The importance of crank length to the cyclist.

[blutto]

it’s fine to share things about yourself. there are plenty of forums for it. in fact you can start a thread fyi. you can talk about yourself here as long as you loop the conversation back to the person who initiated the topic with out malicious intent to destroy them and prop yourself. . The best rule to follow is simply not to jump in too early with something about yourself all the damn time; the earlier you interject, the more likely you are to be making a play to get the attention on yourself. Instead, let the person tell most of their story or problem first, and then share your own experience.

internet conversational narcissists such as yourself always seek to turn the attention of others to back themselves . many posters here might disagree with frank but they believe the intent of this conversation was more cooperative instead of competitive.

he might indeed sell a product. at least he is neither consciously it subconsciously selling himself every sentence.

memo to mods kill this thread and frank lives on. kill this thread and coach has no place to go

...well said...thank you...

Cheers

blutto

 

[CoachFergie]

Earlier in this thread I mentioned that I had changed from 165mm cranks to 175mm after seeing Frank's wind tunnel data. I lowered my saddle by 1cm, so my thighs were coming 2cm higher at the top of the pedal stroke relative to full extension, which ought to be more aero, as it will get more of them behind my arms as well as making the thighs more horizontal. I have made some other changes since my last field test, so am not claiming that this is evidence of the effect of that specific change, but I did some field testing after the change and recorded my lowest ever field test CdA.

I then did my first 10 mile TT since the change last weekend, and improved my power PB by 3W, and my time PB by 25 seconds, with 20:08, a fairly respectable time.

So, I'm not unhappy with my experiment so far, and intend to try 180mm cranks when Rotor makes them available for the 3D models.

As for the benefits of interval training, I've been reaping those benefits for many months, but still managed to do power PBs for my interval sessions after the switch to 175mm cranks. Again, not saying this is necessarily cause and effect, but if Rotor sold a version of their 3D crank that allowed it to be adjusted in 5mm increments over a wide range, I'd personally feel it was worth experimenting with (at the same time as training in the best way I know how to). I think the limiter for me will actually be ground clearance, 175mm is already getting pretty close to the ground, and I think anything longer than 180mm would be unworkable with the low BB of my TT bike, indeed even 180mm might cause problems.

Nice.

The NZ track team pursuit riders appear to be going longer in crank length from 170 - 172.5 to 175 - 177.5. Being Olympic years cards are being kept pretty close to the chest but after London I may ask the rationale behind it.

My experience with intervals is that those who chase power targets or times for set distance usually make improvements.

 

[FrankDay]

Nice.

The NZ track team pursuit riders appear to be going longer in crank length from 170 - 172.5 to 175 - 177.5. Being Olympic years cards are being kept pretty close to the chest but after London I may ask the rationale behind it.

My experience with intervals is that those who chase power targets or times for set distance usually make improvements.

Fergie, what I (and others, it seems) learned from my musing on this subject and from my trip to the wind tunnel is that, it seems, that some riders will benefit from going to longer crank length (if they have a particularly good position now) while others would probably benefit from going shorter, especially if it means they might be able to lower their front end, if they are particularly high now, as long as these changes don't result in huge power differences that might skew the expectations. So, it seems, that each rider would be better served experimenting with this on themselves, to see what works for them rather than slavishly following what the NZ pursuit riders are doing.

 

[CoachFergie]

What the research shows is the benefit is so minimal it's not worth the time when there are far greater things to test like training, recovery, goal setting, nutrition, aerodynamics, coaching etc

Million posts and still no data on this proposed importance of crank length you speak.

 

[TarmacExpert]

What the research shows is the benefit is so minimal it's not worth the time when there are far greater things to test like training, recovery, goal setting, nutrition, aerodynamics, coaching etc

But worthwhile enough for the NZ team to be making changes, as you said.

There are people going to significant efforts to reduce drag by fairly small amounts, e.g. the TriRig aero brake using Andy Coggan's home wind tunnel saving perhaps a couple of Watts, or the UCI illegal Cervelo P5 front fork, which I think they have said saves 1W over the UCI legal fork. If a change of crank length were to improve my power by 2W, and reduce my drag by 2W, that seems worthwhile compared to many of the things people pursue to improve performance.

