The jig was nothing special. I used a piece of 3/4 MDF, maybe 6" wide X 10-12" long, basicallyy the length needs to be long enough to match the radius of the largest tire you think will fit. Cut a hole near one end the size of the center boss that the wheel locates on and holes for a couple lugs. Once bolted up you use the back side of the MDF as a datum to get your back spacing dimension and check for tire width clearance all around. I tried using an old wheel but the 6" wide jig was much easier to get accurate numbers.