Axles are not built in increments that may be needed by a RV trailer manufacturer. Therefore, during the building process the trailer manufacturer has the authority from the DOT to set GAWR values to coincide with the specifications of the trailer to be built. Those GAWR values become the standard for that trailer and are displayed on the vehicle federal certification label.
The very minimum value for tire fitments is to have the ability to carry the vehicle’s GAWR. So, any of the ST235/80R16E tires would be disqualified for service on 7000# GAWR axles. However, the vehicle manufacturer can set those axles at a GAWR value of 6750# and satisfy the safety requirement requiring them to support the maximum weight that may be carried by the GAWR axles.
Owners looking at the trailer’s brochure or individual axle tag are looking in the wrong place. The only official axle load is the GAWRs listed on the certification label.
Here is a picture of a certification label of a trailer with 7000# axles reduced to 6750#.
NOTE: The ST235/80R16E is manufacture with three distinct load capacities, 3420#, 3500# & 3520#. Without wording in the vehicle owner’s manual or on the certification label about which load capacity tires to use they all revert to the lowest load capacity (3420#) making all of them unqualified for use on 7000# GAWR axles.
Another note: I have personally seen GAWR axles set at 5080# to accommodate ST tires with 2540# of load capacity.