I know most will disagree but 275 is perfect for a 10 inch wide rim, so on a 8.5 I think 255 is the max,since ford puts that on a 9 inch rim stock, the rim doesn't put that wide of rubber down correctly when your throwing too big of a tire on., it my look cool but it is a waste of money. If you want more traction get a thicker wheel and then put fat tires on. I dunno, just my opinion.

This is true

PROPER FITMENT? max for premium wheel would be a 255 or a 275 for brembo wheels. Can you go bigger? YES, but it isn't recommended. A tire that is 275mm wide is close to 11 inches wide. That puts a 275/40/19 2 inches wider than a 19x9 rim. Anything bigger than that and you will actually start to lose contact patch from the tire bubbling over the rim.