The importance of crank length to the cyclist.

[coapman]

I think I have done this before but here goes.

1. Why does power increase? I believe the reasons are two main ones.

a. shorter cranks slow pedal speed, making it easier for the rider to apply more force to the pedal. The rider cannot apply any force to the pedal until he gets the foot up to pedal speed. The slower the pedal speed the sooner force can start to be applied.

b. A smaller range of motion keeps the hip and knee joints in a generally more efficient and powerfully leveraged angles such that any given muscle contractile force results in higher pedal force.

So, while it may take more force to generate any given power with shorter cranks, shorter cranks keep the legs in a more efficient configuration for applying force, making it easier to do so than when they are bent too much. Now, I guess I could be wrong here but something has to explain what was found by Martin and by those who are doing these experiments for me.

2. The aero advantages are easy to explain. Shorter cranks and higher saddle will reduce the frontal area presented to the wind. Did you download and read the essay I wrote on the subject? I think that illustrates this point very well.

What you see as advantages, I see as disadvantages. Chain drive power is all about torque not pedal force. Remember the ROTORCRANKS, they enabled you to start your power stroke earlier and also slowed down your pedal stroke. The earlier you start your power stroke, the more of that force is wasted due lack of tangential effect and with the loss of further torque due to the lack of leverage you are using a very inefficient way of powering your cranks. The longer cranked rider has faster leg action, delaying the start of his power stroke and ensuring that his force is applied to the pedal where it is most efficient and most effective between 2 and 4 o'c.

 

[FrankDay]

What you see as advantages, I see as disadvantages.

Beauty is indeed in the eyes of the beholder

Chain drive power is all about torque not pedal force.

Ugh, power= force through a distance per unit time. Torque is simply another way of representing force

Remember the ROTORCRANKS, they enabled you to start your power stroke earlier and also slowed down your pedal stroke.

All Rotorcranks do is slow the pedal speed on the downstroke and increase it on the upstroke. Not sure what that enables regarding timing

The earlier you start your power stroke, the more of that force is wasted due lack of tangential effect and with the loss of further torque due to the lack of leverage you are using a very inefficient way of powering your cranks.

I guess if your only method of applying power is to push down I would pretty much agree with you. However, it you try to push over the top and scrape the mud off the bottom of the shoe at the bottom of the stroke we are talking tangential forces aren't we?

The longer cranked rider has faster leg action, delaying the start of his power stroke and ensuring that his force is applied to the pedal where it is most efficient and most effective between 2 and 4 o'c.

If you believe that power is best applied in a 60º portion of a 360º circle and that the rest of the circle can be ignored I say go for it. We all, after all, should follow our beliefs.

 

[coapman]

Beauty is indeed in the eyes of the beholder Ugh, power= force through a distance per unit time. Torque is simply another way of representing force All Rotorcranks do is slow the pedal speed on the downstroke and increase it on the upstroke. Not sure what that enables regarding timing I guess if your only method of applying power is to push down I would pretty much agree with you. However, it you try to push over the top and scrape the mud off the bottom of the shoe at the bottom of the stroke we are talking tangential forces aren't we? If you believe that power is best applied in a 60º portion of a 360º circle and that the rest of the circle can be ignored I say go for it. We all, after all, should follow our beliefs.

When the lower rotorcrank was at 6 the upper crank was already one third of the way between 12 and 1 o'c. You know I don't waste time rolling my foot over a barrel at 12 and scraping the mud off shoe at 6, I apply max torque there as I also do between 1 and 2 o'c. Try ignoring the rest of the 1 to 5 o'c sector of the mashing power stroke when directing maximal force towards 2 o'c, impossible.

 

[FrankDay]

When the lower rotorcrank was at 6 the upper crank was already one third of the way between 12 and 1 o'c. You know I don't waste time rolling my foot over a barrel at 12 and scraping the mud off shoe at 6, I apply max torque there as I also do between 1 and 2 o'c. Try ignoring the rest of the 1 to 5 o'c sector of the mashing power stroke when directing maximal force towards 2 o'c, impossible.

