Are Your Crank Arms Too Long?
Note: There is some feedback that calculated lengths using this tool are too long (3 MM from feedback). I would not take the calculated lenghth too literaly and lean toward shorter lenghts. I also think that recumbent riders should consider shorter cranks because of seating position.
I have been thinking that I should shorten my crank arms since I started having hip problems but I am not sure that the effect is significant. However, I do know that it will be expensive. A friend is going to let me ride his recumbent with shorter cranks before I proceed but I am prettty sure I will make the change.
So if I do change “What is the correct crank arm length?”.
Well to answer that question I found a neat little web page, Optimum Crank Arm Calculator.
This program by Machine Head Software calculates the optimum crank arm length base upon the riders inside leg measurement. This approach is based upon the technique is from The Racing Bike Book, By Dave Smith, Ben Searle & Steve Thomas (foreword by Sean Kelly), ISBN 1-85960-319-X. The book gives a table of recommended crank sizes in millimeters for inside leg measurements between 72 and 96 centimeters.
From this table of values the following relationship was developed:
Recommended crank length in millimeters = (1.25 * Inside Leg in cm ) + 65
I tried it out and with my very short for my height legs (29″ inseam) it recommends 157 mm cranks instead of the 170 mm I am using now.
See Cranks for more postings about Shorter Crank Arms, where to get them, how to install and remove cranks and Why I love them.