Go Back  Bike Forums > Bike Forums > Road Cycling
Reload this Page >

changing crank arm length

Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

changing crank arm length

Old 01-07-06, 10:20 PM
6000mi in '06
Thread Starter
trekking_TW's Avatar
Join Date: Oct 2005
Location: where am I?
Posts: 326

Bikes: 2005 Trek 5000, 1989 Mongoose hardtail MTB

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
changing crank arm length

Is there any advantage or disadvantage to changing the crankarm length?

I'm changing my cranks and currently have 170mm length 105. I'll be changing to DA 172.5mm unless this would cause major problems for me. I've heard that shorter cranksarms cater more to the spinners and longer cranks are preferred more by the mashers. Is this the case?
trekking_TW is offline  
Old 01-07-06, 10:53 PM
Tom (ex)Builder
twahl's Avatar
Join Date: Jul 2004
Location: Manassas, VA
Posts: 2,814

Bikes: Specialized Allez

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
You generally have the idea right, but height, or more accurately leg length, plays a big factor as well. If you are taller than average a longer crank arm may suit you better, but in my opinion, 2.5 mm isn't going to make a huge difference anyway.

"It hurts so good..."
twahl is offline  
Old 01-07-06, 11:11 PM
Aluminium Crusader :-)
Join Date: Apr 2004
Location: Melbourne, Australia
Posts: 10,048
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by trekking_TW
Is there any advantage or disadvantage to changing the crankarm length?
Some people claim that the longer cranks provide extra leverage (I think I'm one of them
), but some of the 'physicists' say it's impossible when gears are involved -- either way, 2.5mm difference will be barely noticeable.

What you should notice is the drop in relative saddle height. You'll most likely lower the saddle ~2.5mm (assuming it's currently in the right position for you), which means the seat will be ~5mm lower, relative to your knees, through the top secion of the pedal stoke.

Others claim that different crank lengths can improve the biomechancis of the quads once the correct length for the individual has been found, but....yada yada..... The whole topic is inconclusive and complicated, especially when muscle firing preferences and biomechanics are involved
531Aussie is offline  
Old 01-07-06, 11:17 PM
jeff williams
I couldn't car less.
jeff williams's Avatar
Join Date: Nov 2003
Posts: 4,397

Bikes: Ritchey P-series prototype, Diamondback, Nishiki Triathelon Pro.

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
I think it might be more important than manufacturers sale for.

170mm for all.
I need around 168.
The stresses would be reduced in the skeletal. Building a bike i'd order the right length.
jeff williams is offline  
Old 01-08-06, 04:06 AM
Senior Member
AnthonyG's Avatar
Join Date: May 2005
Location: Queanbeyan, Australia.
Posts: 3,859
Mentioned: 43 Post(s)
Tagged: 0 Thread(s)
Quoted: 1736 Post(s)
Liked 12 Times in 11 Posts
See, http://www.cranklength.info for all you ever wanted to know on the subject. If 170mm is the right length for you in the first place then 2.5mm is neither here nor there however if your legs are on the shorter side them moving longer may be detrimental. Going longer may make it harder to be comfortable in an aerodynamic tuck which will wipe out any benifit you may beleive that you will gain.

Regards, Anthony
AnthonyG is offline  
Old 01-08-06, 05:36 AM
Senior Member
biker7's Avatar
Join Date: Feb 2005
Posts: 2,850
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Everybody has a slightly different view of crank length. For kicks I switched from 175 this last summer to 172.5 and didn't like the change so switched back. I have long legs and I thought I may prefer the ability to spin the 172.5mm cranks at a bit higher RPM while being in a slightly shorter gear...wasn't the case for me. Some say that 2.5mm is not noticeable but to me it is. A further argument as to why 2.5mm is noticeable is to consider that cranks are available in only 2.5mm increments = 5mm in circle diameter and crank arms are typically available as std. within a very narrow band width i.e. 170-175 for most cranksets...there are exceptions. The other intangible for me was KOPS and overall balance on the bike. I like the longer cranks for standing as I felt I had a bit more balance and could push a slightly bigger gear with lower cadence with longer crank arms.
Personal preference again weighs heavily for most and like frame size, in spite of what you measure I believe trial and error is still the best teacher.
biker7 is offline  

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

Thread Tools
Search this Thread

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

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.