Cool, although your concerns are off topic. This is a crank length thread, not a pedaling technique thread. It is my understanding that Rotorcranks is about to come out with shorter cranks down to 150. Good for them although I suspect you will ignore this offering.

 

[coapman]

Cool, although your concerns are off topic. This is a crank length thread, not a pedaling technique thread. It is my understanding that Rotorcranks is about to come out with shorter cranks down to 150. Good for them although I suspect you will ignore this offering.

In what type of competition do you believe shorter cranks should be used ?

 

[FrankDay]

In what type of competition do you believe shorter cranks should be used ?

Whatever competition in which they will make you better.

 

[Maxiton]

This thread is great maybe for learning about male primate behavior; not so good for crank length. Nobody looking for info they can actually use on crank length is going to read all this, and if by chance they did, I doubt they'd come away feeling they'd found what they came for.

This thread is kind of a funny joke, but it's still a joke. I suggest closing it and starting something new.

 

[Boeing]

Whatever competition in which they will make you better.

the better question is what type of competition would the cranks you posted a picture of make anyone better?


Off the top of my head I'm thinking hi wire unicycle at cirque du soleil or Ringling bros.

and Frank, with no disrespect I am serious here.

 

[FrankDay]

the better question is what type of competition would the cranks you posted a picture of make anyone better?


Off the top of my head I'm thinking hi wire unicycle at cirque du soleil or Ringling bros.

and Frank, with no disrespect I am serious here.

The circus is a competition?

Again, any competition where performance depends on either power or aerodynamics. But, without trying and testing it is not possible to know whether shorter per se or as short as I showed (very short, around 100mm) would benefit any particular athlete in any particular competition. That is the point!

 

[coapman]

The circus is a competition?

Again, any competition where performance depends on either power or aerodynamics. But, without trying and testing it is not possible to know whether shorter per se or as short as I showed (very short, around 100mm) would benefit any particular athlete in any particular competition. That is the point!

In your article " Is tradition limiting performance gains " , can you explain the following two statements. 1. "The loss of leverage associated with a shorter crank is easily made up for by changing the leverage in the gearing" . Take for example the total torque lost between 2 and 4 o'c. 2. "Pedal speed can be kept the same by increasing cadence".

 

[FrankDay]

In your article " Is tradition limiting performance gains " , can you explain the following two statements. 1. "The loss of leverage associated with a shorter crank is easily made up for by changing the leverage in the gearing" . Take for example the total torque lost between 2 and 4 o'c.

Sure. People tend to focus on the leverage associated with the crank length alone. That is simply a small part of the puzzle because what really counts is the leverage to the tire. So, take crank length, whatever crank length one is at is immediately counteracted by the size of the chain ring one is on. It is the ratio of the crank length to the diameter of the chain ring that determines the "effective leverage" of the crank. Let's look at what happens from 170 to 150, for example, a 12% change. If we reduce the tooth count on the chain ring 12% we now have the exact same total leverage at the front going to the rear cog. This is like going from a 52 to a 46 up front. With this change "torque" delivered to the rear wheel is now unchanged despite their being a shorter crank. (edit: or, if you don't want to change your chain ring up front then we need to ride a 12% larger cog on the back to keep leverage to the tire the same, like going from a 15 to a 17.)

2. "Pedal speed can be kept the same by increasing cadence".

Pedal speed is determined by looking at the circumference of the pedal circle and multiplying that by the revolutions per unit time. Circumference is directly related to crank length through the formula pi*2*r (crank length is r). Using the example above, going from 170 to 150 and keeping cadence the same would lower pedal speed 12%. If one wants to keep pedal speed the same one then need, simply, increase the cadence 12%. Now, I believe that most people would benefit by reducing pedal speed, which may be why many see power increase slightly as they go shorter but if you want to keep pedal speed the same it is easy.

So, by adjusting gearing we can keep the leverage the same and by adjusting cadence we can keep the pedal speed the same, as we change crank length, if we choose to. Does it make sense now?

