I found this on the web. They look like 10 ply..
http://otrwheel.com/products/tires/turf/traction-master/otr-traction-master-hf3-tire-31x15-50-15-detail----------------------
Part Number: T171031155015 31x15.50-15 OTR TRACTION MASTER HF3, Tire, 10 Ply Rating
OTR TRAC MASTER Specifications:
Ply Rating: 10 Ply
PSI: 60
Tire OD: 31.1"
Tire Section Width: 14.6"
Loading Rating: 5050@10 MPH
Tread Depth: .720"
Rim Size: 15 X 13
The OTR Traction Master tire is a high quality HF-3 tire designed by OTR for small equipment.
The OTR TRAC MASTER tire's main design features are:
Herringbone tread designed provide good traction in a variety of ground operating conditions. Benefit: the tire lugs bite effectively into soft ground, sandy or firmer ground conditions to make for excellent footing and grip.
Directional tread style with tire lugs designed for excellent self cleaning properties. Benefit: sticky soil and mud fall away cleanly.
Rubber compound blend and curing process formulated to give greater wear/abrasion resistance. Benefit: high resistance to wear therefore lasting longer and reducing cost of ownership.
Rim Guard design with heavy tire side walls. Benefit: protects the rim flange and protection from side wall penetration.