When Looking at used trailers make sure you closely inspect the tires or just assume they will need to be replaced. Check dates, sidewall cracks, weight ratings. Also be aware that a lot of used trailers wind up with car or truck tires on them which is very much against DOT regulations. Some years ago Pennsylvania DOT was actively pulling over car hauling trailers and handing out tickets for incorrect tire type and/or weight rating. Probably worse now.
IIRC, the use of truck tires is OK, they are weight de-rated for use on a trailer.
Sorry I over simplified that. The manufacturer of the trailer can choose to use either ST or LT tires. The catch is that if the trailer was rated with ST tires then LT tires of the same size most likely don't have as high of weight rating as the ST tires that were rated for the trailer. If you use tires with a lower weight rating than what came on the trailer then that can cause problems with insurance, warranty, and yes DOT. So if your trailer came with LT tires then you certainly can use LTs and probably STs because they would have a higher rating but if it came with STs then LTs will probably have too low of weight rating.
So technically it's not the LT designation that can be a problem it is the lower weight rating of the LT.
