[sourdough]

You said your friend put a "new" set of tires on the trailer but with that combo of tires I think you mean a "different" set of tires on the trailer.

Here is a comment from your first post: "I do load this trailer close to max load sometimes and make hauls for several hundred miles." That comment in and of itself, for me, says you need some good tires on that trailer.

Some comments have been made about how to date the tires etc. are good guides to see what you have. I can't imagine that the friend went out and bought 4 new, various brand tires but maybe he did. Determine the weights and what load range you need and then, if the tires are just mismatched used tires, replace them with 4 new good tires (not TK) and use the best of what you have for the spare (I believe that has been suggested). I have a friend that owns a tire store and has/sells LOTS of used tires (if that is what was put on there) and I can say I would personally never buy a used tire because no one has any idea what that tire has been through or what to expect from it.