Cranks... do women need shorter ones? Huh?

[KenGS]

From that great authority Wiki
I'm no physiologist but I'd expect that shorter cranks have some benefit at the top and bottom of the stroke where the muscles can exert less force. Comparing 175mm and 165 mm cranks I guess if the average force over a 20mm shorter stroke is more than 6% higher then the shorter crank is beneficial.
But as pointed out that applies to both men and women.

[trailgumby]

My son's dually has 170mm cranks compared to my 175mm. I struggle to get on with it - it's definitely easier with the longer cranks when I need to grunt the bike over obstacles, and on steep climbs. That said, I'm apparently leggy for my height.

[Old and Rusty]

I can draw a comparison here, if you are doing leg press at the gym and move the seat too close to the foot pads you will work harder at the beginning of the lift due to the bend in your legs and you greaten the risk of popping a knee or other injury. As you push through the lift and the knee straightens your leverage is better and the lift easier. The same principle applies for compact cranks. My knees are shot and the most stressful part of the pedaling cycle is when my knees are bent the most, so much so that sometimes my foot lift generates more power than the 1st 1/3 of the push down. (best estimate without using measuring equipment). I am considering changing to a compact crank to give my knees a bit of relief.

In a nutshell compact cranks allow you to have your legs spend more time at the most powerful/economic part of extension as I understand it and with the change of gearing you may lose 6% or so of top gear speed.

[MiG]

What do compact gear ratios have to do with crank length? Can't you just shift down a gear, or are you already on the lowest gear?

[toolonglegs]

In a nutshell compact cranks allow you to have your legs spend more time at the most powerful/economic part of extension as I understand it and with the change of gearing you may lose 6% or so of top gear speed.

Compact Crank Sets are Normal Length cranks with a smaller BCD...so they run normally 50/34 or 50/36 instead of the standard 53/39.The crank length remains the same so they don't change anything a part from the gearing.

[Nobody]

...

In a nutshell compact cranks allow you to have your legs spend more time at the most powerful/economic part of extension as I understand it and with the change of gearing you may lose 6% or so of top gear speed.

By compact cranks I think you are referring to shorter cranks. Compact cranks by definition are ones with chainwheels of 34 and 50 tooth as opposed to the standard cranks of 39/53 tooth.

You probably understand this already but you were just a bit brief. You get 6% less leverage going from 175 to 165 (as I did) but you only lose the top speed if you reduce the gearing to match the lack of leverage. For now I have not reduced the gearing but decided instead to stand up more which I find is better for my knees anyway. I wouldn't miss the top end gearing much as I don't use it anyway on my road/commuter bike. By the time I get to that gearing, it is time to coast.

Edit: Beaten to it. I think he understands it guys, he is just mixing terms.

[Old and Rusty]

Sorry should have put more thought into it, I've been looking at shorter cranks with shorter crank gears and just got into the "compact" mindset. I think in 500km I would use top gear maybe 10 times at most and for maybe 200-300 metres each time so to lose a bit of top end wouldn't kill me. Keeping the 39/53 rings would defeat the purpose a fair degree IMO.

[Kalgrm]

I run 145mm cranks and noticed an improvement as soon as I switched to them.

those are freakishly short cranks, do you run those on your road bike or your recumbent?
I have heard you praise these before, I must say I am curious about just how they perform. I have never known anyone who rides with cranks that short so its very difficult to get an opinion. What cadence are you running on average.

Yes, they are on the 'bent. I don't have a road bike - I don't need one. If I could get a conventional frame (non-custom) which would allow short cranks, I might get one just for giggles. Cranks this short require a radical redesign of the tube lengths, so they won't become common place until a time-trialist makes it big on such a frame. My MTBs both have conventional cranks of 175mm.

A TT rider would be the best person to use this "radical thinking" because they want to stay seated as long as possible. Short cranks work best when staying in the seat, and they also help you stay in the seat because your knees/quads are already working mostly within to their optimal flexion range. Longer cranks not only work best when out of the saddle (where you can bring the knees/quads back into their optimal range), they also encourage getting out of the saddle for power application because it's harder to apply power whilst seated with long cranks.

The irony is that most people wouldn't consider short cranks because they feel they can only get power by standing on the pedals. If they had shorter cranks, they wouldn't need to stand on the pedals as often. Still, I'm well aware that these thoughts are not supported by much science, but my own experiences (sample size = 1) and numerous anecdotal stories from US 'bent riders tell me this is a real effect. There is a paper somewhere (I'll look for it soon) which supports the theory that the optimal length for cranks is 145mm, but it needs to be investigated much more thoroughly before it becomes accepted widely.

