If your wheel wells have a black plastic lining, do this area also. Finally, buff the tire down with a terry towel. Check out the Wheel Shield , an inexpensive, time-saving trick the pros use. When a tire is manufactured, a stabilizer molecule is added to the tire polymer. This molecule is called a competitive absorber and will work to protect against ozone and UV damage by capturing and absorbing UV radiation and converting it to heat which is dissipated harmlessly.
Carbon black is the competitive absorber all tire manufacturers use.
This is why tires are black, not a color to match your car or your taste. Ozone, a part of the air, combined with sunlight, causes the degrading of rubber tires which results in dry rot, discoloration, cracking and splitting. The added absorbers do their job but not indefinitely. As carbon black looses its ability to perform, it turns gray. One of the best products on the market, to retard the ozone and UV damage is 303 Aerospace Protectant .