. Having to make a harder effort on every little climb just wears you down on a long ride.
That was the best rock-paper-scissor cheat I have ever seen :) props to Connor for this micro delay
It's not his first rodeo 😂
I was going to say that wasn’t a valid result. LoL.
There was nothing micro about that delay.
Most impressive thing about this video is that Simon did a curl with a 25 kilogram vest, albeit with two arms and only one rep.
Some say he's been getting tips from Dan 👀
Gotta get these gents doing a few more push-ups and pull-ups. Strong arms saved my face during a bike crash ;)
Conor sounded like that cycling friend that waits at the top of the climb and Si did a very goid impersonation of myself when I reach the top.
As a heavy rider who usually blows by the featherweights on the downhills, Yes!
Is that when you choose to attack? 💨
😂 It’s a useless attack because on the next uphill, I know they’re going to pass me like a parked car. But yes!
Me too
@@user-mn8le5tg1o Not useless; if you don't attack they're just doing to do the same thing to you, but starting from in front of you.
I just have to mention that Si's eyewear choice for this video looks awesome! Also, I once had to transport about 20 IV Fluid bags in a backpack for a hospital that ran out of supplies in the aftermath of a category-5 storm here in the Philippines working as a volunteer bicycle messenger for disaster response and I got the chance to (kind of) test this theory as well. While I could swear that I did go faster on the descents because of the added weight my problem was that it also snapped my saddle in two and had to ride the last ten kilometres without sitting down. 😅
From doing pinewood derby contests, I know weight definitely adds speed. I pass friends downhill without pedaling and hate riding in a group downhill, because i have ride my brakes the entire ride down to not over come the person in front of me.
Haha Simons reaction when Conor said that he would do Decent 2 with the vest 😂😂😂 so he wouldn’t have to ride up the mountain with it.
Yep, that face said "should've left the vest at the bottom".
Well, at 6GAP some years back, as a 200lb rider, I got several compliments for my descending speeds, but never any going up the climbs. 🤣🤣
I wish you had included a hill with minimal turns which didn’t require braking.
Or braking.
They even got that wrong in the video.
Exactly! They introduced so many unnecessary variables that it made the results meaningless. Pretend its a soapbox derby race. Find a big straight hill. Start at the top. Time yourself to the bottom. Do it again with the weight vest. Done! Heavier is faster.
We used to have a tandem. Solo riders couldn't keep up on descents unless they could hold our slipstream. I think Bobsleds add weights to make each sled the same weight. I seem to remember that the coach in "cool running" had been disqualified as a competitor for adding extra weight.
A downhill dragstrip?
Indeed. There's a good one in my city with about a 200m descent on a pretty straight (curves, no brakes required) road, and no matter who starts off faster by the end I've invariably caught them or am catching them.
I'm 110kg or so.
I've currently lost 46kg and confess that I never thought about the impact that would have on descending. I've only been interested in climbing gains. The climbing gains have been awesome 😎. I've had the same bike during this time.
First, good job! Second, I would guess the climbing gains by far outweigh the descending loss.
@@stephenauckly Definitely 😁
i'm in the second year of physics university and i have to say that in any cinematic equation the mass doesn't show up. that means that the velocity should be the same and the time as well. we have take into account the equation for the friction of the tyre in which there is the mass. that means that heavier the cyclist is the more grip he has and he could go faster in the corners. on the other hand the center of mass is higher that means that he's not able to bend in corners as lighter rider can do.
at the end we have to consider as well the cda but depends on so many things.
Heavier objects of the same size have a larger terminal velocity which is proportional to the square root of their mass, so would go down faster.
Heavier objects have a greater gravitational force BUT also lower acceleration. So when cornering these two effects exactly cancel out
@@utube7930 when cornering the size of the balls becomes most important
@@utube7930 I think @mb10kx is right. I just solved the relevant equations.
If you equate the gravitational force and the air resistance force and solve for v,
the entire remaining formular is dependant on the squareroot of all factors that go into the equation, mass being one of them.
But you're also correct about intertia.
As Galileo Galilei proved in his experiment, two different masses experience the same acceleration when dropped from the same height
The thing is though, it only affects the acceleration, which doesn't stay constant as soon as you consider air resistance.
I would say that the force acting down the slope is predominantly due to the mass of the rider, which is (proportions being equal) proportional to the cube of their height.
The force acting against that rider is predominantly due to the air resistance against them, which is proportional to their frontal area, ie to the square of their height.
So someone like Conor ought to descend quicker than someone like Simon, given that they are roughly the same shape...
This video is great! Brings me back to old gcn with Matt
I think the real important thing to discuss is Si's amazing Jackie Onassis sunglasses. Properly channeling 1960s American fashions there, lad!
As a heavier rider (217lbs/98kg), I can say that I typically descend faster than many of my riding friends. This despite the fact that I'm taller than almost all of them. I think this is because heavier riders do have more potential energy at the top of a climb than lighter riders. Also, I'm comfortable descending at my weight. In addition, I have to say I used to ride a motorcycle, so I'm very familiar and comfortable with cornering at higher speeds because of that experience.
Well Si, now you know how it is for us heavy riders to ride up a hill :) And the only reason to put yourself through that is the reward of the descend.
Need to rerun this test on a straight road. There’s too many variables involved with the turns.
Agreed. But also there is some data to collect. Because most hills have turns and this kind of test will take in a lot of factors including the psychological effect of being heavier.
@@WillEDC Si pointed out the biggest point, which is the confidence lost by wearing the weighted vest. Had it just been his actual body weight, he would have felt more balanced and confident and would have been able to ride smoother.
I know it’s only anecdotal, but I have myself experienced the extra speed descending with extra weight. I’ve even run my own experiments. I ride with a guy smaller and lighter than myself. On two separate bikes of mine, I have been faster than him down hill. Even to the point of riding the break to allow him to pull away from me, letting go and cruising right past him. Again, this is anecdotal, but I’ve seen my own results go in favor of the heavier rider on more than one occasion.
Great you had the chance to ride Els Angels, Girona. Was fortunate to have the chance last to do the same last year ... without a weight vest. 😀
I'm 86kg and I pride myself on being a fast descender. I think this all shows that on a non-technical descent, the heavier rider may have an advantage. As the the descent gets technical, technique becomes more important. The extra momentum the heavier rider has will need to be scrubbed off with the brakes. I do ask a lot of my brakes. There might also be a lower limit to corner traction as the the heavier rider loads the tires more.
I'm a physics teacher and hobby cyclist and have been wondering about this question every now and then without finding the answer just by thinking about it. So thanks a lot for the experiment and the laughs you delivered on top of it.
Great video guys .
How much were you on the brakes was it more with the vest on ? ???
As a feather weight I know all too well that heavier riders descend significantly faster. I raced the Lotoja last year (longest single day USA Cycling road race). There are three mountain passes. I was in the breakaway with a total of 6 guys. I got complacent along with one other guy who was also a feather weight right when we reached the apex of pass 2. There was probably only a 10 ft gap, but as soon as the 4 guys up front got pulled by gravity I along with the other skinny guy were left in the dust. We were peddling a 120 plus cadence and the others were coasting away. I have to grab a wheel or I’m gone!
Appreciate the cute stickers and slideshow.
Did you adjust the tyre pressure to the changed weight?
A few years ago a load of cycling friends came out to a village I know well in France. In their throng was a young (16 I think) featherweight lad who utterly destroyed everyone on the col de Pierre...he was amazing and nearly broke the kom...but on the descent he was flat last...he just couldn't keep up despite gunning it.... There is definitely a balance to be had....
Did you both ride the same tire sizes? Because the thing that freaks me out about being heavy while turning is just grip when leaning over (on bike thin tires)…
Absolutely loved this content! Welcome to Science Si's new science buddy Science Conor! I'm definitely faster on the descents in the Northumberland Hills (Ontario, North of Cobourg) but there are few switchbacks so almost no braking for corners! I pay for that 'weight advantage 'climbing up the next hill, so it evens out over all! Very thought provoking content. Where is this filmed? Brit's on the right hand side of the road? Hmmmm. Don't get on the wrong side by accident! Thanks for this inspiring video!
It’s really a dream!! Fargo GCN season one !
I always felt I was faster on the long straight descents, but I was much slower going around sharp bends on descents. I think you need to repeat the test on a long descent where you don't need to use the brakes.
Please please do this experiment on the flat. The basic theory that weight only matters on hills overlooks the huge impact mass has on acceleration, and cycling we are constantly accelerating and slowing even with each pedal turn. On a flat ride the theory implies the ride would take the same time, but the reality is likely to be quite different. This is really hard to model, that’s why it would be an interesting experiment.
The weight in increases the rolling resistance so if you just put on a weight vest you will defenetly be slower. But usually heavier Riders have larger muscles and better leverage as well and also worse drag. So on a flat its Not comparable at All because its so much dependant on the Fitness and body Position as well as leg length and so on.
Fat guy here. Years of experience. On gravity descents, I tend to sail to the front. Add pedaling and big plums, we typically blast past everything.
My experience is that as a heavier rider I do go faster down slopes. Often if I start with a friend at the top I'm bike lengths ahead at the bottom even without pedalling - however, that's on short straightish roads so I think perhaps the lighter rider may have an advantage in the twisty descents. Next experiment should be to see where the crossover is!
Thought-provoking video! A recommendation for a future experiment: the weighted vest is significantly less aero than the (weighted-less) plain jersey. Thus, the weighted descents would be actually faster if the aerodynamics effects of the vest were negated.
Els Angels in Girona! Was there last week
Such a great ride! We've had some great times on this climb 👉 ruclips.net/video/XPCjTCd_Exg/видео.html
I went on a TDU group ride and at a hair over 100kg I was definitely one of the slowest going up, but with some degree of confidence and knowledge of the road combined with my size, I was absolutely the fastest on the way down. I was putting in 3 or 4 pedal strokes out of each corner and then tucking to get back up to speed; the guy who got to the bottom behind me said even with mad pedalling out of every corner he couldn't keep up with me. There are a number of factors at play in my scenario, just like there are in this GCN test. A higher centre of gravity and being uncertain about weight distribution I think would make anybody more careful on a descent, even the GCN boys.
In the end, I'll continue to believe it because I have to have some kind of advantage over the lighter riders who prance up the hill like mountain goats compared to me 😁
(Athletic) 240 lbs clydesdale here. Nobody ever passes me on a descent. It's everywhere else I get dropped, lol. Also interestingly, I believe that Zwift takes rider weight into account on descents as I usually fly by other riders on descents with minimal effort.
Match that with a recumbent and you know you are faster. It is significant. We have a hill near to where I live and it is straight, and my terminal velocity is scary, do it again on a long straight hill, pump your tyres up a bit and let us know.
Let me add another thought, I have two recumbents two electric and a normal bike, i can go for a known regular ride and always my average and maximum heartbeat recorded by my Apple Watch are ten or more beats per minute less when I ride a recumbent. Tell me why that is.
There are 2 main forces in play. Force due to gravity (F=mg (aka weight)) and wind resistance. The bike will continue to accelerate until these 2 forces are in equilibrium (balance out). When these forces are in balance, the bike has reached its terminal velocity.
If we have Bike A 75kg and Bike B 100kg
the gravitational force acting on bike A is 25% less than bike B. With all other things being equal, the force from wind resistance is directly proportional to the velocity squared. bike B will have a higher terminal velocity than bike A. i.e heavier riders have a higher top speed on the descent.
What is needed is two riders of similar frontal area but different weights. And a straight road.
Anecdotally tandems descend faster than solo riders - greater mass for similar CdA.
Simon what is doing with those Dame Edna Glasses? A great experiment as my son just so happened to be doing a school report on mass, velocity and kinetic energy.
95kg rider here and my local Strava times downhill say that heavier riders are waaaay faster on Exmoor 👍👍
Connor doing the dubious laugh was hilarious! 😂
I love this. Thanks for sharing. Physics says heavier is faster - but you have to be comfortable in your skin
110kg rider and skiier here! 🙋
I can absolutely confirm that we descend faster but we do struggle to keep up with the racing snakes on the climbs.
One other observation I have made over the years. You know those roads/stretches where it's pretty flat but you get the odd roller (circa 8ft elevation). I as a heavier rider seem to conserve my speed up and over where as the lighter guys slow down quickly! I end up towing the group to keep the speed up, also because I produce a great draft! 😂
Were there no hills with a long straight road that would not require any braking (except at the bottom)? It would not have to be steep. Touching the brakes at all turns this "simple physics experiment" into a very complicated one.
To clarify my previous comment on Conner, I'd gladly take a wheel draft off of him any day of the week it was offered, is genuine kindness is second to none, he's just not a climber's body. He has other gifts.
This has to be great commitment to the bit, making Si ride up the climb twice with the weight vest.
Hmm, this means my descents are going to be slower now, I have currently lost 23lbs and I have a new carbon bike that is 7lbs lighter than my old aluminum bike. But then again, my hill climbing should be much improved. To many things to calculate! :) Great video guys!
We think it should even out 😉 The confidence you have on the new bike will give you some extra speed 💨
Now your just bragging about your new bike😂. Congrats anyway enjoy the easier climbing.
Could you post you times and weights for both rides each please?
As Sia touched on knowing how to control makes the difference. I know from riding with lighter people that are comfy descending, I can easily catch them in the downs.
Another question would be grip due to the additional weight stressing the limit of traction. Also should adjust tire pressure for 25kg difference.
Sram and silca tyre pressure calculator racomand higher pressure. Have you changed it?
I enjoyed this one as I am regarded as one of the fastest (if not the fastest) descenders in the club. I was called "kamikasi", I am probably the heaviest too at 85kgs on our standard club runs. I feel it is much more about the rider's ability, experience and "cojones" or as guys were you were in Girona "cullons". I know how to brake late into corners (even better now that I have a rim disc bike) I believe I am skilled at angling through corners especially tight ones, and know how to accelerate efficiently out of the corners. It is many factors that lead to speed downhill.
Rim disc bike ? Is that bike with both a rim brake and a disc brake on each wheel ? If so, no wonder you are a demon late braker.
Simon what sunglasses re you wearing? i love them
POC Devour WF.😎😉
You guys should do the same test ascending.
As we know, all objects fall at the same rate in vacuum. As this isn't a vacuum there are other forces to consider such as, drag(air resistance), friction(between the wheel and road), rolling resistance, and stopping force. For the sake of argument as (unless proven otherwise) I imagine drag and rolling resistance to be negligible over this distance, I also consider the same for rolling resistance. We are now left with friction and stopping force. At the moment nothing heavy rider and light rider arrive at the same time. If we consider friction, using F=mewR, force of friction = friction coefficient × Reaction force. Where the friction coefficient between the wheel and road are the same in both runs, R the reaction force (the force upwards which is equal to the mass of the bike and rider × 9.81) is larger in the second run. This means that the heavier rider has more friction. Therefore, they can take corners at a higher speed(this neglects how the higher COM will affect cornering however the results would be the same. Finally we look at stopping force, this is much easier. A heavier rider, traveling at the same speed has a grater momentum, therefore they would require a greater force to overcome the momentum. Or, the same force over a longer period (impulse equation). This means that the heavier rider will find it harder to stop over longer distances.
From this we can deduce that, on a route where a rider doesn't have to break (with weights on) they will ride faster. However, with heavy braking zones and slow speed corners the heavier rider will struggle.
I lost the weight of that vest in a year 😅. But there aren’t many descents/climbs in the netherlands.
Is a nice video and I really think weight make difference, you must try these experiment on a straight 1 km descent road!
I believe there should be a Part 2 where you both have to get used to your technique with the vest on. Which means you need to take more than 1 descending run to get used to the weight. Also make a comparison to a straight descending run.
What's the aero penalty for that weighted vest?
105kgs here who loves taking corners and on descents if I'm behind anyone I am on the brakes allllll the time. I would say yes.
Si look at Connor when he said, "He going to ride down without the vest first" is priceless!!
Whilst you were at it, how many extra watts were you pushing up hill? Should be in between 3-5 watts per extra kilo
It would be really interesting to see a climb + descent with and without a weighted vests. How much slower is 10, 20, 30, 50 lbs.
We'll get the vest back out for sure 🙌
Exactly. How much slower were they climbing with that much weight on their bodies. Si clearly looked shall we say winded after climbing with the vest 😂
@@wstokes13it would be super interesting to see if a statistical handicap could be multiplied to climb times to account for weight.
For example, I’m over half a foot taller and about 50-60lbs heavier than a mate who rides. Obviously he is way better than me at climbs. I’d love to know how much slower those extra lbs are causing me to be.
Mathematically, all you’d have to do is have a few GCN riders do a climb with and without weighted vests and then average the % difference. Do that for several weight differences and you could get a fun multiplier that people could do to their own climb times.
Probably sadly, I have thought about this. I think it’s technique and confidence that makes you faster. Confidence doesn’t mean daft - you’ve some experience so you know better what you and your bike can do.
I also ride a tandem. And the tandem is faster downhill everywhere. The systemweight difference is 70kg. On long straight steep parts no one can keep up with us on and offroad. I use a dropper on the tandem and shift my weight over the bars of the stoker. Im tall (198cm) and use a straight bar. So I'm less aerodynamic than cyclists with race bars. And the rolling resistance of the tandem tyres is also higher. So with a racingtandem speed diffrence would even be higher. It's different story on 3 to 4% descents with a lot of curves. I also noticed that on long straights there's a moment the bike is no longer speeding up but holds the same speed. Max speed with solo bike on a downhill I do ride a lot was 105, same downhill with the tandem 119.(I never told her.) Same windspeed that day.
In September I rode up the Kühtai pass near Innsbruck, Austria, approx. 1400m of elevation gain. After a short break on the top I sat my 105kg up on the saddle of the 2022 Trek Domane I had rented for the day and started rolling downhill - like I literally didn't make a single stroke. The bike got faster and faster and faster and I was occasionally tapping the brakes, but before I knew it I was blowing down there with close to 100kph. I don't think a 60kg rider would have done the same. 😅 But it absolutely depends on the type of descent. This one consisted just of really long winding bends. If it gets more technical you'd definitely would lose out to a lighter/smaller rider.
I think at 112kg I descend faster if I aero tuck than if I'm sitting up. I suspect its more down to technique and how brave you are 🙂
Did you adjust the tire pressures? If not, the rolling resistance would have changed considerably and affected the results.
How fast were you going down that hill? A video on descending safely would be awesome!
Heavier = more pressure on tire = more grip
The real benefit to weight in anything that uses tires is you effectively get more grip, up to a point. It's why we have downforce on cars, to add weight (albeit, "free weight") to the tires for cornering.
I don't think the difference would be huge in a straight line but in the corners, a heavier ride can carry more speed theoretically than a light rider.
But i agree that instantly adding that much weight would throw you off on technique. If you remove those things and equalize, youd be faster because of more grip.
As a heavier rider, we do see this often at least in my own group rides. The lighter/ younger blokes have to pedal while I engage my super power (gravity).
At least in a straight line. Once you throw corners into the mix, then you bring in cornering techniques and confidence
As a light weight cyclist, I'm pretty sure my max recorded speeds have been when I've loaded my bike like an abused pack mule, and then gone careening down some steep hills. They just aren't the same when it is just me or without my laptop in my panier!
I think the question is more interesting than actually realized... but I think it comes down to drag. If you work out the COE of this you get the same that v = sort(2gh) and mass doesn't matter (yay Newtonian fizzicks). However, while we know that gravity will "pull" (ok, let's ignore GR for this - though would make an interesting analysis) every object the same, it is a bit like dropping a piece of paper and a book at the same time. While in a vacuum they would impact the surface at the same time, the drag makes this not the case. Even if they are the same size so the same surface area meets the air, the paper will simply waiver down to the ground while the book will fall with a thud (or think a cannonball through the air if you'd rather). It would need to go faster for the same drag effect. Simply, our lighter rider has more of a drag issue, but can be negated if he tucks (or goes Superman). [initial morning thought without putting much more effort into it; but may pose this to my students :) ].
YES!
Long geek answer alert skip to the conclusion at the end if you want. It is the amount of power put in on the descent that makes the difference.
Im not sure if I should be fascinated by your experiment or annoyed...in a kindhearted way. Okay fascinated by your findings. The rule you were referring to was on a vertical drop in a vacuum dealing with the force of gravity isolated by itself. The experiment you did had other forces in play including drag. Velocity equals distance divided by time as determined by its acceleration. Which is the change in velocity over the change in time. The final forces to consider are the effect of gravity on the angle of the hill and the amount of air resistance on the rider. Considering on a hill that gravity acts on an object the same no matter the size on the same hill if they rolled at the same velocity in the exact same path they would end up at the same place at the same time. By the way if you were on an infinate hill at the same angle eventually you would both have reached terminal velocity and ended up at the same speed. The physical laws on the earth like to equalize things out like that. O energy output is stable.
