As of now i have 160mm cranks on my 24x3 muni. I’ve also ridden with 150mm.
I have just put on 125mm cranks to try and it feels a lot faster but with less control.
With experience would my control with 125mm cranks be the same as my control with the longer cranks?
Personally I rode with 140mm, I believe for a while with twin hole cranks, but I decided mounting is easier with 150s and it rides more leisurely with them. I might go faster with shorter cranks, but that’s not why I ride uni. I’d say you will always have more stability with longer cranks, but 160s I’d say are too long.
I‘m in a similar situation, trying to reduce crank lengths on my various unis. On the 36er I started with 165s, then 150s, 145s only to replace them with 140s after a couple weeks or so. Yesterday I rode the 36er and kinda wished for shorter cranks still. My next shorter ones are 125s, which is quite a gap, so I will hold on mounting them to further accommodate to my 140s - IF I replace them at all, because shorter cranks also have a negative impact on my ability to ascend hills.
On my 20er I started with 125s and am currently using 100s. I have to relearn how to ride up curbs. And although I can ride significantly (personal impression, no hard data) faster with the shorter cranks, I usually would ride at about the same pace as before, maybe minimally faster. So I‘m not (yet?) taking full advantage of, well, the advantages that shorter cranks offer.
For me the bottom line is: You will adapt to shorter cranks and as your abilities evolve you will be able to compensate at least for some of the control that you initially lost. Now 165 to 125 is quite a big jump…
I have the following set of configurations:
Here the first tire width is for summer, the 2nd - for winter.
Config. 1. I use mainly indoor to exercise mainly with idling. I never use it for hopping because of the squared cranks fit.
Config. 2 I use for training with idling, start/stop riding, SIF, hops, fwd/back riding and sometimes for a commuting with the use of public transport. This configuration is the easiest to mount for me.
Config. 3 I use for commuting and sometimes for training with idling and hops. Mainly I use 125mm cranks’ setup. Sometimes I use 150mm setup when there is a layer of snow. In icy conditions, there is a noticeable course yaw with these long cranks. When using the longer cranks I lower the saddle ca. 1". A mounting is easy for both setups, but riding is slightly slower for longer cranks. I prefer 125mm.
Config 4. Now I use it rarely, in winter in icy conditions, mainly with 125mm cranks. In summer I use it for a local commuting without the public transport use. I use 100mm cranks to ride in parks for training only. As for a mounting, the easiest for me is the 150mm setup and the 100mm setup is a problem for me to freemount on.
Only time will tell. I can guarantee that with more time on the 125mm cranks it will get better, but can’t predict where your skill will ultimately develop to.
I never realized a great deal of increase in speed shortening my cranks but the ride smooths out after you get used to it from 150 to 125. Mounting is a little harder and you notice the difference on elevation changes. For me a stabile relaxed ride where I get in the groove and just ride is more important than speed.
You know what they say, there’s nothing like ripping down the road at a break neck speed of 10 miles an hour with the wind blowing through your hair, much more exiletating than 9 miles an hour. Of course that’s a joke.
I think i’m going to go with my 150mm and build up a lot of experience with my uni off road.
Then i’ll be better equipped to handle shorter cranks if i decide to change later.
A 24"/125mm setup would feel quite similar to a 29"/150mm setup, which you can ride basically everywhere, unless it’s really steep. I’d recommend you giving 125 mm a shot. If you feel they limit you offroad, and you have to resort to walking a lot, then go for 150s instead. Practicing 125mm will even make you more skilled with 150mm. The shorter cranks you ride,the more “correct” you have to ride (better technique).
If you still chose to start with 150s, don’t wait to long before advancing to 125mm 
Good luck!
