[Fulltiming]

The 12R22.5's have a larger rolling radius so they will decrease acceleration, increase speed in each gear and increase top speed. If you want higher load ratings, make sure you go with H rated tires rather than G. Regardless of size make sure they are rated for 75 mph. Some truck tires are rated for lower speeds. There is 3.3% decrease in revs/mile with the 11R vs the 12R's. Technically, the 315/80R22.5 tires are supposed to be mounted on a 9-9.5" or 9.75" wide rim depending on the tire manufacturer. The 11R22.5 are typically mounted on a 8.25" wide rim. The 12's, even in load range H will have a noticeably higher load capacity and are available in J load range. Try to find steer tires for the front (or all positions if you want to move them around to the front at some point). Usually the 11 and 12's are easier to find if you have to find one in an emergency than a 315/80.