 

[acoggan]

If a change of crank length were to improve my power by 2W, and reduce my drag by 2W, that seems worthwhile compared to many of the things people pursue to improve performance.

If.

Data exist to indicate that changing crank length within the "normal" range (and well beyond) has minimal impact upon either maximal neuromuscular power or submaximal efficiency (which, in the present context, is essentially as good as measuring actual submaximal performance...after all, if changing crank length is going to change submaximal performance, the only logical mechanism by which it might do so is via changing submaximal efficiency).

OTOH, there is very limited data on the effects of crank length on aerodynamic drag...but what there is (e.g., Cervelo's data) again suggests minimal effect.

 

[CoachFergie]

Which brings us back to Jeukendrup's paper on where we should invest our time and money.

http://www.ncbi.nlm.nih.gov/pubmed/11428691

Or the summary...

http://www.cyclesportcoaching.com/Files/HowToSpendMoney.pdf

Most people here choose crank length by copying what others do or tradition. Everyone used to run 165 because they thought the pedals would hit the banking while going slow on steeper tracks. But of course on steeper bankings you have to go a minimum speed anyway (30kph on Stadium Southland 44degree bends) so you can run whatever size you wish.

 

[FrankDay]

If.

Data exist to indicate that changing crank length within the "normal" range (and well beyond) has minimal impact upon either maximal neuromuscular power or submaximal efficiency (which, in the present context, is essentially as good as measuring actual submaximal performance...after all, if changing crank length is going to change submaximal performance, the only logical mechanism by which it might do so is via changing submaximal efficiency).

Huh??? You mean you can only think of one "logical" mechanism by which changing crank length could improve performance? You state that this mechanism is to change submaximal efficiency. Care to give a biomechanical mechanism to explain this change. I can think of one (at least as one goes shorter) but wondered what you were thinking.

Then, perhaps you could explain what you mean by "minimal". Isn't any improvement, even if very small, important to those looking for any edge?

OTOH, there is very limited data on the effects of crank length on aerodynamic drag...but what there is (e.g., Cervelo's data) again suggests minimal effect.

Phoeey. Cervelo showed two riders improved, one rider stayed the same and one rider got worse. While the overall would suggest that, on average, the changes were a wash, for any individual there could be a substantial difference. Hence, the need for each person to experiment for themselves.

 

[Ripper]

...

Of course, crank length aside, power cranks are total crap.

 

[Boeing]

Which brings us back to Jeukendrup's paper on where we should invest our time and money.

http://www.ncbi.nlm.nih.gov/pubmed/11428691

Or the summary...

http://www.cyclesportcoaching.com/Files/HowToSpendMoney.pdf

Most people here choose crank length by copying what others do or tradition. Everyone used to run 165 because they thought the pedals would hit the banking while going slow on steeper tracks. But of course on steeper bankings you have to go a minimum speed anyway (30kph on Stadium Southland 44degree bends) so you can run whatever size you wish.

so you google some empirical evidence to support a claim but leave us with a dogmatic generalization such as this

Most people here choose crank length by copying what others do or tradition

what do you say coachpunter

 

[acoggan]

Huh??? You mean you can only think of one "logical" mechanism by which changing crank length could improve performance? You state that this mechanism is to change submaximal efficiency. Care to give a biomechanical mechanism to explain this change. I can think of one (at least as one goes shorter) but wondered what you were thinking.

Given that there is no logical reason to expect crank length to alter either cardiovascular fitness or muscular metabolic fitness, then yes, the only plausible mechanism by which changes in crank length might influence submaximal performance is via altering submaximal efficiency...which has been shown to not change.

Cervelo showed two riders improved, one rider stayed the same and one rider got worse.

IIRC, changes in all of the individuals were w/in the margin of error of the measurements, and hence could simply be due to chance alone. While there is likely to be little downside to chasing such potentially imaginary gains (since power is not altered), at least at the present time there seems to be very little to be gained even if such changes are real. In contrast, other positional and/or equipment adjustments/choices (e.g., the angle of your forearms, which helmet you use) can have a much larger impact.

 

[CoachFergie]

Then, perhaps you could explain what you mean by "minimal". Isn't any improvement, even if very small, important to those looking for any edge?

At this level the differences are more likely to be measurement errors or poor study design rather a difference in performance.

