Crank size is not dictated by gender. Instead, it is usually determined by inseam or leg length. What is a "medium sized woman racer"? Smaller frames are usually spec'd with appropriate length cranks already.
Crank length is about achieving the appropriate fit on your bike. If you have long femurs and sit too far back on your bike then a longer crank will move you forward. If you have short legs and sit far forward then a shorter crank will move you back.
A lot of people think that crank length is important, for most, it is not. The vast majority of cyclist are served perfectly well by standard length cranks 165-175.
Eur J Appl Physiol. 2010 Jan;108(1):177-82. Epub 2009 Sep 22.
Influence of crank length on cycle ergometry performance of well-trained female cross-country mountain bike athletes.
RESULTS: The aim of this study was to determine the differential effects of three commonly used crank lengths (170, 172.5 and 175 mm) on performance measures relevant to female cross-country mountain bike athletes of similar stature. The time to reach supra-maximal peak power was significantly shorter in the 170 mm condition compared to 175 mm. This effect represented a mean performance advantage of 27.8% for 170 mm compared to 175 mm. There was no further inter-condition differences between performance outcome measurements derived for the isokinetic (50 rpm) maximum power output, isokinetic (50 rpm) mean power output or indices of endurance performance. The decreased time to peak power with the greater rate of power development in the 170 mm condition suggests a race advantage may be achieved using a shorter crank length than commonly observed. Additionally, there was no impediment to either power output produced at low cadences or indices of endurance performance using the shorter crank length and the advantage of being able to respond quickly to a change in terrain could be of strategic importance to elite athletes.
crank length matters to me on my TT bike. All my top 10 mile TT performances were on 170mm vs 175mm
170 I can keep a monster high cadence longer than my standard road/mtb of 175. I also use 180's on my singlespeed because that is 'grunt work and leverage' more than spin when hills pop up. 172.5's I don't use.
in my 'opinion formed by riding different lengths'...if you have a high cruising cadence (I work on it constantly) crank length matters buckets. if you mash 70-80 maybe not so much. if I was 4 inches shorter overall i'd prob have 170's on all bikes, but I am totally generic bike rider sized at 5'8" 30inch inseam
Not sure what a medium sized women is and if I'm medium sized... but I run 172.5mm cranks on all my bikes (road, TT, cross, MTB), and I'm 5'9.5" tall with a 34" inseam. Works out great for the fit on all my bikes. Then again, I've never known anything different, and my knees are way too picky to start messing with sizes of stuff like that.
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