These solutions creep under the dirt and brake dust, loosening and lifting surface grime. Water washes away the natural oils in rubber that keep it elastic. Formaldehyde and petroleum distillates act as a solvent, eating rubber on contact. To protect against ozone and UV damage, a stabilizer molecule called a competitive absorber is blended with the tire polymer. Competitive absorbers work by capturing and absorbing UV radiation and converting it to heat which is dissipated harmlessly.
All tire manufacturers use the same competitive absorber, called carbon black .
This is why all tires are black. However, as carbon black loses its ability to perform, it turns gray. This is one reason why black tires discolor as they age. To protect from further ozone damage, tire manufacturers add a wax compound to their formulas. Tires flex when they are in motion, causing the wax molecules to migrate to the surface.