Are 89mm cranks OK for a 20" cycle

What do you use on your 20" to get a smooth / stable ride.

After a day messing about in the practice alley, I finally managed a technique to ride the 20" on 89mm cranks.

I don’t do trials - this is my “back yard” practice Uni. But it was too wobbly with 127 and 114 cranks.

I wanted the gearing to be the same as my 24", so I by-passed the 102’s and went straight for the little-uns.
They are tiny.

Should I have bought the 102’s instead?

It’s really whatever you practice on. I first learned on 125s for my 20", but now I’ve recently started riding 75s on my 24". The biggest consideration is the extra oomph necessary to get you moving on smaller cranks - freemounting techniques and overall feel are different.

I tend to think that longer cranks are easier to learn on, but given enough practice anything can be learned. I went from a 20" with 125s to a 36" with 114s and that took a ton of practice, but given enough effort it happened.

Reeny, I have 89 mm cranks on one of my 20" unicycles and I’m used to riding it by now. If I can do it, I’m sure you can too.

But there’s definitely more to the crank length business than just the ratio with the wheel size. Wheel diameter divided by crank length seems like a good first-order guide but there’s a difference in the curve that the pedals trace and the way that knees and ankles have to work to follow them, since our legs and feet don’t get shorter when we switch. A bigger wheel also makes pavement bumps seem smaller and the greater inertia helps for rolling over things. With the same ratio on a smaller wheel, it takes more anticipation and force on the pedals to keep the same bump from stopping the wheel. My 20" with 89s, my 29" with 125s, and my 36" with 150s aren’t far apart in ratio but feel totally different to ride.

I was actually trying to get 100 mm cranks for that 20" unicycle, and I definitely did order them, but the shop must have been out of those because they sent 89s instead. I had 114s on it for a while and they weren’t enormously different from the 125s they replaced.

The first time I rode down my driveway, which isn’t terribly steep, after putting on the 89s, I tried to slow down with back pressure and launched myself off the front of the unicycle! I’ve never had that happen on any other unis, even going down much steeper hills. The 89s are an interesting challenge and might be smoother on smooth surfaces when I’m doing something that I do well, but for practicing skills on the average quality paved street where I live, I tend to favor the other 20" with 125s. The extra length definitely makes it easier to make quick adjustments and balance corrections while trying to get reps idling or riding backwards or anything like that that I’m still awkward at doing, and that’s mainly what I use the 20s for.

Thanks for letting me know I am on the right track.
Onwards and upwards.

The knee and ankle comment is valid.
My calf muscles were sore after a few practice runs.

The other difference I noticed is that it is better to ride with my toes pointing inwards on the pedals, then I can use leg pressure on the saddle to steer.
With the longer cranks I would nudge the saddle with my thighs on the up stroke.
There is no upstroke with the 89’s.

Also, you will notice that riding with short cranks shifts focus from balancing with legs to balancing with posture. At least that is what i noticed on my commuter 26" after installing 110mm cranks.

i ride 75mm cranks on my 20". Great for spins, swirls and pirouettes but many tricks are not as easy as on 100mm or 125mm. Needed a bit of time to relearn them all. But now it rides super smooth.

The technique is improving.
Not so much on the 20", but much smoother and steadier on the 24-club using the short crank skills learnt on the little-un.

Saddle time has helped me to get the muscles and brain fully co-ordinated.
I can steer in a straight line with less effort (on either cycle).
And the overall balance, and rhythm are much easier when I am on the easier to ride 24" wheel.

The 114’s were fitted to the 24" a while ago, and have taken a while to get used to.
Two days on the 89’s (20") and it is starting to click into place.

Thanks for the advice and support.
Also - I took the 20x1.95 Maxxis Ringworm off and used the heavier 20x2.25 Kenda Kutlass tyre to try and stabilise the ride.
It seemed to smooth out the wobbles.