The Alcoa forged wheel that comes standard on the SRT is 9 inches wide. The widest tire that you can fit on them, that will perform and wear properly, is a 275/40/20. For clearance under hard cornering, the SRT engineers have recommended that you stay with a 245/45/20 tire for the front. However, if you don't race your car, you can get by with the wider 275/40/20 tire on the front. I intend to have the staggered tire width set-up on my 2009 SRT to get that "old school" look. (Note- You want to buy a 40 series 275 tire to keep the diameter the same and the speedometer accurate).
Some Challenger owners have squeezed a 295 tire on a 9" rim. However, it is not advisable. As I previously stated, it will not perform or wear properly. Look at the center diagram below, (rim too narrow), as compared to the first diagram (proper fit). If you are set on a bigger tire, I suggest that you buy a 10" rim. Then you can even install a much wider 305 tire. I had this set-up on my 340 'Cuda. I had spoked wheels in the front and slotted wheels in the rear. It gave my car a real mean track look.
