The crank length thread

[FrankDay]

You've always said that very short cranks were the solution. I noted my experience and those of others as evidence that they were not the solution and you found it to be unacceptable. My opinion of short-ish cranks remains the same but experimentation was the basis for the opinion as opposed to Voodoo statistics. I always encourage riders to work with their position and equipment and don't default to a simplistic standard except: avoid spending alot of money on equipment until you've trained enough to know what works for yourself.

No, I said that I thought that most people were using cranks that were too long, even way too long. I gave some reasoning and, even, a scientific study to support my view. But, that having been said, I have always said that the only way any one rider can know what is best is to experiment and find out.

edit: here is what I wrote in the 11th post in the previous thread where I brought up the topic.

The fact that the science doesn't exist yet to validate my hypothesis is not a particularly good reason to not act on this data. It is easy enough for each athlete to test this for themselves to see if there is anything to it for them.

 

[Hawkwood]

I think most people "like" what they are used to and this is especially true for those who in the front of the pack as they attribute their success to their choices, whether there is really anything to them or not.

The laughable thing about the "leverage" argument for crank length is crank length is simply 1 out of a series of levers between the foot and the ground. "Levers" in this chain include crank length, front chain ring size, rear cog size, and wheel size. It is a myth that crank length affects leverage since the real thing that people choose that affects leverage is their gearing choice. This is the main advantage of the modern bicycle over the single speed bicycle. And, people advocating for long cranks invariably forget the effect on those other levers that come into play when producing power - the joints in the legs and how crank length affects them.

Anyhow, I think it is clear that the only way to know what is best for any one person is for that one person to experiment with various lengths and see what is actually best for him/her for the kind of racing that person does.

I'm lost, you say that crank length is `...1 out of a series of levers...' and then that `It is a myth that crank length affects leverage...'. I'm thinking back 35 years to school physics - surely there's a way of modelling this?

 

[FrankDay]

I'm lost, you say that crank length is `...1 out of a series of levers...' and then that `It is a myth that crank length affects leverage...'. I'm thinking back 35 years to school physics - surely there's a way of modelling this?

Well, crank length affects overall leverage if you don't change anything else. This was the case back in the days of the penny farthing bicycles where all you had was crank length and wheel diameter. My guess this is where the "crank length affects leverage" thing started. Now, people also select gearing such that if one shortens crank length I would guess they also change gearing to keep pedal speed and, hence, the feel the same. In today's bicycle there are several levers between the pedal and the ground. People are always fooling with (changing) that one in the middle, gearing. Crank length leverage is, essentially, a non-issue. What is the relative change in leverage going from a 175mm crank to a 165mm crank (or, even, a 145 or 135 crank) compared to going from a 52/12 to a 38/23 (or 24/30) gearing combination?

Forget leverage when it comes to crank length. One should be choosing crank length to optimize the rider, not to "increase leverage".

 

[Hawkwood]

Well, crank length affects overall leverage if you don't change anything else. This was the case back in the days of the penny farthing bicycles where all you had was crank length and wheel diameter. My guess this is where the "crank length affects leverage" thing started. Now, people also select gearing such that if one shortens crank length I would guess they also change gearing to keep pedal speed and, hence, the feel the same. In today's bicycle there are several levers between the pedal and the ground. People are always fooling with (changing) that one in the middle, gearing. Crank length leverage is, essentially, a non-issue. What is the relative change in leverage going from a 175mm crank to a 165mm crank (or, even, a 145 or 135 crank) compared to going from a 52/12 to a 38/23 (or 24/30) gearing combination?

Forget leverage when it comes to crank length. One should be choosing crank length to optimize the rider, not to "increase leverage".

Okay, I've used 180s for almost 30 years and like them, I think I'm faster on them but this is a subjective opinion. One thing that has always interested me is do longer cranks enable you to apply force for a greater distance during cycling? For example if your right leg applies force during 30% of the pedaling cycle and 180 cranks obviously have a greater radius than 170s would this be a factor?

 

[FrankDay]

Okay, I've used 180s for almost 30 years and like them, I think I'm faster on them but this is a subjective opinion. One thing that has always interested me is do longer cranks enable you to apply force for a greater distance during cycling? For example if your right leg applies force during 30% of the pedaling cycle and 180 cranks obviously have a greater radius than 170s would this be a factor?

Of course there is essentially zero scientific data that addresses this issue as to what happens to pedaling technique as one changes crank length. I do have some thoughts on the matter though and actually have one datum point to back me up.

I believe our basic pedaling technique (coordination pattern) is ingrained in our nervous system and it won't change just because of a crank length change. So, how do we explain the findings of Martin? I think that is easy. Crank length affects pedal speed. With shorter cranks the pedal will move slower at the same cadence. If the pedal is moving away slower on the downstroke it is easier to apply higher force to the pedal and this compensates for the "loss of leverage". Further, the slower pedal speed makes it easier to "get the foot out of the way" on the upstroke, reducing the amount of negative work done by most on the upstroke and, again, compensating for the loss of leverage many mention.

