The importance of crank length to the cyclist.

[blutto]

I am also very appreciative that this thread has actually turned into a discussion instead of the usual vindictive and unthinking personal attacks. Hopefully those that are new to the thread don't try to slog through the entire thing and skip posts 100-1100 or so.

...have to agree..the discussion over the last little while, whether it has been right or wrong, scientifically correct or not, has been fun, real fun...thanks to all....

...the absence of a certain whiney screechy static has done wonders it seems...

...carry on, this has been great....finally...

Cheers

blutto

 

[blutto]

Testing is good.


I can't believe I got sucked into this interminable thread.

...for the record here is a definition of interminable...

in·ter·mi·na·ble ( n-tûr m -n -b l). adj. 1. Being or seeming to be without an end; endless. See Synonyms at continual. 2. Tiresomely long; tedious

...now if are meaning the first part of the definition...fine... getting perfomance out of a bike rider is in fact an endless task...and that is part of the fun we are having here...so if that is the case welcome aboard and we hope you can bring your considerable experience to bear of this issue that we find interesting...

...if it is the second part of the definition....well...you can probably find better things to do than deign to bless us with you presence and literally insult us guys who are genuinely interested in this with your last line...

...bottom line I really really hope you meant the former because your input would be really appreciated....and heck, we even have Dr Coggan peaking in here and with all this firepower( including you here) we might have a great discussion that may yield some results...

Cheers

blutto

 

[Boeing]

Hmmm.. I would imagine that given aerodynamics is meaningless in that context, there would be much more bias towards whether having long cranks helps or hinders balance and control.. I'd guess longer cranks help...

cirque du soleil dudes use stubbies and rotor rings and a freewheel with mad engagement clipped in. ringling Bros straight up platform pedals, fixed and kinda long. Has something to do with the clown shoes

 

[coapman]

To say he wouldn't have to fight the cranks to get them over the top ignores the fact that it takes energy to push them over the top if one cannot do it themselves, the point of PowerCranks.

Frank, could you explain what you mean in above sentence.

 

[Night Rider]

Here are the images in the order they were tested. The forum restricts me to 4 images at a time so there will be another post to complete the series

First, 180 mm cranks with road helmet.

Next, 180 mm cranks with aero helmet.

Thanks for sharing the information, Frank.

My observations for what they are worth are;

I'm going to come back to my point a week or so ago. Results were going to be dependent on the starting position and I think you could have gained more by starting with a 'conventional' set up. That is 172.5mm conventional cranks and a legal UCI position (not semi-superman). I also think your rider was a bit low.

The range of cranks you tested was skewed in favour of small. If you had started with 172.5mm you could have had a comparison of larger 180mm cranks and several smaller sizes that you tested. I think that would have been beneficial.

I agree completely with what the other posters have said about maintaining saddle to bar drop, that has been mentioned right from the start of this thread iirc.

Lastly, if anything at all be taken out of these results it's shape is more important than getting your back side up as close to parallel with your head as possible. That backs up real world TT positions you see successful riders using.

Is there going to be a Version 2 test?

 

[FrankDay]

To say he wouldn't have to fight the cranks to get them over the top ignores the fact that it takes energy to push them over the top if one cannot do it themselves, the point of PowerCranks.

Frank, could you explain what you mean in above sentence.

It has to do with what is going on during pedaling. To get the foot from BDC to TDC with 170 mm cranks means the foot must be raised about 14 inches. such raising also involves putting potential energy into the leg. That energy has to come from somewhere. Now, when in the aero position unclip and see if you can raise the foot 14 inches above the BDC position 90 times a minute for an hour. 180 mm cranks means Mike even had to lift about 15 inches. He simply could not do it. Now, he would have been able to do it on regular cranks because he can divert energy from the downward moving leg to put in the necessary potential energy in the upward moving leg that it cannot do itself. The problem with this, of course, is it robs him of power. Or, he could have done it if he had not been so low in front. It is why I made the comment that this position was unridable, at least for Mike.

So, in summary, it takes X amount of energy to get each leg from the bottom to the top of the stroke each revolution. If it isn't provided by the muscles of the rising leg then it must be provided by the muscles of the pushing leg. Rather than using pushing energy to, in part, raise the opposite leg, that energy would be more useful if it all went to move the bicycle forward.

 

[FrankDay]

Thanks for sharing the information, Frank.

