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Are You Faster On A Stiffer Bike?

Are You Faster On A Stiffer Bike?


– Stiff bikes are more
efficient, aren’t they? I mean frame flex robs us of power. So a stiffer bike, therefore, would transfer more of our
energy into the drive train. That is a statement that
many of us take as fact. And with good reason, because pro cyclists want stiffer bikes and they get pretty fast. Bike manufacturers sell us stiff bikes because by and large
that’s what we ask for, and probably because bike testers praise stiff bikes to the rafters. But is it actually true? Well, we just got a bit of a mission. (bluesy music) Anyone with a basic grasp of physics knows that the first law of thermodynamics states that energy can be
neither created nor destroyed, just transferred from
one form into another. And when you think about that
in the context of frame flex it can kind of leave you
scratching your head a bit. Energy could be transferred into heat, but I can’t imagine a
rider even of the calibre of Tony Martin really generating anything meaningful through frame flex. Noise could be another one, but while there are lots
of bits of your bike that do make noise, frames don’t tend to, not until they’re about to die anyway. So the question is then, if frame flex really does transfer energy away from your drive train, where then does it go? Maybe, it’s right back into it. (reggae music) We come now to The Bicycle Academy, which is a frame loading
school based down in Frome, just down the road from the GCNHQ, because Tom Sturdy, who’s the
engineer that looked after the design process of
the GCN hand built bike, he’s the head of education
here and he has long been thinking about this frame flex conundrum. And he’s just in there. Now Tom and I were out on a
ride just after Christmas. We were discussing this problem
and you said you had a very simple way to illustrate
just how a flexy frame might deliver that energy straight
back into the drive train. So can you tell us what
we’re going to do today? – Okay, so we’ve got a frame
here that’s moderately flexible and we’ve mounted it into a
turbo train that’s just to hold the bike in one place. – Great. – We’ve got it so that
the rear wheel can spin and what we’re going to do is we’re going to flex the frame. So use some energy to
flex the frame in a way that we can pause it and talk
about the different points and see what happens when we release it. – Cool, all right then. Let’s go for it. (bluesy music) – So what we’ve got is
this very solid block here that’s definitely not going anywhere. – [Simon] I can barely move it. – And we’re going to move the pedal just so that it’s resting a few millimetres, a
centimetre above that block. Okay.
– Okay. – At this point what we’re going to do is we’re going to get side, get on the bike and hold the rear brakes so that the wheel cannot rotate and we’re going to load that pedal, which is going to flex the frame but not spin the rear wheel. – Okay.
Because of the break. – All right, shall I jump on? – [Tom] So the pedal is now resting against this solid block. – Yeah. So the back wheel hasn’t moved. – The back wheel hasn’t rotated because you’ve got the back break on. – [Simon] So therefore the frame– – [Tom] So what has happened
is you’ve put energy into the frame, which has flexed it and lowered the pedal to touch that block. – [Simon] Quite a lot of energy as well. – [Tom] Quite a huge amount of energy. – [Simon] There’s a lot of
power going through that. – [Tom] Yep. (laughs) – Okay, and so, I literally
just release the back break. – That’s right, so just
release the rear break. – Okay, you ready for this? 3,2,1. Whoa! – And so we can see that
the rear wheel has spun as that energy is being
released back into. – Well not just spun, that
was quite a significant, that was quite a
significant spin wasn’t it? – If you want we can go to the
white board and draw a couple of illustrations to work
out exactly what’s going on. – I’d love it, a bit
of white board action. Right, let’s do it. (mellow R&B music) So I’m kind of struggling to
get my head around this, okay. So I’ve seen the back wheel
suddenly spin into life, but I can’t quite work
out how flex in a frame has actually contributed to that. So talk us through what
you think is happening. – So before we start
thinking about the flex, let’s have a look at what’s going on. Here is a seat tube, viewed from the back, joining onto a bottom bracket shell. So we’re going to be standing
on a pedal that’s out here. What happens when this tube is loaded is that it actually flexes around the centre line of the tube. The important thing to
