I had always heard that if you want to be safe and not overload your Motorhome, you should get it weighed. That way you know if you are carrying the right load for your tires.
I was at the Great Lakes Area Spring Spree (Glass) Rally and they were weighing the Motorhomes for the discounted price of $35.00. The normal price is $49.00.
The first step is to fill out the questioner with the motorhome type and the manufacturer of the tires that you have on your Motorhome. The Freedom Bird had a cheap set of 8R-19.5's similar to the ones I put on Shaggy.
I will break down the data for you.
This is what The Free Bird weighed.
This is the load that I should carry at 75 PSI with the tires and load that I had.
These were the changes I need to make to be safe at 75 psi with my tires.
This is the Tire Pressure and Weight Load Chart. Since I was a little heavy for 75 Psi. I carry 85 Psi.