[dragontamer]

I'm not saying "rubber damages concrete" any more than current gas taxes say "gasoline damages concrete".

I'm saying the degregation of rubber is (likely) in direct correlation to the amount of road damage. (Much like gasoline is in direct correlation to miles-traveled, and thus is also an indirect measurement of road damage)

There's no need for causation in this discussion. Correlation is enough to be worthy of a good tax design.