notice is that the height of the bottom bracket changes on the side of the bike
that’s been loaded. And what’s important about
that is the difference in height between the loaded
side of the bottom bracket. – Okay – Okay, and what that
means from a side on view is that you have the
bottom brackets enter there and your pedal, which
is somewhere out here. – Okay – When you stand on the pedal lowers, so the bottom bracket lowers, as we’ve just seen, and the pedal lowers, as we saw to rest on that block. When you then release the energy and allow the frame to flex back, the bottom bracket flexes
back to the starting point and so it rises up. The pedal doesn’t move
because it’s on the block and so what you get is a clockwise
rotation of the chain set which turns the chain
and spins the rear wheel. – Theoretically, and that is
how the energy is getting from your flexy frame back
into the drive train, and also you don’t think, well if that’s happening out on the road, and I suppose that is a big if, then it would be happening
when you start to unweight. That would put less
force through the pedal, which would therefore be at
that point in the pedal stroke, where actually having
some extra contribution would come in handy, be of a benefit. – Yeah, absolutely. This illustration isn’t going to be exactly how it happens on the road because we’ve exaggerated
quite a few things but that’s where the
principal would come in, that as you start to
put less and less force through the pedal, the
frame will flex back and it’s at that point
that you get that useful, clockwise rotation of the cranks, which can make a difference
to what the rider’s feeling. – Yeah, so as an empirical experiment, we’re not suggesting how
much it contributes back, but as an illustration it does show that something is happening, I guess, when you flex a frame and
then it’s contributing back. In terms of possible
holes in the illustration, I mean, where might that energy be stored if it’s not coming from the frame flex? I mean realistically, would there be some torsion in the hub, or by sort of putting the
drivetrain under load, would that contribute, you think? – I think there is going to
be an element of all of that. There’s no way of us absolutely
isolating the frame alone. There’s going to be a
bit of twist and flex in every single part of the chain. So that’s why it’s difficult to say exactly how much the influence
that might have on the road. – Okay with that in mind, I
have brought the stiffest bike that I have at my disposal,
which is my Orbea Orca Aero. Unbelievably fast. Can we stick that on the
trainer and see what happens? – Absolutely, yeah. – All right, let’s see what happens. Okay, I’m loaded up. All right, you ready? 3,2,1. – So I think what’s happening
here is a good illustration, because it’s such a stiff frame, you’re actually having to
put a lot of energy into it to get the frame to flex enough for the pedal to be on the block. So there is a lot of energy stored in it because you’ve had to put a lot in to flex the super stiff frame. – So theoretically then, there
could be no difference at all to your performance out in the road from the stiffness in the frame, as long as it’s within certain limits because if it’s a stiff frame, it’s not going to flex that much and so all your force will be
going against the drivetrain but if it does flex a little bit, it’s going to be giving it back. Whereas if it flexes more, it
will then be giving more back. – Yes potentially, and
that’s where there’s gonna be a big grey area, to where
the actual benefits lie. I guess the key is that,
perhaps it’s not as important as people once assumed. – Well, what do you think about that? I’m hoping this is gonna
spark loads of debate down in the comment section. So do make sure you get involved. Is Tom’s experiment correct? Could that movement of the rear wheel come from something else? And in fact, what do you think about the whole principal of
stiff frames going faster? For me, I just wonder whether frame flex is going to be like the new tyre pressure. So go back 10 years and
we all knew, didn’t we? We just knew that harder
tyres rolled faster and we could feel it as well. Except that now we know that
actually lower pressures can roll faster ’cause
whilst you might get more hysteretic loss, you
get less suspension loss. And so, it is more efficient. So, maybe frame flex is the same thing. Stiff frames feel faster, except, actually maybe they’re not. Get involved in the comment section. And if you wanna watch another video on actually the subject of tyres and hysteretic loss and suspension loss, the truth about wider
tyres and wider rims, then why not click just over there? It’s another good in depth piece.

