ST (Special Trailer) and LT (Light Truck) tires are designed for different purposes. ST tires are specifically designed for trailer axles and can handle higher inflation pressures for greater load capacities. They have stiffer sidewalls to help control sway and are typically used on medium to heavy-duty trailers.
LT tires, on the other hand, are designed for towing vehicles like pick-up trucks and vans. They offer more flexibility and are designed to provide a smooth, comfortable ride. Also, they provide higher acceleration and braking traction, which aren't necessarily needed in trailer tires.