Are You Faster On A Stiffer Bike? 

There is indeed power lost between the cranks and the rear hub. Most of it in the chain. Stiff is better because it's more stable. Not because you actually lose energy by loading a spring. You lose a lot more energy in places that you don't even look. If you're getting chain or brake rub that's an entirely different story. If you're not getting obvious performance problems from the flex you should go search for "lost watts" in the tires and the chain. Once you're close to optimizing that (for what you can afford) then go hunting for "lost watts" in your bearings. You lose a lot more power in a dirty chain than you do in a "flexy" frame (as long as you're not causing friction from bad alignment). When you lose energy in the chain you can not get it back. As illustrated in the video, most of the energy used to load the spring (frame) is returned to you and the actual values are trivial.

@@indonesiaamerica7050 doesn't this suggest that a smoother ride (which could come from a softer frame) is more stable? Also, that clutch derailleurs could help too

the test only shows how much those frames store energy like a spring would it has nothing to do with efficient transfer of energy that would make a bike fast. a bike frame cant be stiff enough. most comfort comes from seat post deflection and tyres anyway.

Jim Hansen There are actually already multiple ok studies about the color red i sports :P

they aren't ....Trek Segafrdo And my Focus is red and it's slower than my Bianchi which is Celeste

That is known as the Bianchi price effect.

This is subjective. Your personal observations are meaningless - we need *REAL SCIENCE* - and everyone knows red bikes are faster.. That's just common knowledge. :D

Ha! I wasn't aware of this scientific "fact." Good to know as my bike is red!

That's a very personal question. But I'd say it depends on time of day. I'm definitely stiffer in the morning.

definitely

I'm always stiff for a fast bike #bikegasm

Is that the same stiffness I am thinking about?

Oh No, you didn't. 😁

very well said, John. I would also add to your comments that not only do I believe the riders weight can make a difference, but correspondingly their strength. Somebody who can really apply torque to the pedals can benefit as well (for similar reasons) to the stiffer frame. Whereas, someone lighter &/or who doesn't peak too high on power would actually benefit from an appropriate amount of flex. This is similar to a golf club. Someone who has a real fast/strong swing benefits greatly from a stiffer club by it's ability to keep the club head more in line with the hands & gets distance on the ball from pure swing/power. However, a person that has more of a slower/modest swing, actually won't hit the ball as far with the stiffer club than they would with a regular or softer flexing club (whichever is most appropriate for their swing/strength), by using the "whip" action of the flexing club shaft to snap the ball & create more energy on contact than the stiff club would.

Taking this to the extreme, a bike frame made of wet ramen noodle would also yield fairly poor results due to low stiffness (among other poor properties).

Michael Albany You're exactly right. Energy conversions from mechanical, electrical, whatever are never 100% efficient. A stiffer bike will lose less energy in this conversion process. Either way great point and great Gcn video.

Yes all the minute losses will add up over the course of a ride

I think that perception of how a bike feels and equating that to a rider not riding it to his/her potential is pretty much rubbish. It certainly is a narrative but it has no basis in technical fact.

Michael Albany as a general rule stiffer frames are not faster you actually experience more energy loss on a stiffer frame then you do on a frame that Flexes in the right way and at the right time. #planing

Michael Albany Yes. How much entropic loss.

I am quite certain they understand that, but if some would ask they had to put up a video for that.

ride what makes you smile I would say. I'm glad I got rid of my previous aluminium bike

Agreed! My top two bikes that I ride are made out of aluminum! Stiff sometimes but they make me smile so I ride them as much as I can.

The science of cycling is, for some, a large component of the fun. It's pretty easy to trivialize non-essential activities.

Exactly, want a bit faster and smoother ride all around? Get an e-bike, even of low levels of assist.

Thanks for the tip! I love reading stuff like this.

Then you might want to have a look at his most recent blog entry on that topic: janheine.wordpress.com/2018/01/28/myth-4-stiffer-frames-are-faster/

Indeed, was reading his articles with alot of joy. And to my surprise I confirmed for myself that the flexy frame I have (Look kg86, first carbon frame from 1986, La Vie Claire) was faster for me than a new, stiff frame from Felt (F1).

I would also add that Jan Heine was also way early touting the performance & comfort benefits of wider tires. He's been quite the "prophet" on these topics.

I recently built a bike highly influenced by the Bicycle Quarterly crew - 650b x 42 tires, lightweight steel tubing that planes, low trail geometry, friction shift 3x10 drivetrain. It’s the funnest, most comfortable, useful bike I have ever had.

