I would once again have to agree with those that say the tire pressure placard on the motorhome applies to the tires originally installed on the chassis. It can also apply to the same brand, model and size made at a later date. However sometimes the tire manufacturer changes the construction of a particular model and updates the inflation tables.
Case and point are the Goodyear G670 RV tires. A specific example is the G670 size 245/70R19.5. Those manufactured prior to 6/28/2006 (I was in error in an earlier post when I stated the change was in 2002) have a minimum recommended pressure of 70 psi.
The same size and model tires built after 6/28/2006 have a minimum recommended pressure of 80 psi. Here's a link to an older Goodyear load and inflation table with this information.
http://www.goodyearrvtires.com/pdfs/rv_inflation.pdf
In the case that the owner selects a different brand of tires the original tire pressure placard also may not apply. Michelin model XRV size 245/70R19.5 load range F require 95 psi to support a load of 4080 lbs. as singles. The Goodyear G670's of the same size and load range require only 85 psi to carry the same load.
https://www.michelinb2b.com/wps/b2bcontent/PDF/RV_Tires_Brochure.pdf
As for who sets the tire pressures, I'm not sure. I do know that when the recommended tire pressure and lug nut torque changed on our 2001 Winnebago Adventurer the letter with the information and the updated placards came from Ford.
