Are You Faster On A Stiffer Bike?

Stiffer bikes are more efficient aren’t they. Frame flex robs you of power, so stiffer frames therefore transfer more of your power to the back wheel.
A lot of us might take that statement as fact. After all, pros want stiffer bikes, bike manufacturers sell us stiffer bikes because that’s what we ask for and it’s a characteristic that most bike testers praise to the rafters. But is it true?
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The question is then, if frame flex does transfer energy away from your drivetrain, where does it go? Well, maybe right back into it.
We have come down to the Bicycle Academy, the frame building school that is based in Frome, just down the road from GCN HQ. Tom Sturdy, the engineer who looked after the design of the GCN handbuilt bike is the head of education here and he has long been thinking about this frame flex conundrum.
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[@Surestick88]

This needs a test: power meter on the cranks and power meter in the rear hub on a flexy and on a stiff frame to see if there's any difference in the power delivered to the cranks vs. that delivered to the rear wheel. Use the same crankset, and wheels. Test with a sprinter and a climber to see if rider weight has an effect. Maybe throw in a flat (no climbs to minimize any effects from weight difference) time-trial with a rider putting out a steady power output on the crank-based power meter to spice things up.

[@indonesiaamerica7050]

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.

[@alessioquaglino4529]

@@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

[@timtaylor9590]

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.

[@paulross8175]

I really enjoyed this video and (as an engineer) it makes perfect sense. What it made me think is that while there is little energy loss due to frame flex (there must be some as materials aren’t perfectly elastic and have internal friction) the difference between a stiff and flexible frame has to do with responsiveness. In other words, the stiff frame won’t flex much and will transfer the energy to the drive train right away (ie isn’t storing the energy to return later) and so the bike “jumps” when you put on a large load like a sprint. On the other hand, a flexible frame will store the energy and return it to the drive train later so the bike will feel “sluggish” when a large load is applied even if the net energy applied is almost the same. A stiffer bike will win in a sprint.

[@dimago11]

Are you stiffer on a faster bike?

[@nickv.7181]

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

[@abrahamalkhatib9762]

definitely

[@jaykan1002]

I'm always stiff for a fast bike #bikegasm

[@caperider1160]

Is that the same stiffness I am thinking about?

[@GordonMoat]

Oh No, you didn't. 😁

[@jimhansen5395]

Let's do some *REAL* science. Figure out why red bikes are always faster!

[@rkan2]

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

[@DarrenJohnson1973]

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

[@palmer3977]

That is known as the Bianchi price effect.

[@jimhansen5395]

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

[@Enigma71559]

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

[@poraktobask]

Quite a while back Jan Heine from Bicycle Quarterly has written about frame flex characteristics and what he calls "planing". The gist of it was that the stored energy can help you be more efficient, if the frame flexes the right amount.

[@StuntpilootStef]

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

[@leporello7]

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/

[@rebellis13]

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).

[@JosephDowski]

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.

[@masondanner6481]

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.

[@Drzhounder]

Physics! Even if you get that energy back, I would bet that some of it is used by a flexible frame. It could generate minimal amounts of heat for example. That energy then being transferred in the the air rather than the drive train. We know that when things flex they warm up at least a small amount. Therefore a stiffer frame that can't absorb as much energy doesn't conduct it to other places like heat and air. That would lead us to believe that the energy is more efficiently transferred to the drive train. Result: Stiffer frames are indeed fast, just by less than we originally thought. It all boils dow to what feels better though. If you don't like how a bike feels you won't ride it to your capacity. We look at tire size and pressure, bike weight, frame stiffness, etc. and the issue always will fall to the engine of the machine, the rider.

[@peterlaskiewicz8252]

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.

[@benwoodland5786]

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

[@archetypex65]

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.

[@archetypex65]

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

[@stuartdryer1352]

Michael Albany Yes. How much entropic loss.

[@andynewsom]

I think the energy stored in a flexing frame is released in the form of a slightly slower crank rotation just after the powerful part of the stroke. In other words, when you come off of the most powerful part of your stroke, the frame straightening isn't going to propel you forward, it will just slightly slow the pedal stroke. So the power really is lost because it didn't get translated to forward speed while there was pressure on the pedals. If the pedals were being turned by a machine that never varied it's power at all, then the energy might be released into the wheel, but people don't work that way.

[@gastonsanudo576]

(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...

[@BradleyTemperley]

My first custom bike in 1988 was a 27” steel frame. Unlike other Clydesdale frames I had seen, there were no stiffening stays or lugs. It flexed liked a flexy, flexy thing. It didn’t take much power to flex the BB. With rear panniers it was like riding an old Porsche 911; I once drifted through a wet roundabout with a bus right behind me! It is now permanently attached to my KICKR where it can do some good. I now ride a Trek Domane, reputed to have one of the stiffest bottoms of any frame, yet supple to ride.

[@willbaren]

I’ve been looking forward to this. Yes, you’ve shown frame flex stores energy and gives it back to the drive train. Excellent, this what we want to know. What would also be nice to see is a comparison where you charge up a steep slope at a set wattage with bikes of the same weight but different flex and time the ascent and also get the rider’s impressions. Anyway, good stuff 👍.

[@bhooshanparikh]

Very interesting...and reminds me of a pendulum effect that once the bike flexes from side to side, that exactly provides the momentum. Very similar to when you're lifting weights, a bit of swing in your body or arms provides that little bit of inertia to make it seem easier to lift the weight compared to a dead lift. However, on the flip side, the flex might also be stretching the chain slightly that when the brake is released, the energy stored in the stretched out chain is released, making the rear wheel spin.

