My personal opinion is that the industry standard ST tire standard is inadequate for the service the ST tires are exposed to. My opinion is based only on my own personal experience, and anecdotal experience of others.
Back in the late 1970s through the early 1980s, I was a boat dealer, and we towed all kinds of boats from 19 footers weighing 2500 lb on a single axle trailer, up to 15,000 lb 30 footers on triple axle trailers - up and down I95 between New Jersey and Florida. We always used the bias ply trailer tires that were available at the time. We would carry plenty of spares, but seldom, if ever, had a problem that could not be traced to a road hazard or axle-bearing-wheel-suspension problem.
Back in the day of cotton tire cords, tires were rated by how many plies they had the more plies, the stronger the tire, and higher load range. If I remember correctly, 2 ply was A, 4 ply was B, 6 ply was C etc. When nylon and polyester came along to replace cotton, it was twice as strong, so a fewer number of plies was needed to make a tire of the same strength. We saw labels such as 2 ply/4 ply rating, 4 ply/8 ply rating, etc.
Still later, Michelin figured out how to make radial ply tires using steel belts, and that really changed things, but the industry stuck to the ply rated terminology even though bias plies were no longer used.
Somewhere during this, the overall quality of trailer tires seemed to deteriorate I personally do not think a modern day load range D ST radial tire holds up anywhere as well as the 4 ply/8 ply rated bias trailer tires we used 40 years ago.
On the other hand, we do seem to ask more of our ST trailer tires as we do our car and truck tires. For instance, here are my three personal vehicles, using the maximum axle rating for each I know none of them are really running at the maximum most of the time, but I bet the Ford and trailer are close when we are towing:
1995 Chevy G20 Van, front 3400lb, rear 3406lb, running 31x10.5R15LT LR C Tires rated 2270lb @ 50psi they are loaded at about 75% capacity.
2002 VW Beetle, front 2183lb, rear 1588lb, running 205/55R16 91H tires rated 1356lb @ 44psi they are loaded to about 80% capacity.
Ford E350 Van, front 4600lb, rear 5360lb, running LT285/75R16 LR E tires rated at 3750lbs @ 80psi they are loaded to about 71% capacity.
2015 Outback 277RL, 4400 lb axles, came with ST225/75R15 LR D tires Chinese tires rated at 2540lbs @ 65psi they were loaded to 86% capacity
We blew on of the LR D tires last winter no obvious hazard, and pressures were OK 150 miles earlier go figure. We replace them with Maaxis LR E rated at 2830lb @ 80psi, so they are loaded at about 77%, which is more in line with the other vehicles.
Hoping for the best, but sure wish there were more commercial trailer tires available in 15 !!
Bill & Kate with Zeke (parti-poodle) & Bailey (std poodle)
Stone Harbor, New Jersey
2014 Forest River Wildcat 272RLX Fifth Wheel
2018 F-250 4x4 Crew Cab 6.2L Gasser