Certainly not worth changing crank length, changing seat height, changing setback, changing the stem height and stem length.

 

[Boeing]

Does your train of thought have a caboose?

 

[FrankDay]

Given that there is no logical reason to expect crank length to alter either cardiovascular fitness or muscular metabolic fitness, then yes, the only plausible mechanism by which changes in crank length might influence submaximal performance is via altering submaximal efficiency...which has been shown to not change.

I am sorry, is cardiovascular fitness or muscular metabolic fitness the only determinants of cycling efficiency? Have you thought about how changing crank length might change effective leverage of the associated joints and how these might affect cycling efficiency? Really? How is one to explain the results of Martin?

IIRC, changes in all of the individuals were w/in the margin of error of the measurements, and hence could simply be due to chance alone. While there is likely to be little downside to chasing such potentially imaginary gains (since power is not altered), at least at the present time there seems to be very little to be gained even if such changes are real. In contrast, other positional and/or equipment adjustments/choices (e.g., the angle of your forearms, which helmet you use) can have a much larger impact.

You don't have to recall, here are the results. I don't remember them giving the margin of error. Anyhow, it simply seems silly to say that the angle of the arms or the choice of helmet should have larger effects when these have never been studied. But, even if you are right, why would one want to forgo even small benefits if they are easily achieved? Just because you didn't see them doesn't mean everyone won't. Just look at the Cervelo data.

 

[CoachFergie]

But, even if you are right, why would one want to forgo even small benefits if they are easily achieved?

Because the potential differences are so small it's not worth the bother of buying new cranks, changing saddle height, saddle setback, stem length and stem height.

From the Cervelo data the differences are so small it is well within the possibility that they are due to measurement error, even more so when there were only 4 subjects.

 

[Tapeworm]

Cycling can even be done by dogs...
http://www.youtube.com/watch?v=Vdto2MAsU0s&sns=em

With a shorter crank he would be so much more aero.

 

[fatsprintking]

Going to shorter cranks made a huge difference to my performance. I dont know why I persisted with the 180's for so long.



Uploaded with ImageShack.us

 

[acoggan]

You don't have to recall, here are the results. I don't remember them giving the margin of error.

The CV of wind tunnel tests of a pedaling, wiggling cyclist is typically ~2%, or ~0.005 m^2. Of the four riders tested, only the results of #2 truly appear to rise above that level of noise (rider #1 changed by as much, but w/ only two runs the trend isn't established the way it is for #2).

Anyhow, it simply seems silly to say that the angle of the arms or the choice of helmet should have larger effects when these have never been studied.

Say what?!? Such things have been extensively tested (including by yours truly, in multiple wind tunnel and field tests).

why would one want to forgo even small benefits if they are easily achieved? Just because you didn't see them doesn't mean everyone won't. Just look at the Cervelo data.

Because, as Fergie has been saying all along, there is no good evidence that changing crank length will automatically yield even a marginal gain, yet doing so requires far more effort (in terms of other positional and equipment changes) than, say, merely replacing your front brake.

 

[TarmacExpert]

if changing crank length is going to change submaximal performance, the only logical mechanism by which it might do so is via changing submaximal efficiency).

Like Frank, I'm not convinced by this argument. If VO2max is limited by demand rather than supply, it's not implausible it could enable greater demand, increasing VO2max. Also, I see no reason to assume that sub-maximal performance is limited by oxygen consumption. As far as I'm aware, the mechanisms for fatigue are still not fully understood, so we can't rule out that a different crank length could change what is happening with respect to a fatigue mechanism that is unrelated to oxygen consumption. Why, for example, can we not simply ride at VO2max until we run out of glycogen? If oxygen consumption were the only limiter, there would be no reason why we couldn't do that.

OTOH, there is very limited data on the effects of crank length on aerodynamic drag...but what there is (e.g., Cervelo's data) again suggests minimal effect.

My 2W figure for what might be ballpark plausible was based on your "low sit" test of 6cm lower giving an improvement of 0.011 CdA. So lets call it 2W for 1cm. Going from 165mm to 175mm lets me lower saddle and pads by 1cm. But it differs from your test in that you didn't change crank lengths. With the cranks horizontal, the two setups are the same, with the cranks vertical one leg creates more drag with the longer cranks and the other leg creates less drag. Overall, I'd say as a ballpark estimate, calling it a wash and therefore still roughly 2W isn't unreasonable.