My observations for what they are worth are;

I'm going to come back to my point a week or so ago. Results were going to be dependent on the starting position and I think you could have gained more by starting with a 'conventional' set up. That is 172.5mm conventional cranks and a legal UCI position (not semi-superman). I also think your rider was a bit low.

I concur pretty much with this comment. My only difference would be that I am not sure I would have gotten more. The results would have looked differently but I am not sure it would have been better.

The range of cranks you tested was skewed in favour of small. If you had started with 172.5mm you could have had a comparison of larger 180mm cranks and several smaller sizes that you tested. I think that would have been beneficial.

It was the recommendation of Len, the consultant, that we make big changes, to save time.

I agree completely with what the other posters have said about maintaining saddle to bar drop, that has been mentioned right from the start of this thread iirc.

As I have said before, if one was doing a study that would be a reasonable approach. If I were doing a study I would now raise the handlebars as I shortened the cranks which would give me the differences due to the leg component. Then, I would repeat the test, changing the seat to handlebar drop while keeping the crank length constant. This would give me the torso component. Then, I would repeat to see if the combined changes that come from shortening the cranks and lowering the bars (or keeping them constant) can be predicted from the two separate components. This would be the most useful information to know, but it isn't going to be obtained in 2 hours

Lastly, if anything at all be taken out of these results it's shape is more important than getting your back side up as close to parallel with your head as possible. That backs up real world TT positions you see successful riders using.

It is clear that flat is probably close to being optimal. It is not clear to me that this data "proves" this is best.

Is there going to be a Version 2 test?

Perhaps. This did raise some other questions for me. If I do I will stay in a narrower range doing something similar to what I mentioned above. And, one other thing I would be interested in knowing is whether the apparent increased drag of the legs when on short cranks can be lowered any by increasing the distance between the legs.

 

[TarmacExpert]

So, in summary, it takes X amount of energy to get each leg from the bottom to the top of the stroke each revolution. If it isn't provided by the muscles of the rising leg then it must be provided by the muscles of the pushing leg. Rather than using pushing energy to, in part, raise the opposite leg, that energy would be more useful if it all went to move the bicycle forward.

This is true but you get the work back on the downstroke. I.e. you lift the leg on the upstroke, giving it potential energy. You can then let the leg drop back on the downstroke, getting exactly the same work back. It's no problem for one leg to be losing potential energy at the same rate as the other leg is gaining potential energy, transferring it from one to the other. The height moved through each revolution doesn't affect this. What WOULD have an impact is if there is some sort of internal resistance in the body to overcome that means the rider is having to do a disproportionate amount of work up in the top few cm of the pedal stroke, as this work would be lost rather than stored to be re-used on the downstroke. My first turbo session last night after changing from 165mm to 175mm didn't appear to show any loss of power.

 

[FrankDay]

This is true but you get the work back on the downstroke. I.e. you lift the leg on the upstroke, giving it potential energy. You can then let the leg drop back on the downstroke, getting exactly the same work back. It's no problem for one leg to be losing potential energy at the same rate as the other leg is gaining potential energy, transferring it from one to the other. The height moved through each revolution doesn't affect this. What WOULD have an impact is if there is some sort of internal resistance in the body to overcome that means the rider is having to do a disproportionate amount of work up in the top few cm of the pedal stroke, as this work would be lost rather than stored to be re-used on the downstroke. My first turbo session last night after changing from 165mm to 175mm didn't appear to show any loss of power.

Of course you get the work back on the down stroke but you get exactly the same amount of work back regardless of how the leg got to the top. Therefore, if you wasted energy meant to be used in driving the bike in order to get that leg over the top then efficiency and power will go down from what it could have been. So, while it is true you do get it back it is not true that it doesn't make a difference. Do you really believe it would make no difference to a rider from a power perspective if he had a condition that allowed him to push as hard as normally but could not unweight at all on the upstroke, i.e., all the potential energy to get the leg up comes from the pushing leg? The more energy that is diverted from the drive train to accomplish this task the more it hurts the ability to maximize power.

Further, all those diagrams showing pedaling forces are usually misinterpreted because they include the forces that come from gravity that is recovering that potential energy. But, they are interpreted as all the drive comes from muscular pushing when a great portion of those "pushing" forces is coming from work that was done on the upstroke. (Edit: And they are further interpreted that because the forces are small on the backstroke that what the upstroke muscles are contributing to driving the bicycle is small and can be ignored. Both of these interpretations are wrong.)

