Wheels: why size matters

Graphic - bigwheels
From http://www.flickr.com/photos/33442021@N00/2547743357

Children often wobble a lot when they ride bikes. Why is this?

The reason is, that every bicycle comes equipped with a pair of gyroscopes that stabilize the bicycle, and keep it going upright and in a straight line. The amount of angular momentum stored in a bicycle wheel depends on the size of the wheel, but how?

Angular momentum of wheels of different sizes

Let’s consider two bikes 1 and 2 being ridden at the same speed. Each bike has wheels of different radii, constructed of the same material. The important quantity we need to calculate is the angular momentum of the wheel since it is responsible for the stabilizing torques.