for a 9" wide rim on a STOCK suspension you want either 5" (0 offset) or 5.25" (6mm offset). More backspace and you'll rub the spring, less and you'll rub the quarter panel. 9" is about as wide as you can go before you need to start modifying things. Max width would be about a 275/285 rim.
I run 275/40ZR17s on my Challenger, and I'm very close all around. I run 0 offset.