Looking for some advice best crank length for larger wheel sizes. I think I’m looking at the 27.5 Nimbus and noticed during the ordering process there are a number of different choices for crank length – from 114mm to 170mm!
I currently run 150s on a 24, so will these feel the same as 150s on a 27.5? I feel that 150s are a bit long on the 24 (I’m 5’8") and think 138s would be ideal, but wonder if that shorter length on a 27.5 would be detrimental in some way.
Thank you for any insights.
Why not order it with 138’s and then change them around with the 150’s when you get them? That way you have the 138’s on the 24 and 150’s on the 27.5.
Upping the wheel diameter will reduce the gain ratio (available torque) for a given crank length. In order to have similar torque to your current wheel, you would need 170mm cranks on the 27" wheel.
Torque is only one consideration though, as the longer cranks will feel dramatically different simply because you’re pedaling in larger circles. When I switched from 124mm cranks to 150mm cranks on my 24" wheel, I found the feel of the bigger circles took a lot of getting used to, both in terms of balance and cadence.
Experimentation is half the fun!
125mm
I’ve run 125s on my 24, so am familiar with how different crank lengths changes the feel.
138s may be the tickets as then I’ll have all three sizes on hand.
I think it depends a lot on where you plan to ride. Shorter cranks are better for road riding, and longer are better for muni. (In general.) You might try going with 138s, which are kind of in-between, and work pretty well with different size wheels, on a variety of terrain. (I like them on my 26, you may like them on a 27.5.)
One thing that surprised me (although it shouldn’t have) is that 150s (for instance) felt about the same to me on a big wheel as it did on a small one. The reason is your feet are still describing the same circle. The available torque may change, but really not all that much. (Just my experience/opinion. YMMV 
)
edit: looks like you came to the same conclusion while I was writing!
is it for road or off road?
I run 125 on my 29 on the road (could go smaller) and 137 off road.
If the cranks are compatible with your 24, then you can swap back and forth so definitely don’t get 150.
You could get the 137s, then down the road get 125s, then you have a wide range to choose from for whatever riding you feel like doing. Or just skip the 137s and go for the 125s, it will feel weird at first but after a few days no problem.
I’m 5’8" with a proportional inseam. There’s a lot of individual variation but I think the answer depends on leg length. I feel for a mountain unicycle I want the largest cranks that fit my stride. My original muni came with 165mm cranks and I downsized to 150mm after a while. Then I tried 137mm and they really felt right and is what I have had on my fixed road unicycle and mountain unicycles for a couple years. I set up a loaner muni with 150mm cranks and could hardly stand riding it. I climb much better on 137mm cranks.
More torque with longer cranks, yes. But. As described above, the circle your feet is doing has an impact on the smoothness of the ride. Also, the dead spot at the 6/12 o’clock position is much bigger.
Personally, 150 is already on the too long side. Love 137 on the 24" muni.