Is crank length super crucial?
how do i know which crank length is best for me? i had the stock compact 170 fsa on my 2013 p2. i changed it for a 6700 standard 172.5 standard. i never consulted fit or anything. is the length super crucial or it shouldn’t affect all that much? why i asked is because I’m potentially getting a quarq riken and don’t just want to order the wrong one
I’ve been studying this myself a bit. This bit from Dan is as good an overview as any, but TT-oriented.
Shorter crank lengths have recently become fashionable (Rapp article in LAVA). But as far as I can tell the evidence of improvement is just anecdotal, and Rapp admits that.
On the other hand, Cancellara, Wiggins, and Zabriskie all use(d) 177.5 cranks in their big-time TTs. And Tony Martin is at 175, so you look more “pro” with long cranks. 
But the main takeaway from everything I’ve read is you’re not likely to go wrong if you avoid the extremes. And neither 170 nor 172.5 is extreme. You’re likely to adapt just fine to either 172.5 or 170.
The reason I was researching was to find if all my bikes should have the same length or not, e.g. if you adapt to a particular length. Haven’t found an answer to that one…
Edit: This bit from Cervelo is also good.
A study came out recently by Dr Martin and it supports the notion that shortening crank length has no effect on power. From one of the studies on crank lenght, they found that optimum length was around .02 of leg length. At a crank lenght of 170, power was only compromised by 0.5% (about 6W at peak of 1200W) for the shortest and tallest cyclists. I’ve shifted to a shorter crank and I’ve noticed no ill effect on power. And, it allowed me to open my hip angle up at TDC.
A study came out recently by Dr Martin and it supports the notion that shortening crank length has no effect on power. From one of the studies on crank lenght, they found that optimum length was around .02 of leg length. At a crank lenght of 170, power was only compromised by 0.5% (about 6W at peak of 1200W) for the shortest and tallest cyclists. I’ve shifted to a shorter crank and I’ve noticed no ill effect on power. And, it allowed me to open my hip angle up at TDC.
I think you meant “.2 of leg length”. Otherwise, the market for 16.5-17.5mm cranks would be booming…
Is crank length super crucial?
Not really.
But if you are tall or very tall, it is likely a good idea to use cranks that are somewhat longer than average. And if you are short or very short, it is likely a good idea to use cranks that are somewhat shorter than average.
I’m 5 8" 173 @ 30" pant length
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It can be very crucial to your positioning. Shortening your crankarms (and raising the saddle) can give some riders in aggressive positions a little relief of too tight hip angles.
Is crank length super crucial?
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I’m 5 8" 173 @ 30" pant length
You’re pretty much in the middle of the male height range. Don’t go crazy, but most typical cranks should work fine for you. There is a link (here) that gives you a good simple formula for a place to start. I might go slightly longer if you you do more than 75% of your riding in the mountains. And I might go slightly shorter if you are in a very bent over road or TT position (the shorter crank sometimes helps you go ‘over the top’ of your pedal stroke when bent over).
I’m 5 8" 173 @ 30" pant length
You’re pretty much in the middle of the male height range. Don’t go crazy, but most typical cranks should work fine for you. There is a link (here) that gives you a good simple formula for a place to start.
Interestingly simple calculation: 30" inseam puts me at a 164.4mm crank. I guess I was justified in switching to 165mm cranks (from 172.5mm)
Exactly. As long you are using the full crotch-to-floor measurement, not your pant inseam.
A study came out recently by Dr Martin and it supports the notion that shortening crank length has no effect on power. From one of the studies on crank lenght, they found that optimum length was around .02 of leg length. At a crank lenght of 170, power was only compromised by 0.5% (about 6W at peak of 1200W) for the shortest and tallest cyclists. I’ve shifted to a shorter crank and I’ve noticed no ill effect on power. And, it allowed me to open my hip angle up at TDC.
I think you meant “.2 of leg length”. Otherwise, the market for 16.5-17.5mm cranks would be booming…
Good eye. Thanks for the correction…I was struggling to post on my phone as auto correct was inserting a zero. 0.2 is correct.
2x It can be very crucial to your positioning. Shortening your crankarms (and raising the saddle) can give some riders in aggressive positions a little relief of too tight hip angles.