PB's SNR did very little to clean the Goodyear and Michelin tires I tried it on. I rinsed off the same tires and sprayed them with EO A2Z and dirt and 'browning' just dripped off the tires, I was surprised just how much more dirt came off the tires using the A2Z. My review of PB's SNR with pics of SNR and A2Z in use is posted over at Autopia if anyone is interested.
IMHO PB's SNR is VERY good at cleaning rims, but it falls well short when asked to clean tires. I don't remember Steve ever claiming or selling SNR as a tire cleaner?
Keep a bottle of A2Z or a strong APC handy if you want to clean you tires, save your SNR for cleaning your rims.