The crank length thread

[CoachFergie]

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[sittingbison]

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Correctomundo

 

[FrankDay]

Correctomundo

Not sure what was so "spammy" about my report on a crank length experiment result (this is a crank length thread afterall) other than I mentioned the product that can't be named and some here, apparently, didn't like the report. So, I will simply report the data reported to me and make a short observation.

Triathlete used to riding in aero position at 250 watts with crank length 172.5 reports immediate improvement to 290 watts on trying 160 mm for same hr/effort.

This amount of improvement is the most I have ever heard of and is certainly not what I would have expected although I think the benefits of going shorter are larger when in the aero position and, as this report suggests, and can be quite substantial.

 

[sciguy]

Not sure what was so "spammy" about my report on a crank length experiment result (this is a crank length thread afterall) other than I mentioned the product that can't be named and some here, apparently, didn't like the report. So, I will simply report the data reported to me and make a short observation.

Triathlete used to riding in aero position at 250 watts with crank length 172.5 reports immediate improvement to 290 watts on trying 160 mm for same hr/effort.

This amount of improvement is the most I have ever heard of and is certainly not what I would have expected although I think the benefits of going shorter are larger when in the aero position and, as this report suggests, and can be quite substantial.

Hmmmmmm seems like a classic case of " If it sounds too good to be true it probably is".

Interestingly, my dear wife just switched from 170mm cranks to 155s a couple of weeks ago and low and behold her power is exactly the same.

Hugh

 

[CoachFergie]

Hmmmmmm seems like a classic case of " If it sounds too good to be true it probably is".

Interestingly, my dear wife just switched from 170mm cranks to 155s a couple of weeks ago and low and behold her power is exactly the same.

Hugh

Yes, the folly of one off reports.

Best to stick to the best form of evidence one can lay their hands on.

Thankfully Jim Martin and his group have provided us with some excellent data in that regard.

http://www.plan2peak.com/files/32_article_JMartinCrankLengthPedalingTechnique.pdf

 

[FrankDay]

Hmmmmmm seems like a classic case of " If it sounds too good to be true it probably is".

Interestingly, my dear wife just switched from 170mm cranks to 155s a couple of weeks ago and low and behold her power is exactly the same.

Hugh

Two questions.

What position was she in when she tested? If she did this testing in the aero position would you have considered her more "aero" with the shorter cranks (if her seat was raised 15mm her drop should have increased 15 mm)?

Anyhow, the point is I recommend that people do the testing for themselves rather than rely upon what others tell them should happen.

 

[sciguy]

Two questions.

What position was she in when she tested? If she did this testing in the aero position would you have considered her more "aero" with the shorter cranks (if her seat was raised 15mm her drop should have increased 15 mm)?

Her back was already essentially horizontal with the 170s so we raised the bars the same amount as the seat. Her hip angle opened noticeably but power is still the same at least out to an hour duration. Perhaps her two or three hour power with be influenced or run off the bike. Since she trains with power it will be easy to see.
Over what work duration did the fellow see a 16% instant improvement?

Hugh

 

[FrankDay]

Her back was already essentially horizontal with the 170s so we raised the bars the same amount as the seat. Her hip angle opened noticeably but power is still the same at least out to an hour duration. Perhaps her two or three hour power with be influenced or run off the bike. Since she trains with power it will be easy to see.
Over what work duration did the fellow see a 16% instant improvement?

Hugh

Essentially horizontal isn't the same as horizontal so there might be something to still be gained (especially if she is as "essentially horizontal" as most of the top women pros at Kona as compared to the top men) as the women's positions, on average, are awful compared to the men's, on average. My sense this is due to crank length being too long for most of these women preventing them from getting flat while maintaining good power. Might be worth another look. Don't know the duration of his test. I asked him to gather some more information at different lengths so some more information and time should lead to more definitive data. One ride hardly is definitive. All I can say is he was totally incredulous, not believing such a change was possible.

Edit: I might add that I don't look at the back but, rather, the chest as being horizontal as being the important metric to look at as it is the chest being up that will scoop in the air and increase the frontal area and drag. What the back looks like can be deceiving depending upon how "arched" it is.

