How many wheels does a moving vehicle require for maintaining horizontal balance

I think it could be zero since moving vehicle doesn't need wheels may be it is just pushed or it is a magnetically levitating or may be it can fly like aircraft.

but if wheels are compulsory then our main purpose is to move without toppling which is possible even with one wheel as we see in case of circus cycles which have only one wheel, it's only a matter of balance and techniques

only one

ever seen a "unicycle"

balance comes from gyroscopic force effects. very complicated math. very skillful rider.

One