Regarding cadence: I usually run around 100-110 rpm, but I do so without any concious effort. Shorter cranks seem to drag your feet around quicker and 100rpm just feels natural. 130-140rpm is quite easy to reach when desired. It's these high cadences which allow power output to be maintained.

Cheers,
Graeme

(PS - many 'bent riders in the US run cranks as short as 110mm, though they are in the extreme. 130mm are more common, even used by blokes who are over 6'5")

[x8pg2qr]

Cranks... do women need shorter ones? Huh?

No. She’s better off after divorce.

[Parrott]

. Cranks this short require a radical redesign of the tube lengths, so they won't become common place until a time-trialist makes it big on such a frame. My MTBs both have conventional cranks of 175mm.

A TT rider would be the best person to use this "radical thinking" because they want to stay seated as long as possible. Short cranks work best when staying in the seat, and they also help you stay in the seat because your knees/quads are already working mostly within to their optimal flexion range. Longer cranks not only work best when out of the saddle (where you can bring the knees/quads back into their optimal range), they also encourage getting out of the saddle for power application because it's harder to apply power whilst seated with long cranks.

Sorry Graeme, I shut up for as long as I could . The fact that time trialists tend to use longer crank arms than on their road bike contradicts the above statements. Use of shorter crank arms isn't radical thinking. I'm sure the prorace teams with their million dollar+ budgets have thought of it, tied it and found it's not faster. Which is why they tend to use longer cranks.

PS one of our female club members recently one the open SA state TT championship at age 51 about 5'7" using 180mm cranks. She loves the longer cranks.

[rustguard]

Cranks... do women need shorter ones? Huh?

No. She’s better off after divorce.

rflmao

My MTBs both have conventional cranks of 175mm.

Thanks for the reply, I new you had a diamond frame of some sort, just couldnt remember, now that you mention it, you may have posted that report in a thread ages back.
A very informative answer, I cant reply other than to say I want to ride a bent. shame they are so expensive.

I'm sure the prorace teams with their million dollar+ budgets have thought of it, tied it and found it's not faster. Which is why they tend to use longer cranks.

I too am skeptical of short cranks on diamond frame bikes. but on a bent you dont have the option of standing on the pedals, so it sounds feasible that if you can get extra power by spinning up to 140crank rpm, you would benefit. kalgrim has made it sound very interesting, I must have a ride on a bent one day. Unfortunately my health has gone down hill the last year, so my rides have got progressively shorter.

age 51 about 5'7" using 180mm cranks. She loves the longer cranks.

I hope its not a recipe for knee reconstruction. Pushing big gears is not cool

[hartleymartin]

I've probably said it elsewhere, but I don't really notice all that much difference between the 165, 170, 172.5 or 175mm cranks that I have on various bicycles. If anything, I tend to favour the shorter ones, despite various crank-length calculators saying that I need 180 to 190mm cranks.

[s-s-a]

.

[brentono]

At the Serotta International Cycling Institute Science Symposium, Jim Martin, Ph.D.,
from the University of Utah presented his study of crank length...
Myth and Science in Cycling: Crank Length and Pedaling Technique - Jim Martin, PhD.
During this provocative presentation, Dr. Martin will discuss several position and equipment strategies
to improve cycling performance and whether there is any scientific evidence that they actually meet
the stated objective of going faster.

Jim Martin is a cycling enthusiast, a bicycle racer, holds a PhD in exercise science
and an undergrad degree in mechanical engineering.
He's a professor at the University of Utah and is as august an academic on the subject of crank length,
as anyone.

http://www.plan2peak.com/files/32_article_JMartinCrankLengthPedalingTechnique.pdf
There are many of Dr. Jim Martin's technical papers on the net, "Google" it.
Have discussed it here...
viewtopic.php?f=39&t=24170&p=429196#p428912
Cheers,
BrentonO

[Ruby]

I too had thought it was height related...and perhaps frame size related? I ride a 44cm frame and have 165mm cranks. When having the bike fit (not by the LBS but by a great physio that does bike fits) nothing to the contrary was raised about crank length.

I must ask a gf who has the same model of bike but in a more adult size what length her cranks are....

WSD is over rated but brilliant marketing. My challenge is finding a frame that fits that doesn't have 650 wheels. I don't want to buy into the marketing but don't feel as though I have a lot of choice.

[Riddley]

I thought it was not so much the length of the cranks, but the circumference.

[Nobody]

I thought it was not so much the length of the cranks, but the circumference.

The crank length or radius and circumference are directly related.