The crank length thread

[FrankDay]

53-11 is indeed a big if in this scenario.

Don't you think it depends on the circumstances. 53-11 is indeed "big" if one is putting out 100 watts and going uphill (or, even on the flat). It is not so big if one is putting out 400 watts and going downhill (or, even on the flat).

 

[FrankDay]

Another anecdotal report from the Slowtwitch forum

from the above thread. Those anecdotes just keep piling up. Good thing they are just anecdotes so it is easy, for those so inclined, to ignore them.

what was your progression like down to 155mm?

Not the OP, but I dropped 22mm and there was basically no time needed to adapt... they felt better right away and no power loss. I do most riding on the road bike with long cranks and switching back and forth isn't a problem. Might not be ideal though. But the way I look at it is everything is so *different* in the aero position anyway... having the same crank length doesn't make it the same.

 

[CoachFergie]

Read the article but more importantly read the many comments...

http://www.slowtwitch.com/Tech/Crank_Length_and_Gearing_4095.html

Particularly amusing...

Devashish Paul · University of Ottawa
Frank Day You know I put those powercranks on 150 mm a while back and really hated it. I did all the saddle height, fore aft changes etc, and never really liked it. It literally felt like speed skating standing up instead of getting low and engaging my glutes more actively at the top of the pedal stroke. I suppose I need to get my torso even lower, to close up the hip angle, but with my neck injuries, that's not fun either!!!

 

[FrankDay]

Read the article but more importantly read the many comments...

http://www.slowtwitch.com/Tech/Crank_Length_and_Gearing_4095.html

Particularly amusing...

Devashish Paul · University of Ottawa
Frank Day You know I put those powercranks on 150 mm a while back and really hated it. I did all the saddle height, fore aft changes etc, and never really liked it. It literally felt like speed skating standing up instead of getting low and engaging my glutes more actively at the top of the pedal stroke. I suppose I need to get my torso even lower, to close up the hip angle, but with my neck injuries, that's not fun either!!!

You found Dev's comments funny haha or funny curious? You do know he has some serious neurological issues from a bike crash he is trying to recover from (and is using the PC's to aid his rehab) don't you? And, at least he has tried to go shorter and then gives everyone another anecdotal report. Anecdotes and Martin. That is about all we have to help us decide. Sorry the science isn't more definitive on this subject. Sometimes life is just that way.

BTW, I found that article to be one of the dumbest things I have ever seen on SlowTwitch. First, the author got something very major very wrong then he went on about keeping the gearing the same by changing the front chain rings. Why not just shift a cog in back unless one needs more gearing at the extremes?

 

[Captain Serious]

I've got a 2-bit theory, but I can't remember if I've put it on here before or not.

Film a rider while they're riding hard off the saddle, measure the knee angle at the start of the application of down-force on the pedal, then adjust the saddle height and/or crank length from that.

Whadda yooz reckon?
I reckon it's a fair idea

 

[FrankDay]

I've got a 2-bit theory, but I can't remember if I've put it on here before or not.

Film a rider while they're riding hard off the saddle, measure the knee angle at the start of the application of down-force on the pedal, then adjust the saddle height and/or crank length from that.

Whadda yooz reckon?
I reckon it's a fair idea

OK

1. How do you know from a video where the rider starts application of the down force?

2. How would you use this data to adjust the saddle or determine correct crank length?

 

[CoachFergie]

I've got a 2-bit theory, but I can't remember if I've put it on here before or not.

Film a rider while they're riding hard off the saddle, measure the knee angle at the start of the application of down-force on the pedal, then adjust the saddle height and/or crank length from that.

Whadda yooz reckon?
I reckon it's a fair idea

Have heard of using the knee angle out of the saddle to adjust the knee angle in the saddle. How would you factor crank length into it?

 

[Captain Serious]

OK

1. How do you know from a video where the rider starts application of the down force?
?

High-speed, close-up camera to detect quad contraction?

Hey, I haven't worked out all the bugs yet.


Gimme something, come on!! It's still a good idea, and I bet you guys are working out how to apply it right now

 

[CoachFergie]

High-speed, close-up camera to detect quad contraction?

Hey, I haven't worked out all the bugs yet.


