Crank Length

Subject:      Re: Crank Length Suggestions
From:         Roger Marquis (marquis@roble.com)
Date:         1997/03/12
Newsgroups:   rec.bicycles.racing

In rec.bicycles.racing Tony Pinto (tony@cttc.org) wrote:
>I was planning to purchase new cranks in a slightly longer length (175) but
>read a section in "Serious Cycling" that said someone of my height 5'10"
>should be using 170's. I have other books that do not seem to agree with
>this recommendation but now I am wondering what the effects will be of an
>increase.

At 5'10 you're borderline for 172.5 cranks, assuming a normal leg
length.  The best all-around crank length could be either 170s or
172.5s depending on your inseam.

Watch out for long cranks, they cause a very sharp bend in the knee
at top dead center right where you begin to apply power.  Too short
cranks don't pose a risk to the knee joint but they also won't be
efficient unless you spend a lot of time at high cadence.

The general rule of thumb is:

  * below 5'10 use 170mm cranks on for general (road) racing and
    training,

  * 5'10 to 6'1 use 172.5mm cranks,

  * 6'1 plus use 175mm cranks,

And modify for specialized events:

  * subtract 2.5mm for track racing (or more on short steep tracks
    or short events),

  * subtract 2.5 to 5mm if you have frequent knee problems,

  * add 2.5mm for time trials and hilly races, (and MTB races),

  * add 5mm for pure hillclimbs.

Roger Marquis
(www.roble.net/marquis)

Source: http://www.roble.net/marquis//crank.length