From reading the Airstream forum on tire issues, I installed the Michelin LTX (P) 235/75R15 XL tires after I got the 2013 International Serenity 25FB home from the selling dealership. With the trailer weight at 6,960 pounds camping ready, the four tires were supporting 5,880 pounds of their derated to 7,940 pounds load capacity. That was about a 26% safety margin.
I was told to inflate them to 44 psi and the ride was softer than GYM tires at 65psi and there was no 65mph spell limit on the sidewall of the Michelins like on the GYM tires. There is a much larger tire patch on the ground with the Michelin which makes for more effective braking action.
I have a photo of the GYM beside the new Michelin tire, both mounted on the original 15" factory wheels in the "images" link below my avatar.
WBCCI Life Member 5123, AIR 70341, 4CU, WD9EMC
TV - 2012 Dodge 2500 4x4 Cummins HO, automatic, Centramatics, Kelderman level ride airbag suspension, bed shell
2014 31' Classic model 30 twin beds, 50 amp service, 900 watt solar system, Centramatics, Dill TPMS, disc brakes, 16" tires & wheels