Special Trailer Service (ST) tires are designed to deliver on-highway service for boat and travel trailers, pop-up campers and fifth wheel trailers. ST-sized tires are not intended to be used on passenger cars, pickups or light trucks.
Original equipment tire sizes installed on your trailer have the ability to carry the maximum load the trailer is rated to carry as determined by trailer manufacturer. It is called Gross Vehicle Weight Rating or GVWR. Never exceed trailer's GVWR to avoid overloading the tires along with the wheels, axles and frame.
Check all trailer tire inflation pressures before each trip. Make sure all trailer tires are properly inflated to carry its load. Underinflated trailer tire can be dangerously overloaded, resulting in excessive heat buildup that can lead to internal structural damage and result in tire failure and a possible blowout. Trailer tire load capacity is reduced and sidewall deflection and heat buildup are increased when tire pressure is too low to carry its load. Set your trailer tire pressure when tires are "cold", preferably in the morning.
Generally, trailer tires with ST designation are restricted to speeds of 65 mph or 104 km/h under normal tire inflation and load conditions. The cold tire inflation pressures must not exceed 10 psi (69 kPa) beyond the inflation specified for the maximum load of the tire. Do not exceed the tire's maximum rated pressure. Increasing inflation pressure of a trailer tire does not provide any additional load carrying capacity.