People with shorter legs - what crank arm length do you use?

livb

Hi,

I'm 5'3'' with 28'' legs and am thinking about changing my crank arm length. I think personally with my current 170 crank arms I'm struggling to keep my pedal stroke as smooth as it could be due to the angle of my knee at the top of the pedal stroke.

So I was wondering if anyone else with shorter legs uses shorter crank arms? Do you find them better? And how is best to go about trying different ones/ choosing without spending too much?

From research currently I am being suggested 155-160 may be best for me ... obviously they are not exactly easy to find at that length!

Thanks

markhewitt1978

I'm 5'6" and take 29" trousers. I used to run 170mm because that's what my bike came with and I didn't know anything other.

I switched to 165mm and I've found it much nicer to use, feels like a more natural length and my cadence is where I want it to be.

The formula did suggest 160mm for me, but 165mm is the shortest commonly available length so I got that.

It's not a cheap thing to change unless you can sell your old cranks on.

lesfirth

I have 29 inside leg. On one bike I have 165 cranks and on two other bikes I have 170 cranks. I can not feel any difference. However, I often read on this forum and elsewhere that " these wheels roll better, this frame is stiffer,these wheels are harsh, etc." and I can not tell any difference so it could be me who is a bit thick.

StillGoing

I have 165mm on the main bike and 170mm on the other. I much prefer the 165mm for the added room they give at the top of the stroke.

paul_onabike

Me 5'8 and 29'' inside leg -
Road 165mm - that is really on the top limit for me. Anything longer and I get back, knee and hot foot problems.
For TT I use 160mm - I can get a good aero position with these, and I don't loose any power output when down on the aero bars. My cadence increases by approx 5 rpm to compensate for the shorter length.
If you need 155 it is possible to modfiy certain cranks to this.

https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwicrY-_yO3KAhVBuxQKHb6VAYoQjBAIKzAD&url=http%3A%2F%2Fhighpath.co.uk%2Fcrank-shortening%2F&usg=AFQjCNHVtVx22_1wxkYECKPgFf4y4tEhUQ

My advice would be get the correct length - not something that is near enough. Too many bikes come with wrong sized cranks for their frame size - its cheaper for manufacturers, not better for customers

markyone

5ft 7, 29inch inside leg and 172,5 cranks

MisterMuncher

5'9", 29" Inside leg and flat, flat feet. 172.5 on the everyday bike, 170 on the best.

Minor differences in pedal stack even it out to about 1mm difference.

lesfirth

MisterMuncher wrote:

5'9", 29" Inside leg and flat, flat feet. 172.5 on the everyday bike, 170 on the best.

Minor differences in pedal stack even it out to about 1mm difference.

Pedal stack makes no difference to the vertical distance your foot moves each rotation and therefore the amount your knee has to bend. Please correct me if I am wrong.

simon_masterson

I have long legs, but I use 170mm - fixed and road. My geared TT bike has 172.5 because they were on eBay at a good price, and I do have a 175 set I used on the road for a little bit as well. It is ludicrous that the availability of 180mm cranks is better than <170mm - imagine if the shops only offered shoes sized 9 and above and trousers with 31" leg and above - but there are a few options, and you can buy 180mm cranks and have them shortened.

ddraver

Sorry Simon but most shops I go to rarely offer trousers shorter than 32"

I'm 173 cm and was recommended 172.5mm by the Trek Precision Fit system which I though was long but they do seem to be fine for me. I use 175 on the MTB. I guess I'm a 30" inside leg

livb

Thanks, for all the response so far. Has anyone actually had their cranks shortened? Has it been useful, or more importantly has anyone regretted it? Has it affected your road racing/TT performance?

Do they asses crank arm length during bike fits?

markhewitt1978

livb wrote:

Do they asses crank arm length during bike fits?

I was told two opinions on that. The first traditional type fit I had the guy was insistent that crank length was irrelevant to the the fit and everything else. Not sure I bought that really.

The second guy I saw after I'd already gone from 170 to 165 said that the majority of the time he doesn't consider crank length, or rather he only ever fits according to the existing crank length just because it's an expensive change. But he did say that for my fit going to the shorter cranks was the correct choice.

Bobbinogs

I have posted it before but I think this article is a very good one that covers crank arm length:
http://bikedynamics.co.uk/FitGuidecranks.htm

ddraver

livb wrote:

Thanks, for all the response so far. Has anyone actually had their cranks shortened? Has it been useful, or more importantly has anyone regretted it? Has it affected your road racing/TT performance?

