The National Highway Traffic Safety Administration says vehicle manufacturers are solely responsible for setting original equipment recommended cold tire inflation pressures (see 571.120). Tire industry standards say that replacement tires must have the same or greater load capacity as the OE tires.
ALL RV trailers, motor homes, cars, light trucks, and multi passenger vehicles are fitted with tires that meet the safety standards in the Federal Motor Vehicle Safety Standards ( FMVSS).
Tire manufacturers do not set vehicle inflation pressures unless one of their retailers is installing plus sized tires in place of OE tires. Then they are just setting a cold inflation pressure to meet the load capacity of the OE tires depicted on the vehicle’s certification label.
NHTSA, via SAFECAR publishes all sorts of information about tire inflation pressures. It’s mandated to be in your vehicle owner’s manual.
Because medium to heavy duty truck tires are often used on motor homes and large fifth wheel trailers does not change the fact that motor homes and RV trailers were initially fitted with OE tires under the guidance of FMVSS regulations. FMCSS regulations do not apply to motor home of RV trailer axles.
It’s an owner’s responsibility to insure safe operation of their vehicles. Inflating RV trailer tires and motor home tires to the load being carried is an unsafe act. There is zero wiggle room with the inflation pressure and zero load capacity reserves. It may be good for the truckers strewing rubber all over our highways but it’s not good for the private citizen.
Most of the large tire manufacturers provide tire information on the WWW. Usually in PDF format. Those PDFs provide the best insight into tire industry standards. The reference attached below is an easy read with current, up-to-date information from a respected tire manufacturer.