You didnt ride the exact same path so now we have some interesting forces to consider. Why does it feel like you were at a greater velocity than at your lighter self? Pe rhaps you were feeling the greater wind resistance and you were accustomed to x amount of wind equals x speed? The extra weight applies greater contact with tbe road surface causing greater pressures on your riding angle and you being an experienced rider associate those pressures and angles with x velocity. There are other finite forces at play here too like the heat disapation of your tyres, air pressure both in your tyres and in the air, wind speed and direction, the aerodynamics of your bike, air temperature, rolling surface, ect.
I think that in this experiment it came down to your perception of what you were feeling to previous knowledge of how fast you were going when you experienced different angles of your bike and wind resistance.
Galileo Galilei allready prooved in the 16th century, that an objects mass has no effect on the acceleration of said object.
The explanation given at 1:30 is somewhat vague and unprecise.
The actual way to go about this, is to equate all the relevant forces, such as gravity, aerodynamic drag and rolling resistance.
If all resistive forces were 0, then there'd be no difference in speed whatsoever.
Scince roll resistance is proportional to the cyclists mass and is also not dependant on speed, it would cancel out.
Air resistance however is depedant on speed and results in a higher terminal velocity for a heavier cyclist.
Of course, we're neglecting effects like probably longer braking distances if the braking forces are equal between both riders,
thus resulting in earlier braking maneuvres, etc..
Appendix:
The formulas needed:
gravitational force: F_g = m * g
acceleration force without drag: F_g' = sin(phi) * F_g
roll resistance: F_r = μ_R * cos(phi) * F_g
aerodynamic drag: F_D = A * c_D * q = A * c_D * 1/2 ρ v²
F_g' = F_r + F_D (insert everything from above and solve for v)
m : mass of cyclist incl. bike
g = 9,81 m/s²
phi : angle of slope
μ_R : coefficient of rolling resistance (prefferably very small)
A : cross-sectional area of cyclist on bike as seen from the front
c_D : coefficient of aerodynamic drag (dependant on shape, surface roughness, can be affected by clothing, aerodynamic helmet etc)
ρ : density of the surrounding air, approx 1kg/m³
v : velocity, aka speed, in this case terminal velocity (the thing you'd look)
Here is some extra science to throw into the mix.
1. Conor is heavier than Si so a 25 kg vest will have a greater proportional weight difference on Si than it will on Conor and will therefore effect Si's handling in corners more that Conor's.
2. When heavier riders are cornering at a given speed there will be greater centrafugal and centripital forces at play. I suspect that means they will need to lean further into a corner resulting in less downward force and more outward force and be more at risk of loss of tyre traction.
So I think heavier riders will be faster out straight out downhill speed while ligher riders should be better at technical descents. Any thoughts anyone.
Descending depends on a lot of variables that weren't covered here. I'm 198cm and 84kg and I am a very confident (some say insane) descender. I can't ever go fast enough.... I run a -20 stem and pull my arms to the stem and knees inboard on flat out sections, so very aero, and I always pull away from my riding mates and those I'm racing against. Add in corners and you're all dropped. :) IMO the most fun discipline of cycling.
I think some characteristic of a good descender comes from driving. For example if you’re excel in corners, either your consciously or subconsciously can recognize the lines and apex of a corner to maximize speed through it
@@WillEDC savvy... I have been to two race car schools, but I've also got 46 seasons of road cycling under my belt. I'm also an avid downhill skier, so yeah, knowing what lines to pick through corners pays huge dividends.
I believe wind resistance is the biggest hurdle to any type of ride. I ride solo and tandem and I believe that the tandem is faster when there is a headwind because we (including bike) are 170% of my weight and one lot of wind resistance. My wife is effectively drafting. Cross head make less of a difference and tail is faster.
As a heavier rider not confident at descending, I totally understand the feeling of uncontrollable inertia coming into corners. Even relatively easier sweeping corners feel like I’m an uncontrollable runaway train sometimes.