100 comments on “Are You Faster On A Stiffer Bike?

  1. What affects peak transfer to the road in speed depends on peak torque during the pedal stroke. If, for example, you put down a peak of 500w at some point in your downstroke, and that gets cut to 400w, with a 100w return, then the peak speed you'll reach is a factor of the peak power. For the same reason that cyclists can take a few power strokes then coast, is the same reason that power losses to the frame affect speed — but because its harder to make speed the higher you go, the less frame flex matters. If your 310w stroke loses 10w down to 300w, the difference in instantaneous speed at the peak of your pedal stroke will not be much, but imagine losing 150w from a 300w pedal stroke. You'll cut a huge amount out of peak instantaneous speed. Even if the frame returns the energy later on, you will have missed the chance to apply the extra speed to the road. And since pedaling is a series of intermittent power applications with each stroke, not steady state power and speed, you will lose a lot of average speed. In reality, it's a small loss, but there is still a loss.

  2. The explanation seems flawed. If the frame and crank arms were made of rubber, how efficiently would they transmit power to the rear wheel? How about an undamped spring suspension that bounced up and down as you pedaled? I suspect that stiffness does improve efficiency, but the tiny difference between various bike frames is so small that it is impossible to tell by riding. The only way to know is to design an experiment that removes all the variables and is accurately measured.

  3. pafnucek
    's explanation is quite correct (mech engineer gearhead athlete in his 50's here). I wanted to add to the discussion. 1. I think this simple test is quite clever but flawed in that it takes a hair of force to rotate a free floating wheel but takes many many times more force to turn the wheel-bike-rider combination with the wheel on the ground. The same test with the wheel on the ground will yield vastly different results that is explained by
    pafnucek
    . 2. Without getting into the nitty gritty of it, but pro racing and the market is where the real life (not lab simulations) results lie. When big money and market forces are on the line in big time races, the sponsored teams and athletes who livelihoods depend on race results will not take chances with inferior technology and or materials. Ive ridden steel for years, aluminum for years and carbon for years. And bike system stiffness and efficiency is definitely an advantage in racing. The proof lies in the hands of pros who's livelihood depends on it. For me personally, light stiff carbon frames perform and ride great. The market decides. Any (most) experienced rider who goes in the flex frame direction (based on this experiment) with his riding will eventually U turn back to stiff.

  4. What’s the difference between 0.2 mm and 0.3mm flex in the bottom bracket? Answer: nothing you can feel

  5. From my point of view, it isn't any Energy loss that makes a stiffer bike better, but if the frame flexes back the rider has to force the pedal in the correct direction, which technically doesn't requier energy but force put strain on muscles as well(try holding something heavy in the air, as long as you don't move it you don't need any energy). And yes, there is as well a little bit of energy loss through heat, but its probably really tiny.
    So a stiffer bike can probably make you faster and ride longer, but most importantly feels better to ride.

  6. In this experiment the wheel will spin faster with a stiffer frame just because it takes more energy to flex it. The force applied on the pedal will have to be made a constant and the spin velocity measured for this experiment to be of any value.

  7. It’s not just about how much energy is released, it’s how quickly it comes back. A stiffer spring will uncoil faster, which increases velocity, which increases drive.
    Did I do my physics correctly here?

  8. The experiment is false , you make turning the wheel due to the elasticity load you have in the chain and in the brake system attached to frame , if you want to see if the frame gives something back , take out the chain , block the pedal rotor an retry , you will see that the whell will not move , the nergy is lost , energy is force multiplied by speed , more you have elastic movement more you loose

  9. the frame deformation , perpendicular to chain axis can non give energy back to the chain because perpendicular , but helps the other pedal to go up 🙂 …. then some energy is given back but the elastic losses due to material deformation is definitely lost ….if you want to see the full effect imagine you cut the frame in the 2 tubes , intall 2 free axix (same axix than the chain ) … and push your new free bottom bracket bike …

  10. Bicycles are the most efficient machines currently. Able to deliver up to 99% of the power of your legs to the wheels regardless of the frame material. Stiff frames just respond quicker to input.

  11. How about testing two frames on a power turbo trainer using pedal power meters to compare input and output? Not a perfect simulator but close?

  12. It's not about whether stiffer is better or not – it might actually be better (or not). The point is: We don't know. There is no sufficient empirical evidence for "Stiffer is better". And there are legitimate doubts. We might all just be stupid consumer sheeps repeating the same marketing stories over and over again. Because we literally bought into it. We are invested in "Stiffer is better". But times there are a changin'. The next story we will buy into is: Flexible is better. It doesn't matter if it is true or not. The contrast of these two stories will make us feel rebellious with our new shiny gravel bikes, 40mm supple tyres and ultra flexible thin wall tubing. But we are not true rebels, we are merely early adaptors.

  13. Im not an engineer, but surely the rear wheel is moving because the relative position of the pedal has changed after release the brake. IE it started at say 90 degrees from the vertical but after it will be say 95 degrees so you have rotated your crank, hence wheel rotation.

    I would think the difference in speed associated with the wheel rotation is then because of the higher force applied to the crank rotation.

    Other things could also come into play such as length of crank, height of bottom bracket, wheel position such as tyre size and psi.

    If all of this were even then perhaps you could read something into the results. But because of difference in stiffness the forces applied would always be different.

  14. I thought your stiff frame actually moved your rear wheel with much higher velocity/energy vs first bike. That would make sense, since stiffer frame would take greater energy to pre-load, therefore we would have equally greater energy when released.

  15. I had a super stiff frame a long time ago, and it put a smile on my face every time I rode it. It was the immediacy of the response that I loved. You pick up the speed, the bike second guesses you and you're off. Surely it depends on where the frame is flexing. If you have a 'ladies' crossbar,  the flex is extreme and only releases the front end to come back in line with everything else.

  16. I disagree with the statement that the greater flex of a steel frame leads to more energetic losses from heat than the rigid flex of a carbon frame. The statement is fundamentally incorrect because steel has a smaller area elastic hysteresis loop than carbon fibre. The area within a hysteresis loop is the amount of total work expended when a material is flexed and then released. A larger loop area means that more energy has been wasted due to heat in order to deforem the material than a smaller area. Hysteresis is not the same thing as a material's elastic modulus, which is the measure of its stiffness. People are confusing hysteresis and stiffness, and are assuming that a stiffer material returns elastic energy more efficiently than a more flexible material.

  17. This also happens with lower air pressure tyres in the city roads.
    You will ride a lot faster and with less effort with about 30-60 psi air pressure on your tyres.
    Its perfect for commute.

  18. This experiment is very flawed. In the real world, the energy stored in the flexed tubes of the frame won't be released until pressure is significantly reduced at the bottom of the pedal stroke, at which point it won't be going into turning the cranks. There's no doubt that the energy will be returned from the frame (unless it bends permanently), but that doesn't mean it's going where you originally intended.

  19. No spring returns 100% of energy put into it. A pogo stick won't bounce a person without them adding energy, and similarly a flexing frame won't return 100% of the power put into it. There is loss in a flexing frame.

  20. The only two patches that touch the ground are your wheels so the only way to get power to the ground is by sending it through the wheels. So I think stiffnes of the frame is irrelevant to the end wattage, as it will still be input wattage minus friction in drivetrain. You could actually take two exact bikes one aluminium one carbon with same drivetrain and try it out. Stiff bike feels faster off the start as it gives energy more directly to the wheels, without bouncing through the frame first. Look at it simply like this. Two springs one is harder to compress the other one is easier. The hard one will give you more of a kickback, but it will also require more power to compress it in the first place…

  21. this flexible bike concept is 100% wrong btw, you want a VERY solid bike, with good tyres and road vibration absorption.
    you dont want a flexible bike, you just want to absorb the road imperfections.
    so this GCN bike will never be successful.

