It's the axle spacing that can cause the most problem when going from 80 to 85. RV trailer manufacturers seem to put axles as close together as possible. Those with a 32" spacing will not allow the use of the 85 tires.
Another dilemma when changing from 80 - 85 is the tire placard and certification labels become invalid, as the tires are not of the same designated size and the load inflation charts for the 80 will not work for the 85.
Here is a ST tire load inflation chart.
https://fifthwheelst.com/documents/C...T-Modified.pdf