According to ICON, the UCAs require a maximum of backspacing of 5" to clear a 12.50" wide tire. The stock wheels have 6.5" of backspace, so by the math, you'd be able to clear up to an 11" wide tire. That being said, we were able to clear a 295 wide tire on one of our project trucks using the stock wheels and ICON's UCAs without issue. In short, you'd be fine using a 275 wide tire on the stock wheels, though you could potentially jump up to 295 wide or do a 285 wide to be safe while still getting some extra width.