The crank length thread

[elapid]

There must be a reason stairs evolved to be 6 to 8 inches high rather than 14" (the height the typical 170mm cranks makes the rider lift the foot).

Safety, pure and simple. The height of steps as stipulated by state/provincial/country codes can in no way be misconstrued into a justification of short cranks and the biomechanics of pedalling technique.

 

[hiero2]

Safety, pure and simple. The height of steps as stipulated by state/provincial/country codes can in no way be misconstrued into a justification of short cranks and the biomechanics of pedalling technique.

Just dropped in to see how the argument was coming along. Reading up the page, everything seems to be pretty normal.

However, as a poster, the whole stair comparison hooks me. First off, the point about the evolution of stairs is rather missed by thinking only in terms of modern building codes. If we take a trip to Mayan ruins, we could find some pretty big rise staircases - but such tall rises in the stairs did not survive in common use. Building codes come in after stairs have already settled on a something like 6-9" range in the rise.

Second, the whole stair comparison may not even be valid. Stairs are designed for a general population, and for general use, not the specific use case /application of mechanical force that is the bicycle. I can see the thought might be useful for thinking out of the box - but the two are mechanically somewhat different in function.

Which brings me to "third". It seems to me that the biomechanical motion of running is a better parallel to the action while bicycling. One doesn't normally run up stairs - the stride is too long. If you run up stairs, you are just as likely to take them two at a time, yes?

And, fourth, and last. Bicycles have also seen a lot of evolution. Thinking too narrowly in terms of comparing to stairs seems to ignore the evolution of bicycle parts and dimensions. There were a whole lot of "test subjects", aka "the marketplace", around in the late 1800's, during the bicycle craze. And, there were also a lot of people experimenting with variants on mechanical themes in that age. We didn't see anything like it again until the computer age - so a gap of over 50 years. During which evolution of mechanical themes still occurred, just not as rapidly.

So, I find the stair argument useful, perhaps, in reminding us to think outside the box, but not useful to convince me that ultra-short cranks are the next biomechanical "thing" for cyclists.

 

[King Boonen]

The stairs argument is a funny one. Stair have levelled off at what, 4"-9"? This will be through redesign and analysis. Surely the same thing has given us crank lengths around 170mm as standard?

I don't see the argument that stair designers have managed to take into account everything bike designers haven't, and that bike design is still in the dark ages with regard to crank length. Both seem to have come to their natural points.

Also, to take the short crank/small stairs argument further, surely Frank should be arguing even smaller stairs are better because it removes the wasted energy in lifting your leg higher than usual?

Basically the stair argument is invalid. The height of stairs was probably determined based on a simple height gain required and least space taken up formula that the average person could deal with.

 

[FrankDay]

Just dropped in to see how the argument was coming along. Reading up the page, everything seems to be pretty normal.

However, as a poster, the whole stair comparison hooks me. First off, the point about the evolution of stairs is rather missed by thinking only in terms of modern building codes. If we take a trip to Mayan ruins, we could find some pretty big rise staircases - but such tall rises in the stairs did not survive in common use. Building codes come in after stairs have already settled on a something like 6-9" range in the rise.

Second, the whole stair comparison may not even be valid. Stairs are designed for a general population, and for general use, not the specific use case /application of mechanical force that is the bicycle. I can see the thought might be useful for thinking out of the box - but the two are mechanically somewhat different in function.

The stair analogy may or may not be valid as it was simply put forth as an analogy to illustrate that there might be a good reason to suspect that current typical crank lengths are too long, especially for general use (the same use that dictated the evolution of stair height). It was put forth to get people thinking about this in another way. It seems to have worked.

Which brings me to "third". It seems to me that the biomechanical motion of running is a better parallel to the action while bicycling. One doesn't normally run up stairs - the stride is too long. If you run up stairs, you are just as likely to take them two at a time, yes?

