Nothing that I have ever used seemed to work. However a detailer I know recommended new motor oil. I tried armourall when it first came out in the 70's or so, but that was back in the day of wearing them out from hole shots so I never had tires laste me longer than a year. Tried formula404, no great shakes. Combined with wesleys tire cleaner and 404 my pirelli's dry rotted in about 16 months... Now I just leave them alone, keep the white letters inside and black outside where I won't be tempted to clean them like the neat little yellow scorpions on the pirellis.