 

[FrankDay]

The CV of wind tunnel tests of a pedaling, wiggling cyclist is typically ~2%, or ~0.005 m^2. Of the four riders tested, only the results of #2 truly appear to rise above that level of noise (rider #1 changed by as much, but w/ only two runs the trend isn't established the way it is for #2).

So, let me get this straight. Are you saying that because there is a lot of noise and because it takes a lot of runs to overcome the noise and because, on average, there is little demonstrated benefit to experimenting with crank length as it affects drag that you don't think it worthwhile for riders to even bother trying? I'll bet riders #1 and #2 would disagree with that assessment. Or would you recommend they ignore that data because it doesn't meet your high standards?

Say what?!? Such things have been extensively tested (including by yours truly, in multiple wind tunnel and field tests).

Could you refer us to a single study in which these other items have been extensively tested as compared to crank length changes such that you can say whether one is large compared to another? Don't you think that whether one change is large compared to another would depend upon the particular set up of each individual?

Because, as Fergie has been saying all along, there is no good evidence that changing crank length will automatically yield even a marginal gain, yet doing so requires far more effort (in terms of other positional and equipment changes) than, say, merely replacing your front brake.

Changing a set of cranks requires "far more effort" than "merely" replacing a front brake? If you say so. Anyhow, Fergie has been saying a lot of stuff all along most of which has little scientific support and much of which is contradictory. Anyhow, as I seem to remember, the lack of evidence is not the same as evidence of lacking.

 

[CoachFergie]

Anyhow, Fergie has been saying a lot of stuff all along most of which has little scientific support and much of which is contradictory.

Well I will take my published research, rather well established concepts like measurement error and signal to noise and the fact that there is no data that a change in crank length makes a significant change in power delivery, efficiency or aerodynamics over musings and anecdotes.

Far more important fish to fry in performance enhancement.

 

[acoggan]

If VO2max is limited by demand rather than supply

It isn't. (It also isn't limited by some putative "central governor", despite what Tim Noakes might try to make you believe.)

it's not implausible it could enable greater demand

Greater demand = reduced effiicency.

Also, I see no reason to assume that sub-maximal performance is limited by oxygen consumption. As far as I'm aware, the mechanisms for fatigue are still not fully understood, so we can't rule out that a different crank length could change what is happening with respect to a fatigue mechanism that is unrelated to oxygen consumption. Why, for example, can we not simply ride at VO2max until we run out of glycogen? If oxygen consumption were the only limiter, there would be no reason why we couldn't do that.

Submaximal O2 consumption isn't limiting (by definition). What it is is an indicator of ATP demand (turnover). In the context of the muscle's ability to generate ATP via oxidative phosphorylation, it is this ATP demand that dictates metabolic responses related to fatigue (e.g., accumulation of inorganic phosphate, depletion of glycogen). Since changing crank length doesn't alter how many mitochondria we have (or the ability of our cardiovascular system to provide O2), it could only act via changing ATP demand, i.e., efficiency - but efficiency is essentially independent of crank length, at least over a very broad range (i.e., from 145 to 195 mm...at least those are the extremes that I recall were tested).

My 2W figure for what might be ballpark plausible was based on your "low sit" test of 6cm lower giving an improvement of 0.011 CdA. So lets call it 2W for 1cm. Going from 165mm to 175mm lets me lower saddle and pads by 1cm. But it differs from your test in that you didn't change crank lengths. With the cranks horizontal, the two setups are the same, with the cranks vertical one leg creates more drag with the longer cranks and the other leg creates less drag. Overall, I'd say as a ballpark estimate, calling it a wash and therefore still roughly 2W isn't unreasonable.

Time may tell whether you're right or not...but at the present, it is still a WAG how much, if any, changing crank length changes CdA (note that in Cervelo's data, even the two rider who might have experienced a change went in different directions).

 

[acoggan]

Are you saying that because there is a lot of noise and because it takes a lot of runs to overcome the noise and because, on average, there is little demonstrated benefit to experimenting with crank length as it affects drag that you don't think it worthwhile for riders to even bother trying? I'll bet riders #1 and #2 would disagree with that assessment. Or would you recommend they ignore that data because it doesn't meet your high standards?