Shorter cranks on a smaller wheel is a very natural feel as opposed to a larger wheel. It’s all about getting that larger wheel moving from the start. I love hopping on the 24 and rolling off, it just feels so natural and easy. As someone that rides a 24 with 125s and have ridden my 29er with 150s I can say they are nothing alike . Don’t get me wrong , I love my 24 Oracle and like to pack it away for traveling, it’s fun to ride on the board walk at the beach and get around town but I never got the feeling it is like riding my 29er with longer cranks, that’s just my opinion, I just can’t draw a comparison .
You don’t have to use shorter cranks.
My road bike has narrow handlebars for a reason, while my MTB has much wider ones for a different reason. I will never have the same level of control on my road bike as I do on my MTB, and I do not want this extra control on the road.
If you force me to keep only one bike, I’ll have to go with the MTB.
The physics behind your cranks problem and handlebar width is the same. Choose your size based on your riding style and pattern.
Obviously the riding experience is quite different, mainly due the bigger, heavier and smoother 29" wheel and the higher pedaling frequency on the 24". And tyre thickness also comes into the equation.
But the felling of pedal resitance, how easy they are to ride up the same hill, and largely what kind of terrain you can ride them on (excluding really technical trails), is also the same, imo. I have ridden a lot of combos of 24 and 29" with “corresponding” crank lengths all around my place.
You are correct, choosing right crank length for the situation Is really what it is all about. Because people ride unicycles for so many different reasons there is really no right answer. Also peoples physical size and weight will also dictate wheel size and crank length. It’s trial and error, only you the rider can decide what you are comfortable riding. When I see long dissertation on this subject where lots of physics equations are presented trying to explain wheel size to crank length they usually leave out the most important parts of the equation: the rider, the riders ability and the actual activity the rider is participating in..
Even though practicing 125mm will make you more skilled, I don’t think people who ride 125 will ever return to 150mm.
In my case I don’t see the point practicing 125mm, because I prefer the 150mm.
Also I don’t know the default crank length on a 20" unicycle. The cranks on both the 20 and 24" uni’s are shorter than 150mm. And I don’t feel I need longer on those small wheel sizes.
So the bigger the wheel, the longer the cranks should be?
From the couple unicycles that I bought without multi-hole cranks, the 26" came with 150mm, the 20" came with 125mm, and the 16" came with 100mm cranks.
On the 26" wheel I’ve since went to 100mm cranks. I did throw on the 150mm cranks after getting used to the shorter cranks and found that I much preferred the shorter cranks. I have 89s on the skinny 700c wheel, though I don’t have much seat time with that one. Next time I order from UDC I’ll probably pick up some 75mm cranks and give that a try
Just a little update.
I tried tonight on my 24x3 with 125mm qu-ax zero q cranks on my decking.
I could mount ok and ride over some small planks i laid out to simulate little bumps.
I could hop and sideways hop over the planks.
Plus i could idle as well.
I think with practice i’ll be ok with them.
My legs moving in smaller circles will maybe stop chaffing on my saddle.
I also tried with my Impact saddle.
I think i just need to build up my confidence with these cranks with regular use.
The pedalling certainly felt smoother.
Update number 2
I’ve ridden some more with the 125mm and although it’s ok to ride with the shorter cranks i admit i’m not much of a fan.
Although longer cranks seem slower i prefer the bigger leg movements.
Riding the 125s my leg circle is smaller and I don’t particularly like this sensation when riding.
I removed my 24" wheel from my Hatchet frame and fitted my 29" wheel with Vcx+ cranks.
I rode with the pedals in the 170mm position for 16km today and it was lovely to ride.
I think i’ll end up using 145mm cranks on my 24" wheel.
I think that‘s a good intermediate length, at the moment. You can always give shorter cranks a second try if you feel like it down the road.
Is it on a muni? I guess so since you say the tire is 24x3. 137 might be the sweet spot - I do love this size on my 24 muni. On the city one, I’m at 110 and will go lower soon. But it has a 2.4" wide smooth tire, so barely any rolling resistance.
Yes on a muni.
I have a pair of Koxx tubular cranks size 135mm i could try.