Climbing: Efficiency of standing up vs crank length

Last couple of months I have been riding my 27.5 Muni with a road tire because a lot of tracks were too muddy to be any fun.
When I switched the tire I also changed the crank length from 136 to 110 mm to speed up my rides.
This is my first time riding such "short"cranks.
It took a little getting used too but soon I could comfortably ride with them. Even climbing is not too much of an issue.

But on the steeper slopes I noticed something :
WHen the going gets tough, standing up doesn’t seem to add much to the climbing ability.
But with the 136 cranks I can feel a clear benefit.
On the 24" there is also a difference between 125 and 145 mm cranks but there is still a big benefit when standing up.

With the longer cranks you really get the “stairmaster” experience and power your way up.
I don’t think it is really a gain* issue, to me it feels more like at 110 mm the stoke / steps are just getting too small to get extra benefit

What are your experiences?

Note: I’m not talking about a small / short incline than you just tackle at high speed and rely on momentum.

  • ratio between crank length and wheel size

My guess is: Standing up helps the “strong” part of the stroke on long cranks but may create a weaker “weak” part of the stroke. Conversely, I feel like I am “spinning” the cranks more when I am not standing, when I am firmly anchored on the seat (and leveraged into place with two hands on the bar ends).

I think there’s some degree of momentum in most scenarios. Except for some of my riding conditions that are so bumpy, my wheel will come to a momentary stand-still. So, the choice of long vs. short cranks may be influenced by the “flowy”-ness of your riding conditions.

For the brief time I experimented with shorter cranks for muni, when hills got tough, I had to rely more on a weight-shifting method of getting through every half pedal rotation. This is where the rider shifts their weight forward/back to compensate for the weak/strong part of the pedal stroke. To do this may require “standing” on the pedals.

So, maybe standing on long cranks accommodates downward slogging, while standing on short cranks accommodates the weight-shifting method I mentioned above.

There’s a magic crank length (depending on the slope) where the wheel’s inertia/momentum lets you do what the road bikers call “dancing on the pedals” - where the pedal offers just the right resistance to support your weight as you drive it down.

If the crank is too long, the pedal just sinks down without enough resistance, or if the hill is so steep that you get the resistance, you can’t keep up the speed. If it’s too short, you can’t drive the pedal down with enough authority.

Anyway I really noticed the difference when I went from 145 to 125 on my 27.5+ sized wheel - there were hills that were a real slog on the long cranks, where I could just zoom along on the shorter cranks. It didn’t work on the steepest hills, but it worked on a lot more of them than I expected.

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There seems to be a length that’s too long for hill climbing as well. On my 27.5, I can climb better on 145mm cranks than on 170mm. The 170’s are just too slow and overcoming the 6/12 position is harder than with 145’s. On my 36er however, 170’s climb better than 150’s. I think the extra rotational mass of the 36" wheel and tire help carry it through the dead spot and the lower “gear ratio” with the longer cranks makes climbing easier.

I’m basically the opposite. Once I go long on a 36er I feel like I have to do the power strokes and can’t spin up hills fast like I usually do. I will say that before the Nightride Lite there were a couple of occasions where I’d considered going to 127 or 137s for my commute (from 110s) but the lighter tyre changed my mind. I’d love to get the carbon rim and some custom drilled Spirits at like 93mm.