I normally use 175mm cranks on my MTBs, SS or geared, just as thats what I've ended up putting on them
While I can just about grunt my way up most of my local climbs with a SS setup I seem to struggle more with spinning along on the flat (especially the road) with very little resistance for any length of time.
Might 170mm* cranks be a good idea to help obviously with losing out on 5mm extra worth of cranking uphill? When I have used 170mm cranks I noticed I was able to spin better circles (on a geared hybrid)
*170 just because 172.5mm etc would be a bit pricey
I use SPD's, though its not often that I have a completely unworn set of cleats in a completely unworn set of pedals (they always seem to have a bit of play, even when tensioned right up), making deliberate cirles that bit more difficult than it seemed when I first got some)
(I've used a crank length recomending online tool linked from a thread or 2 on here and at 6'2"/34" inside leg it reccomended 175mm)