Davide Archetti I’ve done exactly that with my Colnago C40 vs Tramac SL3 and no difference. I’ve also done varying watts with the same PM. 300 watts and 550.

(I hope i can write properly in English....) In addition, any time the frame flex, it causes to lose the straight line between both wheels (more precisely they get away from the same plane, where they mast be), and it results in a mesh of not parallel forces (both tires tend to go in different directions) that generate a high loose of energy. Also, as both tires tend to go in different directions, there is a loose of energy due to increased friction forces between tires and road...

Worth noting that tyres generate grip through 'slip' at the macro scale. Because the tyre is rotating, cyclical side loading will cause a pathline that meanders side to side - think of a little sine wave. Accordingly, the losses in such a setup are not tied solely to the lateral stiffness of the tyre and the hysteresis associated with 'non-slip' side loading (in say a non-rotating tyre). In short, the losses aren't the same physics as vertical compliance of larger section tyres and rolling resistance.

This is the video I want to see

Gonna agree on most of this. The efficiency of the frame probably doesn't change a lot in the minute details from frame to frame, BUT this isn't the same to be said for handling. A stiffer frame will handle better and this is where I believe the sensation of stiffer=faster originates: simple human misinterpretation.

Sounds like you're describing a suspension fork that has semi-independent L/R travel. This would affect balance first, and loss of balance (and energy required to correct/maintain it) would lead to less power available to turn the cranks smoothly. If we consider a suspension fork or a FS mountain bike, some of that power goes to compress the suspension, but the return on the shocks (if the bike goes down after a bump) sends power back to the crank the same way this video shows (as long as the cranks are still being turned at that point). If the rider bounces while riding on flat, the energy of the return can be used to move the rider back up, and this feels like lost power, but then the rider regains potential energy as they are higher. Do they use that potential energy to power the cranks? If they go higher than their initial position, yes. If not, it was extra energy output that did *something* but did not power the drivetrain. This sort of "accidental" energy redirection is what we really want to avoid, right? I can't quite tell if this same redirection away from the drivetrain happens when flexing a rigid frame on a road bike... Any thoughts?

Besides, even if everything that happened in the test was accurate, which I agree it's not, according to the 2nd law of Thermodynamics states basically that " In any given exchange of energy, there will always be energy lost", which basically means that with all the exchanges in the experiment the losses will be bigger than with a stiff frame which will produce no such exchanges.

and a wrinkled lab coat, of course

if i can assume that u're british, so this comment is funny, but otherwise not somuch

Probably to very small degree. So small it's pointless to care about it.

Definitely less than 10% less than 1%? who knows?

Have you ever made your frame warm by flexing it?

Measure the temp change and then you can calculate the wattage required to cause the increase. Bingo there is the amount of watts you wasted heating up your frame .002 degrees

1%? Never... much less than 1% lol. That would be ridiculous.

Thanks a lot for saving me the typing :) Especially when sprinting (while not being seated) this becomes visible in the 6o'clock position. To visualize the problem let's assume the frame being a perfect spring (that means, it will return all the energy it absorved). And we shall only look at the vertical part of the flexing, so just put a spring vertically on a table. To compress it, you have to apply a downwards force on top of it. If you put a weight on it, the gravity-force will compress the spring to a certain level. On the bike, the compressing force is made up from gravity and the muscles straightening the leg. Back to the spring: Action=reactio, the gravity on the weight is keeping the spring compressed, but the spring is pushing back with it's own force which increases with compression - so that the spring will only be compressed to the level where the spring's extending force equals the gravity force. When is the spring going to release energy? While extending back to it's normal size again, which can only be done, when the weight on top of it is removed (or reduced). On the cyclist that translates to lifting the leg or reducing the power with which the leg was straightened to push down the pedal, which in turn means: The frame can only flex back when the cyclists let's it push it's foot upwards again. In the end, the frame flex is not giving much energy back - you only use your energy to compress it and maybe even need some uncompress it. Anecdote: Cycling home from shopping with a heavy backpack (weight increase ~30%) I tried to sprint. I noticed that while sprinting I usually would "jump" when my foot reached about 6o'clock - with the backpack, I couldn't. I was just compressing the frame and get back to where I was before jumping. At 6o'clock. Compare that to a trampoline. Stand still on the trampoline, compress your legs and then jump. Your legs extend, but because of the springiness of the trampoline you're only raising your body by a few centimetres instead of getting about half a meter off the ground. Wasted energy.

