Friday, September 22, 2006

Crank it

My new bike is going to have 175mm cranks. So what? Well, I have been using 177.5mm cranks exclusively for 4 years. I swapped by circumstance not design: in essence I couldn't find a cold forged 5 arm crank with a square taper in anything *but* 177.5mm, so I bought 3 and had done with it. I felt they helped for pushing the singlespeed up steeper hills, but otherwise no major difference. Afterall, they were only 2.5mm longer than 'usual'.

I revisited this decision several weeks ago, when getting new cranks for the IF. Having ridden my friend Biff's Jones, I was impressed with the stiffness, power transfer and looks of the Jones mod'ed xtr cranks. So what length?

It is oft quoted there was a tendency for the old school 29"er riders to use shorter cranks. Indeed, rumor has it Wes Williams wouldn't have anything to do with cranks longer than 170mm. Perhaps this is more applicable to geared bikes (for spinning the gear) But one could also look at the track riders using 160-165 cranks, and they don't hang about when it is time to transfer power to the wheels (and neither are they universally short of stature).

I ordered 175mm, and I am glad I did. A more prolonged ride on Biff's bike this last week end led me to believe I can feel no detrimental difference whatsoever. A post on mtbr got me thinking further and after reading Leonard Zinn's diatribe on crank length, how to measure it and the pros and cons of changing, I decided to go all bio-mechanical. Turns out with my femur length, I should be using 170mm cranks, whereas with inside leg measurement I should be using 176-180mm length cranks. So there we go. Conclusions will be drawn after a prolonged time on the IF.

(pic courtesy of Jeff Jones)

1 comment:

Nick said...

Bernard Hinault and Cyrille Guimard discussed crank length in detail in the 80's and were less conservative even back then than the current pro-peloton.