My trailer is #5000 GVWR and weighs every bit of that..
It came with 13" LR "B" tires on it.
I upgraded to LR "D" tires in the same size many years ago and no issues..
I really didn't have any issues with the "B" tires, but I have gained more weight since then, so just want to be sure..
I pump them up to 60 psi and don't worry about it.
Never a blow out and the only reason I replace them is due to age..
17 year old trailer owned since new and have a lot of 13" old trailer tires and wheels stacked and don't know what to do with them.. ;)
Good luck!
Mitch