When i was a boy i watched a Disney movie about a claver kid that made a bike that could jump. Main character could jump even over a fence if he tried hard. He used a combination of speed, muscle power and a rocket or pneumatic tube to have a jump. That was really impressive. As far as i remember the boy used pneumatic tube that was pointed down. Or may be some rocket. I think that can be fun to try to make such a bike. This is the movie: http://www.imdb.com/title/tt0088742/ Concept: P.S.: will post additional information if i can find it.