this is what Goodyear says about the "ST Speed Limit"
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.
o Do not exceed the maximum pressure for the wheel.
o If the maximum pressure for the wheel prohibits the increase of air pressure, then the maximum speed must be restricted to 65 mph.
o The cold inflation pressure must not exceed 10 psi beyond the inflation specified for the maximum load of the tire.
My steel rims are rated at 50 PSI. Although I had them put high pressure stems in the rims, I run my Marathon D tires at 50 PSI cold (since I am right at 2050 pounds per tire) and try to stay at 65MPH or less when traveling.
Assuming you DID weigh the camper and actually know what the real wheel load is. You can use this chart to fill your tires to the correct pressure for the weight being carried by them.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW