The importance of crank length to the cyclist.

[Ripper]

Because both riders actually have their knees very close together (the lead rider just has massive quads).



Again, there are plenty of data showing that having your knees very close to the top tube leads to minimal drag. As well, there are data showing that the closer your feet are, the lower your drag (hence bikes w/ narrow b.b.s, e.g., GT SB-1 and SB-2, Walser, the special Trek TTX that was made for Armstrong
but ridden to an Olympic gold medal by Ekimov, etc.). You should therefore stop wasting everyone's time by pretending that this is not true.

This is interesting! Honest question - do you know how 'trainable' it is to move the feet/knees to make them narrower?

On another note, wow, this thread has some really idiotic comments!

 

[Martin318is]

This is interesting! Honest question - do you know how 'trainable' it is to move the feet/knees to make them narrower?

On another note, wow, this thread has some really idiotic comments!

In almost all cases it is pretty easy to train to be narrower (or wider). the key things to look for though is that the movement of the feet in that one dimension does not also require a movement of cleat / saddle / etc. This is what I was getting at about giving physiology priority over aerodynamics when making such changes. To simplify that comment a bit further so it doesnt get pointlessly disected all over again. All I am saying is:

"as with any change of cycling position, pay particular attention to ensure that the new position will not cause you injury in the future before committing to it. If the most 'aero' position is not achievable for you, move back until you get to the most aero position that will not cause injury."

 

[Ripper]

In almost all cases it is pretty easy to train to be narrower (or wider). the key things to look for though is that the movement of the feet in that one dimension does not also require a movement of cleat / saddle / etc. This is what I was getting at about giving physiology priority over aerodynamics when making such changes. To simplify that comment a bit further so it doesnt get pointlessly disected all over again. All I am saying is:

"as with any change of cycling position, pay particular attention to ensure that the new position will not cause you injury in the future before committing to it. If the most 'aero' position is not achievable for you, move back until you get to the most aero position that will not cause injury."

OK, so try to change one variable at a time. Move the cleats in a little, perhaps 2 mm, and see how that works. I can see a possible adjustment in saddle height might be necessary after, but one thing at a time. And do not push it with respect to pain.

 

[Martin318is]

OK, so try to change one variable at a time. Move the cleats in a little, perhaps 2 mm, and see how that works. I can see a possible adjustment in saddle height might be necessary after, but one thing at a time. And do not push it with respect to pain.

Personally, I'd go a step further and go to an experienced bike fitter and have them do an assessment and any adjustments for you. Unless you are trying something dramatic, you should be able to make most of the changes on the one day - if done correctly. Changing Q Factor is theoretically a minor change but it depends what your starting point is. In my own case, my position had seemed fine but on inspection I was already irritating the ITB. Any movement of my feet closer together would have made this worse.

 

[coapman]

Because both riders actually have their knees very close together (the lead rider just has massive quads).



Again, there are plenty of data showing that having your knees very close to the top tube leads to minimal drag. As well, there are data showing that the closer your feet are, the lower your drag (hence bikes w/ narrow b.b.s, e.g., GT SB-1 and SB-2, Walser, the special Trek TTX that was made for Armstrong
but ridden to an Olympic gold medal by Ekimov, etc.). You should therefore stop wasting everyone's time by pretending that this is not true.

You appear to be a person with all the answers, why is there no significant improvement in performance when longer cranks are used.

 

[Ripper]

Personally, I'd go a step further and go to an experienced bike fitter and have them do an assessment and any adjustments for you. Unless you are trying something dramatic, you should be able to make most of the changes on the one day - if done correctly. Changing Q Factor is theoretically a minor change but it depends what your starting point is. In my own case, my position had seemed fine but on inspection I was already irritating the ITB. Any movement of my feet closer together would have made this worse.

Thanks! The good news is my position has already been dialed in by an experienced fitter, with some minor tweeks made once I adapted, so I have a pretty decent baseline.

 

[acoggan]

why is there no significant improvement in performance when longer cranks are used.

You seem to be confused - performance clearly IS impaired when your cranks are too short (or too long). It is just that:

1) "too short" (or "too long") are well outside the range of what any experienced cyclist would consider normal, and

2) the reasons for the impairment have nothing to do with the mechanical leverage of the bicycle itself.

 

[FrankDay]

From the Project 96 tests I mentioned previously:

(Funny, I never noticed before that the figure was mis-labeled! Obviously the top line corresponds to the highest speed, not the lowest speed, and vice-versa.)

Wouldn't it be nice if we actually had all the details that led to this graph so it could be discussed. Just where is this study (my attempts to find it on google seem to fail)? What does "spacing" mean? What bike was tested? How on earth did they achieve spacing of 5 cm on a bike that could actually be ridden? What position was the rider in? Where was "spacing" measured?

Anyhow, let's assume you are correct, drag increases as the legs get wider and wider and wider. What is the mechanism that explains this phenomenon (after all, frontal area doesn't change)? And, how do you explain my findings in the wind tunnel, where drag remained essentially constant despite a "flatter back" and smaller overall frontal area as one shortened the cranks?

 

[FrankDay]

You seem to be confused - performance clearly IS impaired when your cranks are too short (or too long). It is just that:

1) "too short" (or "too long") are well outside the range of what any experienced cyclist would consider normal, and

2) the reasons for the impairment have nothing to do with the mechanical leverage of the bicycle itself.

1. Actually, performance (power) is affected by crank length as shown by Martin. Within a certain range this affect seems small but if one is truly interested in optimizing performance one should take this into account.

2. And, crank length also affects positioning on the bicycle which can affect both aerodynamics and comfort. Again, if one is truly interested in optimizing performance one needs to consider this affect also.

3. 1 and 2 can interact with each other making the determination of optimum even more difficult.

4. The fact that these issues remain unresolved after over 1300 posts (and close to 75,000 views) suggests it has not been well studied and that there is quite a bit of interest in this issue because it is evident that this area presents, at least, the potential for improvement over the status quo.

5. This thread would be much better served if you actually entered the discussion rather than seeming bent on making pronouncements on how stupid I am for even asking the question.

 

[coapman]

You seem to be confused - performance clearly IS impaired when your cranks are too short (or too long). It is just that:

1) "too short" (or "too long") are well outside the range of what any experienced cyclist would consider normal, and

2) the reasons for the impairment have nothing to do with the mechanical leverage of the bicycle itself.

I am referring to cranks in the 145 to 195 range.

 

[coapman]

Two year old's I have taught to ride a bike have a better instinct for pedalling than you do! And (to keep things on topic) they have the disadvantage of excessively long cranks relative to their leg lengths.

What would you say to a seven year old who after looking at a pedaling torque graph came to you and asked, Why after over 120 years of research can we still not apply any torque when the pedal is at the top (12 o'c) ?
As for that disadvantage, Frank's shorts PC cranks could give them a double advantage, suitable cranks and an opportunity to learn the objectives of circular pedaling.

 

[CoachFergie]

1. Actually, performance (power) is affected by crank length as shown by Martin. Within a certain range this affect seems small but if one is truly interested in optimizing performance one should take this into account.

2. And, crank length also affects positioning on the bicycle which can affect both aerodynamics and comfort. Again, if one is truly interested in optimizing performance one needs to consider this affect also.

3. 1 and 2 can interact with each other making the determination of optimum even more difficult.

4. The fact that these issues remain unresolved after over 1300 posts (and close to 75,000 views) suggests it has not been well studied and that there is quite a bit of interest in this issue because it is evident that this area presents, at least, the potential for improvement over the status quo.

5. This thread would be much better served if you actually entered the discussion rather than seeming bent on making pronouncements on how stupid I am for even asking the question.

Nice side step of all the data and effect size of ANY of theoretical benefits to changing crank length. Some people never learn or it just doesn't fit their marketing plan.

 

[acoggan]

What would you say to a seven year old who after looking at a pedaling torque graph came to you and asked, Why after over 120 years of research can we still not apply any torque when the pedal is at the top (12 o'c) ?

Because being really good at applying force to a bicycle pedal when it is as 12 o'clock does not provide you a reproductive advantage.

 

[acoggan]

Wouldn't it be nice if we actually had all the details that led to this graph

It would, wouldn't it?

Anyhow, let's assume you are correct, drag increases as the legs get wider and wider and wider.

Not an assumption: fact.

What is the mechanism that explains this phenomenon (after all, frontal area doesn't change)?

The likely answer to that question can be found by reading wind tunnel studies of flow around cylinders (both singly and in pairs).

And, how do you explain my findings in the wind tunnel, where drag remained essentially constant despite a "flatter back" and smaller overall frontal area as one shortened the cranks?

Your anecdotes don't concern me.

 

[FrankDay]

The likely answer to that question can be found by reading wind tunnel studies of flow around cylinders (both singly and in pairs).

