[CR]Crank length, today and yesterday

Example: Racing:Wayne Stetina
From: "garth libre" <rabbitman@mindspring.com>
To: <classicrendezvous@bikelist.org>
Date: Thu, 20 Sep 2001 18:39:58 -0400
Subject: [CR]Crank length, today and yesterday

I have been looking around at modern bicycles and checking things such as crank length as it relates to frame size. From what I can see, most of the older bikes had 170mm cranks in any of the sizes from say 52 to 56 cm, but when the frame sizes got to high 50's and 60's the crank length jumped to 175.

The modern bikes have established a trend of putting 172.5 mm cranks on their 54 and 56 cm frames, but 175 on 58cm and above, and 170 on 52's and 54's. I noticed that Trek does not usually offer an intermediate size crank of 172.5 mm on their 56 cm bikes but goes right to 175 on some of their 58's.

Now 2.5 mm's is a mighty small distance, and even 5mm's is so small that it is less than 1/4 of an inch. What was the theory that caused bike companies to stick to 170 for most mid sizes? What is the theory now which causes companies to incrementalize crank sizes. Has anyone experimented with different crank sizes and noticed an appreciable difference? Would one feel the difference between 170 and 172.5 on a 56 cm frame, and what would they feel? These are time consuming tests to be done, and I was wondering about the history and the science behind it all. Garth, still looking for a real edge in the quest to classically tame the pelaton, Libre