I agree. However, when one runs up stairs one usually does so only when sprinting for short periods. The question is which is most efficient and powerful. If one goes to the gym and asks an athlete on the stairmaster to climb as fast as they can for 1 minute, 5 minutes, 30 minutes, and an hour I expect one will see the freely chosen "stair height" will fall for each interval. This is probably because the other thing that affects athletic performance is cadence. To climb at a high rate with a small stair height would require a higher stride rate than is efficient or possible so the athlete is forced to increase stair height and does so because he knows the time will be limited. This is the same problem encountered by the cyclist except the cyclist doesn't have the freedom to change crank length based upon immediate need.

And, fourth, and last. Bicycles have also seen a lot of evolution. Thinking too narrowly in terms of comparing to stairs seems to ignore the evolution of bicycle parts and dimensions. There were a whole lot of "test subjects", aka "the marketplace", around in the late 1800's, during the bicycle craze. And, there were also a lot of people experimenting with variants on mechanical themes in that age. We didn't see anything like it again until the computer age - so a gap of over 50 years. During which evolution of mechanical themes still occurred, just not as rapidly.

While bicycles themselves have seen a lot of evolution I don't think the same can be said for bicycle cranks. Show me how crank length has evolved from the time of the penny farthing to now that suggests it is a reasonable to conclude that current crank length is the result of evolution to what is best, especially when riding in a completely different way (aero position) than how essentially everyone rode just 30 years ago.

So, I find the stair argument useful, perhaps, in reminding us to think outside the box, but not useful to convince me that ultra-short cranks are the next biomechanical "thing" for cyclists.

The stair argument should not be sufficient, in and of itself, to convince you to change. However, it seems it has served its purpose as it has you, at least, thinking about this issue.

 

[FrankDay]

The stairs argument is a funny one. Stair have levelled off at what, 4"-9"? This will be through redesign and analysis. Surely the same thing has given us crank lengths around 170mm as standard?

I don't see the argument that stair designers have managed to take into account everything bike designers haven't, and that bike design is still in the dark ages with regard to crank length. Both seem to have come to their natural points.

I see zero evidence that crank length is "bike design" is based upon anything other than what is customary. Show me some evidence that there is any "evolution" involved. Especially any evolution when it comes to what is optimum for the aerodynamic position, something that has only been around for about 30 years.

Also, to take the short crank/small stairs argument further, surely Frank should be arguing even smaller stairs are better because it removes the wasted energy in lifting your leg higher than usual?

No, shorter stairs require a higher step rate to go fast. The body is also limited by how fast we can repeat such activities. As with most things, what is optimum seems to involve a trade-off between two competing limiters.

Basically the stair argument is invalid. The height of stairs was probably determined based on a simple height gain required and least space taken up formula that the average person could deal with.

Huh? Why does this reasoning make the analogy invalid. Climbing stairs and riding a bike both involve doing work (in the physics sense) using a similar motion with the legs. Why wouldn't the limits be similar?

 

[CoachFergie]

It's like wheel size on Mountain Bikes, First 26" then 29" and now 27 and a half inch. All with claimed benefits over the other.

At the end of the day the claimed importance to power delivery and efficiency from changing crank length is not backed by any credible evidence.

Aerodynamics is a red herring as there are numerous factors that affect that on a bike.

 

[FrankDay]

...Aerodynamics is a red herring as there are numerous factors that affect that on a bike.

LOL. And what might those factors be?

 

[CoachFergie]

I guess when the only tool you have in your tool box is a adjustable crank length independent crank set you think that is the only solution to everything.

LOL? What adult says that???

 

[FrankDay]

Here is a link to one of my favorite podcasts that has something to say to this debate. https://itunes.apple.com/us/podcast/freakonomics-radio/id354668519 click on "The Folly of Prediction" show. At about 16minutes you will hear this.

Q. What are the characteristics then of a poor predictor?
(thinking pause)
A. Dogmatism!
Q. It can be summed up that easily?
A. I, I think so. An unwillingness to change ones mind in a reasonably timely way in response to new evidence. A tendency when asked to explain ones predictions to generate only reasons that favor your preferred prediction and not to generate reasons opposed to it.

