Look for a specialized whitewall tire cleaner in the automotive section of a department store or hardware store. Regular cleaners like Comet can work well to remove dirt and discoloration on the tires, but they can dry out the tires in the process, leading to early wear. Cleaning products containing alcohol or chlorine bleach should be avoided for the same reason. For the best results, opt for all-natural whitewall tire cleaners (e.g. Simple Green). Use an SOS pad for regular cleaning of whitewall tires. Use a hose to wet the tires. Wet the SOS pad as well. If your chosen tire cleaning product is in spray form, spray it directly onto wet tires. If it is a liquid, mix the product in a bucket with water (as per the directions on the label). Soak your SOS pad in the mixture. Put a generous effort into cleaning your whitewall tires thoroughly. The effectiveness of the cleaning is just as contingent on the duration and intensity of the scrubbing as it is to the products used. If the work is too intense to tackle on your own, enlist the help of a friend or family member. Rinse your tires every few minutes while you wash them to see how clean they are getting. Reapply your cleaning product and continue until you are satisfied with the results after rinsing. After you have scrubbed your tires clean, use the hose to rinse them off thoroughly.

Summary:
Use a specialized cleaner. Wet the tires and cleaning pad. Apply the cleaning product. Scrub tires thoroughly. Rinse off your tires.