From: jobst.brandt@stanfordalumni.org
Subject: Re: Crank Arm Length
Newsgroups: rec.bicycles.tech
Message-ID: <3jZkc.9237$Fo4.116722@typhoon.sonic.net>
Date: Sun, 02 May 2004 02:47:27 GMT

Joe Dewberry writes:

> What is the criterion for choosing crank lengths?

Looking at crank lengths available, you'll notice that nearly all are
170 or 175mm, 180mm and 165mm being way out.  Short cranks are used
mainly by track riders who turn extra high revolutions or people under
5'2" height.  Long cranks are used by people who naturally ride a
lower but more forceful cadence, something that becomes apparent after
many miles of tiding and good conditioning.

As far as I can see the equation says larger riders should use longer
cranks... BUT because they have larger heavier leg, they should use a
shorter crank.  The upshot is that unless you are extra tall and pedal
naturally at unusually low cadence with higher than average force,
you'll do fine with 170 or 175mm cranks.

Since there are two effects opposing one another, the span of useful
lengths are limited by human muscular response to two lengths.  Of
course there are those +-2,5mm sizes but they are oddities.  There
will always be those who see themselves as outside that range and
demand to use shorter or longer cranks but unless you are an
experienced rider and have a known effective pedaling rate, you should
probably start with the cranks that come with the size of bicycle you
bought... if it is a high performance bicycle.  I can't guess what a
Wallmart bicycle would have.

I doubt that there is a simple answer beyond that.  Ride bike and then
make specific choices.

Jobst Brandt
jobst.brandt@stanfordalumni.org