I posted sometime ago about my little experiment with shorter cranks. I actually have had two bikes set up now with the shorter arms, (170mm, to be exact) and here is my take on what it is like so far.
First off, the Salsa El Mariachi is the geared bike with 170mm arms and to be honest, I had completely forgotten that I had put 170mm arms on there! So in terms of feel, I guess I never noticed anything different about my pedal stroke. It feels totally normal every time I get on it.
The next thing I would have an impression about is this: The El Mariachi seems faster to spin up to speed than some of my other bikes. Granted, I have a really nice set of hoops on it, very light for a guy my size at about 1800 grams for the set, but I also have that on another bike. Oddly enough, that bike has 180mm cranks and seems to promote my slower twitch muscles or something, because I just don't feel that it easy to get leg speed up on that bike. Is it all in my head? maybe, but the longer cranked geared bike seems slower to speed.
On the El Mariachi, this translates to a bike I always want to grab for single track rides. I know, (or at least I "feel like it does") it will come out of corners faster than my longer cranked rigs will. I mentally like this bike better for some strange reason, (keeping in mind,I forgot it had shorter cranks), and this may be a reason why. If I think it is faster, it is, no? I figure there is something to that. I'll keep riding, knowing it has the short crank set, and report back later.
The other rig with the short arms is the Blackbuck. And I know this has shorter arms! How could I forget, since I had them anodized antifreeze green before I slapped them on the bike! It is a reminder of that fact every time I ride this rig. Anyway, as many of you know, the Blackbuck is a single speed. The 170mm cranks are definitely not conventional wisdom here!
Okay, so how has it been? Well, I rather like the shorter cranks here too. The spin up is there, yes, but I feel I can roll the crank arm up into the power section of my cadence easier on climbs. I can spin up some steeps that I would have been hammering at with 180mm cranks at a slower speed. The only time I feel that 180mm cranks might be an advantage here is when I am at or below walking speed on a steep climb, hammering out each pedal stroke like a guy swinging a sledge hammer. That longer arm seems to get you a bit further up the hill with every laborious stroke. Other than that, I would choose my 170mm arms for every other single speed situation. A big advantage goes to the 170mm arms on the flats when you can maintain a high cadence without bouncing yourself off the saddle.
Is any of this 29"er specific? Well, since I don't really ride 26"ers anymore, I can't really address that. I know the Crested Butte guys thought so back in the early part of this decade. I can say that there are some things positive going on with the idea. Enough so that I feel encouraged to pursue it further and keep testing it against my longer cranked bicycles here. I'll keep ya'all posted, but until then, there is a lot of riding to do!