I used to use any 6:00- 16 used tire I could find . One came off of a late 1930s passenger car. One was a snow tire . They all worked ok, even using my front end loader. They can't be too wide, though, or they rub on the axle extension housing that contains the spindle. The problem with buying old used tires, however, is that they rot and leak and need replacement too often. I prefer the implement type smoother tread for the front tires, although the deep ribbed type also works, but leaves deep trenches in soft ground ( like my lawn). I bought my last deep ribbed front tire from a Goodyear dealer, although it had to be ordered a couple of days earlier. I have one of each on my Ferguson front end. I also broke down and bought new rear tires (12:4-28) and tubes , since replacing old rotten ones was a chore.