Two pressures that are nearly ALWAYS wrong are....
The one molded into the tire,, (Actually it is correct if you read the FULL sentence which is something like Maximum Load 20,000 pounds at maximum pressure of 100 PSI" most people only read the "Maximum pressure 80 psi" part)
And the one on the sticker somewhere inside (door, glove box, cupbord wherever)
The proper pressure is found by: Load for travel, Weigh the Wheel (All of them in most cases we call it "4 corner" weighing more in a paragraph or two.
Then look up the tire maker's inflation chart and find out what THEY say, not the dealer (he's clueless) the tire maker. Many folks like to add 5PSI, I agree with them.
How to do 4 corner weights 2 methods.
1: RV Safety & Education Foundation
and follow the links to weigh my rv.
2: Find a FLAT segmented (optional) scale.. MUST be a FLAT scale, not a bridge scale.
Drive onto the scale so each axle is on a different segment, Get the printout
Now drive so only one SIDE of the vehicle is on the scale, again each axle on its own segment.
now you have wheel weights for the side on the scale
Substract those from the first pass and you have the other side.