rk911 wrote:
the 120-psi on the tire is the maximum pressure the tires are rated for. and while you can inflate them to the max the result may be a very hard ride along with possible handling issues.
the 80-psi on your placard may be the optimal air pressure for the RV's weight when it left the factory or for the GVWR (gross vehicle weight rating) of the MH. using this air pressure will result in a much better ride but it still may be too low or too high for your MH's actual weight.
I would not overthink this. if the manufacturer specs 80-psi, go with 80-psi. Your handling will improve dramatically. Currently with your tires set at 100-psi, i'll bet the back end wanders all over the road and the handling is exhausting.