If anyone wants to know, you can install 275/40-20 tires on stock 9" wide wheels on the front and rear of a 2008-2010 Challenger SRT without clearance issues. The 9" wheel (rim width) is right in the sweet spot for 275/40 tires. Essentially, the 275/40 is a "plus zero" size up from the stock 245/45 tire. The diameter and sidewall heights remain the same. You are just shifting the tread width size and compensating with a lower aspect ratio. Here is a photo of the rear tire clearance.