Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

crank arm length

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

crank arm length

Old 09-21-10, 07:25 AM
All work and no play...
Thread Starter
Oysterboy's Avatar
Join Date: Sep 2010
Posts: 144
Likes: 0
Liked 0 Times in 0 Posts
crank arm length

I have a question concerning the best crank arm length for my current build. I am 5'11" and have a 29" inseam. The bike frame (TT bike) is a medium size (55 cm) and has 650C tires. My current MTB has 175 cm cranks and this seems perfectly fine, but is there perhaps some sort of equation or magic that can be used to calculate the optimum crank arm length for this bike? Or is this best left to trial and error?
Oysterboy is offline  
Old 09-21-10, 07:54 AM
Senior Member
Kimmo's Avatar
Join Date: Dec 2009
Location: Melbourne, Oz
Posts: 9,556

Bikes: https://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=152015&p=1404231

Liked 726 Times in 516 Posts
If you think you'll spin more than on the MTB, 172.5s might be more appropriate.
Kimmo is offline  
Old 09-21-10, 08:08 AM
All work and no play...
Thread Starter
Oysterboy's Avatar
Join Date: Sep 2010
Posts: 144
Likes: 0
Liked 0 Times in 0 Posts
I don't really understand.
Oysterboy is offline  
Old 09-21-10, 08:28 AM
TimeTravel_0's Avatar
Join Date: Mar 2010
Posts: 536
Likes: 0
Liked 0 Times in 0 Posts

take it with a grain of salt.
TimeTravel_0 is offline  
Old 09-21-10, 08:48 AM
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,598

Bikes: 8

Liked 1,361 Times in 867 Posts
Q: Pedaling style.... are you a Masher, or a Spinner?.. foot flat across BDC?
or toes point down. ?

I no longer worry about 'Best'; have 170s and 180s, and 175s
on different bikes , and ride them all.

Last edited by fietsbob; 09-21-10 at 09:02 AM.
fietsbob is offline  
Old 09-21-10, 08:56 AM
Senior Member
Join Date: Jun 2010
Location: Pearland, Texas
Posts: 7,579

Bikes: Cannondale, Trek, Raleigh, Santana

Liked 5 Times in 5 Posts
Oysterboy, Because the circumference is less with a 172.5 mm crankarm vs. a 175 mm crankarm there is less distance to pedal for each 360 d. of rotation allowing for a slightly higher cadence for a given amount of time.

All in all I think cyclists are pretty adaptable to crankarm length. What is the crankarm length on your road bike?

bradtx is offline  
Old 09-21-10, 01:25 PM
Senior Member
Join Date: Aug 2008
Location: Madison, WI
Posts: 811

Bikes: '08 Trek 7.3FX

Likes: 0
Liked 0 Times in 0 Posts
Keep in mind that usually you're going to want longer cranks on a mountain bike than a road bike.

29" is your cycling inseam or your pants size? Not that a 29" inseam on a 5'11" person is unusual, it's just not average. That's why I'm asking. You measure your cycling inseam by straddling a level while barefoot and pulling it up to your soft tissues to simulate where the saddle would be, then measuring to the floor.

I have a 30.25" inseam and I ride 165mm cranks but I'm a spinner. I'm usually pedaling over 90rpm. If your cadence is lower then shorter cranks are going to feel very odd. I personally would put 170mm cranks on a mountain bike as there is more mashing involved, but I can't say what is right for you.
shouldberiding is offline  
Old 09-21-10, 01:29 PM
Kid A
TurbineBlade's Avatar
Join Date: Aug 2009
Location: Alexandria, VA
Posts: 1,778
Likes: 0
Liked 5 Times in 5 Posts
I'm supposed to ride 175's but currently ride 170's. They spin fine and I couldn't care less. As someone above said, most peope are pretty adaptable to a general ballpark range of lengths.
TurbineBlade is offline  
Related Topics
Thread Starter
Last Post
Fitting Your Bike
03-02-15 11:15 AM
Classic & Vintage
10-05-12 02:03 AM
Singlespeed & Fixed Gear
09-21-12 01:33 AM
VT Biker
Road Cycling
05-11-11 10:25 PM
Singlespeed & Fixed Gear
01-26-10 09:29 PM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Your Privacy Choices -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.