  22. A stiff frame is a stiff legged machine. There has to be some flex in a bike frame. Not spongy flex. Flex that snaps back quickly when the pedal is unloaded.

  23. The pros ride what sponsors give them. Not long ago both the pros and their sponsors thought 20mm tires were really fast and a bit longer ago they thought that going through the alps on 42×23 is fast because you are pedaling really really hard. During the same time touring people were riding 28mm tires and going through the alps with 30×28 pedaling at a reasonable cadence and not at 50rpm and felt it was a lot better and smoother. Touring cyclists were slower because they have less power but they were a lot smarter without any sponsor money… Now everyone is buying the super stiff story (and now adding rubber suspension everywhere because the frames beat you up like the 20mm tires did….)

  24. I want you to do that with a Scott cr1 limited 61 cm frame. If you can compare that with a Terrifirma frame of the same size..

  25. The energy that move the rear wheel came from stretched chain. The flexed Bottom bracket actually moved the big chain ring forward and stretched the chain in which pulled the rear cassette but wheel movement was stopped by the brake until it released. If you move the front chain ring to small one and rear cassette to the big sprocket then the energy transferred will be way less. In my opinion, flexible frame is not ideal for sprinting which require instant energy transfer.

  26. just pack a steal frame back with 20kg and climb a mountain. it will wobble like crazy you will loose energy and speed. ride with stealbike across stoney gravel road you will be more quick than a stiff alubike because stiff bike start to stutter and loose speed. steal will absorbe the ride and be more quick because of that. i had all kinds of bikes that i traveled with. the worst bike a had was a steal koga worldtravel. what a wobble bike that was. i never will buy steal bikes again. i think they are nonsence. just buy alu or carbon and use thick tires. Steal is nonsence…….

  27. I remember my first ride back in the days when TITANIUM was introduced to the bike world. it was so flexible that I thought I was riding on chewing gum. Almost impossible to ride – and sooooooo expensive I did not dare to stop anywhere in the city 😉 HOWEVER since than I love Titanium bikes, even if the first experience was worst case scenario. Somehow like other things that were frustrating doing at first time…….

  28. I think the only way to test this out would be to use a dynamometer to get the actual power transfer to the road, and compare it to the power at the crank. Do both full sprints and a 1 minute average or something like that.
    If the hypothesis is correct, the stiffer bike will have the least disparity between the wheel power and crank power. Both bikes should use the exact same chains, group sets, rear wheels, and tyres.

  29. A little bit of flex actually makes the bike more comfortable to ride long distances but I have owned bikes that I could flex the bottom bracket to the point that I always got chain noise…….I got rid of that bike…….now I ride a derosa

  30. Some part of this flex energy is transormed to thermical, so you lose some of it when the flex is big enough. So, that been said, it better for a frame to be stiffer. So it's not all marketing trick, part of it is really true, the other part how much of force can create an average rider, to flex a contemporary frame.

  31. That was great. I had a LOOK back in early 2000. Was a fairly flexible frame. I could easily tell. I loved that bike though. It was pretty fast geometry-wise (thanks for the other video with Tom) and when I got to climbing, I could feel that effect – especially out of the saddle, which felt wonderful. The bike felt alive. There was a give on the one side and a spring on the other as you pedaled – subtle but it was there. I've always been thinking due to the stiffer is better mantra that the bike was inefficient. Really liked how it felt. Turns out, I just rebuilt it yesterday. I'll get to ride it again with this in mind, having since been on really stiff aero frames.

  32. Sean Kelly on a Vitus 979. (regarded about as stiff as a wet noodle)
    https://youtu.be/uqEnvZ1ynng
    My Vitus 979 was about as stiff as my Ishiwata 015 frame. I preferred the Ishiwata, because it was much more comfortable.

