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Difference of 170mm / 175mm cranks.

Rapplez

Chimp
Apr 27, 2010
23
0
Marysville Wa
I currently run 170mm cranksets on my bikes. DH, girlfriends AM, and my 20". I realize if I jump up to a 175mm the leverage ratio, feel, speed changes per each rotation. But will I feel that extra 5 mm per side? will I feel a drastic change? What else can I expect? lets hear your input? Thanks

-Rapplez
 
Last edited:

JRogers

talks too much
Mar 19, 2002
3,785
1
Claremont, CA
The conventional wisdom is that longer cranks are better for taller riders and people who ride at a lower cadence. There's a lot of information out there about crank length in terms of studies and such. Basically, what I've seen indicates that conventional sizes are not that different from each other when it comes to performance. Yes, there can be differences in this range, but they are not likely to be particularly large. Even some fairly big length changes (well below 165 and well above 180) will, for some variables, not change that much.

Personally, I have had bikes with 165, 170, 172.5 and 175. I don't notice much of any real difference between these (though, usually, I am only switching between 175 and 172.5 these days). Maybe a sensitive rider could, but I think some riders tend to overstate how much 5mm or even 2.5mm makes a difference. In any case, most people can acclimate pretty quickly to those sorts of changes. The only time I did notice some difference was switching from 175mm to 165mm on my DH bike-just about the only thing I noticed was I seemed to be tagging rocks a bit less (I had a very low bike in a rocky area).

In short, I wouldn't buy new cranks just to change the length unless you are currently having a real problem. I doubt you'd notice the change; it certainly is not likely to be drastic. And if you start digging into the literature and columns out there, you'll see that there are lots of different opinions and lots of counterintuitive findings (like how one study found that 170mm cranks took significantly less time to get to roughly the same peak power than 175mm...seems counter to the "more leverage" conventional wisdom...same study also found no big differences between 170, 172.5 and 175 in terms ofmax sprint power, VO2 max and constant pedaling at 50rpm [think grinding up a climb]).