At the present time, I'd recommend that people not waste precious wind tunnel time "chasing ghosts" (to quote John Cobb).

Could you refer us to a single study in which these other items have been extensively tested

Sure: the M.I.T. work evaluating dozens of helmets. (Sorry, not at work at the moment so can't cite the exact issue of Sports and Engineering Research or whatever the name of the journal, that is was published in...but I'll bet you could turn up the student's master's thesis on the web with just a little sleuthing.)

Changing a set of cranks requires "far more effort" than "merely" replacing a front brake?

Definitely, because when you change crank length you need to adjust many other things. With a front brake, though, it can be as simple as loosening then tightening two bolts.

 

[FrankDay]

It isn't. (It also isn't limited by some putative "central governor", despite what Tim Noakes might try to make you believe.)

I know you believe that VO2 max is output limited but that theory cannot explain why, in the same person, VO2 max will depend upon how it is tested. If it were really heart limited it should test the same regardless of testing protocol. VO2 max depends upon how many muscles have been aerobically trained and how many are being stressed in the test. therefore, rowers and XC skiers tend to test higher than runners and runners higher than cyclists. And, the same person will usually test higher if tested as a runner than as a cyclist.

Greater demand = reduced effiicency.

Huh? I presume you have evidence for this that applies to all circumstances.

Submaximal O2 consumption isn't limiting (by definition). What it is is an indicator of ATP demand (turnover). In the context of the muscle's ability to generate ATP via oxidative phosphorylation, it is this ATP demand that dictates metabolic responses related to fatigue (e.g., accumulation of inorganic phosphate, depletion of glycogen). Since changing crank length doesn't alter how many mitochondria we have (or the ability of our cardiovascular system to provide O2), it could only act via changing ATP demand, i.e., efficiency - but efficiency is essentially independent of crank length, at least over a very broad range (i.e., from 145 to 195 mm...at least those are the extremes that I recall were tested).

that is a pretty bold statement to say "it could only act via" when changing crank length also changes the muscle contraction excursion (which can affect force and efficiency) and the angle and range of motion of several joints which have various mechanical advantages based on joint angle.

Time may tell whether you're right or not...but at the present, it is still a WAG how much, if any, changing crank length changes CdA (note that in Cervelo's data, even the two rider who might have experienced a change went in different directions).

Which goes to my wind tunnel findings that suggests that how one will respond depends upon whether their current aerodynamics are torso/head dominant or leg dominant. Further, the Cervelo data does not address the issue of how "fit" is altered as crank length changes. Our experience suggests that shorter cranks allow for lowering of the front end beyond the previous "optimum". This is another fly in the ointment that neither the Cervelo data nor my own wind tunnel experiment looked at.

 

[FrankDay]

At the present time, I'd recommend that people not waste precious wind tunnel time "chasing ghosts" (to quote John Cobb).

Is this the same John Cobb who reported a 30% reduction in drag when going to shorter cranks and when I asked him about this he said it was because of the more compact positioning he was able to obtain because of the shorter cranks

Sure: the M.I.T. work evaluating dozens of helmets. (Sorry, not at work at the moment so can't cite the exact issue of Sports and Engineering Research or whatever the name of the journal, that is was published in...but I'll bet you could turn up the student's master's thesis on the web with just a little sleuthing.)

The reference you posted before failed to look at the issue of body position on the magnitude of the effect. So, a large effect when sitting upright might be a very small effect when already very aero (as I found in my wind tunnel experiment). And, of course, there is no work looking at the magnitude of crank length effects (especially if one considers the potential of improving fit from this change compared to the change itself) as to the magnitude. If the report of Cobb above is true then I would suggest that the potential of crank length dwarfs all other effects in some people.

Definitely, because when you change crank length you need to adjust many other things. With a front brake, though, it can be as simple as loosening then tightening two bolts.

LOL. I guess if you are talking about doing a bike fit after each change then that would be the case. But then we are talking what John Cobb did. Now, if you don't think a 30% reduction in drag is worth the effort compared to what one can get from changing the front brake then let the world know now so we can better understand your priorities.