Your only going 20mm wider in the rear. The other change will be your overall tire diameter. The factory tire in a 255/35/19 is 26.03" O.D. The 275/35/19 is 26.58" O.D. Basically that says that the 275 is about a 1/2 inch bigger overall in diameter. Will it slow you down enough that you will notice, not likely. The 275 should fit fine in the wheel well on the factory wheel. The 275 will "bulge" a little bit more than the 255 as far as looks. My 2 cents!