I have a 29" inseam and recently went back to 170s from 175s. I noticed I lost some power - ultimately about 100-150 watts in my jump (i.e. peak power), based on my current readings. My 5 second and 10 second power seem to be a bit higher (+100 watts) so it seems my 18+ years of training on shorter cranks is worth something. I rode 175s for a good 5-6 years, had great success on them. When I swapped cranks my sprint went from a sorry 31-33 mph to a much better 41 mph 4 weeks later on my next ride on my road bike. To be fair I wasn't fit, I was overweight, but at least everything on the bike except the cranks were the same and I did the sprint on the same road at the same time of night.

When I decided I'd train more last summer, I went and got some 170s. I have trained more and so far the cranks are okay. I'm worse than I normally am in the spring (March/April) - I attribute that to the lower leverage of the shorter cranks. Right now I'm a bit better than expected, and I attribute that to my better fitness (I'm well over my 2007 total training hours already, so I have much more fitness than I did any of the last three-four years).

I'm convinced that longer cranks help riders who are at less than 85-90% fitness. Long cranks boost the mid-range (i.e. 70-90 rpm) at the expense of the higher range (120+ rpm). It's like an engine - do you want a high revving 4 cyl or a grunty V-8?

I've posted a few comments on long cranks and such so I'm sure the regulars are tired of them. But, for most people, I think a longer crank is a better one. Only those who are extremely fit will be able to utilize the shorter crank's higher speed.

cdr