The GT Radial Maxmiler ST is a long-lasting ST tire. ST stands for Special Trailer (or Specialty Trailer). These tires are purpose-built strictly for boat trailers, utility trailers, cargo haulers, pop-up campers, and fifth wheels. They are engineered for free-rolling axles and cannot be used on cars or motorized trucks. The GT Radial Maxmiler ST offers great value and durability.