 

[sciguy]

Essentially horizontal isn't the same as horizontal so there might be something to still be gained (especially if she is as "essentially horizontal" as most of the top women pros at Kona as compared to the top men) as the women's positions, on average, are awful compared to the men's, on average. My sense this is due to crank length being too long for most of these women preventing them from getting flat while maintaining good power. Might be worth another look. Don't know the duration of his test. I asked him to gather some more information at different lengths so some more information and time should lead to more definitive data. One ride hardly is definitive. All I can say is he was totally incredulous, not believing such a change was possible.

Edit: I might add that I don't look at the back but, rather, the chest as being horizontal as being the important metric to look at as it is the chest being up that will scoop in the air and increase the frontal area and drag. What the back looks like can be deceiving depending upon how "arched" it is.

Her position is similar to that of Julie Dibens. An more rotated forward makes the view up the road too hard since she doesn't have eyes in the top of her head.

 

[FrankDay]

Her position is similar to that of Julie Dibens. An more rotated forward makes the view up the road too hard since she doesn't have eyes in the top of her head.

It would be better if that were more of a side view but I see there is a lot to be gained there. Her "back is flat" for about 12 inches then it bends down to the pelvis. But, look at her front. Her shoulders are substantially above her pelvis such that she is scooping in quite a bit of air to reach the body. Further, her head is sticking way up above her shoulders, adding to her frontal area. I liken that position as looking more like a parachute than an arrow. Her only saving grace that might minimize that affect is she actually has boobs that tend to direct air away from the torso. So, it might be ok. However, her head is up so high I think if she stays like that she could really benefit from an aero helmet. She isn't as bad as amanda Stevens (her back is "flat" also)

but not nearly as good as Michelle Vesterby, IMHO

Of course, only way to know for sure would be to do the testing.

 

[Polyarmour]

A 40W increase for shorter cranks, no refs, no explanation given, sample size of 1? I'll run with the Martin study on that one thanks.

I must admit however I find the aero argument a slightly compelling one.
If I read Martin right he supports the idea too?

And yes I understand that aero positions can be obtained by tweaking other variables. But crank length is not a bad one. Why aren't more people doing it? What's the catch?

 

[CoachFergie]

Already aero enough. Can only get the head so low without causing neck issues. Some aero issues are caused by inflexibility or my excuse, a beer gut.

 

[FrankDay]

A 40W increase for shorter cranks, no refs, no explanation given, sample size of 1? I'll run with the Martin study on that one thanks.

Of course, the Martin study wasn't done with riders in the aero position. And, even though the difference wasn't statistically significant, the highest power was seen at 145mm crank length.

I must admit however I find the aero argument a slightly compelling one.
If I read Martin right he supports the idea too?

Yes, he does.

And yes I understand that aero positions can be obtained by tweaking other variables. But crank length is not a bad one. Why aren't more people doing it? What's the catch?

We only touch the bike at 3 points. Crank length determines both seat height and (depending on flexibility) handlebar height.

 

[FrankDay]

Already aero enough. Can only get the head so low without causing neck issues. Some aero issues are caused by inflexibility or my excuse, a beer gut.

Ah yes, the good enough argument. Anything to avoid the hard work to get better.

Anyhow, lots of riders are able to get lower without issues. What sets them apart? Why wouldn't you get lower if you could without losing any power? How do you know what you can or cannot do without trying?

 

[Tapeworm]

We only touch the bike at 3 points.

?? I count five.

 

[FrankDay]

?? I count five.

I guess it is all how one looks at it. If you look at how people describe bike fits you will see them mention only two, saddle height and handlebar position - crank length (and it's effects on foot position) is ignored even though the foot position at the bottom of the stroke determines saddle height in most systems as the foot position at the top of the stroke determines handlebar height. Since most of us are symmetrical the fit on the left side of the bike usually isn't different than the fit on the right so I think it reasonable to describe us touching the bike at 3 points. So, in describing a bike set up, you can use 5 points, I will use 3, while the rest of the world seems to use only two.

 

[FrankDay]

I contacted the researcher who is going to study this issue to see how it is going. He indicated he will be starting data collection in two weeks. Maybe we will have something more than anecdotal reports soon to "discuss".

