I’m not writing tire posts to be argumentative. I research what I say and have references to support the information in my posts. How a person perceives my messages can be clouded by the way regulations, rules and standards are written or disseminated.
A big confusion factor about replacing RV trailer tires is the lack of standardized recommendations from the trailer manufacturers. You drive your car, truck or other motorized vehicle into a tire retailer’s location to inquire about replacements. They will search their data base for acceptable replacements for your vehicle. They already have all the vehicle manufacturer’s recommendations and can immediately give you a list of tires by size and brand to choose from. That procedure is nonexistent for RV trailer tires. The best you can hope for is a list of the same designated size shown on your trailer’s certification label with a variation in load ranges when available. A call to the RV dealer/manufacturer will in all probability result in the same selections.
Here’s some official stuff.
Vehicle owner’s manual wording:
To maintain tire safety, purchase new tires that are the same designated size as the vehicle's original tires or another size recommended by the manufacturer. Look at the tire information placard, the owner's manual, or the sidewall of the tire you are replacing to find this information.
Tire industry wording:
Never choose a tire that is smaller in size or has less load-carrying capacity than the tire that came with the vehicle.
Tires should always be replaced with the same size designation — or approved options — as recommended by the vehicle manufacturer.
The correct tire size designated for your vehicle should always be verified with the information in your vehicle owner’s manual and/or the vehicle certification label.
In the USTMA industry standards from the RV chapter page # 43 has this caveat; “However, never use inflation pressure lower than specified by the vehicle tire placard, certification label or owner’s manual. Nor should inflation pressure exceed the maximum pressure molded on the tire sidewall.”
There is an industry standard used to set recommended cold tire inflation pressures for replacement tires having a different size designation than the OE tires. It stipulates that they must provide a load capacity equal to the OE tires by inflation pressures.
Like Jim pointed out above, these are none binding standards for the consumer unless there is a state regulation that enforces them. However, they are minimal standards and when you are operating outside those standards you can be held accountable for your actions.