In my efforts to educate myself on everything 29"er back about eight years ago I noticed something that kept coming up and I thought it was a bit strange. That was how several early 29"er freaks were spinning 170mm long crank arm sets.
I had always been in the "whatever works" category for years before that. I mean, what choice was there? Most crank sets came in 175mm lengths for mountain biking. Then I noticed that you could get 180mm crank arms in the mid-90's, so I bit and got myself a set of Race Face Turbine LP's in anodized blue. 180mm long arms, which I still have, by the way! I thought I rode better and in a taller gear than without them. All from a measly 5mm extra length in each arm.
About the same time, Leonard Zinn published his now famous crank arm length tests in Velo News. It was an inconclusive test, but the articles seemed to indicate that getting crank arms in proportion to your leg length was a smart idea. So I felt justified in my 180mm long arms. This is where I was at when I first came into the 29"er thing, so these suggestions that a 170mm arm was a better way to go on a 29"er seemed odd.
I let it go at the time and got a single speed set up on an old set of 177.5mm Cooks Brothers cranks and that seemed okay to me. Since then I have run the "standard" 175mm long arms on gearies, and 180mm arms on single speeds. Pretty typical stuff for most 29"er guys.
However, this 170mm arm length thing was still in the back of my mind, so I had been secretly collecting some 170mm arm length crank sets for future experimentation. Well, I have ridden a set on a single speed for awhile now. I think there might be something to it. I was tipped off several months ago by a certain 29"er dude out west that the shorter arms helped him stay on top of a gear longer. Hmm.....so I thought I'd throw a set on, and sure enough, I could see what he was saying.
So, enter the newest build in The Lab: the Salsa Cycles El Mariachi. I am going to try a triple crank with 170mm arms this time around. We'll see if the same idea transfers over to a geared set up, as the first was done with a single speed set up. It'll take some time, but I'll post back with an update.
We'll see if the early 29"er freaks were right. I've a feeling that they were.