I came up with this last thought when I saw some actual data along this line. We were telling a coach/fitter to the pros in Italy about our findings/thoughts and he simply refused to believe it. But, he was willing to get on a bike that measured crank torque and see (probably trying to prove us wrong). He was blown away by the results and sent these two screen shots comparing 170 and 150 cranks. This is a 90 second interval at essentially the same power. The technique graph is too compressed together here to see if it changes but we can see how the peak positive and negative torques change between runs as crank length is changed. Note how much smaller the negatives are on the 150 cranks compared to 170. Also note how unbalanced he is, especially on the upstroke which mostly accounts for the total r/l imbalance seen. What happens on the upstroke does matter.

150 crank

170 crank

This would be a good project for some scientist looking for an "easy" paper that will actually expand our knowledge base.

 

[CoachFergie]

Yes crank length matters. However as Martin over several studies has pointed out, just not significantly.

 

[FrankDay]

Yes crank length matters. However as Martin over several studies has pointed out, just not significantly.

The word significant can have several connotations. Of course, there is scientific significance (Martin's use of the word) which simply means that the any difference seen demonstrates (usually) a less than 1 in 20 chance of being due to randomness. And, then there is individual significance, does the individual think any improvement seen important enough to them to be called significant.

The failure to reach scientific significance by Martin may simply reflect an study design that was inadequate to uncover a real differences. His study should be repeated using a larger cohort to see if there are "real" differences. As they currently stand, Martin's findings cannot be taken as "proof" that there is no difference or that the difference seen is not important. If he had determined that the differences were "scientifically significant" it would only mean that there is less than a 1 in 20 chance that his findings were due to randomness and we would be arguing as to whether the magnitude of the difference was important. It would still be up to the athlete to determine if the magnitude of the difference was large (individually significant) enough to to make it worthwhile to make the change.

The tough part of science is not the gathering of data but the interpretation of it.

 

[CoachFergie]

Coach Ferg adds Revisionist Statistics to the list alongside Physiology, Biomechanics and Research Design.

 

[King Boonen]

I thought this thread was meant to be different to the last one?

 

[CoachFergie]

I thought this thread was meant to be different to the last one?

The research on the area didn't change overnight.

http://www.plan2peak.com/files/32_article_JMartinCrankLengthPedalingTechnique.pdf

Remains the best summary of just how important crank length is.

 

[King Boonen]

Oh I agree, physics hasn't changed either last I'd heard, some people seem to think it has though.

But without mentioning shorts cranks this has already descended into the same discussion as the last thread.

 

[FrankDay]

The research on the area didn't change overnight.

http://www.plan2peak.com/files/32_article_JMartinCrankLengthPedalingTechnique.pdf

Remains the best summary of just how important crank length is.

Perhaps it would be better to say this is the best summary of the state of the science on this topic. Martin, in his notes lists a total of three studies, one looking at maximum power, one looking at metabolic cost, and one looking at fatigue. I think it is important to note that he uses the terms "substantially improve" or "substantially compromise" as if serious riders don't care about small improvements or differences.

But, I guess, in the eyes of some at least, those three studies analyzed for "substantial" differences is certainly enough to scientifically settle the question. LOL

 

[Oldman]

Oh I agree, physics hasn't changed either last I'd heard, some people seem to think it has though.

But without mentioning shorts cranks this has already descended into the same discussion as the last thread.

It is quacking like the same duck....

 

[CoachFergie]

But, I guess, in the eyes of some at least, those three studies analyzed for "substantial" differences is certainly enough to scientifically settle the question. LOL

Also safe to say that all some have tried to add to the debate is a series of meaningless anecdotes that in no way show any importance of crank length.

0.5% maximum improvement for only the very tallest or very shortest of riders moving away from a 170mm crank is hardly worth pursuing compared to the gains one can make in terms of training, diet and recovery.

 

[FrankDay]

0.5% maximum improvement for only the very tallest or very shortest of riders moving away from a 170mm crank is hardly worth pursuing compared to the gains one can make in terms of training, diet and recovery.

I didn't realize it wasn't possible to do all at the same time. And, while we are at it I guess we should ignore the possible aerodynamic benefits at the same time since they haven't even been scientifically studied let alone validated. Yes, I see your point now, surely not worth the effort.

 

[CoachFergie]

I didn't realize it wasn't possible to do all at the same time. And, while we are at it I guess we should ignore the possible aerodynamic benefits at the same time since they haven't even been scientifically studied let alone validated. Yes, I see your point now, surely not worth the effort.

I didn't realise changing crank length was the only way to improve aerodynamics on the bike. Please enlighten us.