Oh, and there might be an internal resistance to this motion also, if the body is bent over so far and the range of motion is so large that soft tissue interference takes place. Put yourself on your bike in the tourist position and unclip one leg and see if you have much trouble getting the foot to TDC. I'll bet it goes pretty easily. Now put yourself in the aero position and try again. Tell me, is it just as easy to do? Can you even do it at all without some help from a friend pushing it as high as it needs to go? Why not, when it was so easy to do this sitting up? Circus contortionists would probably be able to do this but most of us cannot. Something has to explain why people lose power when they get too low.

 

[coapman]

It has to do with what is going on during pedaling. To get the foot from BDC to TDC with 170 mm cranks means the foot must be raised about 14 inches. such raising also involves putting potential energy into the leg. That energy has to come from somewhere. Now, when in the aero position unclip and see if you can raise the foot 14 inches above the BDC position 90 times a minute for an hour. 180 mm cranks means Mike even had to lift about 15 inches. He simply could not do it. Now, he would have been able to do it on regular cranks because he can divert energy from the downward moving leg to put in the necessary potential energy in the upward moving leg that it cannot do itself. The problem with this, of course, is it robs him of power. Or, he could have done it if he had not been so low in front. It is why I made the comment that this position was unridable, at least for Mike.

So, in summary, it takes X amount of energy to get each leg from the bottom to the top of the stroke each revolution. If it isn't provided by the muscles of the rising leg then it must be provided by the muscles of the pushing leg. Rather than using pushing energy to, in part, raise the opposite leg, that energy would be more useful if it all went to move the bicycle forward.

I thought we were only supposed to be referring to getting that rising foot up and over the 12 o'c mark. As I see it, the PC'er is using the circular style which makes it very difficult to get an independent crank up and over the top. This should not arise if you were an unweighting masher. He does not have to worry about losing any torque from his downstroke and the momentum of his downward foot/pedal from about 5 o'c can be used to drive the other rising foot up and over 12 o'c instead of going to ground and increasing rolling resistance.

 

[TarmacExpert]

Put yourself on your bike in the tourist position and unclip one leg and see if you have much trouble getting the foot to TDC. I'll bet it goes pretty easily. Now put yourself in the aero position and try again. Tell me, is it just as easy to do? Can you even do it at all without some help from a friend pushing it as high as it needs to go?

FWIW I tried single leg pedalling in today's session, in the TT position (12.5cm saddle to pad drop) with 175mm cranks, and it was no problem. I have a feeling that part of this is down to the fact that I train every day on the turbo, always in the TT position, and I think this has enhanced my ability to move my leg through that part of the pedal stroke. I suppose it's partly like training with PowerCranks in that respect, obviously nowhere near as extreme.

Does Mike do all his training in the TT position? If not, I'd guess that 6 months of training every day in the position he considered unrideable may well make it rideable.

 

[FrankDay]

FWIW I tried single leg pedalling in today's session, in the TT position (12.5cm saddle to pad drop) with 175mm cranks, and it was no problem. I have a feeling that part of this is down to the fact that I train every day on the turbo, always in the TT position, and I think this has enhanced my ability to move my leg through that part of the pedal stroke. I suppose it's partly like training with PowerCranks in that respect, obviously nowhere near as extreme.

Well, my guess is you are an outlier. Few have both an excellent position and the ability to pedal one legged "no problem". Even fewer train exclusively in the TT position indoors. Two anecdotes along this line might interest you. First is Courtney Ogden, a pro triathlete for about 10 years who was able to win his first IM after switching to 145 mm cranks and a lower front end. He believes the new, lower, position is saving him about 15 minutes on the bike. Second, is Sam Gyde, a Belgian triathlete, who trains somewhat similarly to you, almost exclusively indoors and in the TT position. About two years ago he went exclusively to training on PowerCranks (he got on them mostly to aid his run, being already a strong cyclists) and last year he won his age-group at IM World Championships, having taken about 40 minutes off his previous time with a sub-3 run and sub 9 overall, as I remember. This year after experimenting he has shortened his cranks to 135mm which has allowed him to lower his front end an additional 10 cm. He will be a good test to see if such a change gives any additional racing advantage. His first big test will be Eagleman in July.