Gimme something, come on!! It's still a good idea, and I bet you guys are working out how to apply it right now

http://www.posetech.com/

Uses knee angle out of the saddle to determine knee angle in the saddle. Still not sure how you get a crank length from that.

One study on the technique suggests that changes in application in power around the pedal stroke occur but this does not led to improvements in efficiency. Hmmmm sounds familiar.

http://www.ncbi.nlm.nih.gov/pubmed/21127899

 

[CoachFergie]

http://www.youtube.com/watch?v=5M8OkK9i1Xk

This outlines the POSE method of bike set up. This is part of a bigger scheme of things covering several sports and surprise surprise a certification programme to become an instructor.

We see this quite a bit from various individuals making various claims that, surprise surprise, link back to a product or service they market but with very little evidence to support them or to even provide a physiological or mechanical basis for their claims.

So they resort to posting anecdotal claims which ignore the majority who don't use a product, service, technique and make similar, often better, improvements.

The NWA wrote a song about it!

 

[FrankDay]

Another anecdote from ST crank length article

Frank Day fiddled a bit in the last month and ended up with 165mm (down from 175 on my tri bike). Still collecting data but power output appears to be up about 3% and, most importantly, I can run faster off of the bike. Hip angle is huge. IIRC mine opened up from ~15 degrees to ~25 degrees. BTW: damn [product that shant be named] are hard!

 

[FrankDay]

Another anecdote from the ST article (FB comment)

I have fitted custom 155 mm cranks to my tri bike ,,165 to my rd ,,wattage much the same ,comfort improved and cadence a few rpm higher ...Have found the cadence "performance window" is smaller so gear choices may need to be changed or just diving for a lower gear a little sooner in order to keep cadence at an optimum rpm "as indicated by h/rate and wattage/powertap" Only done approx 1,000 km on the 155 ,,if any want to know progress,, most welcome to pm me...safe riding

 

[coapman]

Another anecdote from the ST article (FB comment)[/QUOTE


While perched on the front of his saddle, in what direction is a TT rider applying the pedal force at 1 o'c or when does he start applying effective crank torque.

 

[FrankDay]

Another anecdote from the ST article (FB comment)[/QUOTE


While perched on the front of his saddle, in what direction is a TT rider applying the pedal force at 1 o'c or when does he start applying effective crank torque.

This will vary from rider to rider depending upon the pedaling style they are using and how much power they are generating. It probably is affected by crank length also. Anyhow, it is not possible to answer this question without measuring those forces in any individual.

 

[FrankDay]

Here is an interesting study that looks at cadence but I am including it in this thread because changing cadence also changes pedal speed so one could, presumably, get the same result by changing crank length since Martin found pedal speed more important than crank length as a variable in this regards, as I remember. Changing cadence from 100 to 80 reduces pedal speed 20%. Changing crank length from 175 to 140 reduces pedal speed 20%. Someone needs to repeat this study using crank length as the variable. The link gets you the entire study.

Stebbins: EFFECTS OF CADENCE ON AEROBIC CAPACITY FOLLOWING A PROLONGED, VARIED INTENSITY CYCLING TRIAL

Abstract
We determined if high cadences, during a prolonged cycling
protocol with varying intensities (similar to race situations)
decrease performance compared to cycling at a lower, more
energetically optimal, cadence. Eight healthy, competitive male
road cyclists (35 ± 2 yr) cycled for 180 min at either 80 or 100
rpm (randomized) with varying intensities of power outputs
corresponding to 50, 65 and 80% of VO2max. At the end of this
cycling period, participants completed a ramped exercise test to
exhaustion at their preferred cadence (90 ± 7 rpm). There were
no cadence differences in blood glucose, respiratory exchange
ratio or rate of perceived exertion. Heart Rate, VO2 and blood
lactate were higher at 100 rpm vs. 80 rpm. The total energy cost
while cycling during the 65% and 80% VO2max intervals at 100
rpm (15.2 ± 2.7 and 19.1 ± 2.5 kcal·min-1, respectively) were
higher than at 80 rpm (14.3 ± 2.7 and 18.3± 2.2 kcal·min-1,
respectively) (p < 0.05). Gross efficiency was higher at 80 rpm
vs. 100 rpm during both the 65% (22.8 ± 1.0 vs. 21.3 ± 4.5%)
and the 80% (23.1 vs. 22.1 ± 0.9%) exercise intensities (P<
0.05). Maximal power during the performance test (362 ± 38
watts) was greater at 80 rpm than 100 rpm (327 ± 27 watts) (p <
0.05). Findings suggest that in conditions simulating those seen
during prolonged competitive cycling, higher cadences (i.e., 100
vs. 80 rpm) are less efficient, resulting in greater energy expenditure
and reduced peak power output during maximal performance.