 

[coapman]

It would be better if that were more of a side view but I see there is a lot to be gained there. Her "back is flat" for about 12 inches then it bends down to the pelvis. But, look at her front. Her shoulders are substantially above her pelvis such that she is scooping in quite a bit of air to reach the body. Further, her head is sticking way up above her shoulders, adding to her frontal area. I liken that position as looking more like a parachute than an arrow. Her only saving grace that might minimize that affect is she actually has boobs that tend to direct air away from the torso. So, it might be ok. However, her head is up so high I think if she stays like that she could really benefit from an aero helmet. She isn't as bad as amanda Stevens (her back is "flat" also)

but not nearly as good as Michelle Vesterby, IMHO

Of course, only way to know for sure would be to do the testing.

Could number 119 use PC's in that forward position and what percentage of her upper bodyweight is on those elbow rests. Does an extreme forward position shorten your effective downstroke.

 

[FrankDay]

Could number 119 use PC's in that forward position

Yes

and what percentage of her upper bodyweight is on those elbow rests.

Don't know

Does an extreme forward position shorten your effective downstroke.

Don't know but doubt it.

 

[Swampy1970]

Yes, the folly of one off reports.

Best to stick to the best form of evidence one can lay their hands on.

Thankfully Jim Martin and his group have provided us with some excellent data in that regard.

http://www.plan2peak.com/files/32_article_JMartinCrankLengthPedalingTechnique.pdf

You should try and read the article that you link and put it into context for once Fergie dear chap.

From Kona to sub Kilo effort in one link - you go boy! I see nothing has changed over the years.

The only position that I find effects my ability to hit ~1,000W is sitting straight upright and not holding on the bars. Elbows bent and nose somewhere close to the stem even. Ask me to ride like that for any length of time (ie > 30 seconds) and the position and my flexibility, or lack thereof, has a big effect on what power I can maintain. I could definitely see a gain in power possible for someone switching to shorter cranks if they were at the point where they were attempting to get lower than they were truly able to ride in on 'regular' cranks.

 

[Swampy1970]

Could number 119 use PC's in that forward position and what percentage of her upper bodyweight is on those elbow rests. Does an extreme forward position shorten your effective downstroke.

If she could ride PC's in that position I'd be in awe.

As for effective downstroke, I'm not sure if it really changes but after a few months you tend to forget the upstroke and spend more time relaxing and smashing the downstroke - at least I did. It feels like you start pushing earlier and longer but without data it's just that - feels.

 

[CoachFergie]

You should try and read the article that you link and put it into context for once Fergie dear chap.

From Kona to sub Kilo effort in one link - you go boy! I see nothing has changed over the years.

Power Output and Pedal Speed account for 98% of the varaibility in metabolic cost in this group of 9 cyclists. 99% of the variablity for each individual

Of the remaining 2% variability, crank length and pedaling rate each accounted for 1% or 0.02% of total

Ask me to ride like that for any length of time (ie > 30 seconds) and the position and my flexibility, or lack thereof, has a big effect on what power I can maintain. I could definitely see a gain in power possible for someone switching to shorter cranks if they were at the point where they were attempting to get lower than they were truly able to ride in on 'regular' cranks.

Or you could stretch more and save some $. And in my state I could eat less and save $$$.

Not sure if I mentioned it on CyclingForums but all I had to do to drop my handlebars 4cm without losing the beer gut was tilt my saddle up a little which allowed me to rotate the pelvis forward. I would be looking at options like that before changing cranks length and all the other necessary equipment changes that may necessitate.

 

[sciguy]

From Sam Gyde

I thought this was interesting feedback from Powercranker Sam Gyde over on the Slowtwitch forum.

"I have been experimenting with lengths ranging from 130-180.
In short my findings - which are very personal:
- any length between 155-175 is fine for me (in terms of long term power output)
- shorter than 155 is a bit hard on steep hills (unless I adjust gearing which I didn't)
- 130-155 still is ok in terms of power output but it affected my flexibility (I should say inflexibility) and some tendons in the groin area from pulling to actively during races

Some sidenotes:
- I have very tall legs (95cm inseam), so for me, a 175 crank feels not too long
- shortening cranks means increasing saddle height which is already high in my 175 setting. This poses problems with TT frame geometries and seatposts that usualy can't accomodate this height
- my steep position with short cranks (130) made the transition from bike to run tough for me (my core muscles cramped up) in the races I used short cranks.
- there seems to be no aerodynamic benefit riding short cranks (we thought there was)

My preference:
- I think I would prefer 160 but only if a frame had a BB drop of 85mm instead of 70mm. Such frames don't exist.