Does Mike do all his training in the TT position? If not, I'd guess that 6 months of training every day in the position he considered unrideable may well make it rideable.

I doubt Mike does much training in TT position since he spent almost all winter racing cyclocross. While he probably could train himself to ride those longer cranks it is not clear to me that he could do so without losing substantial power.

 

[CoachFergie]

Well, my guess is you are an outlier.

Maybe your n=1 was the outlier. This is why real research uses a large group of subjects.

Few have both an excellent position and the ability to pedal one legged "no problem". Even fewer train exclusively in the TT position indoors. Two anecdotes along this line might interest you. First is Courtney Ogden, a pro triathlete for about 10 years who was able to win his first IM after switching to 145 mm cranks and a lower front end. He believes the new, lower, position is saving him about 15 minutes on the bike. Second, is Sam Gyde, a Belgian triathlete, who trains somewhat similarly to you, almost exclusively indoors and in the TT position. About two years ago he went exclusively to training on PowerCranks (he got on them mostly to aid his run, being already a strong cyclists) and last year he won his age-group at IM World Championships, having taken about 40 minutes off his previous time with a sub-3 run and sub 9 overall, as I remember. This year after experimenting he has shortened his cranks to 135mm which has allowed him to lower his front end an additional 10 cm. He will be a good test to see if such a change gives any additional racing advantage. His first big test will be Eagleman in July.

Again these anecdotes are meaningless unless you can compare them, and preferably a large group, against a control group or a test the athlete in a conventional set up. Many athletes get results in spite of their position, equipment, training, diet etc.

 

[FrankDay]

Sam Gyde just wrote about his first real test on shorter cranks here.

… Anyway, since a few months I ride these ridiculously short (although Frank still thinks they are too long) cranks. And I like them! At first I thought I would have to change gearing or pedal a much higher cadence to attain the same power output because of the smaller leverage of those cranks. This is not true: for some reason I manage to generate the same power output with the same gearing and almost the same cadence. I think the reason for this is the more efficient angles of your joints when the cranks are in the best position to generate power which is in the upper quarter of the pedal movement.
So I was quite confident that riding short cranks wouldn't affect my bike performance (from a biomechanical point of view) too much. If there really were aerodynamic benefits I expected to gain some extra speed from going short.
This weekend was the first real life test during a long distance duathlon in France. The bikeleg was 85km long on a rolling course and there was a terrible wind and part of the course was a quite heavy traffic area. Despite all this I manged an average speed of 38.5 km/h which was much faster than I'd anticipated at this early stage in the season and this gives me confidence that going short really might have some real benefits! Next real life test is scheduled on June 10th at Eagleman 70.3. To be continued!

Since my time in the wind-tunnel I will no longer be pushing him to continue to try even shorter.

 

[CoachFergie]

Since my time in the wind-tunnel I will no longer be pushing him to continue to try even shorter.

Based off a n=1?

Whenever I am in the wind tunnel I apply the results to that person only.

 

[CoachFergie]

Highly amusing that you started this thread asking us to experiment with short cranks because one guy rode an event an hour or so faster a year later going the opposite (shorter) direction using shorter cranks.

And now you are saying it depends because of one person in the wind tunnel doing limited testing.

"The day the science died"!

 

[FrankDay]

Found these two pictures that I hope will work. First, Sam's position with 130 mm cranks.

Second, what he looked like in the race (pink socks to draw attention to the short cranks, he says)

Note that he was able to sustain that speed with a road helmet. And, as you can see from this last photo he did this race on PowerCranks, a second change that might be accounting for his performance other than the short cranks. Anyhow, I continue to be surprised that not a single other person has made a comment on my observation that my data suggests that aero helmets seem to be of less benefit the lower one is in front.

 

[Martin318is]

Anyhow, I continue to be surprised that not a single other person has made a comment on my observation that my data suggests that aero helmets seem to be of less benefit the lower one is in front.

Oh, I noticed that - and i assume others did too - but that is clearly a topic for a seperate thread.

 

[FrankDay]

Oh, I noticed that - and i assume others did too - but that is clearly a topic for a seperate thread.

It would seem reasonable to discuss it here since the data is here (and, quite a few people seem to be following this thread) or, I guess, YOU could start another thread if you are interested in the topic by itself. Where is that thread?
Otherwise, it seems typical of most cycling discussion threads, people would prefer to just let things die that don't agree with their bias.