Anyhow, regardless of what the "experts" here (including me, I suppose) are predicting the science will show I suppose we all have to just wait and see what it really shows. Will those who were wrong remember they were wrong? I suppose we will have to wait to find out. I can hardly wait. LOL

 

[FrankDay]

I guess when the only tool you have in your tool box is a adjustable crank length independent crank set you think that is the only solution to everything.

LOL? What adult says that???

Fergie, I really do hate being a pain in the b*tt but for you I make an exception. You really did forget to answer the question. I repeat: "And what might those factors (involved in aerodynamics on the bike) be?"

Oh, and thanks for the product plug.

 

[CoachFergie]

Here is a link to one of my favorite podcasts that has something to say to this debate. https://itunes.apple.com/us/podcast/freakonomics-radio/id354668519 click on "The Folly of Prediction" show. At about 16minutes you will hear this.
Anyhow, regardless of what the "experts" here (including me, I suppose) are predicting the science will show I suppose we all have to just wait and see what it really shows. Will those who were wrong remember they were wrong? I suppose we will have to wait to find out. I can hardly wait. LOL

What is the word for someone who argues against the evidence that is already there?

 

[FrankDay]

What is the word for someone who argues against the evidence that is already there?

Wise? Prescient? Especially when the so-called "evidence" constitutes pretty awful science. What is the word for those who dogmatically rely on such awful science. Dogmatic, I suppose? Thanks for participating.

 

[CoachFergie]

Fergie, I really do hate being a pain in the b*tt but for you I make an exception. You really did forget to answer the question. I repeat: "And what might those factors (involved in aerodynamics on the bike) be?"

And I do love to point out the intellectual laziness you develop when questions are asked of your product that has not yet been shown to improve performance in any capacity.

Are you even too lazy to look at Google these days?

http://www.beknowledge.com/wp-conte...g and development of cycling aerodynamics.pdf

http://bbaa6.mecc.polimi.it/uploads/abstract_files/TR03_STAMPA3.pdf

http://eduweb.hhs.nl/~fietsproject/fietspositities pagina4(23).pdf

http://digitalcommons.brockport.edu...l=en&as_sdt=0,5#search="cycling aerodynamics"

 

[CoachFergie]

Wise? Prescient? Especially when the so-called "evidence" constitutes pretty awful science. What is the word for those who dogmatically rely on such awful science. Dogmatic, I suppose? Thanks for participating.

Someone who has never carried out any research himself criticising the heavily cited and published in quality journal's work of others. Keep dreaming Frank.

 

[FrankDay]

And I do love to point out the intellectual laziness you develop when questions are asked of your product that has not yet been shown to improve performance in any capacity.

Are you even too lazy to look at Google these days?

http://www.beknowledge.com/wp-conte...g and development of cycling aerodynamics.pdf

http://bbaa6.mecc.polimi.it/uploads/abstract_files/TR03_STAMPA3.pdf

http://eduweb.hhs.nl/~fietsproject/fietspositities pagina4(23).pdf

http://digitalcommons.brockport.edu...l=en&as_sdt=0,5#search="cycling aerodynamics"

So, let me get this straight, you put in four links to something that all brought us back to right here? You didn't get the links right. You might fix this for those that follow. Anyhow, why can't you say what your take is from these and then link them for support. That is what most academics would do.

 

[CoachFergie]

So, let me get this straight, you put in four links to something that all brought us back to right here? You didn't get the links right. You might fix this for those that follow. Anyhow, why can't you say what your take is from these and then link them for support. That is what most academics would do.

They all work for me.

What do I take from them? Aerodynamics is multi-factorial. Anyone who suggests that crank length is going to make a big difference to performance doesn't understand the complexity of the subject.

But people can read that for themselves and draw their own conclusions. That is what most academics would do.

 

[hiero2]

Coach and Frank - put a chill on the personal diatribes, thank you. Resist the impulse to always reply, thank you.

We've managed to live together somewhat civilly for a few months now. Thank you.

You know, there is a website now, "happier.com" - they suggest writing down three moments of happiness each day. Helps us to better remember the good things in life. Puts them in long-term memory, and with practice, they out-compete the negative things. Might be something to that.