Conclusion:
- It is interesting to experiment with different cranklengths
- Better a crank a bit too short than too long
- You can change cranklength, seat height, handlebar setup but unfortunately, the position of the bottom brancket is fixed and I would prefer that to be lower when riding shorter cranks.

As I said, these are my personal experiences and I am sure there are lots of people that don't agree or have experienced other setups that work better for them. You have to find a balance between position, aerodynamics and power output and the determination of your optimum cranklength is for sure an important factor.

Hope this helps
Sam
samgyde.com "

 

[FrankDay]

I thought this was interesting feedback from Powercranker Sam Gyde over on the Slowtwitch forum.

"I have been experimenting with lengths ranging from 130-180.
In short my findings - which are very personal:
- any length between 155-175 is fine for me (in terms of long term power output)
- shorter than 155 is a bit hard on steep hills (unless I adjust gearing which I didn't)
- 130-155 still is ok in terms of power output but it affected my flexibility (I should say inflexibility) and some tendons in the groin area from pulling to actively during races

Some sidenotes:
- I have very tall legs (95cm inseam), so for me, a 175 crank feels not too long
- shortening cranks means increasing saddle height which is already high in my 175 setting. This poses problems with TT frame geometries and seatposts that usualy can't accomodate this height
- my steep position with short cranks (130) made the transition from bike to run tough for me (my core muscles cramped up) in the races I used short cranks.
- there seems to be no aerodynamic benefit riding short cranks (we thought there was)

My preference:
- I think I would prefer 160 but only if a frame had a BB drop of 85mm instead of 70mm. Such frames don't exist.

Conclusion:
- It is interesting to experiment with different cranklengths
- Better a crank a bit too short than too long
- You can change cranklength, seat height, handlebar setup but unfortunately, the position of the bottom brancket is fixed and I would prefer that to be lower when riding shorter cranks.

As I said, these are my personal experiences and I am sure there are lots of people that don't agree or have experienced other setups that work better for them. You have to find a balance between position, aerodynamics and power output and the determination of your optimum cranklength is for sure an important factor.

Hope this helps
Sam
samgyde.com "

A couple of comments.

His experience isn't my (or others) experience. I believe everyone should find out for themselves. Sam saw no power change with different crank lengths and, apparently, his starting position was good enough that there was little aerodynamic benefit to be gained. The power no-change isn't the experience of the cyclist who just called me with his report. And, the vast majority of cyclists have room for huge improvements in aerodynamic positioning. Of course, one never knows what will happen to them until they try this stuff for themselves.

I am not sure what his concern regarding BB height is. I suppose it would be better if the BB were lower on a road bike with short cranks (it would lower everything a bit and wind speed increases with height above the ground) but I don't see the CG changing much with this change since the front end usually gets lowered as much as the saddle gets raised making CG changes pretty much a wash.

Going very short may involve getting special seat posts to accommodate the change, especially in bikes with special aerodynamic seat posts with minimal adjustment capability (I had to get a special long seat post on my commuter bike when I experimented with crank lengths less than 110mm). They are available. That seems a minimal obstruction if failing to make the change prevents a substantial improvement. Why people want to let the bike manufacturers determine how good they can be by simply accepting what came with their bike makes no sense to me but people do (a lot of them hang out here). But, Sam didn't need it.

As I found when I went to the wind tunnel, shorter cranks seem to increase the drag of the leg component of the total drag. If one is in a very good torso position it seems any improvements seen there from going shorter are countered by an increase in the leg component. Therefore, the benefits one might see, if any, depends upon their current position and what happens to power and drag when they make the change. One cannot know this without trying it for themselves. Sam tried this experiment for himself. You (and everyone) should too.

Anyhow, I agree with his conclusions that it is interesting to experiment and that too short is better than too long. I don't understand his concern regarding the BB.

 

[FrankDay]

If she could ride PC's in that position I'd be in awe.

Well, of course, it would depend upon whether she had trained herself to do so and whether her crank length was such that she could do so for 5 hours or so. Shorter cranks facilitate being able to be able to ride in and sustain such a position, especially in those of us who do not have the flexibility of circus contortionists.