 

[FrankDay]

I thought we were only supposed to be referring to getting that rising foot up and over the 12 o'c mark. As I see it, the PC'er is using the circular style which makes it very difficult to get an independent crank up and over the top. This should not arise if you were an unweighting masher. He does not have to worry about losing any torque from his downstroke and the momentum of his downward foot/pedal from about 5 o'c can be used to drive the other rising foot up and over 12 o'c instead of going to ground and increasing rolling resistance.

Huh? PowerCrankers use whatever style they feel works best for them be it "circular" (as you call it) or "unweighted masher" (as you call it), whatever each of those really are. Either works well with the PC's as long as there is no negative force anywhere on the circle.

 

[CoachFergie]

Anyhow, I continue to be surprised that not a single other person has made a comment on my observation that my data suggests that aero helmets seem to be of less benefit the lower one is in front.

Some of us have tested enough subjects to know that the results are very individual.

 

[Martin318is]

It would seem reasonable to discuss it here since the data is here (and, quite a few people seem to be following this thread) or, I guess, YOU could start another thread if you are interested in the topic by itself. Where is that thread?
Otherwise, it seems typical of most cycling discussion threads, people would prefer to just let things die that don't agree with their bias.

Frank, you are making up ghosts again.
Lack of interest, lethargy, etc is not equal to bias. Frankly I dont care either way as I dont ride time trials (we've covered this point more than once so lets just move on). This is why I have not bothered to create YOUR thread for you.

No, it is NOT reasonable to discuss the topic here - what does a helmet have to do with the optimal length of cranks for a cyclist?

CN a discussion forum. One of their wonderous features is that if you wish to discuss two topics at the same time you can do so in seperate conversations taht dont cloud each other. people are not discussing helmets here because if they do come to this thread it is due to their interest in the crank length discussion. Likewise, they have not started talking about shoe covers or the wearing of watches in any detail either.

Build the thread and they will come.

 

[FrankDay]

Frank, you are making up ghosts again.
Lack of interest, lethargy, etc is not equal to bias. Frankly I dont care either way as I dont ride time trials (we've covered this point more than once so lets just move on). This is why I have not bothered to create YOUR thread for you.

In posting my data I said I drew two major conclusions from the data. One had to do with short cranks and the second had to do with the fact it appeared aero helmets offered little benefit once the rider was pretty low in front. Now there are some pretty serious time-trialists who hang out here (apparently you are not one of them) and I find it pretty amazing that not one of them has even bother to post that they disagree with me on that point (or that this data is well known amongst serious time trialists or anything else). What seems like a pretty interesting data point has simply been ignored.

No, it is NOT reasonable to discuss the topic here - what does a helmet have to do with the optimal length of cranks for a cyclist?

Sure it is reasonable. Sometimes threads evolve. But, it hasn't. So, I guess I will have to start a separate thread on this point so I can see what others think or know about this.

Build the thread and they will come.

We will see.

 

[sciguy]

I And, one other thing I would be interested in knowing is whether the apparent increased drag of the legs when on short cranks can be lowered any by increasing the distance between the legs.

Frank,

When you say "increasing the distance between the legs", do you mean by increasing the "Q" factor? I wonder if the test bike had been equipped with an aero seat tube if there might have been a significant difference in drag. The problem is those darn cylindrical legs are terrible in terms of their individual aerodynamics.

YMMV,

Hugh

 

[sciguy]

something to keep this thread alive a little (or lot) longer. Today I sent in a deposit to reserve some wind-tunnel time in mid-April to test the ideas in my paper and more.

I have an athlete who has been experimenting with different crank lengths and has tested himself the last 3 weekends at 145, 125, and 105 mm. He tells me he tested best at 105 but I don't have all the data yet. And, his coach wants to repeat the testing to be sure (and I want him to test even shorter since he apparently hasn't gone beyond his max yet). He has agreed to be the subject for these tests. With him we should be able to get a good sense of the effects of crank length on both aerodynamics and power and be able to then make some predictions as to the effect on speed. This should be fun for everyone who has an interest in this (or almost everyone anyhow).

Frank,

Could you tell us what Mike meant by "test best at 105"? Was it power and if so for what duration of test?

Thanks,

Hugh