Pro's and cons of shorter crank arms?

natsnoz

Im a 5ft 8" with short 29" legs. Would a shorter crank help or hinder me? At the mo i have a 172.5 chainset.
What are the characteristics of shorter or longer crank arms?

thescouselander

I'm not sure what will be best for you but I'm convinced crank arm length makes a difference. I went from 172.5 crank arms to 175 when I changed bikes earlier in the year and this made a significant difference that I cant put down to anything else.

What I have found is that I'm able to spin higher gears and although the effective gear should be the same I can keep up a higher speed which consistently knocked off 1 minute from my journey to work.

All I can suggest it to try and find a bike with the crank arm length you think might work best and give it a go.

Bobbinogs

I am not convinced that increments of 2.5mm makt that much difference, but that is not me saying I don't believe those who do. The idea is shorter cranks help cadence, longer cranks help power but we are talking about the extremes.

Here is a useful paper on the subject:

http://bikedynamics.co.uk/FitGuidecranks.htm

Nowt wrong with a little experimentation although bear in mind that the saddle height will need to change too.

thegreatdivide

I'm 5' 7.5" with a 29" inside leg and post bike fit I use a 170mm crank.

MichaelW

Before talking about "short" or "long" you have to establish your "normal" which will be different to someone else's normal (much as your shoe size will differ).
I suspect that 172.5 is a bit long for your legs but it depends on the length of your upper leg rather than the whole length..

Given a normal crank, then going longer will make you pedal at slower revs in a higher gear and a shorter crank means pedalling faster in a lower gear. It wont alter your power output or speed but may help your endurance.

Short cranks provide better ground clearance for fixie riders and reduce toe clip overlap.

Changing by 2.5mm provides marginal improvements unless you are already at or beyond the range of a properly fitting crank.

fast as fupp

ive got 170 on one of my bikes-172.5 on another and 175 on the third

cant tell the difference

Evil Laugh

I swapped my 172.5 to 175 and was horrible. Stretched my thigh muscles all wrong, couldn't get comfortable spinning. Dunno my leg length but 178 tall, 76 saddle height, fitter reckons I'm borderline 170/172.5. Back to 172.5 now, much better. Made quite a difference to me, that 2.5mm.

cougie

I can't tell the difference between crank lengths. I used longer ones when they were in vogue but when one cracked I rode for a few weeks with one shorter crank. Didn't make any difference then either.

thegreatdivide

Interesting article (and links) on crank length http://www.cptips.com/crnklth.htm

jgsi

Evil Laugh wrote:

I swapped my 172.5 to 175 and was horrible. Stretched my thigh muscles all wrong, couldn't get comfortable spinning. Dunno my leg length but 178 tall, 76 saddle height, fitter reckons I'm borderline 170/172.5. Back to 172.5 now, much better. Made quite a difference to me, that 2.5mm.

oh dear, stay away from Spin bikes then, they have ridiculous short 160 cranks

indjke

I'm 5'8" and spent 2 seasons on MTB and old road bike with 175 mm cranks both.

recently bought my new roadie and it have been equipped with 170mm cranks. With the first turn I felt more comfortable, dunno how to describe it exactly.. maybe "more concentrated" spin.

When I return to MTB w/ 175 mm it seems like I do noticeably more "wasted movements", and do not so fluent circle pedalling.. I loved 170 mm with the first glance)

Gazzaputt

I have 170mm on one bike and 172.5mm on the other.

Yes there is a slight noticeable difference but adjusting the seat height to compensate alleviated this.

natsnoz

thegreatdivide wrote:

Interesting article (and links) on crank length http://www.cptips.com/crnklth.htm

Fantastic reading, thanks for all the responses. Looks like a shorter crank for short ass me!

stevie63

I'm 5 foot 7 and have a 30" inside leg and I swapped from 172.5 to 165 last year. Seems to work for me.

Anonymous

5'6" use 170mm tried 165mm and didn't notice any difference at all. If I had come from 172.5mm or bigger I may have done but 5mm was neither here nor there for me

StillGoing

Maglia Rosa wrote:

5'6" use 170mm tried 165mm and didn't notice any difference at all. If I had come from 172.5mm or bigger I may have done but 5mm was neither here nor there for me

Maybe it has but you're not appreciating how it has made a difference. I moved down from 172.5mm to 165mm for my main bike and 170mm on the second around 2012. I can tell the difference. I use a high cadence on my main bike (90-100rpm plus) which is comfortable on the 165mm especially when keeping a high rpm going up hills. On the 170mm it's harder to maintain for long periods due to the bigger size of the full pedal stroke. The shorter crank arms are also less stress on my knees and lower back.

cycleclinic

I am a shade over 6ft a 35" inside leg i have 165mm crank 170mm 175mm and 177.5mm cant tell the difference either. Seat height is affected though. Shorter cranks can help a bit if pedalling through tight turns. Had bit of pedal strike in the last race. 165mm cranks may have helped a bit.

amrushton

Your feet are turning smaller circles using smaller cranks (pi x d) so in effect a smaller lever, higher cadence but your seat height goes up. Both Wiggins and Cavendish use 170mm cranks and those 2 are a few inches different in height.

