[JRTJH]

Buzzcop,

You are correct, the "max safety margin" decreases the heavier the trailer gets even if equipped with the same tires. I may be missing what you're asking, but ST tires are designated to be used on trailers only. They are not rated or "certified" the same as LT or P series tires. There is no requirement to have a "safety margin" on ST tires used on a towed RV. Theoretically, the manufacturer could put 3500 lb axles under the trailer, equip them with tires rated at 1750 lbs each and if the tongue is carrying 1000 lbs, assign a GVW of 8000 lbs. That's 7000 for the two axles and 1000 on the tongue. Yes, this is an extreme example, most RV's are equipped with axles/tires that give some slight leeway to a safety margin, but in the interest of building RV's with the "least amount of different parts" you will find several models built on the same Lippert frame/axle assembly. Some may be 24 ft long and weigh 4800 lbs dry and the other end of that "frame model run" may be 30' long and weigh 6500 lbs dry. You may well find all the models built on that frame have the same tires/axles under them. This will allow for more "leeway" in maximum tire load capacity on the lighter RV's built on that frame, and barely "squeek by" on the heavier units.

Since there's no "requirement" for a safety margin, the manufacturer builds and we buy........