The disinformation in this thread is likely what is most dangerous. 1. You can most certainly use an automotive tire on a trailer, what you can not do is use a trailer tire on a car. As for what the DOT has to say about it, the DOT itself is a branch of the U.S. government and as such is incapable of speech... An employee AT the DOT may be another story, and they are not all properly informed and educated either. They can write you a ticket, but whether that's because the tire is a violation or they're having a bad day? 2. Two years is about the most you're going to get out of tires on a dual axle trailer. 3. On a dual axle trailer any more than 6 plies isn't really helping, two years is two years, your tires are wearing because of the turns, dual axles stay rigid through out the turns and that is what causes wear, more plies spends more money but it doesn't keep the tread from getting roughed around. 4. You want longer lasting tires, get radials but you're still not getting much past 2 years on a dual axle.