Hey, let's don't actually expend any energy riding bikes—we could just replace our front wheels with a RevoPower and never have to pedal our bicycles again. Well, not quite. This little 1.1HP, 23cc, two-stroke internal combustion engine-that-could revs up to 7500RPM and its maker says it can reach speeds of 20 mph on a flat surface.
The remarkable thing about this engine is that it's less than 3 inches thick, but it might be a little awkward since it adds 12 pounds to your front wheel. The good news is, it's capable of 200 miles per gallon. Available in early 2007, the reduced fitness it brings you will cost you $400.