Florian Schlumpf is the Swiss engineer, & maker of planetary 2 speed bicycle cranksets, and an avid Uni rider.
so he has a 2 speed uni hub.. you can build a 24" wheel and kick in the 2nd gear,and it acts like a 36" wheel.

I've seen a rider on an actual 36" wheel, keep up with traffic thru town ..

Others have done mountain tours, Bhutan, for example.. mastering the trials riders positioning bounce
with a brake under the saddle nose to lock the wheel ..

a really fat 24" tire is made by QBP, Pugsly stuff. rims too..