 

[Oldman]

Didn't you guys already have a private room? We can still hear you.

 

[King Boonen]

Crank length on a mountain bike. As important or not?

 

[CoachFergie]

http://www.ncbi.nlm.nih.gov/pubmed/19771448

 

[King Boonen]

Thanks, currently reading on my lunch break. Will put questions/thoughts as I go along so hopefully it isn't too disjointed...


The SD on the ages seems to vary in the text (3.8) to the table (9.5). Guessing it's a typo.

Glad to see position is corrected for each crank-length, not kept as absolute.

Very interesting. So it seems to have a significant effect on time to peak power but nothing else. I wonder if it's related to the fact that you need a larger force to turn the same gear with a smaller crank, causing the athlete to apply a higher normalised force when using shorter cranks due to the increased difficulty of turning over the gear?

 

[FrankDay]

Thanks, currently reading on my lunch break. Will put questions/thoughts as I go along so hopefully it isn't too disjointed...


The SD on the ages seems to vary in the text (3.8) to the table (9.5). Guessing it's a typo.

Glad to see position is corrected for each crank-length, not kept as absolute.

Very interesting. So it seems to have a significant effect on time to peak power but nothing else. I wonder if it's related to the fact that you need a larger force to turn the same gear with a smaller crank, causing the athlete to apply a higher normalised force when using shorter cranks due to the increased difficulty of turning over the gear?

The potential aerodynamic improvements that can be seen going to shorter cranks is not a consideration, usually, for the mountain biker. But, there is one advantage of shorter cranks that is probably of great concern to the mountain biker - increased ground clearance. If there is no loss of power, an improvement in how fast one can increase power (thanks for the link Fergie), and increased ground clearance, then it seems to me that the mountain biker should be going as short as they can until something starts to deteriorate.

 

[CoachFergie]

More assumption.

Why would a off rider not be concerned about aerodynamics?

There is simply no evidence that changing crank length is the only way to improve aerodynamics on the bike.

 

[veganrob]

I didn't realize it wasn't possible to do all at the same time. And, while we are at it I guess we should ignore the possible aerodynamic benefits at the same time since they haven't even been scientifically studied let alone validated. Yes, I see your point now, surely not worth the effort.

I thought you already did the testing in the wind tunnel and found no aerodynamic benefit to the shorter cranks. I could be wrong.

 

[FrankDay]

I thought you already did the testing in the wind tunnel and found no aerodynamic benefit to the shorter cranks. I could be wrong.

I believe that what I found was that there was no aerodynamic benefit to going shorter once the upper body was in a very good (reasonably flat) aerodynamic position. The improvements in the upper body would be canceled by the detriments seen from the leg changes. (Edit: Once this condition is reached the only reason to go shorter would be if one saw a power increase or an improvement in comfort with shorter cranks.) However, for those who have relatively poor upper body positions because of poor flexibility or other reasons going shorter, if it helps them achieve a much better upper body position, can still result in an aerodynamic benefit because the upper body improvements should outweigh the leg decreases. So, it depends upon where you are starting. Looking at the average age-group triathlete I believe many of them would see substantial aerodynamic improvement from going to shorter cranks if that allowed them to get their torso/head lower.

Anyhow, my one time in the wind tunnel certainly isn't conclusive on this question and each person should probably experiment for themselves on this question.

 

[sciguy]

I believe that what I found was that there was no aerodynamic benefit to going shorter once the upper body was in a very good (reasonably flat) aerodynamic position. The improvements in the upper body would be canceled by the detriments seen from the leg changes. (Edit: Once this condition is reached the only reason to go shorter would be if one saw a power increase or an improvement in comfort with shorter cranks.) However, for those who have relatively poor upper body positions because of poor flexibility or other reasons going shorter, if it helps them achieve a much better upper body position, can still result in an aerodynamic benefit because the upper body improvements should outweigh the leg decreases. So, it depends upon where you are starting. Looking at the average age-group triathlete I believe many of them would see substantial aerodynamic improvement from going to shorter cranks if that allowed them to get their torso/head lower.

Anyhow, my one time in the wind tunnel certainly isn't conclusive on this question and each person should probably experiment for themselves on this question.

Frank,

Many of us feel that flexibility is rather unimportant in regards to getting into a good aero position. This from a very aero Jordan Rapp:

"Flexibility is a red herring. If you can touch your knees, you can ride like Dave Zabriskie. Flexibility is rarely a limiter to a good bike position,"

Jordan and I both contend that finding a saddle that meshes comfortably with your nether regions is vastly more critical to attaining and maintaining aero than pretty much any other factor.

http://forum.slowtwitch.com/cgi-bin/gforum.cgi?post=4413231#4413231

Now if your belly is so large that it interferes with your quads while trying to ride aero then that's a whole different problem and one better solved with diet than shorter cranks

YMMV,

Hugh