Dedicated trailer tires are marked as ST. This will be marked on the tire’s sidewall along with the size of the tire. The tire may also say, “trailer use only.” ST tires have stronger sidewalls that allow them to carry a heavier load that standard Passenger car tires or Light Truck tires. There are two kinds of ST tires; bias-ply and radial. Which kind of tire you buy will depend on what came on the trailer originally, how you use your trailer, and your budget. In short bias-ply trailer tires are cheaper and are recommended for infrequent short haul applications that include off-road or heavy loading. If you plan on long highway driving trips you should consider replacing those bias-ply tires with radial tires. Radial trailer tires are made to run cooler for longer hauls, and to have a longer tread life. Never replace radial tires with bias-ply tires without consulting the trailer manufacturer or a tire professional. more