[@st47591]

Very interesting demonstration, but there might be a different interpretation. With the bike on the stand and the rear brakes applied, pushing the pedal down 1 cm causes frame deformation but it also stretches the portion of the chain running from the top of the chain ring to the cogs on the rear wheel (energy is stored in the stretched portion of the chain). When the brakes are released, the energy stored in the stretched chain pulls on the cog, leading to the dramatic spinning of the rear wheel that we saw. That's the simplest explanation I can think of. As for the benefits of frame flex, maybe the energy of the bottom bracket moving the other way helps lift the rider's leg up on the back part of the pedaling. Just a guess on that one...

[@sireevessireeves5072]

I think there's a lot to be thought about within this debate. If we examine a damping spring mass oscillator, that is a spring with some weight attached to the end, and we apply a force to the weight - we will find that it oscillates, but the oscillation decays due to damping of the spring. I think that a "flexy" bicycle frame will be analogous to this oscillator in that kinetic energy will be lost by restoring the frame to its original shape before applying some to the drive train. Will this loss be noticeable? Maybe not, maybe it is in the marginal gains territory.

[@keithbowen9561]

The static test isn't comparable to a dynamic test for a few reasons but simply put in the dynamic test the load coming back does so through the riders legs which have moved past their optimal stiff position. Having said that and as others have said my 'feel' is that there is a sweet spot for some frame flex for rider comfort which ultimately will cause fatigue and reduce your efficiency anyway.

[@5pence55]

It seems to me the wheel spinning is mostly from the potential energy stored in the chain, at around 4 minutes you see the chain jolt/twitch forward upon releasing the brake. IMHO for 99% of us the majority of frames are stiff enough and frame flex (on most bikes) isn't that big a deal and not another thing we have to worry about upgrading. Ride upgrades don't buy 'em.

[@ricard9566]

I thought frame manufacturers were aware of this and incorporate specific amounts of flex into their designs. I was reading that a prototype Specialized Demo bike was seen with varying thicknesses of carbon which had been crudely adjusted during testing. The explanation was that they were tuning the amount and type of flex. And yes, perhaps akin to tyre pressure, a stiffer harsher ride could fatigue the rider sooner, negating any power gains that may have been achieved.

[@grigorbrowning]

With due respect, your experimental setup doesn't represent what happens in real life. You were reacting the frame torsion with the turbo trainer. On the road however, it would be reacted by side load in the tyre. The frame itself will have low hysteresis (steel especially) but the tyre certainly doesn't. So, the cyclic torsional loading of the frame does come at a cost. I would still agree that frame stiffness is a 'feel thing' to a large degree. However, that doesn't mean it's not also beneficial. It is impossible to generate load without something to react it. Imagine a super flexy crank - you'd never be able to push hard against it as it will bend out of the way. If we were perfect engines it wouldn't be a problem - we'd just load it up. But, we provide power with alternate legs and to differing loads round the cycle. So, flex in the system causes a lack of reactive load at the point of peak power generation. The load doesn't simply fall out of phase, the peak drops too. In short, static tests and analysis of an inherently dynamic system, can lead to flawed analysis. Not that I'm saying my hypothesis is correct either though...

[@grigorbrowning]

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.

[@drewmonteith8480]

This is the video I want to see

[@Plazthespaz3]

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.

[@JamieClark]

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?

[@CervezaDeGaraje]

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.

[@mindfulbroker]

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.

[@guilhermeponte4402]

I think the chain is under tension and the frame is being puled by that tension on chain so when you let the brake of, the frame acts like a spring on the chain, puling it making the wheel turn

[@howheels]

As a material flexes repeatedly, you are bound to lose some energy in the form of heat. To what degree? Who knows.

[@michwoz]

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

[@rkan2]

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

[@maxsievers8251]

Have you ever made your frame warm by flexing it?

[@kevinthomson6324]

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

[@MicroageHD]

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

[@K1989L]

I lost a tremendous amount of energy due flexing when my steel single-speed mtb flexed in a corner while mashing the inside corner pedal. Causing me to drop the chain and the sudden drop of the pedal sent me flying to the ground.

[@angelocharlsison5335]

In my opinion, they both transfer a similar amount of energy. The biggest difference is the reaction time. Stiffer bikes react faster to load switching between handlebar and two pedals (for road bikes). On the other hand, the less stiffer bike reacts slower but is good at absorbing external forces ( for cycle cross or mountain bike).

[@StuntpilootStef]

A flexible frame will have more losses, because that flexing creates heat. It's not a lot, but it is there. Also, flexing will effectively delay the pedal stroke, therefore hurting acceleration and makes the bike feel sluggish. There has been a lot of research into frame stiffness in motorcycle racing. The trend used to be to get the frame as stiff as possible. It only ended when the lean angles became so extreme that the suspension wasn't doing anything. So they strategically introduced flex into the chassis to act as a primitive form of suspension when leaned over. The current consensus is that flex within a certain range is good. So it seems stiffer frames definitely are faster in a straight line. But when taking road surface into account when, you might say a little flex is good. How much? It depends on the road surface and the weight of the combined rider and bike. And then there's the fact that we don't tend to corner that much... TL;DR I'm sticking with my stiffer frame.

[@st3ange21]

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.

