As mentioned the 4.88s are because of the 318. I ran 235/85/16's on my 88 D350 360/435/4.56 Dump for years and it was about the best combo for load, mileage,braking/accel/cruise I could get w/2-4 tons on it. I had a 75 D-600 I put 9.00/20's on it up from the 8.25's it came with trying to "gear it up" and it sapped all the power out of it. 318's get overwhelmed easily on heavy vehicles. Sounds like a set of lock out hubs would help.