When I had my 52 1 ton dually, I tried 17.5's and they would not even work on the inside rear. The factory 18's barely clear. 19.5's will work but are not easy to find with the early 1/2" lug holes and correct diameter center. I had a set of 19.5's but sold them to a member here. I know some have changed to a later rear axle to get better gears and be able to run a 16" wheel and tire.