[@Isaillasers173114]

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/

[@st3ange21]

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

[@StuntpilootStef]

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.

[@Isaillasers173114]

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.

[@playandteach]

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.

[@singlespeedchronicles7640]

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

[@pskonejott2568]

imo, in line with the mechanic, stiff frame will feel faster as the flex is lesser so it feels more responsive as you load those drive train. whereas less stiff bike will feel sluggish or lost of power as there is a time delay for the transfer of energy. ideally, you want responsive bike to attack at the right moment so stiffer bike is still the better option. lastly, the flex of bike frame is commonly compensated with the slight twist of handlebar to maintain balance. that may result in a utter different finding.

[@Adurianman]

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.

[@TeslaOsiris]

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.

[@HaloTupolev]

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.

[@richbaker4962]

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.

[@galenkehler]

It's all about timing, or as many others call "planing". When you apply a force to the pedals, there are time delays as the various components stretch. These might be only microseconds but they tend to smooth out the force over time. When you add it all together, (shoes, pedals, cranks, chain, wheels, tires, and frame) you might be looking at a lot of energy. So what does this feel like? Depends on your pedal stroke and how you apply force. If you spin super smooth, the constant force will keep everything loaded and you won't get out of time with your bike. In the steel frame old days this lead to the idea that you had to spin circles to be efficient; you kind of had to with the old flexy bikes. If you mash a flexy bike, some of your force will load the bike, stretch the chain, and wind up the spokes, and then potentially be released at the top and bottom of the pedal stroke, when your feet are no longer applying much pressure. So really its about timing, if you can match the timing of your bike to your personal style of force application, you will find that golden ride. I found this once personally with a 2011 Opus Cresendo w/Mavic Ksyrium wheels, that sweet spot where every push of the pedals matched perfectly by the timing of the bike.

[@timtrial3971]

My conclusion is: ride what you own and stop worrying about other people's bikes and marketing hype

[@QiuyuanChenRyan916]

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

[@yspegel]

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

[@CuddlyStingray0731]

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.

[@danielashleybaker]

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

[@Lolimaster]

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

[@ch2263]

I once had a go at calculating the lost power due to an inch of sideways flex at the bottom bracket. It came out as about half a watt if I recall correctly.

[@Adurianman]

I personally am more interested in frame flex during cornering, if it helps the tire track the road better like a rear suspension in mtb or does the change in angle of wheel relative to frame might cause instability like a flexing chassis in a non performance oriented car.

[@rkan2]

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.

[@archetypex65]

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

[@paddlehard5722]

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.

[@duodecaquark3186]

The biggest problem I have with this demonstration is that the load which flexes the frame peaks where his pedal was and drops off towards the bottom of the pedal stroke. This means that the frame bending back to its original position at a 6 o'clock would merely move the pedal out to the right and not cause any additional rotation or therefore put the power back into the drive system.

[@Messugga]

Some significant errors in the argument being followed here. The flex on the frame decreases when the force component in the original direction that caused the flex, decreases. This will be when the pedal in question is at six o'clock. Releasing the flex in the frame only when the pedal is in that position, will result in no wheel drive as seen in the experiment performed in the video. Instead, the rider's weight will counter the force, in other words, the rider's legs will absorb the energy. A stiffer frame will carry less energy to the six o'clock position, pushing more energy into driving the rear wheel. A perfectly stiff frame will carry no energy into the six o'clock position. In other words, a stiffer frame would be faster. Is the performance worth the tradeoff in comfort? Depends on the situation.

[@jan4946]

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.

[@jan4946]

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.

[@R1Gato]

Perfectly stated. You must also be a mechanical engineer.

[@archetypex65]

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

[@nelsonphillips]

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?

[@AndrewMSmalley]

There is also the matter that more sideways movement has an effect on the rider. If the frame flexes it will cause your body to move slightly to the side. This can be compensated, by pulling on the bars and/or using core muscles to balance. Either way, these muscles are using energy which could be going to your legs. An exaggerated way to exemplify this is how you feel after a road ride compared to a mountain bike ride. For the former, just your legs are tired, for the latter, your whole body is tired from moving around on the bike and levering it into position. I imagine the difference between modern road frames is pretty marginal though. Personally I always ride a steel, moderately flexible frame on road because if I used a super stiff carbon frame on the roads where I live, I would have no spine left after a few weeks.

[@UKBROOKLYN]

This would have been a much more accurate test if you had both been wearing your science glasses.. What were you thinking Si.. attempting science without the correct tool.. shame..

[@IraklyShanidze00X]

and a wrinkled lab coat, of course

[@ilhamfachriza3163]

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

[@K1989L]

I think the flexing frame moves some of the energy to the dead spot. Stiff frame feels fast because you have almost all the power going in the same space of crank revolution. That might not make much of a difference. Unless the the frame acts as a damper and eats the energy. But flexy frame has a lot to contribute to rider comfort.

[@nwimpney]

No research needed. The explanation is fairly simple, and it's not damping/thermal loss as a lot of people are suggesting. The bike is "returning" the power, but not at a useful time. It's holding onto the extra energy that you're trying to put into propelling you forward, and giving it back later, through the crank when you release the pressure on the cranks. A good analogy would be tying heavy weights to your feet. Any energy you put into lifting your feet is given back when you put your feet back down. But if you try and run, it's going to be a lot slower.

