Why do dirt bike tires turn blue after riding?

Question

My boyfriend rides a Yamaha dirt bike, and after he rides (regardless of which track he is on) the tires have a blue tint to them. Anyone know why? He asked me, and so help me look smarter than he is! :-)

Answer 1

Its the surface that he's riding on.

If he's riding on shale (brick dust) it won't happen, but if he's riding on a granite surface the tyres will go a blue colour

Answer 2

Exhaust from the dirt bikes exits and the heavier partials, unburned oil partials, fall into the dirt. The rubber tires have a reaction with the oil making them slightly blue. So the answer is the oil in the dirt.