Dish soap and water rinsed well, or simply pass on it entirely. They're tires and will get dirty in use. It's their Karma, and you might as well accept that.
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Chain-L site
An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.