[@RunPJs]

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

[@YuryYurevich]

The experiment has one condition: the leg doesn’t move when the frame springs back. On a road that won’t be true. Basically, the frame’s flex will work towards lifting the leg rather than moving the bike forward.

[@markconnelly1806]

One of my bikes frame cracked at the seat tube and down tube just above the bottom bracket. It did not break all at once. It was gradual. The first symptoms was a self shifting rear derailleur. Then as the crack got bigger, the frame flexed more and the crank felt soft on the down stroke. It felt soft since the crank was flexing inward and the result was a noticeable loss of power as some of the forces was being directed inward instead of downward. If a frame is too flexy your pedaling force may not be be optimized to forward motion. Kind of like climbing or sprinting out of the saddle and rocking the bike slightly. Rocking the bike may enable to dig in more power, but flex of frame and change of wheel angle will be a little less efficient to forward motion. You can test yourself by cutting slightly into your frame to start a small crack. One note also about the test in video, the wheel is not clamped perfectly tight and still, so that could affect results a bit. Also in real riding, that much crank flex would cause wheel to spin since brake is not holding wheel still. So amount of flex in frame would even be less. I think how frame flexes in regards to the line of travel is important too. If a frame flexes, the energy could cause the head of the bike to change line and produce more road and wind resistance, whereas as stiffer frame would not deviate as much.

[@leonlin2106]

I put my old aluminum TCR and new carbon TCR on the trainer and found huge differences on frame deformation. The softer frame killed me on my KOM event.

[@mrfdtt2675]

I recently built a new road bike around a different frame model. At first it felt like I needed some time to get used to it - regarding not only the handling, but also how exactly it transfers power. Thanks for the video to explain the background!

[@velowibble]

So the brake goes on, then the pedal moves down which puts tension on the chain (and flexes the frame as the chain can't move). Of course the wheel will move when you release the brake, you've essentially just pulled the chain a bit. Yes, the frame 'absorbs' the tension and releases it but I don't think that says much about frame stiffness.

[@erik_midtskogen]

This doesn't require a lot of fancy lab gear to figure out. Just get a yoga ball, put it against the wall, and step on it forcefully and repeatedly for a few minutes. Getting tired? Of course! It's called isometric resistance. First, your muscle compresses the ball, and then your muscle also resists that same force as the ball decompresses. So when your bike frame acts like a spring bouncing up and down and side to side with each pedal stroke, at least some of the energy exerted winding it up just goes right back into your muscles on the "negative" part of the repetition. So some of your own energy is being used against your muscles to tire them out even faster instead of going into the drivetrain to propel you forward. This is probably the main reason my carbon road bike is 2-3 km/h faster on a flat surface than my similarly-configured steel frame bike which (much as I love it for relaxed group/century rides) has a lot of frame flex.

[@bremneshatten]

Back in 2015 when I was tossing up whether to get a new bespoke steel bike or just an off-the-rack Carbon Fibre bike. At the time I was reading claims from one or two steel bike builders about the benefit of steel frame flex/power transfer. Googled this matter but found nothing else on this issue. Consequently bought my plastic Giant Propel. No regrets purchasing CF. I love the feel of the ride. One thing I am absolutely sure about is CF has much better power transfer. On steel, I literally had to fight to stay with on fast club rides after every traffic stop. (Hated it but it really made me much stronger). CF is so easy to take off with. I am not an Engineer and so dont know the reason, but I can say whatever flexie power transfer a steel bike provides, it is not as efficient as simply having a stiffer CF bike. My guess is that you probably lose more power from the flexing process than what you get back.

[@thomasjohnson5681]

This experiment is fundamentally flawed and does not answer the question. The flaw: when you apply load to the pedal and the frame flexes, the pedal becomes immobilized between the block and force applied to the pedal. When you release the brake, the frame moves back to center while the pedal is still immobilized; however, as the frame moves while the pedal doesn't, the crank moves. This occurs because the crank axles moves upward with the frame while the pedal remains stationary; thus the crank turns. All you have done is pre-loaded energy into the system and forced it to the rear wheel. If you move the pedal to Bottom-Dead-Center and repeated the experiment, the results would differ because the rear wheel would not move. Most likely frame stiffness contributes little to power gain or loss due the dynamic nature of pedaling. Frame stiffness is more likely to contribute to handling.

[@valeccylinder8703]

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

[@jonathanzappala]

I’ll start by saying I love the feel of my propel, even if it’s just psychological. To borrow from hockey sticks, a whip flex (65) can really make a puck fly but they break more easily. That’s why people use the medium flex (85) Then big guys break those too so they have stiff flex (100). Now if you built a hockey stick so strong it wouldn’t break it wouldn’t be flexible enough to shoot well. There is an idea balance point somewhere. So maybe it’s really all about the stiffness to the amount of watts you put out. Hence the pro sprinter being on the stiffest gram with the stiffest head tube and wheels. So is my frame too stiff for my power output, not being that of a pro, or big guy for that matter? Somebody has to build a test rig now for some real experiments.

[@SaltehBalleh]

Hmmm, anyone want to buy my old flexy frame? :D

[@malachiruddy3296]

I have long puzzled over this, and hade come up with a similar conclusion. But it is cool tp see in a demonstration like that, vary cool

[@drjwbriand]

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...

[@esmolol4091]

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

[@ralfhoehne1927]

Seams like the energy is stored in the chain.??

[@TheMTBChannel]

Yep, thats what i was thinking...

[@sebastianalmlof404]

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

[@st47591]

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.