 

[FrankDay]

Here is an interesting study that looks at cadence but I am including it in this thread because changing cadence also changes pedal speed so one could, presumably, get the same result by changing crank length since Martin found pedal speed more important than crank length as a variable in this regards, as I remember. Changing cadence from 100 to 80 reduces pedal speed 20%. Changing crank length from 175 to 140 reduces pedal speed 20%. Someone needs to repeat this study using crank length as the variable. The link gets you the entire study.

Stebbins: EFFECTS OF CADENCE ON AEROBIC CAPACITY FOLLOWING A PROLONGED, VARIED INTENSITY CYCLING TRIAL

As I have been thinking about it this study really supports the position I am coming to. That is that the reason cyclists tend to ride at higher cadences than is energetically optimal is because we are wired for running and our most efficient running cadence for long distances is normally between 90-100. Therefore, such cadences feel "right" to us. But, the crank lengths we currently ride are such that pedal speed at that cadence is too high for optimum muscle functioning. So, it feels right but it isn't best. Therefore, it seems to me that optimum performance would come at a crank length where a pedaling cadence of 90 (or so) achieves optimum pedal speed for efficient power generation. In the above study, to achieve the same pedal speed seen after dropping from a cadence of 100 to 80 (a 20% drop) and keeping the cadence 100 would require going from a crank length of 175 to 140mm. If we wanted to ride at a cadence of 90 with the same pedal speed we would need to use a crank length of 155.

Someone really needs to do this work.

 

[coapman]

As I have been thinking about it this study really supports the position I am coming to. That is that the reason cyclists tend to ride at higher cadences than is energetically optimal is because we are wired for running and our most efficient running cadence for long distances is normally between 90-100. Therefore, such cadences feel "right" to us. But, the crank lengths we currently ride are such that pedal speed at that cadence is too high for optimum muscle functioning. So, it feels right but it isn't best. Therefore, it seems to me that optimum performance would come at a crank length where a pedaling cadence of 90 (or so) achieves optimum pedal speed for efficient power generation. In the above study, to achieve the same pedal speed seen after dropping from a cadence of 100 to 80 (a 20% drop) and keeping the cadence 100 would require going from a crank length of 175 to 140mm. If we wanted to ride at a cadence of 90 with the same pedal speed we would need to use a crank length of 155.

Someone really needs to do this work.

While crank length is considered another form of gearing, the crank is also the source of the power that can be generated and for this reason I believe a rider should use the longest crank with which he is comfortable.

 

[CoachFergie]

While crank length is considered another form of gearing, the crank is also the source of the power that can be generated and for this reason I believe a rider should use the longest crank with which he is comfortable.

Is a crank a source of power in the same way a that a SRM is meant to improve performance?

 

[sittingbison]

now now Hamish, lets not go there please.

same conditions apply on this thread as powermeter and everywhere else.

cheers
bison

 

[CoachFergie]

now now Hamish, lets not go there please.

same conditions apply on this thread as powermeter and everywhere else.

cheers
bison

No probs.

Can Noel explain how a crank is a source of power?

 

[coapman]

No probs.

Can Noel explain how a crank is a source of power?

In cycling the crank is a vital part of the power generating system and all generated chain drive power must from the crank to the chain ring.

 

[CoachFergie]

In cycling the crank is a vital part of the power generating system and all generated chain drive power must from the crank to the chain ring.

How does a piece of metal generate power?

 

[sittingbison]

grrrrrrrrr......not happy jan

can it

bison

 

[coapman]

How does a piece of metal generate power?

Thanks for that.

 

[CoachFergie]

Thanks for side stepping the question.