No-Fork project, bicycle geometry hacked

With a broomstick, you move the support (your finger) whilst the mass (broom head) remains pretty stationary. On a bike, the support (the point where the tyres touch the ground) stays in the same place, but the mass moves around relative to it.

Not quite; we actually move the wheel contact points under us, as conservation of momentum makes them the most mobile part due to the hugely greater mass of the lump on top. The only people who move their body mass around to keep the wheels in the same place are trials riders balancing on beams (see also tight rope walkers etc.). Recumbulent riders can't really move their body mass around at all, but they still manage to ride single track vehicles.

Oh, and this bloke knows all about both moving his body mass and riding with the wheels at an angle to the surface:
[ame=http://www.youtube.com/watch?v=k3LOKfQ3y2Q]http://www.youtube.com/watch?v=k3LOKfQ3y2Q[/ame
]