[@adamross4013]

I would like to see an extension to this video involving an actual ride comparing the two frames by taking power at the pedal and at the wheel simultaneously to see how much power (if any) is lost. You could even swap over the drivetrain and rear wheel for ultimate parity!

[@tomshield9730]

The feel is a timing or tuning issue. Just like string tension in a tennis racket or golf driver shaft stiffness (pros will use higher/stiffer here too), the frame stiffness affects *when* the stored energy is released back during your pedal stroke. If it comes back at the wrong time the bike will feel slower, even though you are losing very little energy regardless of the frame stiffness. Roughly the higher your cadence the stiffer, and hence faster spring back, you are likely to prefer. Of course there is both mass and geometry of the bike involved in its dynamic response, so it won't be that easy to correlate to just the stiffness. It probably varies with rider strength too.

[@benstanden8784]

Flexible frames obey Hooke's Law. When you apply a force to a frame (push down on a pedal) the frame will be displaced, as F=-kx. When you release that force (at the bottom of the pedal stroke), the elastic potential energy, due to the displacement (U=1/2*k*x^2) is released. That energy just goes back into the drivetrain due to energy conservation laws (ignoring the very minor efficiency losses). This is the first time I've seen it demonstrated empirically, and it's a very good demonstration, kudos to Tom Sturdy - never thought about it like that - great video! My only minor dispute would be the focus on the vertical movement, as it's simply a component of the overall displacement. Assuming 100% mechanical efficiency, even the energy lost via the work done to displace the frame horizontally is recovered as the frame flexes back to its starting point, therefore, Work in = Work out so the net change (loss) is zero.

[@danielevigano8731]

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.

[@reissm93]

I would assume a rider would be using energy to counteract the frame and keep the bike steady. Incorporating more stomach and back muscles this would increase rider temperature showing where energy is being converted. Another factor could be aerodynamics tiny flexes in every revolution would cause the rider and bike to cut through the air less efficiently. As a straight line from A to B is always shorter a 2cm flex at the seat would be exaggerated at the riders head, meaning power is used moving more air out the way. Really interesting content once again GCN, keep it coming guys.

[@az149keyjoecoil4]

In this experiment the rear wheel is fixed and when the pedal is loaded the distance between the rear wheel axle and the bottom bracket axle is increased so the chain is prolongs and when the pedal is released the chain backs to its normal size and the wheel start to spin.In the flexible frame the distance between the axles under the load changes not so much( the rear triangl bends) so after the load is gone the wheel will spin not so much respectively as with the stiff frame.So the stiff frame has a better efficiency.

[@retardno002]

I love a bit of flex in my frames, that's why I chose to ride 2 steel bikes and one Alu. The softest steel is the 'liveliest' subjectively and therefore more enjoyable to me, but definitely the slowest (weight and drive train play a huge factor here, not saying the steel is responsible).

[@georgstreitz6003]

Two thoughts: 1.) The resonance frequency of an body depends on its stiffness to weight ratio and resonance phenomena are related to energy absorption. Thefore if the excitation frequency is in the range of the resonance of the frame, the energy "loss" could be higher. 2.) If the deformations of the frame are leaving the linear elastic region of the material, the osscilating stresses could lead to a hystersis loop. This could also mean energy absorbtion.

[@alexk8985]

This might explain why I am as quick on a titanium bike with standard external bearing bottom bracket as I am on my carbon bike with bb30 bottom bracket and a massively oversized tube set. Fascinating.

[@woody9382000]

I think that after a frame flexes under load, when less load is being applied (top dead centre?) and the built-up energy is being released that most of that released energy is transfered back to the crank and pedal where it slows down pedal rotation marginally. This would be the flow of least resistance of the energy and if this hypothesis is correct then a flexy frame would indeed be slower than a stiff frame. The best way to test the idea of flexy vs stiff frame may be to use 2 identically equipped bikes that weigh the same up a very steep gradient.

[@IraklyShanidze00X]

In case of Orbea at least it was quite evident from the slo-mo video that flexibility of a chain played a pretty significant role in spinning the wheel. To make the experiment cleaner, one needs a stiff chain.

[@patrickhance7348]

If it doesn't flex your bike will krak in two.pat from Belgium 🚲

[@pieteroelofse7298]

Stiffer frames channels your power input directly into the drivetrain, with minimal elaatic energy being stored when you pedal. Flexible frames channels a bit less energy directly into the drivetrain immediately, but gives it back with the elastic return later on. So stiffer frames are essentially more responsive and crisper in feeling whereas flexible frames may feel like its blunting the power input slightly, but the frame can feel like its moving with you. My old aluminum Raleigh was more flexible thanmy Cervelo, and I can feel that I am moving more relatively to the Cervelo's frame because its much stiffer, but it feels much crisper and more responsive, so if I put power down, I instantly feel the bike reacting and going faster. Id say its a bit like the frame geometry argunent - slacker geometry gives more comfort and is more forgiving, but more aggressive frames are more twitchy, more responsive and less forgiving...

[@ciaranfinnegan8935]

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

[@owyn768]

Frame stiffness, and general racing components is all about maintaining geometry under load. Try riding a flexy track bike flat out round the banking and it'll take some keeping on the black line, a stiff setup will stay nailed to it. Same reason you put strut braces and similar on racing cars.

