Wheel size, crank length and body weight.

Hi there!

I’ve been thinking lately about the “perfect” crank length on my unis.
The factors i thought of as being important in this case are:
the size of the wheel, the type of riding and the terrain, my body weight.

i weigh about 60kg so that’s about the maximal force i can put on the pedals without pulling on the grab handle or handlebar.

For riding on road with my 24" i use 125mm so far, this feels kinda good to me and i did master every ascent or descent i encountered so far.

On my 26" i’m now using 150mm, on raod as well as offroad (may be called XC) and also did master everything in my way so far, at least after some training. I never tried the 125mm holes and thought about trying 137mm but i’m not sure if i should wait with this until i buy a new tire which sure will be something lighter than the Duro 3".

On my 36" i was using 165mm so far nearly clearing everything i can ride on the 26", but i’ve only been riding about 100km with it. Last week i changed to 150mm, slowly getting used to it when mounting and getting the wheel moving, haven’t tried it offroad so far and only managed about 2/3rd of the ascent to the subwaystation on my way home from work.

What crank length do you use/prefer, under what circumstances?



5’8", 150lbs

  • 19/20" for flatland/trials type riding: 137mm, though maybe I’d prefer a bit shorter.

  • 24" muni: 137mm

  • 29" muni: 150mm; road: 125mm

  • 36" offroad, very steep hills, or having to get on and off a lot: 150mm, all other circumstances (almost all types of road regardless of hills): 127mm.

I have wondered what the theoretical maximum slope one could climb with a given wheel size and crank length would be without pulling on the handle or with application of a specified force to it. I haven’t worked it out, but it seems like rider weight would be negligible. Any increase in rider weight would bring a corresponding increase in force available for pedaling against that weight. Maybe I’m wrong. It happens. All it would take would be for the relationship to be logarithmic, rather than linear. Unicycle weight would probably figure in a bit because it isn’t contributing to the force applied to the pedals. Rolling resistance would increase a bit with increased total weight at a given air pressure, but you can pump up some tires pretty hard.

So far, I’m using what came on my unis. On my 24, it’s 125, and on my 29, it’s 150. I do mostly road riding through residential areas, and have been riding for less than a year. Lots of hills. The ratios of crank length to wheel size are about the same between the two, and I can climb anything on one that I can on the other. I started having knee problems after switching to the 29/150, and I can only think that that is because of the larger circles. I think I’m past that now, but I might expect something similar if I were ever to switch to, say, 165s.

I’ve just ordered a pair of 125mm cranks to put on my 29, so we’ll see how much that hurts my hill climbing ability and how long it takes to build up to being able to do the bigger ones again. I haven’t been using the lift handle for extra force, and I don’t know if I’ll be able to continue that way with the shorter cranks. 137 wasn’t an option at the place I was ordering from; they had only 4", 5", and 6" sizes. So my 125 is probably really 127.

I might try sticking the 150s on the 24 for riding around in my very hilly yard once I’ve finished learning to idle and ride backwards on it. Doing that would make it kind of silly for road riding. My hubs/cranks are square tapered, so I have to consider such choices carefully before spending my limited install/remove cycles.

I find 125s on a 29 is just fine, but it took a little time to get used to it. After that, I bought a 36 and I think riding the 29 with shorter cranks helped me to feel comfortable with the 36 quickly. After a week I switched from 150s to 127s on the 36 with little issues.

Here’s another point: even if you can ride with shorter cranks, sometimes I want longer cranks depending on the style I feel like riding that day–even on the same terrain. For example, the uni I keep at work, a KH29…I keep it there so I can quickly get around my rather large work campus. Most of the time I use the 125mm holes. But sometimes I feel like taking some detours on my way to a meeting, jump some stairs, have a little more fun with obstacles etc…in that case I use the 150s. Yes I keep a pedal wrench at work…:slight_smile: and I love KH dual hoes for the versatility they offer. The 150/127, or 150/125 cranks are especially versatile for most wheels and types of riding.

Ok let’s start I’m 230lbs ish
19-137 trials street flat
20-114 messing around
24-150 messing around
26-137 street
26x4-150 muni xc
29x3-150 xc dh

Weight doesent really matter for crank length, maybe power to weight ratio but that is more difficult to quantify. Anyway there are many factors and no one right answer so I made up a chart a while ago that is just a rough guide on where to start.

I have an updated version on my computer with the 32" wheel

I don’t know how to coppy image addresses on this thing

That’s a nice guide!

24" 150 for muni.
29" 137 for XC, up to 170 for harder terrain
36" 165 for XC, 137 - 114 for road

In my opinion, cranks shorter than 125 it is better to use a bigger wheelsize/gearing

Here is the updated chart.

32" wheels make the chart look so much better, lets hope it’s a wheel size that is here to stay.

Like I said before it is just a rough guide. As you become a better rider you might find your preference shifting to shorter cranks.

I have the chart printed and taped to my loaner parts box

Thanks for adding the 32" column to the chart, Eric. Very helpful.

I run 150s on my 26 and 36, and I think I’ll start with 150s on the 32 that’s currently in process. (I ride the 26 off-road, and the 36 on the road.) I’ve tried 125s, but I like the control/torque from the slightly longer cranks. I know a lot of guys go shorter, especially with 36rs, but I’m not comfortable with them at this point. (I’m still a newbie, started about a year ago.) I think that the feeling of pumping my legs too much with the 150s will be ameliorated by the addition of the geared hub on the 32".

I like the 137s or 140s or whatever they are on my road uni. Having less “pumping” as you say to deal with, compared to 150s, easily makes up for the lower mechanical advantage. I’m going to switch my 20" to 110s and then I’ll have some 125s to try out and see how radical that is, but going a half an inch shorter was pure win for me.

About body weight: You are right that for climbing this would cancel out somehow (more weight to move uphill vs. more weight to push down on the pedal).

The bodyweight to uni/wheelweight ratio will effect riding ability, more for lightweight riders. My 36" for example has 9kg, to get this 9kg moving i have to push down on the pedals with X times 9kg, where X is greater for shorter cranks or a bigger wheel.

About my experience with 150s on the 36": Slowly getting used to it, mounting got easier once i adjusted the seat height accordingly.
Riding itself is much more fun because spinning feels so much better than with 165mm.
This “comfort circle” does vary from one rider to another and may be somehow linked with inseam length. (Mine is about 80 cm)



Well done Eric!

Almost forgot to add:

Thanks for the nice chart saskatchewanian.

Thanks for the info in this thread. I was trying to figure out what size cranks to get for my 26 muni. I think the KH 127/150 will be a fine fit. 150 muni and maybe 127 xc. I’ve been at unicycling almost 2 months and am loving it.

I still smile every time I see ;
“You don’t want to go there”


That sounds like a good choice for a 26 muni

I just put the 165/137 spirits from the 36" on the 26" Muni (the 36" now has 150/125 spirits), raised teh seat a little bit and the first meters i got to ride with it felt awesome smooth with the pedals at 137mm.
I am also getting used to 150s on the 36".
These two lentgths seem to provide enough leverage at an adequate radius for my kind of riding.