Charles, you need to start with the speed you want to reach. If you are after the record then add at least 2% to that speed, and factor in the rear end ratio you are going to run, the tire size, and the rpm you think the motor will pull. You have three choices, 26, 28, and the M/T 30 inch tire. I have run both the 28 and 30 inch tires in stock Stude wheel wells with no problem. By the way, the Ford 9" 2.47 is about the highest ratio you will find, unless you add a quick change rear end, which will take up to a 2.19 with the 4.10 ring gear, but you would need about 1500 h.p. minimum to pull it............Bob