Oh - but that's ot. Hmmm - well, I'll say this.

As for crank lengths not having evolved with the beginnings of the bicycle craze? One of my points, last post, if it wasn't clear, was that EVERYTHING on a bicycle evolved in the late 1800's. I don't think you can find a single development in bicycle mechanics that didn't have a predecessor idea during that era. Now - the problem is finding proof. I'm not a historian, nor do I have sufficient time or resources to do a patent search in patents of that era. But materials available at that time, and the needs of the marketplace resulted in some inventions of that era never making it to market or never being successful. If crank length - something that could readily be experimented with - were NOT played with, I would be surprised. Lord, we've had enough other wacky experiments since then - with right-angle cranks being one example that has come up more than once. The latest version being a spiral crankarm. Wow.

 

[FrankDay]

As for crank lengths not having evolved with the beginnings of the bicycle craze? One of my points, last post, if it wasn't clear, was that EVERYTHING on a bicycle evolved in the late 1800's. I don't think you can find a single development in bicycle mechanics that didn't have a predecessor idea during that era. Now - the problem is finding proof. I'm not a historian, nor do I have sufficient time or resources to do a patent search in patents of that era. But materials available at that time, and the needs of the marketplace resulted in some inventions of that era never making it to market or never being successful. If crank length - something that could readily be experimented with - were NOT played with, I would be surprised. Lord, we've had enough other wacky experiments since then - with right-angle cranks being one example that has come up more than once. The latest version being a spiral crankarm. Wow.

Cool. I will submit that crank length probably evolved in the first 10-20 years of the bicycle, when the penny farthing was the dominant bicycle. However, I know of zero evidence to suggest that there has been any evolution since the invention of the safety bicycle or the ability to change gears on the fly or the development of the time-trial position (a rather recent development for which it should be easy to find any evolutionary documentation I would suspect, if it existed). It is the dominant opinion here and elsewhere that crank length hardly matters and that shortening crank length would lose leverage so longer crank lengths should be more powerful. Or course, there is no real scientific support for that view but that is the predominant view.

 

[CoachFergie]

The prevailing evidence would suggest that crank length either way is unimportant.

The major delusion some people have is that small changes in position or application of power around the pedal stroke can make big differences to the delivery of power to the pedals. A large number of studies highlight that no significant difference in power has been shown.

Cycling is not limited by application of force. While we may race around 200-400 watts most of us can easily deliver 800+ watts to the pedals. Delivery of power is not the question, sustainability of that power is!

 

[FrankDay]

They all work for me.

I didn't realize those were links to pdf's. My computer downloaded them so fast all I saw was a shudder and I was back to where I started. The downloads did not open automatically.

What do I take from them? Aerodynamics is multi-factorial. Anyone who suggests that crank length is going to make a big difference to performance doesn't understand the complexity of the subject.

Am I the only one who actually reads this stuff. You linked to 4 documents. The first three were pretty useless to this discussion because all the addressed was what constituted a good aero position without regard to how that position might affect power production. Anyone actually paying attention to the "short crank" argument would know that the main argument for them has to do with their ability to better maintain power as one gets into a good aero position. That brings us to the 4th link, the paper by Too. (The Effect of Body Configuration on Cycling
Performance) in which it was studied how hip angle affects power production and endurance. I want to thank you for that paper Fergie because it supports my position. Here are the relevant graphs from the paper:

Note that at some point power starts to fall when the hip angle gets too cramped. But, the other papers point out that reducing the frontal area is an important consideration in improving aerodynamics and the only way to do that effectively is to lower the torso/head in relation to the hips, which necessarily reduces the hip angle. So, some people when they increase their aerodynamic efficiency will be, necessarily, forced to reduce their hip angle which could reduce their power and endurance. However, one way of opening the hip angle is to shorten the cranks. So, we know from the Martin paper that power is maintained over a wide range of crank length when riders are in an open positon and we know that closing the hip angle too much when in the time-trial position can adversely affect performance. Hence, shortening the cranks could improve power in the some, especially when in a good time-trial position. That is my argument. This paper supports that argument. Thanks again for that.

