It's an annoying concept hey! Once your head is around it though, you never forget it.
I'm running 18x9 +26, and I would only really want to run maybe +35, tops, with 255's on them.
Wait, hang on, I've run 275's before.. Hmm. Maybe the suspension is different.. But yeah, if you want x9's, try and get between +25 and +35. With my +26 and 255's on the rear, they feel like they line up perfectly with my rear rolled guards; much fatter and it'd scrub on the outside... not sure how much room on the inside I have though.