A certified tire specialist told me to put in the pressure that is posted on your placard inside the RV however tires for semi-trucks and DPs do not follow the same rules. Big DPs are very heavy (I’m pushing 32,000lbs) and are a very different situation from a vehicle and trailer that are much lighter. You can inflate to the max pressure and be perfectly safe! But, the ride will be very rough.
I toured the factory who built my pusher. When I was there, I asked the staff “how do I know the proper tire inflation pressure?” They told me to weigh my rig, and then go with what the tire manufacturer data tables say. I asked about the 120psi on the placard, and they explained that they just print the max inflation pressure of the tires on the placard, because they have no idea how the rig is loaded, and they don’t want to post too low of a pressure.
My rig is built on a Freightliner Chassis. I attended Camp Freightliner to learn about my rig, how it works, and how it should be maintained. Freightliner also states to use the tire manufacturer’s data tables for best performance. I would also add that Freightliner also recommends that you check your axle weights against the max weight rating for your specific axles so you don’t overload them…
The inflation pressures that result are not always one particular pressure. For my weights, I use 105psi on the front tires, and 85 psi for everywhere else.
I am a systems engineer – I learned throughout my career to do my own research. Been burned before by blindly accepting advice from people who should know the right answer… “Trust, but verify…” I think one of the big problems with posting answers to people’s questions on the internet is that perfectly qualified people can post exactly the correct answer for their situation, but it may not be applicable to everybody’s equipment…
All that being said, I run Michelins on my DP. Here’s what Michelin has to state on inflation pressures and maintenance on their RV tires: https://www.michelinrvtires.com/reference-materials/ It gives lots of tips on getting the most life out of your tires. So, my advice is please read what the tire manufacturer recommends and draw your own conclusions….
Another good read is http://www.rvtiresafety.net/