Good info on trailer tires here
An interesting quote
"All "ST" tires have a maximum speed rating of 65 mph."
A PDF from Carlisle is where I got the quote below:
"High speed towing in hot conditions degrades Trailer Tires significantly. As heat builds up during driving, the tire's internal structure starts to breakdown, compromising the strength of the tire. It is recommended to not exceed 60 Miles per hour (MPH) while towing a trailer."
And another from Goodyear Marathon:
"Industry standards dictate that tires with the ST designation are speed restricted to 65 MPH under normal inflation and load conditions unless a different speed restriction is indicated on the sidewall of the tire."
" Based on industry standards, if tires with the ST designation are used at speeds between 66 and 75 mph, it is necessary to increase the cold inflation pressures by 10 psi above the recommended pressure for the load.
* Do not exceed the maximum pressure for the wheel.
* If the maximum pressure for the wheel prohibits the increase of air pressure, then the maximum speed must be restricted to 65 mph.
* The cold inflation pressure must not exceed 10 psi beyond the inflation specified for the maximum load of the tire."