I was at Daytona for bike week and went to see the Metzler crew about my front tire cracking on the side walls. First question they asked was how do you clean your white walls. They pretty much told me to go pound salt, that the cracking was just superficial. I went back the next day and told them that I fixed the cracking Metzler tire by replacing it with a Dunlop and also told them that I would never use another Metzler.
How do you clean it? If you use bleaches it will cause the oils to come out of the rubber causing cracking,much like the UV from the sun does!