This of course also applies to the 3o'clock position as shown in the video. But in the video, the energy was transfered back to the wheel, because the weight was taken off the pedal. When cycling, you push downwards until you reach 6o'clock - so the frame flex introduced at 3o'clock is not released at 3 but rather after 6 - where you won't have any more gains from it.

Perfectly stated. You must also be a mechanical engineer.

Eon du Plessis don't think so... #planing. #janheine

Yes to this but, I will add that if the frame at particular points then this would transfer loads into the drive train decreasing the efficiency of the drive train. A better experiment would be to increase the load on the frame and measure the efficiency of the drive train. The drive trains are very quiet so there is likely to be very little energy being lost there, but possibly in heat. Again the principles describe above would be the likely loss, transferring it into the rider by delaying the power transfer. Does anyone know how the manufactures test the frame stiffness in the dynamic sense, eg as a rider analogue?

Exactly - if the returned power is at the wrong time it will work against you

I could only think of the concept of ressonance to support the frame plane hypothesis. That will probably mean that frame plane will only occur at a certain power/cadence combination, which again will make it pretty useless in practical use.

Stig Aannø If it's resonance that gives the benefit then it would apply to all power outputs as long as your cadence was near the natural frequency that the frame flexes at. You would only need to worry about maintaining cadence, which is easier with more and more gears on the bike, as long as you don't go 1x.

Erik H you are of course right, it will depend on the frequency and not the amplitude. But still, the ressonance frequency will be a product of a combination of the frame and wheels. Maybe we will see people tuning their wheels through spoke tension to set the preferred ressonance frequency in the future? Well I think I myself will go for the stiff bike/wheelset combination. Look up my other post to see why I think this is the best option.

Stig Aannø Bikes can plane. That is proven. Read Bicycle Quarterly! It is very relevant in the real world and it depends on your power and weight, not on your cadence.

Max Sievers you made me read what was available without paying and now I am even more sceptical. The stiffness of the wheels will for example make up a lot of the characteristic of the stiffness of the bike. I do not see it even mentioned. They mention measuring power, but I don't see if they measure at the pedal or at the wheel hub. It is a crucial difference given the thesis they are trying to prove. They tell that this is the secret of covering ultralong distances like Paris - Brest - Paris, which make it really look like quasi science (I have covered a distance of 540km more or less non-stop on a stiff carbon frame and wheelset, my legs were fine, my ass hurt and I needed sleep). Boats plane, frames can theoretically resonate, but I do not buy that it has much to do with your weight and power (due to certain laws of physics). I think the biomecanical argument makes a compelling case for oval chainrings, but not for a wobbly frame.

Hahaha haha, luv your comment. Let's all just ride a noodle

StuntpilootStef precisely! The difference between the two frames are the time that the frame use to bounce back. A stiffer bike means less comfort on a crappy road but it'll have a really ready response compared to the flexible one. I've got a steel fixed gear for my commuting and it is super flexy but I always enjoy to ride it even to do some climbs, and still can go hell fast if I want.

Intuitively a stiffer frame makes sense in terms of power transfer, and in most cases stiffer probably is better, however there is an interesting area of study into what has been dubbed "planing" or basically if more flex can lead to better power transfer in certain cases. There definitely isn't a large depth of study in the field to prove either hypothesis, with logic being on the side of a stiffer frame, however it is a really interesting idea to explore. You should take a listen to this podcast, it is very interesting and very thorough. cyclingtips.com/2017/06/cyclingtips-podcast-does-frame-stiffness-matter/

janerney I'll fo that! Thanks for the tip;)

janerney I have just read about that for the first time and that Heine also experimented with polymer bushings. He seems to find quite a difference between different bikes. The differences were there with quite subtle changes in stiffness. I do wonder how you are going to find the right one by any other means than trying out all possibilities. Because it does seem quite easy to get wrong and there are a lot of factors involved. You have the weight of the rider and the bike stiffness, but also what BB you use, maybe which tires, groupset, chain, rims, etc. It does make things bloody difficult and almost impossible to get right for anybody that's not a pro cyclist.

Yeah, i get what you are saying. It is so nuanced and there are so many variables fro scenario to scenario that it is hard to see any quantifiable real world benefits. Interesting to examine and read about, definitely, but is it something that i am going to think about when buying my next bike, definitely not.

