here is info I got from Goodyear
Special Trailer (“ST”) Tires
Goodyear Marathon trailer tires are widely used in a variety of towable
trailer applications and are designed and branded as “ST” (Special Trailer)
• Goodyear Marathon Special Trailer tires, with the “ST” size designation,
are speed rated at 65 MPH (105 km/h) under normal inflation and load
• This speed rating is based on Tire and Rim Association loads and
inflation pressures for ST trailer tires without a service description for
speeds up through 65 mph. (ref: TRA 2013 Year Book)
• If Goodyear tires, with the ST designation, are used at speeds between 66
and 75 mph (106 km/h and 120 km/h), we recommend the cold inflation
pressure be increased by 10 psi (70 kPa) above the recommended pressure
based on the trailer placard for normal inflation and load conditions. You
should also consult your trailer manufacturer’s Owner’s Manual for maximum
operating speed recommendations for the trailer.
o Increasing the inflation pressure by 10 psi (70 kPa) does not provide any
additional load carrying capacity.
o Do not exceed the maximum pressure for the wheel or the valve.
o If the maximum pressure for the wheel or valve prohibits the increase of
inflation pressure, then the 65 mph rated speed must observed as the
o It may be necessary to dismount the tire from the wheel to determine the
maximum rated inflation for the wheel and valve. *
*Details about wheel and valve inspection:
a) If the rated (maximum allowable) inflation pressure is not visible on
the wheel, consult the wheel or trailer manufacturer.
b) Tubeless snap-in type valves, depending on the type valve, are rated for
a maximum inflation pressure of 65 or 80 psi for nominal 0.453” diameter
valve holes. If a higher cold inflation pressure is used, a clamp-in valve
such as TR416S valve (200 psi maximum inflation) must be installed.
Important trailer tire care information and load / inflation tables are
available on Goodyear’s Recreational Vehicle web site at
. Encourage your trailer tire customers to use this
• Drivers should always obey posted speed limits and reduce speeds when
necessary based on vehicle, road, weather, or traffic conditions.
• Light Truck (“LT”) designated tires do not have the same load carrying
capacity as ST tires. If LT tires are used on trailer applications, the
inflation pressure and/or tire sizing will need to be adjusted to match the
load carrying requirements of the trailer.
• Cold inflation pressures should be checked every morning during trips and
monthly while in storage.
• Vehicles or trailers should not be overloaded. The tire information
placard, vehicle certification labels, and/or owner’s manual should be
checked for the maximum Gross Vehicle Weight Rating (GVWR) and the fully
loaded trailer must not exceed that weight.
• Vehicle speed, load and inflation pressures, all of which are within
control of the driver, are critical factors for the safe and enjoyable
operation of any vehicle.
Jennifer - Consumer Relations