I have a 2015 Z71 with the 1500's at top setting and is about 1.75" lift, I test fitted 285 65 18 (32.6 x 11.2) which is just about the same as a 295 55 20 (32.8 x 11.6) and the fit just right. IMO, anything bigger (305 55 20, 33.2 x 12) will look like you are trying to stuff the tire in and looks funny without at least a 2.5 or 3". I will say that the B1500's are night and day compared the Z71 Ranchos that I replaced.