  33. Not so sure there is much of a difference, but I would like to see this done using a power meter "mythbusters style" before I make up my mind
    In the mean time, I would suspect that while you are unloading the frame, there would be less force but the same weight, so the frame would still be flexing but unloading at a far smaller rate that only the very lean and very strong cyclists could benefit from.

  34. Stiffness is great for accelerations over 1000w but not going to make much difference at a constant 200w, and you get into a better rythm with some flex.

  35. Very well put together film . Nice one Simon.. I ride a very comfy hybrid Whyte Sterling which does have flex from the tubing. I also ride a very aggressive Raleigh Milits bike which is super light and pretty stiff. I love em both for totally different reasons. The Hybrid though will not do the "Cragg Vale loop" under the hour no matter what, where as the racing bike will shave 3 minutes on a good day and up to 6 if I am really fired up. The difference is always riding position and the gains from Aero dynamics. Not the bikes rigidity. Cracking channel and love the reviews you do . https://youtu.be/ItK1vfqVqfYCheers GCN.

  36. As some people have said, the top end of the power is shaved and is distributed throughout the pedal stroke. So one pedal stroke on a stiff frame that generates 1000W, might only generate a peak of 900W on a flexible frame. Split second power is not what causes acceleration. Overall energy per second is what accelerates rider and bike. So it would be interesting to know if the total quantity of energy delivered over the entire pedal stroke is similar on different frames, for example 1000 Joules per pedal stroke. But the distribution of those Joules over time is definitely more even on a flexible frame, meaning a more constant speed for hillclimbing rather than the constant variation in power of a stiff frame leading to twitchy acceleration decelleration with every pedal stroke which could be demotivating. However during a sprint you might find it more motivating to feel the raw peak power being delivered into the angry tyres as they grip the road for accelleration. If there was less energy delivered overall by a flexible frame it wouldn't necessarily change race results unless as you could always just shift down a gear to get more revolutions and therefore more energy delivered per second (ie. more Watts!). This might sometimes necesitate a higher cadence but it wouldn't tire you out as much as a similar cadence on a stiffer frame. So you'd ecpect it to be excellent for endurance races or long hill climbs.

  37. This discussion/demonstration only showed that SOME of the frame distortion (flex) is returned to the force of acceleration (in opposition to the deceleration of air/friction).  It does not contribute to the discussion of whether more or less of that distortion makes a substantial difference in efficiency.  Terribly unscientific.  A system of controlling as many variables as possible and measuring input and output forces is the only thing that is meaningful.  Surely if Si put the same amount of force on the stiffer bike then less deformation would create less wheel rotation (if hub friction/wheel inertia were the same) AND less heat would be created from the lesser frame deformation.  Less heat, less energy loss.

  38. I'd be MUCH more concerned with MECHANICAL MALFUNCTIONS as a result of excessive frame flex rather than wasted/absorbed energy from frame flex. For example: Disc Brake rub causing drag/wear slowing you down while climbing/accelerating/sprinting; tires rubbing on the chain/seatstays with tight tire clearances during frame flexing; 'ghost shifting' from out of alignment derailleurs during frame flexing and such. This should have been mentioned as THE MAIN deterrent for purchasing a wet noodle of a frame.

  39. If the wheel spins forward when you load/unload the right pedal, what happens when you load/unload the left? Seems to me it would want to reverse the direction of wheel spin, but the freewheel would prevent it, so that would definitely be an energy loss.

  40. Well this was a waste of time. No solid metrics and no meaningful science that I could discern. Try speaking to a real engineer next time.

  41. I have had a flexible aluminum frame and went to the middle or back of the group when i had been at the front on the carbon. All in one weekend. Tried it again the next weekend… and the same thing. Weight was very similar. Same happened in the races.

