5 years max on ST tires. It's because of how they are twisted when turning! The forces are extreme. LT's are a bit stronger so they last longer, but I would still say even those may go 7 years, although I have never used them on a trailer.
I told my buddy to replace his 5 year old tires this spring. Well he didn't and lost one on his trip, fortunately it didn't do any damage. And one of the others have a shifted belt that is ready to come apart. He has 14" LR C good years. I told him to go with Carlisles if he can. Maybe even step up to a 15" rim if he has the room!