Did you say 'ladies'???? So 1950's....

also worth noting the importance of stiffness in the front end as well. You want the bike to steer as soon as u point it right or left as oppose to just flex and then bounce back to steer whenever the frame feels like it... which at the end of the say will also make you slower as you corner with less precision and confidence

That's theory. Makes me wonder if you even ride a bike

Or maybe you are riding a really noodly bike in which case I'm sorry for that comment

Tobias Grätzer Go watch some videos of a racecar hitting a rumblestrip in slow-motion, you will see the science in its truest form.

A frame that planes for you is responsive and it can corner well.

Theoretically though, according to the video, torque should be returned before the end of the pedal stroke, so power will be returned before 1/2 of a revolution on the pedal. Assuming pedalling at around 80-90 rpm, thats only about 1/3 of a second. I personally don't think (at least at most people's riding level) that will make too much of a difference.

Feeling faster ≠ actually faster Case in point: bigger tires at lower pressures feel slow but are measurably faster while skinny tires feel faster but are comparably slower.

The handlebar twisting as people pedal isn't just from frame flex, but also from: 1-The rider putting uneven hand force on the bars through their pedal stroke. 2-The response of the steering geometry (i.e. trail) to the rider rocking the bike.

You are on the right track. The faction of the 1/3 of a second of your muscle exerting effort while the spring loads and unloads adds up as it happens on every revolution. Think of a stiff frame as your muscle working for a slightly shorter duration every pedal stroke to deliver the same power. If the frame were infinitely stiff, the muscle would have shortest possible duration of effort. I agree people will feel the stiffness, but that little extra effort will also add up. My guess is this can be significant.

Adrian L Good point.. Usually, espevially with skinny tires, corner performance is underestimated. My empirical evidence suggests stiffer frames give me more confidence in cornering.

Adrian L that is a very keen observation because that's exactly what the Grand Prix in world superbike teams are working on. More torsional less lateral stiffness

I felt instability over the comfort in fast cornering sections with my former steel xc mtb. I’d rather feel the ground below, not a flexi bike frame in between, trying to do some mediation. But if you’re not doing a sports ride, this feature can be comfortable. But than again, sitting on the couch in front TV is even more comfortable.

I think you nailed it on the head. It’s not necessarily more stiffness that make a bike “faster” because even super stiff frames still flex. I feel it’s stiffness in certain areas of the frames that brings greater acceleration when cornering for example. As a surfer, I can see the similarity with surfboards and especially surfboard fins. Super stiff boards or fins don’t accelerate well in corners, but the “foil” or actually profile of either one will create better performance, having stiffness at high speeds, but also great acceleration in tight corners when making sharp turns. I think this is going to evolve as technology and testing reveals more proof of efficient carbon profiles.

Why is that? Steel has roughly the same stiffness per weight as aluminium.

Thomas Johnson This is the only right opinion. My man!

Christian Holmstedt I think the force is still carries in the spindle of thr crankset.

It might, but it would be in the opposite direction as the force applied on the right side.

That was my point.... the force is opposite. GCN needs to do some quick science to check. :)

Christian Holmstedt Sorry for the confusion. I was trying to reply to rkan.

Johnny Cab I disagree in part. The experiment does exaggerate the amount of flex in the frame, but the bottom bracket does move, and that movement would provide force to the chain (or slack when applied to the pedal opposite the drive side).

Exactly, I proposed this very test in an earlier GCN video wherein flexy was deemed to be energy lossy. Hell, use power pedals/crank arms/bottom bracket/rear hub meters and test with seated versus standing and so forth. Flat road, up hills, around corners, the whole schmear. Light rider, heavy rider, amateur rider, pro rider. Swap meters to other bike, calibrate, repeat. Science, in other words, not conjecture and thought experiments.

I'm not sure power meters are accurate enough to generate any meaningful data. 1.5% is about the best you can find, I think you'd probably need 0.01%!

Si, you've just restated exactly what I'm bitching about. 'I'm not sure' 'I think you'd probably need'... How about measuring for meaningful data, publishing the results, and commenting on that? If you can't measure a power difference from noodly frame to uber stiff wonder bike, then it doesn't exist in a meaningful way, and that's important. The 'method' employed in this video is dubious, as many have pointed out. We have actual tools: please use them. Thanks.

Okay then, let me rephrase. There would be absolutely no point in doing the test you suggest as the tools to measure meaningful data don’t exist. The levels of accuracy in current power meters would leave vast statistical errors.

