I’m about to resume learning to uni after a couple of weeks lay off, having only done a couple of hours.
I have a Nimbus II 20" which came with 114mm cranks.
Is this a bit short for learning on, as others seem to have longer cranks?
What is a good length for a total beginner, and what effect do shorter or longer cranks have on the learning process ?
I should say that I have posted this question in an earlier post, but having done a couple of hours of practice, I wanted to ask again as I am not making great progress and wonder if longer cranks might give me more control ? 
It’s definitely on the short side. Will it make learning harder? Possibly, but probably not too much harder. You could always pick up a pair of 125’s, that seems to me to be a better size for all around use. I think the 114 is more of a freestyle size.
Seems like your only a few hours into learning, it took me 30+ hours to get it, but I was a bit older (almost 40). Seems to take longer the older you get.
Crank length is a very debatable subject as it differs from each rider.
Usually, the shorter the crank, the more stable it is when spinning fast but it make starting a bit harder (as you have to push more as the lever is short).
On the other hand, longer cranks means easier start-up (as you had a bigger lever) but you risk more the unicycle bite on a small wheel (when the pedal hit your chin bone).
At your level, it won’t matter much as you need to practice again and again. And to feel a real difference on a 20 inches wheel when changing the cranks, you will have to get really longer ones or shorter ones. One size up or down won’t be as noticeable as on a bigger wheel.
The best would be to have a fellow rider in your area that can lend you different size of cranks or just enable you to experience how it feels on another configuration.
There may be some differences between 114mm cranks and 125mm cranks but I doubt that they would make significant impact on your progress. How old are you? What progress have you made? A couple hours is not very long. My advice would be to keep at it on your existing setup making sure to keep your arms out, keep your weight on the saddle, and have enough forward momentum. If you don’t have local unicyclists that can give you realtime tips and still have trouble you could post a video to get more advice.
I’d suggest, if you’re comfortable changing cranks (you’ll need a crank extractor tool to get the 114’s off), try some 125’s.
Longer cranks give more leverage and so, more control- for learning, a longer crank would help.
Of course, there’s only 9mm difference between 114 and 125, but that does equate to 10%.
Do you know if the isis crank extractor is the same as a square tapered cotterless extractor (which I already have) ?
No- it’ll be different. Though I believe some isis extractors have a removable bit that makes them usable on square tapers? Not sure if some square taper extractors have adaptors to make them usable on isis.
But, if you got your nimbus from unicycle.co.uk, give them a call on the freephone number to ask them if it’s do-able, or, if not, which extractor you can order which will work.
I have both and actually prefer my square taper crank puller. You just need to find something (I use a smaller bolt) that fits down into the hole of your crank and covers the crank bolt hole on the axle. Just drop it into the crank bolt hole to cover it up and give the puller something to push against. Just make you use something that won’t get pushed down into the bolt hole, then you’re “screwed” 
I know it sounds confusing, well mostly because I made it sounds confusing, but it’s real simple. I can post a picture if it will help.
So, are you saying that the inner thread of the extractors is the same on both?
I guess picture should fix any confusion 
The puller on the left is my square taper puller, the one on the right is an isis puller.
The little bolt to the very left is what I use to block off the bolt hole in the axle, I just drop it in and the head covers the threads and gives something for the puller to push against to remove the crank. So you don’t use the inner threads, only the outer threads. Does that make sense?
You can also place a small coin or washer (about 17mm dia.) on the end of the ISIS spindle and use your square taper crank puller. The coin pictured is a euro penny. The coin/washer needs to fit inside the crank splines and rest directly on the spindle. If you use a washer the hole needs to be smaller than the foot of your crank puller.
If this hasn’t completely morphed into a crank-changing thread, I’d say you’re fine with 114mm. You can over-focus on it, but learning to ride is just hard. On a 20", the shorter cranks will help you roll smoother once you get going, so I consider them a plus. Also they’re a great size for all-around riding on a 20". 125 is on the long side, as the pedals can hit the ground when you turn.
The old Schwinns came with 140’s (same as the 24-inchers). Those pedals hit the ground all the time.
I’ve never hit the ground on a 20" with 125’s, and, personally, find the 125’s do give sufficient extra leverage to make the unicycle easier to control.
When it comes to a beginner learning to unicycle, given a choice, I’d recommend 125’s over 114’s every time.
I think you’d have to do some pretty sharp turns to hit a crank on flat w/ 125’s. I’ve never even touched a crank w/ 150’s, which I first tried soon after learning the basics. They definately made riding a bit easier than the 125’s, for me mostly it was because I could more comfortably ride slow reducing the intimidation of speed.
I know of at least a couple of riders who preffered 150’s, admitedly they were both trials riders.
Looks like my Park Tool cotterless crank puller
OK, so this is getting interesting.
UDC have 145mm cranks in stock.
What’s the general opinion on my using 145 cranks while I learn? These would give a 27% difference.
Hi,
145mm will definitely be a handicap except if you plan to jump right away from beginner to skilled trial rider 
If your hub is an ISIS one, you have choice:
=> either the Qu-ax 125mm in sale at UDC
=> or some Sinz 135mm on eBay (got a pair of 145mm for my muni 26).
They can on 114s as well, that’s why I use 102s for hockey. I’ve only once managed to ground a pedal using 102mm cranks.
My Ringmaster started with 125s, so that’s what I learnt with. I never grounded a pedal until I started playing hockey.
I certainly wouldn’t suggest anything shorter than 114mm for a beginner, but I think you’re right that 114mm should be fine. The smoother rolling could even make them a better choice than 125mm.
FWIW my wife learnt on 114s (although she’s never got beyond 3 wheel revolutions, because she’s not really interested) and my daughter rides quite happily with 114s (having learnt on a 12" wheel with 90mm cranks).
Do you mean that 145mm will be a problem even for learning, as I would plan to run the 114’s as soon as I felt more competent ?