Crank arm lengths

[Monsieur Remings]

Am just about to order a new bike where, given the Shimano Tiagra option I've taken, is either 170 or 175. I'm currently on 172.5 which is a SRAM on my summer bike.

I have an inside leg of just under 32' and am 5'10.

Which one would you go for and why...and does it make a major difference?

 

[mcshroom]

Are you a natural spinner or grinder? Shorter cranks are supposedly easier to spin with. I have the same measurements and use a 170mm crank (well two actually surprisingly enough ) but that's just what my bikes have always had so I don't know if 175mm would be any better.

I doubt you'd notice 2.5mm either way too much really though.

 

[black'n'yellow]

My suggestion would be to order whatever size you are using at the moment (assuming you are ok using that size at the moment). If you are going to be switching between bikes, then commonality is good. In practice, there's probably not a lot of difference, but anything you can do to minimise potential bike fit issues has to be a good thing...

 

[slowmotion]

Monsieur, type "crank length" or "crank arm" into the Search box of YouTube and quite a lot comes up. Here's someone who says shorter is better.
[media]

]View: http://www.youtube.com/watch?v=HFxBg7BnFlQ[/media]

 

[black'n'yellow]

Here's someone who says shorter is better.

In other words - "here's a youtube video with lots of graphs, but no actual science to support it"

 

[slowmotion]

Quite possible.

 

[PpPete]

Changed from 170 to 175 a while ago
175 being surely more suitable for me at 6'2" and 35" inside leg.
Did I notice the difference?
No.

 

[Arsen Gere]

I looked in to this and could find no evidence to say one way or the other. I found one paper http://www.springerlink.com/content/va0wx2ke5qv05edt/ that says 170mm cranks don't compromise power output.

Sheldon Brown on the matter http://sheldonbrown.com/cranks.html

Here is a stab at a formula for crank length http://www.nettally.com/palmk/crankset.html

This lot reckon 5cm around the optimal size for you is only worth about 1% of your mean and max power output.
http://www.tandfonline.com/doi/abs/10.1080/00140138308963449

I read somewhere ( but can't find a reference ) that having the cranks closer together was a way to improve output power. I always avoid bikes that need cranks that are bent..

So based on the measurements you are looking at you probably won't notice a difference. However I (1.78 m) prefer 170mm cranks because they seem are easier to pedal faster that 175's. So if you pedal fast I'd go for the shorter and if you are a grinder go for the longer and take a tiny bit of stress off your bones.

 

[Monsieur Remings]

Many thanks one and all...

...looks like it'll have to be 170, 172.5 or 175 then...

 

[mcshroom]

Glad we could help

 

[black'n'yellow]

Many thanks one and all...

...looks like it'll have to be 170, 172.5 or 175 then...

you have 172.5 on your best bike - why would you want something different on another bike?

 

[Monsieur Remings]

No option on the bike I was looking at fella', just 170 or 175. No problem.

 

[Nebulous]

I have about a 30.5" inside leg and my bike came with 172.5 cranks. Other bike had 170 mm cranks. I moved best bike to 170mm as well as I got a cracking deal on a crankset in a sale. I've never noticed any difference. I moved from a 50/36 to a 52/39 at the same time and that probably confused the issue enough to hide any difference in crank length.