My then new 32' 1997 5er with two sides and 6 lug 5200 lb tandem axles came with ST225/75-15 load E tires.
I sold the 15" ST may pops/wheels and went with 6 lug 16" trailer wheels and BFG Commercial TA/2 LT215/85-16 E at 2680 lb ....110720 lbs total capacity.
Ran the first set for 55k miles per set ....2nd set for 53k miles and with 48k miles on the 3rd set.
I'm looking at a new set this spring. No issues at all at legal highways speeds
WE make long trips and mileage adds up.
There is no better tire for 5200 lb trailer axles than a commercial grade LT 16" E like we ran on our 3/4 and one ton trucks. With 15 and 16/32" of tread depth they last longer (miles of service) than any 16" ST E tire on the market.
I sure wouldn't put a load F or G on any of my rv or non rv work trailers with 5200 lb axles.