I'm assumming you have 15" tires. When upgrading 15" tires from 65 psi to a 80 psi make sure the wheels have the higher 80 rating or a 2800 lb load rating.
Having several trailers on the road and running derated tires (lower pressures) simply didn't work the best in the long run. I found no gain in using a derated load E tire at 65 psi other than a hotter running/shortened life, tire than the D tire.
The 15" D tire gives you 10160 lbs of capacity.
Towmax = blowmax when we look around the net at all the different rv and non rv trailering websites. Sell them on craigslist. Lawnservice guys can use them as most never see the open roads and all day trips.
I would suspect any ST tire under a trailer that has sat for two years.
The Providers or Endurance ST tires would be my 1st and second choice.
