Project Orion-cycle

The bicycle is a perfectly acceptable invention. The in- line 2 wheel thing has gone remarkably well, as it turns out humans are pretty good at the whole balancing thing. The bicycle does suffer from poor rough terrain performance however. Sure, you can slap on a couple of big nobbly tires and you're able to ride over the slightly bumpy bits of the Earth's continents. What about the rest?

The common, or garden variety Orion space ship utilizes massive explosions and a big sprung plate to elevate the ship into and through space. How about two of these plates, one fore one aft of a standard-ish mountain bike. The plates could be mounted on long levers with a sort of parallelogram arrangement for alignment, to a fairly conventional suspension system. The plates have holes in the center through which small blobs of plastic explosive are dropped.

Essentially, the thing then stays in the air with grenade- sized explosions every second or so, front and rear propelling the massive sprung plates up before the springs push them back down. I suppose some slight rear-ward weight bias and a steerable front plate would give theoretical control over direction, but who cares.

Unlike the spaceship, this doesn't need to be made out of unobtainium. It will however be very loud and dangerous. Ear defenders advised.