Bigger Wheels Roll Down Hill Faster: The Reason?

[daniel_i_l]

I noticed that if two bicycles roll down a hill, then the one with bigger wheels will get to the bottom first (I tested this with my brother). I could only think of one explanation: The bigger wheels make less revolutions and thus have less friction. Is that the reason? Are there other ones?
Thanks.

 

[Kurdt]

Differing wheels do make a difference as the energy goes into rotation as well as movement. E(translation)=1/2mv^2 + E(rotation) = 1/2 I w^2. Where w= 'omega' = angular velocity. I is the moment of inertia which depends on the structure of the wheel.

 

[daniel_i_l]

But that would mean that a bigger wheel would roll down more slowly.