Therefore, you're declaring there's no meaningful difference between frames in terms of the rider's energy reaching the rear wheel and moving the bike forward. Thanks for clarifying your position.

The same thing happens, just mirrored. Therefore, it was a bit odd that he said the effective "clockwise" motion of the BB - on the non drive side it will be an effective counter clockwise motion of the BB that gives you the little kick when the frame returns into its normal position.

This is exactly what i thought. He's testing the "clockwise" side of the bike. (Maybe due to the setup being against the wall and inherently wanting to see the drivetrain during tesing). On the other pedal the return kick would produce anti-clockwise energy?? Would this cancel out the clockwise energy produced in the previous half stroke [hence his IS Wasted energy] ?? Would this if tested similarly, force the drivetrain backwards and no wheel spin created, since it would just spin the freehunb? Or would it still "create" energy since no matter which direction clockwise or anti, still be energy and movement thta the bike has, and that is used for movement...? (I ride a reasonable flexy cheap Allez so would love to know!)

The clockwise/anti-clockwise energy is at the level of the crank, but is applied in different points of time. All is transferred into "clockwise" (forward driving) energy at the level of the drivetrain. It's just a perspective thing. By the way, this doesn't imply the theory of flex-restored-energy is correct, just expanding the theory to the non drive side.

I would say that you see the same amount of flex on both sides. There may be a small variation as they are mechanicaly asymetrical, this may be insignificant, but pro teams with pedal stroke analysis may say different. On a more flexible frame you would see a pendulum effect. As you are on the upstroke of the right pedal the frame flex is unloading to the right, while also being flexed to the right by the downstroke of the left pedal. As the left pedal is on the upstroke the frame flex is unloading to the left, while also being flexed to the left by the downstroke of the right pedal. Even the stiffer frame seemed to store energy though. A stiffer frame may still have same effect, perhaps to a lesser degree, just that the flex isn't so noticably focused around the bottom bracket and spread around the whole of the seat tube and down tube flexing to a lesser degree.

Yep, thats what i was thinking...

And in the spokes? They are put under pressure and thereby functioning in the same way as a spring in a wind-up clock, I would presume

Yes. I hadn’t seen your post before I posted. With the brake applied, turning the crank down 1 cm visibly pulls the chain ring rearward.

You either dont have a clear understanding of whats going on here(the physics), or you didnt understand the video.. They literally diagram out the opposite of what you are saying.. The BB gets flexed(deflected downward), while the pedal stays in place.. When the system unloads the BB moves back up into its unloaded position while the pedal stays in place. This causes a FORWARD motion in the pedal stroke.. not a backwards one.. Thats is what is returning energy into the system.

Golf clubs are engineered for various amounts of flex in the shaft so that the quantity of energy storage and the timing of its release maximize clubhead speed at impact. A stiffer bike stores more energy for the same amount of flex (E=0.5Kx^2, K is the modulus and x is the deflection), but it also returns the energy faster. Perhaps if flex were engineered (in the crank arms?), the release would occur during the dead spots in the stroke, maximizing acceleration. It would have a negligible effect at steady state, though. In the meantime, a stiff frame feels better and accelerates faster, so all else being equal, is better.

Agree, this was a great isolated test where the stored had energy had more or less one way to go. Out on the road, the stored energy would probably not dissipate so cleanly to our benefit. One path for the energy release could be a sideways rolling moment very slightly rolling the frame and then some of it being transferred to the rider. There could be other paths as well. Si, please do us a real-life test to see if this is anything more than negligible.

I do! This is GCN Tech, it's supposed to talk about these topics. If you don't like it, that's fine. Go watch something else :)

i like these type of videos, but i do agree, just ride :)

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Well, bike designers care. And people buying custom bikes care. And people buying bikes off the rack care. But you don’t have to care, because the caring has been done for you.

Loss of energy is not zero, there is little loss maybe in the frame but the tranfer of it through all the transmission components is not negligible, and above all there is the tire. Whatever it is the compound the gum suffer form hysteresis which probably wastes all the energy returned from the frame flex that managed to get there. There is also the problem of fatigue, when you repeatedly put the frame under load within the elastic range the material is weakened by a tiny bit due to imperfections. If a frame flexes too much that could shorten the life of it.

This is exactly what I'm thinking! It's a nice test but assumes that the crank is held rigid when the spring is released, which it isn't.... The energy is going to be sent back through the riders legs in a negative way.