Crank arm length?

I know this is a dumb question, but what is the effects of longer crank arms.

Better for flats?

Its not about longer or shorter.

It is part of bike fit.

There is only one correct crank length for any given leg length.

__________________
Cheers,
George.

yeah, it's more about fitting the rider than leverage or cadence.

for instance, if a 5'7" guy thinks he's going to get more power by using 177.5mm cranks, he most likely won't because his knees will be in his face and he won't be able to push them properly

I'm 6ft, and in 2005 I persisted with 180s for about a year, but they were too big. The day I went back to 175s, I felt like superman because I could 'get on top of' the pedals properly and pound the crap out of them more effectively

I have no idea how all the short riders out there can use 170, 172.5,or even 175!

You got to try it for youself. Dont' listen to anyone (except me

Go to ebay and buy some cheap cranks and test them out for a few weeks. You can always get your money back by selling them on ebay.

I set up bikes for 4'11" "Little jackie".

Her best crank length is 157mm.

I fit 152mm One Piece Cranks on her Huffy MTB and 160mm Sugino on her Giant OCR3W. Her Felt F100 still has the original 165mm, but with all the complaiing of sore knees after each ride on the Felt, I will be organising a set of 160mm 30/39/50 cranks in the summer.

__________________
Cheers,
George.

But there is also the factor of what sort of riding you do! If you want to spin as fast as possible, a shorter crank will be better. If you need the leverage for climbing a longer crank will be better.

I am 6' tall, and use a 172.5 crank on both bikes. As soon as I can, I am going to swap out the crank on my single-speed for a 165. I just can't spin fast enough to get my speed up where I want it.

__________________
"If you don't keep turning the crank, you won't get where you're going." -Albert Kong

http://www.deitchman.net/blog/

Look 595 (with SRAM Force kit)
Bianchi San Jose (SS or Fixed)
Rock Lobster Steel CX

Agreed. It is not correct to say that there is only one good length for the leg length you have. I have used 170 172.5 and 175mm just fine on various different bikes.

Many factors weigh in like leg length, proportion of that length above and below the knee, muscle shortening or lengthening and torso inclination. Position will very likely need to change (sometimes quite radically surprisingly).

You just have to try it out and see if it works for you.

I ride almost exclusively on the flats, its hard to find a hill in Louisiana. I'm 6ft tall with 33" inseam. I have a standard geometry steel framed bike. I have been planning on upgrading the crankset. Currently use 170s, thinking of 175s. 1/2 centimeter does not seem like a big difference, but I'm learning as I go. I'll prbably get the 175s and see how it goes, I hope I don't have to put the old set back on.

Well, your inseam length is an inch longer than mine, so the slightly longer cranks may be right for you for some situations.

__________________
"If you don't keep turning the crank, you won't get where you're going." -Albert Kong

http://www.deitchman.net/blog/

Look 595 (with SRAM Force kit)
Bianchi San Jose (SS or Fixed)
Rock Lobster Steel CX

170 is really short for your height. I'd recommend changing to 172.5 first before making the jump to 175. It is a noticeable change. I have two bikes, one with 172.5's, one with 175's, I prefer the 175 bike for hills, but the 172.5's in the flats. It can spin that much easier.

They used to put 172.5's on 58cm bikes, but then switched over to 175 being more of a standard. it's all preference.

From (which offers custom cranks)
http://www.zinncycles.com/cranks.aspx

Here is the formula I recommend:
Crank length (mm) = Inseam (mm) X 0.216
Or, more conservatively for tall riders:
Crank length (mm) = Inseam (mm) X 0.21

Hi

Guys like Indurain started their season with shorter cranks, as they build up for the Tour and get stronger they shifted to longer cranks.

Regards

I'm not shooting the messenger, but......

I don't like that formula, in fact, I don't think anyone does
There's no pro in the world over about 5'5" is using cranks relatively that long. I don't know how Zinn still gets away with it. I'm only 6ft, and the "conservative" formula puts me on 188mm cranks. It's crazy!

Does that mean you have abnormally long legs? I get 171 or 175 when I use that formula (6'0" with 32 inch inseam)...

__________________
"If you don't keep turning the crank, you won't get where you're going." -Albert Kong

http://www.deitchman.net/blog/

Look 595 (with SRAM Force kit)
Bianchi San Jose (SS or Fixed)
Rock Lobster Steel CX

Hmm, I'd say you have unusually short legs. Is that your pants inseam or your real inside leg measurement, crotch to floor? That is VERY short for someone 6ft. You've got shove the tape or the clipboard right up there to get the right measurement.

What is it with every Yank knowing their pants inseam? Is it part of the college curriculum?

I do have longish legs: my inside leg is ~35.2" (89 to 89.5cm, 'depending'..)