[@MrHomelessinspace]

Heres the answer for you. So the frame flex shifts the position of the bottom bracket on the downstroke. But the pressure gets released on the upstroke, thereby putting the energy into reversed pedaling. Thats a clear loss right there. There is no gain or recycling of energy happening as explained in this video. Im surprised this wasnt discovered earlier, and that this idea reached so far. If anything, this experiment shows that a stiffer frame is indeed faster. Sadly nobody will read my comment anymore... Thumbs up please.

[@uhohDavinci]

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.

[@5irefly]

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.

[@wraith01mg]

There is a net loss in heat generated by flex, though small, its not insignificant, and also the stored energy released by unloading the frame comes at a different moment in time to the power stroke, so the effect will be (on a bike that flexes more) a more sluggish response, though a more compliant feel.

[@bugboy152000]

#GCN I’m guessing that a frame free from the constraints of a trainer will not flex much. While this experiment is extremely interesting and enjoyable to watch I doubt it will make a fraction of an advantage/disadvantage. Either way that guy is 10X more smart than I am so I digress! Awesome show and great episode.

[@turner02]

who cares, just ride!

[@StuntpilootStef]

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 :)

[@Zeben84]

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

[@honeybadger3599]

gofundme.com/cycling-goals

[@ChlorophyllCrusher]

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.

[@fastnb]

Nice video. Good amount of frame flex has another benefit, you have more mechanical tyre grip as the "suspension" frame flex in corners. Race motorcycle's use this principle aswell.

[@marcusthornton2844]

I think the advantages of a stiffer frame are more about responsiveness than overall efficiency. It just feels better as a rider to gain acceleration instantly from applied pedal pressure than from delayed energy returned from being stored in the system.

[@alexgrinage]

Yes. This experiment has multiple things wrong with it. the biggest thing would be that they pressed on the pedal and held it down. which just the frame right now is acting like a spring but because you're holding a single pedal down 99% the forces allowed to go back into the drive train. but when were peddling were alternating legs which means we're not constantly holding pressure on one side. when were actually pedaling alternating which side is relaxing and which side is applying Force. So this means that the frame is always flexing in the direction of the side with the least amount of force. so this means that the force is going in the opposite direction of the drivetrain weather be back into the frame and into your leg this equals force/power loss

[@phenoge]

in a laboratory setting you get energy return but keep in mind the rear wheel is being held solidly in place. Out on the roads the wheel will follow the frame's flex each time leading to a slight side-to-side movement and not contributing to forward movement. Thus, I'm all for an efficient stiff frame vs a light-for-the-sake-of-it frame.

[@brepkenyi]

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.

[@BioStuff415]

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.

[@scottishjohn]

Nice to see an attempt at showing the principals involved here. I know that its going to be hard to give a perfect experiment when your not in a lab and can test for all sorts of variables. Though it at least shows that perhaps due to conservation of energy we shouldn't be so concerned that if there is some flex in your frame then you are just wasting all of your energy just to make a frame flex instead of making you go forward which is what your looking for. I am sure that some more more testing in a lab would help a little more but good one to get the ball rolling! Nice to also show you don't need to chuck out that steel/aluminium frame because it will flex.

[@richbaker4962]

I guess I should have added the place the lost energy goes is into the rider. The human is a great damper and absorber of the energy from the spring back at the bottom of the pedal stroke. It is also the largest element in the system by far.

[@fishontrack]

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.

[@dbibah]

Here's one way you could quantify the difference between frames of different stiffnessUse two power meters, one measuring the power input from your legs (eg. pedal based or crank based), another measuring combined output (hub based or a turbo trainer with power measuring capabilities)By comparing the power readings from the two power meters you could work out how much energy is "lost" through frame flex

[@st47591]

Ralf Hoenhe had already brought up what I just posted about the energy being stored in the stretched chain in this demonstration (I didn't read all the comments before posting). To see if there's any merit to this idea, they could do the experiment with an old worn-out chain and see if there's any visible stretch in the chain. My guess is that they used a new chain that would only deform very slightly and not be visibly stretched. More energy would be stored in a new chain being deformed by a 1 cm pedal movement (because more force would be needed). An old compliant chain would be more easily deformed by the 1 cm pedal movement and wouldn't store as much energy.

[@parmijo]

Sean Kelly won paris nice 7 times and a zillion other races. He won most of his races on a Vitus bonded aluminum bike that was a flexy noodle. Damon Rinard, top cervelo engineer and now at Cannondale says that they don't design the supersix for ultimate stiffness but ideal stiffness.

[@glebivanovsky7886]

One thing that was completely neglected is that when the frame yields under load gears and chain are no more aligned properly and this can be draining energy straight into friction and heat. Actually, this may be even more of an issue for belt drive systems where alignment is very important. Mine starts to make noise when I push harder and I have a suspicion that it may be because of the frame flex. Rear triangle tubes are quite thin on my bike.

[@CauliflowerEars1]

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.

[@michahalczuk9071]

Flex on steel bikes is *purely elastic,* and therefore this action itself loses no energy, just acts like a spring. Different angle on crankshaft _might_ increase resistance, but because crankshafts have angular contact bearings, the difference between complete straight action and slightly angled stroke will be negligable. On the other hand, because steel frames can flex on small bumps, they can actually *lose less energy on rubber in wheels bending more heavily, which loses this energy on heating up.* Do a serious test in normal conditions but with power level measured and normalized to check if there is a difference.

