Agree - Tire Cleaner
I have used the Westley's whitewall tire cleaner that Rich recommended and it's magic. It also works great on the rubber Nicro vents when they start to gum up on the surface. I have always had a mild concern about the impact the bleach may have on the rubber, but I used this product for about 18 months and so far absolutely no problems at all and I get a beautiful new looking surface each time. The gunk literally wipes off in about 2 seconds then just rinse it very well. Rob