But people can read that for themselves and draw their own conclusions. That is what most academics would do.

No, most academics would be willing to tell others how they interpret the paper and then engage others, who might disagree, in conversation about the areas of disagreement. That is what I try to do.

 

[CoachFergie]

No, most academics would be willing to tell others how they interpret the paper and then engage others, who might disagree, in conversation about the areas of disagreement. That is what I try to do.

You're trying to sell a worthless product. Keep trying.

 

[CoachFergie]

So, some people when they increase their aerodynamic efficiency will be, necessarily, forced to reduce their hip angle which could reduce their power and endurance. However, one way of opening the hip angle is to shorten the cranks. So, we know from the Martin paper that power is maintained over a wide range of crank length when riders are in an open positon and we know that closing the hip angle too much when in the time-trial position can adversely affect performance. Hence, shortening the cranks could improve power in the some, especially when in a good time-trial position.

It doesn't improve power! You would in theory not lose power.

But rather than d1ck around with crank length requiring a change in saddle height and fore-aft, handlebar height and fore-aft another option is to look at pelvic rotation of the hip. By rolling the hips forward on my bike I was able to drop my bars 4cm.

Based on numerous bike fittings that is an easier option. The only riders I have seen with issues maintaining an optimal hip angle are those with a large belly. Changing crank length would be a soft option and a band-aid compared to losing body fat and the added benefits of improved power to weight and lower frontal area.

 

[hiero2]

Cool. I will submit that crank length probably evolved in the first 10-20 years of the bicycle, when the penny farthing was the dominant bicycle. However, I know of zero evidence to suggest that there has been any evolution since the invention of the safety bicycle or the ability to change gears on the fly or the development of the time-trial position (a rather recent development for which it should be easy to find any evolutionary documentation I would suspect, if it existed). It is the dominant opinion here and elsewhere that crank length hardly matters and that shortening crank length would lose leverage so longer crank lengths should be more powerful. Or course, there is no real scientific support for that view but that is the predominant view.

Yep - we went from the penny farthing to the safety bicycle, with lots of variations tried and abandoned as less than workable or impractical. There were tricycles and quadcycles and steering mechanisms galore. So, betting that there was some variation of crank length experimented with in that time is more than safe, it is more likely certainty. Ok - so the safety bicycle becomes dominant.

Now, during the next phase, we see development of crank design. One-piece cranks, 3-piece cranks. Some variation in crank length involved there too. Nobody dictated 170mm as an automatic standard. Little bitty cranks could be found on little bitty bikes. Etc. Even in the "modern" age of bicycles - since 1960 - more cranks were available then just 170mm. During that period we also had a mass movement of ridership who grew up on the Schwinn StingRay - with shorter cranks - and what grew into BMX - with shorter cranks. Some of those riders continued to ride 20" wheel frames, but using the shorter cranks available didn't follow the same path.

So, my thinking is that "the crank remained untinkered with" for over 50 years is also disproven, based on historical events. First, we have that shorter cranks, albeit marginally shorter, were available for the Euro-style road bike. One would expect that IF you get a mechanical or biomechanical advantage from a shorter crank, that the effect would be incremental. If you get an advantage from significantly shorter cranks, you get a percentage of that advantage from slightly shorter cranks - yet nobody went down that road.

Next, you have a significant cycling population - bmx and off-road or mountain bikes - that was "anti-establishment" vis-a-vis Euro road cyclists, and quite verbally and openly so. A large segment of this population developed their own manufacturing channels and preferences - and they had shorter cranks available in the mix. But they did not adopt shorter cranks in anything like a sub-movement. They are a population of experimenters and early-adopters - but we don't see shorter cranks.

I don't believe the marketplace is omnipotent, nor omniscient. Market preferences are rarely for the most rational or logical choice - but when a marketplace preference is noted, the likelihood that the choice is the most rational or logical goes up significantly.

Which all adds to why I think there is significant reason to doubt your enthusiasm for short crank arms.

