Impossible wheel

The impossible wheel, also known as the BC wheel (after the comic strip B.C), represents the most basic type of unicycle, consisting of a single spoked wheel with pegs extending from the axle. The rider mounts the wheel by jumping onto it while in motion. This contraption has no pedals, so when the wheel's inertia runs out due to gravity and friction, the ride ends.

The impossible wheel has of course no practical place in general transportation. In practice, the pegs would rotate with the wheel, making it, as the name implies, impossible to stand on.