3 years is a new one on me. There's been a lot of longstanding advice that RV tires age out at 5 years or so due to oxidation and UV damage. But the manufacturers are a bit cagey these days. They won't put a time frame on it - probably so they don't get hammered by competitors and customers.
Much of the information I find is conflicting. One person says Light Truck Tires are better that ST Tires. Another article states that Light Truck Tires do not hold up to the hard turns to which Trailer Tires are subjected.
I'll share my view of the conflicting information. But at the end of the day, we all have to do our own research and make our own decisions.
I generally go with what the manufacturer says, because their statements are usually going to start with the engineers (who have the expertise). Unfortunately, the lawyers usually get involved in editing the language, often watering it down.
I also look for "expert opinion" offered by people who have been doing failure analysis on tires for many years. They rarely dispute what the manufacturer says, but they will say much more because there's no lawyer editing their opinions.
I discount anecdotal information; e.g. "I've had them for 30,000 miles without any problems." Ok, but that's a sample of one. When you get to 10,000 samples, I'll be very interested.
I discount advice from tire retail outlets. There's no way to know their level of expertise, and a lot of what they say is going to fall into the anecdotal category.
I discount recommendations that essentially boil down to "my experience is worth more than the tire company's research." For example, when the tire company says that trailer tires need a stronger sidewall fiber to deal with the stresses experienced by trailer tires, I believe there is solid research backing that up. Arguing to the contrary is essentially arguing that either the tire companies are lying, or the engineers are stupid.
ST vs LT gets a little complicated when you look at tires like Goodyear G614. As I discovered recently, they carry an LT designation (which requires them to to additional certification testing compared to an ST tire). But they've been designed to work in more than one application, including use as a trailer tire. Does it have thicker fibers? I don't know, but if I were betting, I'd say it does. I'm told it also has bead-to-bead steel belts, rather than having the steel just under the tread, so the sidewalls are much stronger. In this case, I think it's got design features of an ST, plus more, plus the tougher certification of an LT tire, and more steel. What more could you want? There may be other LT tires that are designed for multiple applications - but which ones?
Wait, if the certification of LT tires is tougher, should we all get LTs? Not so fast. The LT tire MAY have a lower weight capacity than the ST tire, both having the same Load Range. Sometimes when you switch a LR E ST tire to a LR E LT tire, you may end up overloading the tires because of the lower capacity.
Yes, it's difficult to figure this all out.