I'm 5'9" and have spent almost all of my cycling time since 1968 on 170's;
didn't realize I was riding 172.5's for a few years until I looked at the
cranks when cleaning the bike--this is on my main single bike. It is
interesting to note that large numbers of cyclists who started with mountain
bikes have never ridden shorter than 175mm--this for riders as short as
5'4"--and don't appear to be suffering ill effects from it. It is also
interesting that since the early 70's, the normal size of stock road bike
cranks has become longer--172.5's start on 54cm bikes, 170's used to be
fitted to bikes as large as 64cm a couple of decades ago. Also interesting
that very small stock bikes don't have proportionally shorter cranks; you'd
think that there would be more 165 and even 160mm arms available if
manufacturers really cared about all that "bike fitting the rider" stuff.
Jan Heine made some interesting comments about crank length in Vintage
Bicycle Quarterly ( A 400K Brevet ). He commented about the fact that with
shorter crank arms you can lower the Bottom bracket height , get a better
cornering more stable bike and have the additional advantage of being able
to continue pedaling thru the corners without fear of kissing the pavement ,
not to mention you also save your knees from the stress of longer cranks. I
remeber reading somewhere that in the 50's the Randoneurs typically used
crank lengths of about 165mm and smaller gear ratios.
I can also recall that this long crank thing has been tried before by the Professional racers again I think it was in the 50's or 60's and they moved back to more knee forgiving lenghts after a few years. What does anyone know about this?