since this was a thread on fifth wheel speed, I think one issue that has been overlooked is ambient temperature. Pulling a trailer through California or NM right now adds quite a heat load to tires, and my understanding is heat is a prime factor in tires coming apart. TPMS systems tell you when air is low but not how hot your tire is. I wish they did both...
My little motorhome has door stickers saying 62 pounds in all six tires. Yet the tires are rated to 80 pounds. I put 70 pounds in each tire just to be safe and super high temps are not an issue on East Coast normally.
Is there a common sense rule where if it's over 90 outside maybe we should not do 75mph? Not that I would anyway...