Brian,
It is fairly common for trailers to be specified with tires that are too small (load carrying capacity-wise) - particularly older ones like yours. I'd recommend getting the trailer weighed - fully loaded - and by individual tire if you can, but by axle at a minimum and then figure a 10% side to side weight variation. Do a google search for ways to get individual tire loadings.
Next, I'd recommend not loading any tire more than 85% of its rated load. That applies to ALL vehicles, including trailers. That's just good engineering practice that somehow got lost until the Ford/Firestone thing back in 2000/2001 time frame. Trailer manufacturers were (are?) slow to pick up on this.
My best guess and why you had tire failures was 1) tires got too old, 2) too much speed (ST tires are speed restricted to 65 mph), and 3) uneven loading (the rearward tilt needs to be fixed!)
Now for some comments directed to others who have posted in this thread - some stuff based on a tire engineer's perspective:
The difference between an ST tire and an LT tire is in the details. For practical purposes, there is no difference - except for tread depth, tread width, and tread pattern. Notice nothing was said about the casing itself. That is because the loading for both is based on the same formula, except the ST tire is speed restricted to 65 mph and that results in higher loading. - BUT - compensate for the speed restriction and you'll get the LT tire's load carrying capacity.
The Ford/Firestone thing in August of 2000 changed a lot about the way tires were specified on vehicles and the way tires were designed. Prior to that it was common for vehicle manufacturers to specify tires with BARELY enough load carrying capacity. Cars figured out on their own that larger tires (load carrying capacity-wise) resulted in better handling cars, so when Aug of 2000 arrived, they were already fixed. But trucks and SUV's had to be adjusted and that was complete by 2008.
Trailers may or may not be up to date. (From my perspective I can't tell what is going on with trailers, but I'm sure about cars and trucks because tire manufacturers supply tires DIRECTLY to car and truck manufacturers, but through a wholesaler for trailers.)
The net effect of the FORD/Firestone thing is that not only were cars and trucks changed with regard to the way tires were specified, but the tires were designed differently, too! (Cap plies!)
This was not true for trailers. Not only were the trailer manufacturers not paying attention, but the trailer tire manufacturers weren't either. To make matters worse, only 2 of the ST tire manufacturers were also produced LT tires (not exactly true, but the exact situation is too complicated to explain in this post!) - and those 2 tire manufacturers were Goodyear and Maxxis. They should have picked up on the changes, but were slow to do so. They other ST tire manufacturers are more or less niche tire manufacturers and don't have a good feedback system to see how well their products are performing.
Which brings us to today.
I am confident that Goodyear's Endurance ST tire line is performing well (So far! It has only been 2 years since they were introduced.)
Maxxis ST tires may need a bit of a tweak.
The deal with Sailun is that they have Load Range G tires (everyone else is producing LR E.) - built just like a heavy truck tire (over the road variety). Many trailer owners are using higher pressures to get the higher load carrying capacity so I don't think it's a fair comparison.
Carlisle? Too small of a sample size to tell what is going on with them.
And one last thought: Because of the restricted space under a trailer's fenders, it is common for folks to be stuck with the existing wheels, but some of those wheels have a 65 psi inflation pressure limit stamped on them and theoretically one can't use the LR E's 80 psi. I've talked to 5 wheel designers/engineers and have come to the conclusion that the pressure limitation isn't the important item (Load is!), so it would be better to use the 80 psi to get the load carrying capacity in the tire as wheel failures are fairly rare! (Note: This would also be true of Sailun's LR G 110 psi spec vs an 80 psi wheel.)
It is fairly common for trailers to be specified with tires that are too small (load carrying capacity-wise) - particularly older ones like yours. I'd recommend getting the trailer weighed - fully loaded - and by individual tire if you can, but by axle at a minimum and then figure a 10% side to side weight variation. Do a google search for ways to get individual tire loadings.
Next, I'd recommend not loading any tire more than 85% of its rated load. That applies to ALL vehicles, including trailers. That's just good engineering practice that somehow got lost until the Ford/Firestone thing back in 2000/2001 time frame. Trailer manufacturers were (are?) slow to pick up on this.
My best guess and why you had tire failures was 1) tires got too old, 2) too much speed (ST tires are speed restricted to 65 mph), and 3) uneven loading (the rearward tilt needs to be fixed!)
Now for some comments directed to others who have posted in this thread - some stuff based on a tire engineer's perspective:
The difference between an ST tire and an LT tire is in the details. For practical purposes, there is no difference - except for tread depth, tread width, and tread pattern. Notice nothing was said about the casing itself. That is because the loading for both is based on the same formula, except the ST tire is speed restricted to 65 mph and that results in higher loading. - BUT - compensate for the speed restriction and you'll get the LT tire's load carrying capacity.
The Ford/Firestone thing in August of 2000 changed a lot about the way tires were specified on vehicles and the way tires were designed. Prior to that it was common for vehicle manufacturers to specify tires with BARELY enough load carrying capacity. Cars figured out on their own that larger tires (load carrying capacity-wise) resulted in better handling cars, so when Aug of 2000 arrived, they were already fixed. But trucks and SUV's had to be adjusted and that was complete by 2008.
Trailers may or may not be up to date. (From my perspective I can't tell what is going on with trailers, but I'm sure about cars and trucks because tire manufacturers supply tires DIRECTLY to car and truck manufacturers, but through a wholesaler for trailers.)
The net effect of the FORD/Firestone thing is that not only were cars and trucks changed with regard to the way tires were specified, but the tires were designed differently, too! (Cap plies!)
This was not true for trailers. Not only were the trailer manufacturers not paying attention, but the trailer tire manufacturers weren't either. To make matters worse, only 2 of the ST tire manufacturers were also produced LT tires (not exactly true, but the exact situation is too complicated to explain in this post!) - and those 2 tire manufacturers were Goodyear and Maxxis. They should have picked up on the changes, but were slow to do so. They other ST tire manufacturers are more or less niche tire manufacturers and don't have a good feedback system to see how well their products are performing.
Which brings us to today.
I am confident that Goodyear's Endurance ST tire line is performing well (So far! It has only been 2 years since they were introduced.)
Maxxis ST tires may need a bit of a tweak.
The deal with Sailun is that they have Load Range G tires (everyone else is producing LR E.) - built just like a heavy truck tire (over the road variety). Many trailer owners are using higher pressures to get the higher load carrying capacity so I don't think it's a fair comparison.
Carlisle? Too small of a sample size to tell what is going on with them.
And one last thought: Because of the restricted space under a trailer's fenders, it is common for folks to be stuck with the existing wheels, but some of those wheels have a 65 psi inflation pressure limit stamped on them and theoretically one can't use the LR E's 80 psi. I've talked to 5 wheel designers/engineers and have come to the conclusion that the pressure limitation isn't the important item (Load is!), so it would be better to use the 80 psi to get the load carrying capacity in the tire as wheel failures are fairly rare! (Note: This would also be true of Sailun's LR G 110 psi spec vs an 80 psi wheel.)