One problem here is that the question is not fully defined -- what is meant by faster, and what timescale are we thinking about? There are two distinct phases of motion: acceleration up to terminal velocity, and continuing at terminal velocity. Modelling a point mass on an inclined plane at 5 degrees and taking some reasonable (constant) values for air density, rolling resistance and CdA gives me an equation of motion of:
dv/dt = 0.815 - 0.21v²/m
where v is the velocity at time t and m is mass. I can't remember at the moment how to solve this equation, but it's clear that a heavier rider will accelerate faster to begin with, and will also be going faster at terminal velocity when dv/dt = 0 so (approx) v = 2√m
Solving the equation will provide full details of the motion of the rider, but right now I'm off to ride my bike. Any glaring errors in the above, please point them out to me.
I've done the sums. On a straight road with a 5 degree slope, assuming that heavier and lighter riders have the same CdA, an 80 kg rider wilil accelerate faster and reach a terminal velocity of 63 kph, while a 50 kg rider accelerates more slowly to a terminal velocity of 50 kph.
2:50 if there is something bigger than Si’s ankles, it’s Si’s nose in big glasses.
Could you try this again with a straight decent? I imagine the confidence in the corners must have been minimal with their centre of gravity being all off.
It’s true. Air flows faster over a smooth round beer belly than rippled abs (creates vortices). Cheers 🍻
02:30 now you know what being me is like, Si!
Why don't I feel descending faster on Zwift as a heavier rider? It feels like everyone descends the same, even though ~20-30Kg difference on body weight.
My basic understanding of the situation (I'm an a level physics student)
Air resistance slows down the cyclist but even thou they've increased the mass the overall volume and surface area hasn't increase that much so the effect of the resistance wont have increased by a substantial amount so the bike will travel nearly the same speed. This may seem counter intuitive but it can be shown with 2 balls of the same size but a different mass, if dropped from the same hight with the same force applied they will both hit the ground at the same time. Essentially mass is negligible when it comes to things like this but you do have to take into account the confidence of the riders with the weight and how similarly they rode the decent to their first time and there are so many other factors that all play a part.
I haven't watched this yet, but from a physics point of view, if you add more weight, then the resultant force from that of gravity along a downward slope will be higher, and you will reach top speed (non-pedalling) when it equals the sum of rolling and aerodynamic drag resistance. If rolling resistance goes up in proportion to weight, then that cancels out. That leaves aerodynamic drag, and as long as that increases at a lower rate than the increase in weight, then you will travel faster. Note, this is excluding the effect of bends, which introduces a whole lot of other complications. Note that you will not accelerate faster from slow speeds when free-wheeling, but the effect will get greater the faster you are travelling as drag becomes more and more important.
I should add that most gravity races have limits on weight for that reason. Now to see if theory agrees with practice.
OK - just 1:48 into this video, and the physics explanation given is way, way wrong. It is nothing at all to do with kinetic energy...
nb. call me a cynic, the puffing over the extra effort climbing with the weighted jacket would have been a bit more convincing if you'd turned off the engine on the camera bike in he filming at the top of the climb.
Do this with a Hi Tensile Steel frame where the weight will be in a useful place.
The camera bike could have absolutely carried that vest for Si. 😂
question for @global cycling network ...what is slower uphill a 4kg heavier bike or 4kg heavier rider?
Assuming total system mass is the same, the heavier rider will be faster - at least some of the weight will be muscle, blood supply, etc, which adds to performance, while the heavier bike is just dead weight.
Absolutely
I'm 6'5" and 117 kilos. I descend rather quickly. So quickly that I always over-take the other riders and have to belt into the next hill because then everyone over-takes me.
My schoolboy phyiscs... F/m=a. However, at the start the main F is gravity, and the force due to gravity is proportional to the mass, so gravity vector * m/m=a, the mass in the equation cancels out. So before rolling and air resistance, the acceleration should be the same. Interested to hear if I've got this right? Momentum is proportional to amss, so the heavier rider will have more momentum.
MMM interesting it could be, cause I do remember going down hill in a group ride, and having to brake to stop running into guy in front, I just put it down to a more aero Ish bike and wheels, but it could also be I could have been maybe 10 kg heavier. This was more or less a straight down hill run with maybe a couple of slight bends so no need to brake, but then momentum being what it is.....
Maybe if you drop the weight closer to the center of gravity or below then descending mite feel more stable which could equal faster?