  42. If that happens pushing the right pedal, and you release a force clockwise, if you did it with the left one, you would rotate backwards, which is a straight loss of energy because the wheel won't move if pedaling backwards

  43. The older I get. (67 years) ,,, the faster I was on my 1972 Derosa ,,,,…12 Derosa’s later in my stable , is very hard to see which one is faster,,,,

  44. I think pro cyclists and serious cyclists like stiff frames because when you pushing the pedals hard you don't want the bike to move all over the place.I had a trek emounda which I never felt was very stiff and I was actually afraid to go fast for fear of losing balance.When I got a BMC roadmachine what a difference.The geometry of the frame and stiffness means I don't only get a comfortable ride but I can go as fast as possible and feel the bike won't lose balance.

  45. ok so physics aside, i weigh 265 lbs . so, if i ride a noodle of a frame and i build up kinetic energy for say 50 miles flexing all over the place, in theory i should just coast and allow all that energy to slingshot me the last mile? hmm…

  46. Which bike is faster: a full suspension bike on a non suspension bike on a flat or hill climb? I'll take the stiff One, be One =

  47. Flawed pseudo science here. The energy will not be put back into the drive train, because once you make a full stroke, there is no way for that to happen. What really happens is the energy is just transferred back and forth between the right and left side of the frame while pedaling, and once you stop pedaling depend where in the stroke you are it may be put back into the drivetrain. Either way you are wasting a little power with more flexible frames because transfer of energy between left and right is not 100% efficient.

  48. Wrong. The frame flexes when you are peddling down. The energy is released when your leg is at the bottom. You could get some of the energy back if you push the pedal backwards at the bottom while the frame is moving back to center.

  49. free energy! perpetuum mobile! Sky to introduce super flexy frames next year to accumulate energy from bumpy roads… marginal gains! You heard it first here!!!

  50. My steel MTB frame flexes however it never felt or seemed slower than a stiffer bike but it does smooth out the pwerstroke putting the enegy back when less force is applied resulting in considerably less wheelspin and better traction going uphill.

  51. Ride a bike with a non-true frame, where the rear wheel isn't precisely pointed in the direction of travel, and you'll realize how torsional flex in the frame can result in energy loss.

  52. This test only shown frame flexibility wheel spinning is from energy that can be stored in flex frame more than stiff frame. But In real road the delaying of energy return(for sure not 100%) will make me frustrating a lot.

  53. In effect you’re loading a spring and releasing it. Take a spring with a weight on it. When you release the spring, does the weight bounce back to the exact same position? Of course not, the spring will oscillate, losing energy each time it does. The stiffer you make the spring, the less potential energy energy loss, until eventually there is none with a perfectly rigid structure. Is it a significant amount? That depends on how heavy the weight is, but I think a rider is pretty heavy. With a bike frame you aren’t even loading the spring in a totally vertical direction, which means much of the energy lost will be in a direction (horizontally) not conducive to driving the wheels. You can look up the physics of a simple spring and mass to try to quantify it, but the frame is no simple unidirectional spring, so the math will be far more complex, requiring finite element modeling to even come close. The fact that you can feel the difference is a testament to the sensitivity of human biology. Since you can sense it, your brain will usually want to pick the one that’s easier to ride, no matter how few actual Watts it is. That’s where the belief that you’re riding a more efficient machine will make you faster, it’s simple cycology!

  54. To those who say that we're just buying into "stiffer is better", I really don't get your logic. GCN did an absolute rubbish job with this experiment, but it's not really rocket science, is it? Doesn't energy transfer relate directly to power output? So more power loss = more power xfer loss AND less power loss = less power txfer loss? Wow….. Whowouodathunkit?

  55. Stiffness is important for efficient. But need different flexible for different conditions. There is no good or bad. Thank You for video

  56. After riding my old Surly Cross Check all winter, going to my caad5 aluminum bike, the difference on accelerations was big, felt like superman.