 

[coapman]

Sure. People tend to focus on the leverage associated with the crank length alone. That is simply a small part of the puzzle because what really counts is the leverage to the tire. So, take crank length, whatever crank length one is at is immediately counteracted by the size of the chain ring one is on. It is the ratio of the crank length to the diameter of the chain ring that determines the "effective leverage" of the crank. Let's look at what happens from 170 to 150, for example, a 12% change. If we reduce the tooth count on the chain ring 12% we now have the exact same total leverage at the front going to the rear cog. This is like going from a 52 to a 46 up front. With this change "torque" delivered to the rear wheel is now unchanged despite their being a shorter crank. (edit: or, if you don't want to change your chain ring up front then we need to ride a 12% larger cog on the back to keep leverage to the tire the same, like going from a 15 to a 17.)
Pedal speed is determined by looking at the circumference of the pedal circle and multiplying that by the revolutions per unit time. Circumference is directly related to crank length through the formula pi*2*r (crank length is r). Using the example above, going from 170 to 150 and keeping cadence the same would lower pedal speed 12%. If one wants to keep pedal speed the same one then need, simply, increase the cadence 12%. Now, I believe that most people would benefit by reducing pedal speed, which may be why many see power increase slightly as they go shorter but if you want to keep pedal speed the same it is easy.

So, by adjusting gearing we can keep the leverage the same and by adjusting cadence we can keep the pedal speed the same, as we change crank length, if we choose to. Does it make sense now?

You beat me to it, I had spotted the answer to the second question. But you were claiming the advantage came from the slower pedal speed of the shorter crank, because it gave you more time to apply torque. As for the first question, if you are correct with your answer, the fact still remains, by reducing chainring size in keeping with the shortening of the crank, you are also reducing your range of gears. What happens on a long descent with a tail wind in a tt, what cadence would you expect to be using. I will have to give this some more thought.

 

[FrankDay]

You beat me to it, I had spotted the answer to the second question. But you were claiming the advantage came from the slower pedal speed of the shorter crank, because it gave you more time to apply torque.

Actually, what I am trying to do is explain the findings of Martin and my own guinea pigs, that their power tends to increase as they shorten their cranks. How does one explain this? One possible explanation has to do with reducing pedal speed. Power is the combination of pedal speed and force on the pedal. Maximum force can be applied when the pedal speed is zero, but then power is also zero. No force can be applied when then pedal speed is faster than you can move the foot so, again power is zero even though pedal speed is high. Maximum power occurs when we have the best combination of pedal speed and applied force. It is my impression that most people ride at a pedal speed higher than is optimum for what they are trying to do. That has yet to be proven though. There might, of course, be other explanations.

As for the first question, if you are correct with your answer, the fact still remains, by reducing chainring size in keeping with the shortening of the crank, you are also reducing your range of gears. What happens on a long descent with a tail wind in a tt, what cadence would you expect to be using. I will have to give this some more thought.

I don't see how reducing crank length reduces one's range of gears. I guess one might spin out faster on a 46-11 compared to a 52-11 when going down a straight 10% grade but these conditions occur so infrequently, compared to what the majority of most races entail, that it can be effectively ignored.

 

[coapman]

Actually, what I am trying to do is explain the findings of Martin and my own guinea pigs, that their power tends to increase as they shorten their cranks. How does one explain this? One possible explanation has to do with reducing pedal speed. Power is the combination of pedal speed and force on the pedal. Maximum force can be applied when the pedal speed is zero, but then power is also zero. No force can be applied when then pedal speed is faster than you can move the foot so, again power is zero even though pedal speed is high. Maximum power occurs when we have the best combination of pedal speed and applied force. It is my impression that most people ride at a pedal speed higher than is optimum for what they are trying to do. That has yet to be proven though. There might, of course, be other explanations. I don't see how reducing crank length reduces one's range of gears. I guess one might spin out faster on a 46-11 compared to a 52-11 when going down a straight 10% grade but these conditions occur so infrequently, compared to what the majority of most races entail, that it can be effectively ignored.

Is it true that Martin's conclusions came from testing done by means of a 4 sec maximal sprint.

 

[FrankDay]

Is it true that Martin's conclusions came from testing done by means of a 4 sec maximal sprint.

Something like that is my understanding.

 

[42x16ss]

Something like that is my understanding.