[@ChlorophyllCrusher]

Jan Heine calls the energy returned by frame flex under pedaling load ‘planing.’ Its hard to understand, but I personally believe it’s a thing, and I believe I feel it occurring. When I ride my flexier bikes. Basically, different riding conditions and loads require different frame characteristics. If you ride crits in a punchy manner and sprint out of the saddle standing up at 1800 watts, your optimal bike will be fairly stiff. If you use 300k brewers and churn a moderate cadence at 200w on hour long climbs and never spring above 1000w your optimal bike will be fairly ‘flexy’, at least, in the seat-tube. Horses for courses.

[@enpluson1539]

i believe that a stiffer frame still massively increases your speed on the road because in the power-phase of the pedal-stroke, the amount of force is reduced as the frame loads up like a spring, and in the inactive phase of the pedalstroke, when there is no load on the pedal, the frame flexes back. the problem with this experiment is keeping the pedal loaded and at a fixed postiton, whereas in a realworld szenario, the pedal would move instead of the rear wheel, because there is no significant force holding it.

[@JippaJ]

I have been thinking about this a lot. I agree with this to a point. Most of the energy goes back into your cranks of course, but you load it in a different direction than your pedal stroke is positioned when your legs ease off the power. So your crankset gets it's energy back in the wrong direction, not adding to your speed at all.. I think.

[@Rubicmeat6]

I suppose what you have demonstrated is that lateral (side to side) stiffness is marginal to performance, but in a sport where marginal gains can make the difference between winning and losing the loss in energy in a frame that isn't stiff could be detrimental at the top level. For the everyday rider however, stiffness translates into that planted, secure and direct feeling when you are pedaling, as well as contributing to the overall ride quality of a bike. After riding different bikes, I can comfortably say that regardless of any performance differences, I'd want to be riding something stiffer because of the better feel.

[@DEFKNIGHT]

That way I look at it, there are two related dynamics to consider. Stiffness/amount of flex and flex/ rate of spring to true. It could be that this is a dynamic that can engineered and likely already is with companies that have the budgets for 5hat kind of research. Wanting a stiff bike that allows a combination of transference of power and flex to allow spring to occur and engineering a high speed of recovery springing back to True. For custom builds this could be beneficial for weight and average load could be measured and taken into consideration when calculating rate of stiffness and spring. I think many people confuse actual squat with flex. Meaning, sure too much flex robs you of your power when applying force and the whole system is loaded, but lacking flex at all you Rob yourself of your excess energy that is transferred and returned in the form of spring. Interesting video highlighting that.

[@sufyansaleem9771]

So, I would like to add when the break was released, the resistance from the wheel from spinning is less than the resistive forces of the frame. However when at top output your application of power matches the resistive forces to moving forward. therefore when at a top sprint you will only lose power rather than getting it back. It is illustrated by the brake in the example in the video, where the force is only released back when the resistance drops.

[@robertopics]

There's a theory that I've subscribed ascot frame flex/stiffness 1) a stiffer frame is usually a bit more responsive, but not substantially 2) tires, and wheel components (mainly spokes and rims) negate benefits of frame stiffness as they tend to flex before the frames do. 3) unless you're climbing there isn't that many opportunities to overload your frame with energy as shown on the experiment. 4) a certain level frame stiffness is important specially with tighter drive train spacing you avoid ghost shifting, unnecessary noise and excessive chain flex. 5) flex is good as it helps compliance to have vertical compliance whether, it's at the wheels, frame, saddle, bars or seat post.

[@andymonis9944]

A more rigid frame is more consistent to ride and if there is a requirement to have some 'flex' it can be achieved in a controllable way ( suspension for roubaix, carbon layup etc ) to add the subtlety where needed rather than relying on inconsistent bending and twisting of bottom brackets.

[@williamclements918]

I agree that the flexing of a frame will produce some heat and that is a loss of energy as far a propelling rider and bike forward goes, there fore one would think a stiff frame is faster and on a glass smooth surface that may be true but just as we now ``know`` lower tire pressures to be faster, I believe that there will be a distance where the flexy frame will be faster due to less rider fatigue (most flexy frames are also less fatiguing due to better damping of vibrations from the irregularities on the road surface). Admittedly the distance where this occurs may be way beyond the grasp of most riders, but when riding multiple days such as a grand tour the effect will compound. This is why I love my Titanium frame

[@PeakTorque]

A flexy bike that obeys Hooke's law as closely as possible (steel pretty well) will never lose power. But it may become out of sync with the timing of your inputs, which is why it feels better to pedal a stiff bike.

[@James-zu1ij]

I can imagine that the more damping you have on a frame or in a frame the less power gets to the road. Im thinking of Bianchi countervail technology. If a frame material obeys Hooks law then a flexible frame would not loose power. It only makes a difference to how the bike feels i.e. the timing of your power inputs. As long as any input to your bike returns to its starting position (handle bars, pedals) and is undamped then no power is lost

[@sandrochiavaroBeerCircles]

Make sense to me. We may discover that bike “feel” is the new frontier. As the wider tires with less pressure example has proven, the frame tube sections will keep evolving to insure comfort and fast acceleration, but also cornering flex witch Si test doesn’t take account of. Still super interesting. More tech to come on this I am sure.

[@James-zu1ij]

sandrochiavaro I'd imagine if you were a very strong sprinter you would want have a stiffer frame to minimise any deflections. Also descending at 60 mph, resonances and flex isn't your friend. Possibly the countervail technology of the Bianchi might be worth losing a watt if it steers well.

