From my research, the ST did not come in an 85 size.
ST tires are going to be 235/80R16
LT tires are going to be 238/85R16 -
There isn't much difference in size, but this is what I found when researching tires.
I have 7 year old GY Marathon tires (ST 235/80R16) and had a blow out this past week in Idaho, however, the blowout was due to a failure of my suspension shackles, not the age of the tires. But, I need new tires and should have bought them before this past trip. Not the point however as I was told something would have blown regardless of the age of the tire...
I spent a day at a repair shop waiting for parts. The conversation turned to tires. We talked about the Sailun tires which they sell, the other off brand they sell vs Goodyear LT tires. He wanted to sell me the Sailun but I can get Goodyear LT tires for $100 less per tire. His comment was that LT tires are designed to take a beating, roll for 50K miles or more in all weather, go off road, etc. Basically due what a tire is supposed to do. The ST tires are designed to get driven occasionally, typically only highway, some will put on lots of miles but most drive them in the summer a few trips. Most trailer tires wear out due to age - 5 to 6 years, not due to mileage. Some years ago, manufacturers didn't make specific trailer tires but then marketing saw an opportunity to make a specific tire that didn't need as much research as a truck tire. So, basically, it is a basic tire. Sure, the Sailun G rated is a 16 ply tire vs a LT 10 ply tire. But, in my case, my trailer is 8-9K lbs on the tires, never enough to overload 4 LT tires. As a case in point, I also have a horse trailer. It came with LT tires that lasted 10 years. I now have 4 years on the a set of GY LT tires and they look new. They get driven more often than the 5th wheel, but they are not drying out at all.
The point I am making, if you don't need a G rated tire due to weight, the tire will wear out due to age before it wears out due to mileage. You can spend $1000 bucks on Sailun G rated tires and replace them in 5 or 6 years, or you can put LT or a good ST E rated tires for $600 or less and replace them in 5-6 years.