Ah yes. That was exactly the point of Len Brownlie when we were discussing this issue at the wind-tunnel in explaining our findings at the time. This is what led me to ask the 'Q' question because, if one looks at those studies then one would naturally come to the conclusion that at some point, the cylinders would stop affecting each other and the drag would have to drop. Hence, the question, at what 'Q' does that start to occur? Perhaps you didn't understand what I had written on this before. Or, more likely, you didn't care.

Your anecdotes don't concern me.

Which is why you shouldn't be participating in these threads devoted to some of these anecdotes. Further, if your understanding of the science can't explain all of the observations being made then you shouldn't be here pretending that your understanding is complete and coming here criticizing those of us trying to discuss some of these more "off the wall" things.

 

[CoachFergie]

"off the wall" things.

I think you mean meaningless. Like Jim Martin suggesting the maximum benefit for only the tallest or shortest of rider changing from 170mm cranks was 0.5% which was 4sec in a 40km TT.

Small change when you consider the benefits of training, diet, recovery etc.

Perhaps Andy may care to share some of the findings from the wind tunnel he has built in his basement

 

[acoggan]

Ah yes. That was exactly the point of Len Brownlie when we were discussing this issue at the wind-tunnel in explaining our findings at the time. This is what led me to ask the 'Q' question because, if one looks at those studies then one would naturally come to the conclusion that at some point, the cylinders would stop affecting each other and the drag would have to drop.

You need to re-read those studies (assuming, of course, that you ever read them at all). The flow around paired cylinders is quite complex, depending upon their orientation with respect to each other, such that you can't automatically assume that increasing the distance between them will reduce drag. Moreover, since the bicycle is located between the legs, the *possibility* exists for interactions with it as well (although as the data I posted demonstrate, this does not seem to occur).

(Hmmm...I just remembered that Cervelo has also assessed the effects of reduced pedal stance width on aerodynamic drag, and commissioned Jim Martin to determine the effect on power. While I have not seen the data, clearly they were expecting/pursuing a reduction in drag, not an increase as you have hypothesized.)

Which is why you shouldn't be participating in these threads devoted to some of these anecdotes. Further, if your understanding of the science can't explain all of the observations being made then you shouldn't be here pretending that your understanding is complete and coming here criticizing those of us trying to discuss some of these more "off the wall" things.

Au contraire. If people like me didn't participate in threads you start, the world would be left completely misinformed.

(BTW, you'll note that I never claimed to be able to predict the aerodynamic behavior of a complex object such as a cyclist on a bicycle...only reported what others have repeatedly observed.)

 

[acoggan]

Perhaps Andy may care to share some of the findings from the wind tunnel he has built in his basement

Well, I can tell you that a Simkins Egg brake isn't as aerodynamic as most people seem to believe (apparently due - once again! - to the paired cylinder effect).

 

[CoachFergie]

Well, I can tell you that a Simkins Egg brake isn't as aerodynamic as most people seem to believe (apparently due - once again! - to the paired cylinder effect).

Nice, always good to discuss this with people who have spent more than just one session in a wind tunnel or have got off their backsides and read the wealth of research out there.

 

[coapman]

Because being really good at applying force to a bicycle pedal when it is as 12 o'clock does not provide you a reproductive advantage.

Please explain or could it be you are out of your depth here in the matter of applying constant max torque from 12 to 3.

 

[coapman]

Nice, always good to discuss this with people who have spent more than just one session in a wind tunnel or have got off their backsides and read the wealth of research out there.

As a person who has read all this research could you state the most important discovery that has resulted from it, or will you run for cover as you did with every other question I asked.

 

[CoachFergie]

As a person who has read all this research could you state the most important discovery that has resulted from it, or will you run for cover as you did with every other question I asked.

Aero is important.

Perhaps if you asked questions that had any relevance to form or fitness people would respond.

 

[acoggan]

Please explain

I thought my explanation was perfectly clear: the reason that things haven't changed is that, from an evolutionary perspective, humans haven't changed .

 

[acoggan]

Aero is important.

And, while individual differences clearly exist, general guiding principles (e.g., keep your legs close together) can still be stated, thus saving people from wasting a lot of time chasing uninformed speculations.

 

[CoachFergie]

And, while individual differences clearly exist, general guiding principles (e.g., keep your legs close together) can still be stated, thus saving people from wasting a lot of time chasing uninformed speculations.

Excellent advice. It's why when I go into the tunnel to test individuals I am guided by those general principles and the time is spent working on fine tuning.

It's also why I don't experiment with crank length as the research suggest's it's not worth the time. Especially when there are areas that provide far greater improvement (see reviews from Jeukendrup and Faria).