  57. Frame flexibility has nothing to do with wheel rotation here. You can see that cassette rotates, so pressing on a pedal pushed force to a chain

  58. You turned the pedals without allowing the wheel to rotate. Am I supposed to be surprised when the wheel rotates after you take the brake off? What else would happen? Pretty much the only possibility is that the chain or chain stays are plastically deformed and the whole bike is broken.

  59. Possible frame flex experiment…

    Ingredients: two bikes (one flexible, one very stiff), a short traffic free hill, one rider, one assistant, make up weights (to equalise weight difference in bikes), one piece of chalk, one measuring tape.

    Method: Select bike 1. Face it uphill.

    Rider stands on pedals at 2 o’clock position with straight leg, bike brakes fully on. (Assistant keeps rider upright)

    Rider releases brakes and lets his/her full weight (with straight leg) turn the crank until 6 o’clock position. Measure the distance travelled uphill until the bike stops.
    Repeat three times and take an average distance.

    Repeat above with bike 2. If possible use the same wheels, drivetrain and gear ratio. If not at least use the same  chain and crank length.
    See if there’s any difference in the distance travelled.
    NB. The rider must ‘fall’ exactly the same distance every time. The rider must not add any muscular energy (so must use a straight leg in every run).

    It would be interesting to see the results! Not very ‘Glam’ but it’s a real-world test!

  60. Pre Science in Bikes: Old frame builders such as MacLean knew this and actively built in flex. It was I believe even a sales point. What goes around comes around. The only truth is that sales count, so then it was flex, today it's stiffness. The differences in lab level tests are there, same watts, same room. In the real world the flexy one could win if (for instance) it was bumpy at that moment and the stiff one if it wasn't. How many of us are at pro level where every watt counts?

  61. I imagine it is the same as anything, tuning for the individual. I think theres probably a sweet spot based on rider weight, and power output as well as riding style ie stiffer stronger frame for downhill. something to consider is the material side of things im no expert in composites but i imagine stiffer= heavier due to the use of thicker carbon fiber. I hope you guys do more coverage on this. nice video

  62. It is turned into heat but the heat is displayed throughout the frame, also the frame flex while pedaling in the road causes the free hub to spin backwards turning your energy into the free hub spinning backwards which, the brake test throughout the video does NOT replicate actual conditions, also lets say that his theory is correct, the uneven slowing and speeding up would cause aerodynamic inconsistencies which would maximize air friction and lose you power, frames aren’t just built stiff in all parts with compliance built into the carbon where needed to reduce how much the small road bumps will slow you down

  63. The wheel might move because of tension on the chain so when u release the back brake the chain contracts and moves the back wheel

  64. Better to take a sprinter instead a time trial specialist to put an example of the flex of a frame

  65. Seems like you put a hundred pounds of force and get a TINY amount (negligible amount) transferred back into the drive train. How much energy does it take to spin a free floating wheel a few revolutions? Almost nothing.

  66. This explanation is flawed. True the energy is not lost if the material is in elastic range, BUT the frame could flex back after the downstroke, which would leverage your leg's damping properties more, and also it make your upstroke potentially easier (not necessarily what you look for). This is due to the lag in the response of the frame versus the excitation, sometimes referred to as phase angle in the dynamic modulus (complex modulus).

  67. At least with my bikes, nothing so far to note, I have always noticed a flex along the horizon line along the chain bending on the chain side between the peddle and rear gears. There are times the flex causes the chain to change or close to change. Just thought I'd say… I'd also imagine this "grey" area is more about the strength of the cyclist. Someone very strong with high endurance would need a stiffer bike; when typing this is seems common logic knowledge… but I don't think it is… ha! I think the example shown in the video is great, but also believe that energy we saw will never happen while on an unhinged bike and the energy will go into the tires, granted hard stiff tires would observe less energy.

  68. cycles are so far behind motorcycles or have hit a plateau. is it because there is no load transfer or is it because C of M is irrelvant in a bike ?

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