Bf Goodrich brown walls

Coupe said

Tires bloom because antiozonant pushes its way to the outer edge of the rubber casing with time. As the element comes into contact with oxygen, it leaves a brown residue on the surface of the tire. Antiozonant is organic and helps tires last longer as it slows deterioration due to oxidation.
https://www.google.com/url?sa=t&sou...QtwJ6BAgXEAE&usg=AOvVaw3PS78c1rVthX3jc5NMFhfV

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That stuff comes off with mild soap and a brush. The brown that discolors the white letters could be the same stuff but it isn't easily removed with dish soap and a brush. Tire and whitewall cleaners don't work. Sandpaper doesn't work that well. I used a Scotchbrite pad on a die grinder but the stuff comes back.