[@08svalbard]

A more flexible frame will allow more lateral flex under loading which can cause fishtailing when you increase power output in a short period of time. I've been in races on less flexible frames when sprinting (>1500W) has caused the rear wheel to move laterally, losing propullsion. Quite a scary experience in close proximity to other riders. Haven't has these problems on bikes with stiffer BBs/frames even with an increase in power output to 1800W. Also when the bike on the video is on the turbo there is only once place the force can be released which is through the drivetrain and into the wheel.

[@JohnLumapaskeith]

I think it's all about feel and preference.

[@jonpaulgallery]

Great video and great comments! Love seeing this. The cycling community is fantastic. One piece of context that is important (sorry if it's been brought up already) is the reality of who is riding the bike. Just as a 69 year old triathlete going 15 MPH isn't getting benefit from their aero frame....that rider doesn't have the strength to force energy through their pedals, a stiff frame and into the wheels to move the bike without great fatigue in a short amount of time. Perhaps the "softer" frame is exactly what 70% of average riders need? The physics and engineering are intriguing! Context is very important.

[@duanedaylebaliatan5209]

Stiff frame can make you faster, this is because the power transfer on the bike is so direct, while on a flexi frame, the power transfer is a bit delayed, it’ll be like an airbag, the power will be distributed around the bike instead of the drivetrain. And when the frame flexes back, some power is directed to the drivetran and some are directed to your orher leg. I hope it makes sense. Example: if you are doing a track stand, you apply both pressure to bothe pedals, all your power is not directed to the drivetrain, but it is directed to your other leg to balance out the power. I’m just speaking this hypothetically

[@RobS49120]

Simplistically, the frame etc. act as a spring. It stores energy as you flex it and releases the energy when un-loaded. As long as there are no losses during this cycle, it doesn't hurt. Less simplistically, there is likely some damping in the system which will result in small losses due to friction and such so you don't get back quite what you put into it. Would be interesting to expand this test to accurately measure the energy input and output. Good start and thought provoking!

[@GibParadox]

In my opinion, the energy applied on a stiffer frame is transmitted "directly" to the drive train. In a flexing frame, the energy used to flex the frame (let's discard the fraction that is actually transformed into heat at molecular level) is stored and will "spring" back, BUT the spring action will happen when there is no input from the rider (when the cranks are nearly vertical). At this point, given the bike in moving, the small amount of energy that the frame stored would not have the same effect (would not actually push the weight of the bike + rider) as it would "together" with the rest of the energy on a stiffer frame, all because of the way pedaling happens. I might be wrong tho. In any case, a static test is leaving out many factors in play in a dynamic situation.

[@davidmorganrn]

Jan has been decades ahead of real bicycle science/research; and I just LOVE my Ishiwata (flexible steel) RB-1, RB-T, and MB-1 feel AND PERFORMANCE. Jarring out ones teeth fillings, jarring ones skeletal system, getting premature muscular fatigue and losing traction on road/trail with stiff frames and high PSI tires is NOT performance enhancing. I am a muscular 100K guy, BTW.

[@deanbutler1467]

Sorry if already mentioned, but... a basic flaw in this experiment is that it only looks at frame flex from one side of the bike? What happens if you put the block on the other side? As others have mentioned, just put a power meter on the crank and a power meter on the turbo trainer for both frames (keeping all other components identical) and see what the real losses are.

[@aaronclark1022]

Fascinating video/test! I am not a scientist but I reckon the problem here is that real life use of the bike is not on a trainer. Meaning that the bike does not remain upright and held in position during the torsional flex that loads the frame and drivetrain. If the trainer was not there for your test, the bike would shift sideways when loaded to compensate or neutralize that flexion. The issue appears to be that you have isolated the wheel into only allowing the stored energy to propel the wheel forward whereas in real life that energy is driven into lateral forces right and left per pedal stroke. I have an old 1997 Litespeed Ultimate ti frame that I have always referred to as a slinky on wheels....Its BB is very flexy and when sprinting the bike torques so much that it fish tails side to side. Maybe this is not so much an issue of loss of energy but rather misdirected energy. Watch old slo-mo videos of pro RR sprints from above. Those bikes are fishtailing all over the course. Watch modern videos and the fishtailing is much harder to detect and the speeds reached are higher....stiff means fast. That fishtailing is surely energy lost in lateral movement at the expense of forward momentum...instead of having that power move me forward its skidding out the rear tire to the side. On a stiff frame forward momentum is only limited by tire traction and wheel stiffness (other factors that could see wasted/misdirected energy going laterally instead of forward). This is all for a road bike where the frame is pivotless. Take this same test to a full suss MTB and you have a whole additional set of factors (or at least they are exacerbated) that lose energy that could/should be directed to forward momentum with a stiff frame. The goal here is to eliminate as many factors that misdirect energy as possible until they begin to counteract the benefits. If you feel beat up due to ultra stiff frame,wheel,tires, bars, post, etc. then your sprint will be weaker from fatigue. At least this is my opinion and my experience. Pretty cool stuff.

[@jseski9209]

there is also a difference between a frame's flex that causes a dampening effect, & frame flex that will rebound (which is primarily what you're talking about above). Not all frame flex is the same - sometimes by design (or should I say, done on purpose), sometimes just by the material/angles used (non-intentionally).

[@arneliis]

I think they should have used adjustable height plate instead of that metal plate, so that when Si stands on the pedal you can adjust the height right up to that pedal, so equal potential energy is given on both bikes.