Reply to "JTs GT5's New Wheels"

Jim

I determined the optimal offset, for my flares, by using a nut to attach 12mm x 1.5 threaded rod to three of the existing wheel studs. By threading another nut on each threaded rod extension, I was able to move an 18" Fiske wheel, that I have on my L, forward and back a fraction at a time to gauge appearance and interference. I wwrpped a hose around the 18" 1335/30 tire to obtain the 27.2" tire diameter of the 345/30/19" tire.

After removing the shock absorber, I was also able to move the suspension through its range of motion with the tire/wheel asembly in place to determine the best compromise of offset and interference under compression with the top of the fender flare. At least on my GT5, the further outward the wheel/tire, the sooner it contacts the top of the flare. The wheel tire assemble does not tuck in at a fast enough rate under compression to clear the bodywork. This was the case with the stock tires and a larger diameter only exacerbates the problem. Understanding this compromise was critical to optimizing offset. I used a digital inclinometer on the lower suspension arms to learn how much compression I had until interference with the stock tire diameter and them did comparisons at various offsets with the larger diameter wheels to find a suitable compromise. A pic of the process is attached. The end result, was to move the tire in closer toward the frame.

My final dimensions were

GT5 Profil 13 Fikse Diameter FS BS Width Tire Diameter
Front 18 6.875 3.875 10.75 outer lip to lip 285/30/18 24.76"
Rear 19 7.5 5.5 13 outer lip to lip 345/30/19 27.2"