Can anybody explain to me why idling gets harder the bigger the uni and the shorter the cranks?
I’ve been practicing how to idle my 24" for a month now and still can only idle 6 or 7 times before I bail.
It does seem however like a really important skill to master. I figure if I understand the science behind it perhaps it will make it a bit easier.
shorter cranks = less leverage, saying that, i’ve idled on 65mm cranks on a freestyle uni
with a bigger wheel it’s less of a back and forth swing and more of a roll back then roll forwards again, but it’s still doable 
Idling does take quite a lot of practise, you’ll get it!
I’m guess it’s due to the cranks turn ration. Meaning it takes less of a turn the larger the wheel or shorter the cranks to get the same affect, meaning there is less room for error and the optimum zone for idling is a lot smaller. Example- on a 20 in you can go from 3 to 9 to idle, but on my 36er I idled at something more like 5-7.
Most people forget that, just like riding, you must keep your weight on the seat for stability. Try to remember that when you practice.
it also has to do with inertia, to throw in a physics term. it takes more force to move back and forth on a heavier wheel than it does with a small wheel.
The bigger the wheel is, the more momentum it has. When idling, you have to stop the wheel from speed and accelerate it up to speed twice in every cycle. On really big, heavy wheels like the Coker, people don’t bother idling; they hold onto something or hop in place.
The difficulty with idling on a 36" wheel is that with each idle cycle, your changing the earth’s rotation.
sure feels like it
Bigger wheel? Yes. As the wheel gets bigger, the mass of the wheel is farther and farther away from the axle, making it more work to change the wheel’s direction. Also bigger wheels are generally heavier.
But a taller unicycle is not harder to idle. In fact it’s easier to idle a tall giraffe than a regular unicycle. Not a super-tall one though; maybe up to 10’ or so. Beyond that, the weight starts getting up there again, along with “other” factors.
Shorter cranks mean more leverage. In a way, it’s like going to a bigger wheel. You can idle on a 36" unicycle, but you don’t see people do it much because it’s too slow, too much work, and takes up too much space. I will idle my 45" wheel in a parade, but it’s to show off, not for functional reasons. People would rather see me get off and then back on again. 
The physics of unicycling is similar to upside-down pendulums. Think of balancing a yard stick or broom vertically on your hand, you move your hand to keep the top of the stick as stable as possible. The same is true of idling, keep your body stable and move the wheel under you. If you try chasing the wheel instead you are doomed.
Now, try balancing a yard stick with a weight on the bottom. It’s more difficult!
Then try a ruler instead of a yardstick; same thing. Then, if that’s too easy, try a pen. Longer is easier, which is why tall unicycles are easier to idle on.
BTW, correction to my post above: Shorter cranks mean less leverage (more power needed).
more idling
Wow thanks for all the feedback! I’m going from a KH24 with 170mm cranks to a KH29 with a Nimbus wheel set that has 125mm cranks.I was curious as to what my chances of success would be idling the 29". Basically what I hear people saying is that the bigger wheel has more weight and thus is harder to control?
Also that I should be aiming for smaller movements.
Can you do everything on a 29" that you can do on a 24"? I really love my KH24 and am staring to get a bit worried that I made a wrong purchase getting the 29". It doesn’t seem as “agile” and I can’t turn on it etc. like I can on the 24"
you will love the speed and you will get used to controlling it. i went from a 20 to a 36er and i can now do u-turns(in a large circle)
The yardstick analogy has been a great help so far! I’m sure I’ve improved just by trying this…out of curiosity you ones out there who can idle proficiently - how long did it take you to achieve this?
I remember spending 2-3 months, nightly trying/learning to idle on a 24". Took a while, luckily once you get it, you got it. However, for me, idling on a 36" wheel is constant struggle for improvement.
Where is most of your weight while you are idling?
I’ve read both that most of your weight should be on the lower pedal, and that most of your weight should be on the saddle. Which is correct? Or are there different ways to do it?
I learned to idle with my weight on the one pedal, and can idle maybe 10 cycles, but I find that the wheel is moving in an arc - rather than straight back and forth (maybe better for lateral balance?), and I get tired very quickly.
I tried 1-foot idling today for awhile (holding on to a support), and the only thing that makes sense is to have all your weight on the saddle, and just put force on the pedal to change directions at either end of the swing. Is that the same for 2-foot idling?
you just helped me a bunch. ive never succeeded with one foot idling and that may be why. i do the same arc thing as you implying that i have too much weight on the pedal. thanks
Weight on the seat. What you may have read about weight on the pedal is that one foot does all the work. The top foot is just kind of along for the ride (that’s why it’s easy to learn the one foot idle).
so for one foot idling, where do i put my weight? the unicycle always shoots out behind me when i try. i guess that means when idling i use both feet for control
Try pressing down hard with your other foot on the frame. Eventually you will require less support from the non-pedal foot, at least that worked for me.