He was probably simulating a 65 kmh + sprint, which requires a large gear, at least a 52x12 or 50x11.

Guess what Frank, this is required at the end of almost all road races and criteriums when sprinting for the win. I for one wouldn't want to try and push that kind of gear with some of the crank sizes you have mentioned in this thread and I doubt I'm the only one

 

[Semper Fidelis]

Crank arm length is awesome

Most def. awesome!

 

[FrankDay]

He was probably simulating a 65 kmh + sprint, which requires a large gear, at least a 52x12 or 50x11.

Guess what Frank, this is required at the end of almost all road races and criteriums when sprinting for the win. I for one wouldn't want to try and push that kind of gear with some of the crank sizes you have mentioned in this thread and I doubt I'm the only one

Well, I suppose if you aren't going to even try then would won't know if there is any benefit to you. The one thing I think I have been pretty consistent about in this thread is I believe people should at least be willing to experiment with this to see what works best for them. To each his own.

 

[coapman]

Something like that is my understanding.

In that case it has to be dismissed as unreliable, "pulling up" can be beneficial in a 4 sec sprint effort, but in a 10 m TT the situation is reversed. On Slowtwitch we have the example of a rider who tested 172.5 and 155 cranks in 10 mile TT's, his cadence increased from 82 to 101, he was faster using the longer cranks. But I believe reliable testing can only be done in 4k track pursuits where conditions remain almost unchanged.

 

[CoachFergie]

People should experiment when there is a proven benefit but when the research indicates a maximum benefit of .5% to only the tallest and shortest of riders using a 170mm crank you would be better spending your time experimenting with training methods and diet where the potential benefits are much more substantial.

 

[FrankDay]

In that case it has to be dismissed as unreliable, "pulling up" can be beneficial in a 4 sec sprint effort, but in a 10 m TT the situation is reversed.

Really? Not trying to turn this into a pedaling technique thread but do you have data to support that statement?

On Slowtwitch we have the example of a rider who tested 172.5 and 155 cranks in 10 mile TT's, his cadence increased from 82 to 101, he was faster using the longer cranks. But I believe reliable testing can only be done in 4k track pursuits where conditions remain almost unchanged.

Ugh, I think you need a little more information before you should draw any conclusions from that one anecdotal report but I guess that isn't stopping you. For instance, 172.5 is only 11% longer than 155. Why did the rider find it necessary to increase his cadence 23% when making the change? Were the weather and course conditions similar for these efforts. How much time did he spend training on each length before these efforts? I could go on but that is enough for now.

 

[CoachFergie]

Ugh, I think you need a little more information before you should draw any conclusions from that one anecdotal report but I guess that isn't stopping you.

Nor did it stop you from using the anecdotal report of a rider doing a faster time a year apart on a different course as evidence of the importance of crank length despite nothing in the sport science literature suggesting any importance of crank length.

 

[42x16ss]

People should experiment when there is a proven benefit but when the research indicates a maximum benefit of .5% to only the tallest and shortest of riders using a 170mm crank you would be better spending your time experimenting with training methods and diet where the potential benefits are much more substantial.

But that would involve stuff like, actually, ummm, TRAINING.

Come on Fergie - we can't have that now can we

 

[CoachFergie]

Might have to also get our heads around not producing more power which is really easy, but sustaining the power we have for longer. I could produce 430 watts of peak power more than Chris Boardman but can only sustain his power for 60mins for 1min 29sec

 

[42x16ss]

Well, I suppose if you aren't going to even try then would won't know if there is any benefit to you. The one thing I think I have been pretty consistent about in this thread is I believe people should at least be willing to experiment with this to see what works best for them. To each his own.

You are the one with the short cranks, you have the motivation to prove they work and most importantly, you are the one challenging the industry standard.

If short cranks are beneficial to road racers (not triathletes, not TT'ers) get out there and show us. If not you then one of your athletes. As much as you might mock guys like Alex and Hamish, their athletes have results to back up their methods and assertations.

It might seem frustrating to you but you are the one who is trying to change peoples perceptions and habits - just give us some real reasons to and trust me, we will listen.