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Old 03-13-01, 10:23 PM
  #11  
roadbuzz
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Only people with really short legs and track sprinters (riding fixed gears) use 167.5s. A rule of thumb I read somewhere is that if you ride up to a 55 cm (c-t) road frame, you should use 170 mm cranks. Starting at 55 you might consider 172.5s... it becomes a matter of personal preference and physiology. I forget the rules above that point, since they have no bearing on me.

There are plenty of great (like G. Lemond) and not so great (like me) cyclists who, for whatever reason, tend not to spin really high rpms. Which, by the way, doesn't necessarily mean we mash in low gears, either. I prefer the slightly longer cranks, since they don't interfere with my spin, and the give slightly better leverage (and hence torque) on climbs.

The biggest potential drawback is that the overall range of knee motion per rev is increased, which can cause knee distress. With longer cranks, when you get your seat height dialed-in, the top of your stroke is higher by 2x the crank length difference, i.e. your foot will be about .2 inch higher with 172.5s over 170s. Not much, but it can cause problems.

I guess the point of my diatribe is that for maybe 95% of riders, the cranks that came with the bike are probably fine, if the frame fits. For the others, there are a lot of factors to consider when deciding whether to go with longer or shorter cranks.

Last edited by roadbuzz; 03-13-01 at 10:29 PM.
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