 

[FrankDay]

Yep - we went from the penny farthing to the safety bicycle, with lots of variations tried and abandoned as less than workable or impractical. There were tricycles and quadcycles and steering mechanisms galore. So, betting that there was some variation of crank length experimented with in that time is more than safe, it is more likely certainty. Ok - so the safety bicycle becomes dominant.

It is pretty easy to document all of those innovations and variations you mention. It is impossible (AFAIK) to document any innovation or real experimentation with crank length during this time. So, while you may think it a safe bet, I would think it would be a fools bet. Just look at the history of the bicycle since the introduction of the time-trial bicycle and position. I'll admit that there have been a few advocating different crank lengths but they have mostly been advocating for longer cranks (Zinn). It has not been until the last couple of years that anyone (I think it started with me) have been pushing for shorter cranks. And, yet, pretty much all I get is opposition despite the existence of the Martin study. In fact, the Martin study is used not as a reason to experiment with crank length but, rather, as justification to stay with the current standard.

Now, during the next phase, we see development of crank design. One-piece cranks, 3-piece cranks. Some variation in crank length involved there too. Nobody dictated 170mm as an automatic standard. Little bitty cranks could be found on little bitty bikes. Etc. Even in the "modern" age of bicycles - since 1960 - more cranks were available then just 170mm. During that period we also had a mass movement of ridership who grew up on the Schwinn StingRay - with shorter cranks - and what grew into BMX - with shorter cranks. Some of those riders continued to ride 20" wheel frames, but using the shorter cranks available didn't follow the same path.

The crank length variation you speak of is insignificant. The variation in body height and leg length in adult cyclists varies about 30%. Readily available frame sizes vary about 30%. Readily available crank length (at least until very recently) varies about 5% (I have been told that the Shimano distributor in Italy will not import a crank length shorter than 170)! That is, essentially, a one size fits all standard.

So, my thinking is that "the crank remained untinkered with" for over 50 years is also disproven, based on historical events. First, we have that shorter cranks, albeit marginally shorter, were available for the Euro-style road bike. One would expect that IF you get a mechanical or biomechanical advantage from a shorter crank, that the effect would be incremental. If you get an advantage from significantly shorter cranks, you get a percentage of that advantage from slightly shorter cranks - yet nobody went down that road.

A marginally shorter advantage is too small for anyone to distinguish. Hence it is not obvious that the change should be made, especially when the argument for staying long (leverage) is so loud albeit flawed.

Next, you have a significant cycling population - bmx and off-road or mountain bikes - that was "anti-establishment" vis-a-vis Euro road cyclists, and quite verbally and openly so. A large segment of this population developed their own manufacturing channels and preferences - and they had shorter cranks available in the mix. But they did not adopt shorter cranks in anything like a sub-movement. They are a population of experimenters and early-adopters - but we don't see shorter cranks.

I simply haven't seen that experimentation. Perhaps you can point me to where it occurred. BMX seems to have evolved to even longer cranks. I suspect this is because acceleration is so important to that kind of racing so they have fallen for the "longer crank length gives more leverage/power" argument. Real experimenting requires a scientific approach. Martin's study was a good first effort and those interesting results were essentially ignored by pretty much everyone.

I don't believe the marketplace is omnipotent, nor omniscient. Market preferences are rarely for the most rational or logical choice - but when a marketplace preference is noted, the likelihood that the choice is the most rational or logical goes up significantly.

OK. But, it is a pretty weak argument. Show me some science. The automobile evolved to what it was in the 50's when the manufacturers consistently argued that people didn't want seat belts or better fuel economy or that it would cost too much etc. The fact that the marketplace has evolved to a certain place is not particularly good evidence that a product is optimized or, even, very good.

Which all adds to why I think there is significant reason to doubt your enthusiasm for short crank arms.

So be it. But, that is not a very persuasive argument as far as I am concerned. Show me some science to prove me wrong. I have linked to what science I can find that suggests that I am right. I have not seen any science that suggests I am wrong. Fergie keeps trying to find some but he consistently gets things backwards.

 

[Boeing]

How long should the cranks be on a clowns unicycle at the circus?