Somewhat related. I picked up some 75mm cranks the other day. I’d been curious and was also ordering other things. As I have a couple of unis with cotterless cranks, I decided to go cheap. Being cotterless, steel cranks they cost almost nothing (€8.32/£7.24/
$9.97/
$12.86/
83.42kr).
Let’s just say I won’t be making these my “one length to rule them all” 
but they worked ok on a 24" with a tyre at fairly high pressure. I doubt they are much of an improvement over the 89s I have generally run this unicycle with (when using it for road usage) but they were usable and not a massive slow down either. I have a 36" with a cotterless hub as well, so I perhaps I will try them on that, just for the fun of it. I also have a 54" wheeled penny farthing that has a cotterless hub but to be honest I wonder if I could even turn the wheel with such short cranks.
Here they are held up against my 36er which is currently mounted with dual hole 125/150 cranks
And mounted on my 24
Here is my test ride
