Balancing on a Bicycle: Weight Distribution Explained

[bill nye scienceguy!]

why is it that bicycles are extremely hard to balance on and wobble when youre going very slowly, but are easy to balance on and go straight when youre cycling quickly? a friend suggested it might have something to do with weight distribution...

any revelations much appreciated.

 

[Homer Simpson]

look up "trail" on bikes steering:
http://www.phred.org/~josh/bike/trail.html
when the bike is moving, trail provides a torque to keep the wheel straight. As for not just falling over while moving with the wheel straight, when the bike is moving and starts to lean left, the natural response is steer left into the lean which puts the bike back under the center of gravity and uprights the bike.