Do they asses crank arm length during bike fits?

The trouble with assessing it during a bike fit is that, as mark says, its a very expensive change and the second you change it it throws all the rest of the stuff out...

With regard to performance I don't think it's going to make a huge difference it's just a personal preference thing. If you re a spinner you ll probably like a shorter crank, if you mash you ll probably like a longer crank. Although we all judge riders on their smoothness it actually makes very little difference - see Thomas Voeckler

I suppose that if you re doing the Trans Continental or PBP that it might be the sort of thing to get right however so it's worth thinking about if you re replacing a crank anyway

markhewitt1978

https://www.youtube.com/watch?v=vUygkHlcVMQ GCN did a video about this recently.

simon_masterson

livb wrote:

Thanks, for all the response so far. Has anyone actually had their cranks shortened? Has it been useful, or more importantly has anyone regretted it? Has it affected your road racing/TT performance?

Do they asses crank arm length during bike fits?

Assuming that you are comfortable and not experiencing any pain, power output varies very little between crank lengths - or so Phil Burt says (IIRC), and he should know. Some pros do seem to be adopting short cranks.

In terms of TT performance, an alternative angle would be that since lowering your body to the top tube can lower drag, it's better to use the longest cranks and the lowest stack height pedals (i.e. Speedplay) you can.

ddraver

^^..that has made me wonder if the cause of some of my back issues on the MTB could be due to having longer cranks...

Simon....or the opposite, as shorter cranks will let you get lower. There was a thread about that on here a while back

ugo.santalucia

shorter legs = longer penis
shorter legs = looks good on a horse back

I'll take my coat

StillGoing

It isn't any differences or lack of in power with crank arm lengths, but more how soon you can get to the power stroke in the rotation. With crank arms that are too long, with the saddle height set correctly, you have a choice of over stretching at the bottom of the stroke, or of being compressed at the top. With a shorter crank arm, you can have the correct leg extension at the bottom of the stroke and have more room at the top of the stroke to be able to get over the top and onto the power stroke.

Someone will be along in a moment and go on about it being mm differences so has no effect. But let's say with 172.5mm cranks your seat height is set at 900mm from seat top to centre of the crank spider. Changing to 165mm length crank arms means your seat height can be increased to 907.5mm. Add the shorter crank length at the top and you gain leg clearance at the top of 15mm. You might be surprised how much difference that 10 or 15mm difference makes to your comfort and fatigue and allows you to spin faster.

MikeBrew

lesfirth wrote:

MisterMuncher wrote:

5'9", 29" Inside leg and flat, flat feet. 172.5 on the everyday bike, 170 on the best.

Minor differences in pedal stack even it out to about 1mm difference.

Pedal stack makes no difference to the vertical distance your foot moves each rotation and therefore the amount your knee has to bend. Please correct me if I am wrong.

Assuming saddle height is adjusted to compensate for changes in stack. If you increase stack without increasing saddle height then it's going to affect hip and knee angles ; especially in the top half of he stroke.

MikeBrew

ugo.santalucia wrote:

shorter legs = longer penis
shorter legs = looks good on a horse back

I'll take my coat

So are you saying John Wayne was hung like a squirrel and looked rubbish on a horse ? My coat's the one next to yours, could you grab it too please.....

simon_masterson

ddraver wrote:

Simon....or the opposite, as shorter cranks will let you get lower. There was a thread about that on here a while back

Yes, that's the other possibility. Xavier Disley advocates Speedplays because of this, but I would think that it depends on the rest of the setup as to whether you're better off being lower to the ground or lower to the front of the bike. I have long legs and a short torso, so a frame with the right top tube length will tend to give me a fairly big drop at the front anyway.

livb

Ok I think I'm going to try 165 as a first step...that won't entirely break the bank. I can always go shorter and sell it on if it doesn't feel short enough

N0bodyOfTheGoat

My Wazoo came with 175mm cranks and had have diddy legs for someone ~5'10" at ~30.5".

My knees giving me a little niggle could partly be explained by the extra effort of 10cm wide tyres but also, I set the saddle up to be the same height as my Felt, forgetting it has 172mm cranks IIRC. If anything, I want the saddle a bit higher on the Wazoo, even if is only for when I'm on-road.