The majority of RV trailer tires are specifically designed for trailer axles and are designated as Special Trailer (ST) tires. But, all Department of Transportation (DOT) highway certified tires can be fitted to the RV trailer axles by their manufacturers. The second most popular fitment is the Light Truck (LT) tire. Then comes the medium duty truck tire followed by the Passenger (P) tires which must have their load capacity reduced by about 10% for trailer axle fitment.