It had to happen sometime: IOTD reinvents the wheel (again).
A wheel (in this case of a bicycle) is replaced by two sectors. Each of these can rotate independently about their common axle. The bicycle is moving right to left. When the sector marked ‘a’ has come close to the end of its tyre’s contact with the road, the other sector marked ‘b’ is flipped around the axle counterclockwise to take its place, just in time to provide smooth forward motion (with much lower rotational inertia than normal).
Such a setup requires a spring mechanism to drive the sector and a robust trigger to activate the process. The axial spring would be wound by the forward motion of the machine and the triggering could be quite crudely coordinated using a mechanical latch.
This arrangement also allows a greatly reduced weight and space requirement for a fold-up machine. It’s also rather a cool way to ride about, always looking as if one is about to fall off.
Rather than flip counterclockwise from a to b, the sectors might swap places by raising the rear one off the ground and ‘stepping’ clockwise from position a to b (at the cost of added complexity). This would save some frame height (and the cost of material) as well as reducing the energy drain from the system.