Alan,
I run 26X12X12 Swamp Witch ATV tires on my 317 and LOVE them, they grip like crazy. The Firestone's on my 112 are 2 ply and my Chin Skin's on the 110 are also 2 ply the ATV tires are 6 ply. Neither of the "tractor tread" sets grip nearly as good as the Swamp Witch ATV tires.
I ordered mind from Tucker Tires ebay store, the same place I got all the tires and tubes I have needrd for my Deere's.