How do I clean rust stains off my white sidewalls? PROBLEM SOLVED

George Jets said
I really doubt it is rust, where would the rust be coming from?

It's the brown base coming up from the white wall. Just like the same brown staining problem with raised white letter tires.

I hope they believe you George because there's a bunch that have never listened to me. Yet the nay sayers have never had a BFG with the browning letters. BFG knows of the issue and has replaced tires because of it under warranty.