Giraffoto

It's probably better to have too short than too long - children's bikes and smaller adults' bikes often make the mistake of having them too long though.

fenix

amrushton wrote:

Both Wiggins and Cavendish use 170mm cranks and those 2 are a few inches different in height.

7 inches difference apparently. Not sure what their leg lengths are like though. Bet Sky have all the data though...

Anonymous

philthy3 wrote:

Maglia Rosa wrote:

5'6" use 170mm tried 165mm and didn't notice any difference at all. If I had come from 172.5mm or bigger I may have done but 5mm was neither here nor there for me

Maybe it has but you're not appreciating how it has made a difference. I moved down from 172.5mm to 165mm for my main bike and 170mm on the second around 2012. I can tell the difference. I use a high cadence on my main bike (90-100rpm plus) which is comfortable on the 165mm especially when keeping a high rpm going up hills. On the 170mm it's harder to maintain for long periods due to the bigger size of the full pedal stroke. The shorter crank arms are also less stress on my knees and lower back.

No. It made zero difference for me. My times didn't change. My power output didn't really change. Climbing wasn't really effected. I also average around 95rpm and can spin just as comfortably on 170mm some people may find a difference somewhere. Same way some swear by oval chainrings. For me it there was no change so I stayed on 170mm as I had more chainsets that length that cost more.

mallorcajeff

Ive always ridden 172.5. My last bike i put together i could only get a 170mm chainset so bought it and coukdnt tell the difference. Sold that bike and just got new one and bought a used chainset for it, didnt say in the advert it was 175.00 but i did 110 miles two days ago on it and i cant tell the difference.

Inutero

https://www.youtube.com/watch?v=eMAxH_Ud8YE

StillGoing

Inutero wrote:

https://www.youtube.com/watch?v=eMAxH_Ud8YE

For every video out there that says crank length does or doesn't matter, there is one stating the exact opposite. Some people are more sensitive to difference than others in much the same way a good motorcycle racer will know in a blindfold test whether the suspension has been raised or lowered a few mm or the tyres have been changed for different widths and profiles. Bad ones will have to look. Some cycle riders grind, some spin. If you spin, shorter crank arms help.

the_chief15

Due to a manufacturer packaging error I was running a 172.5 RH crank and a 170 on the left, never noticed the difference.

lesfirth

thecycleclinic wrote:

I am a shade over 6ft a 35" inside leg i have 165mm crank 170mm 175mm and 177.5mm cant tell the difference either. Seat height is affected though. Shorter cranks can help a bit if pedalling through tight turns. Had bit of pedal strike in the last race. 165mm cranks may have helped a bit.

I have some FSA Gossamer 165 cranks. The pedal hole is a long way from the end of the crank. I think they use the same cranks for all the different crank lengths and just alter where they drill the holes.

ajmitchell

the_chief15 wrote:

Due to a manufacturer packaging error I was running a 172.5 RH crank and a 170 on the left, never noticed the difference.

wow thats startling and worrying.

ajmitchell

Inutero wrote:

https://www.youtube.com/watch?v=eMAxH_Ud8YE

That GCN video is not good on several levels. I prefer this one, much more balanced https://www.youtube.com/watch?v=Yl90KFqDW-Y

Giraffoto

the_chief15 wrote:

Due to a manufacturer packaging error I was running a 172.5 RH crank and a 170 on the left, never noticed the difference.

Obviously your legs are different lengths, you should stick with it.

ravey1981

I call BS on anyone who says they can tell the difference between a 170 and a 172.5 etc. Its 2.5mm, If I came and raised your seat by 2.5mm without you knowing you would never, ever know. If they only made two lengths with about 15mm difference, one for shorties and one for the longer legged person then I could understand it. I've got different lengths on all my bikes pretty much because either they were cheap at the time or its what the bike came with.

DeVlaeminck

Well I reckon I can tell the difference - I'm not saying it's huge but I feel marginally more cramped up with the longer cranks. That said I'm not about to start getting people to swop in different length cranks on my bike just to prove whether I'm right or not.