It never ceases to amaze me that every time we take our vehicles into the dealer for normal oil changes and the like. They open the drivers door , look at the "recommended" OEM tire air pressures and proceed to set all my tires to the Manufactuers recommended tire pressure. So you say, what is wrong with that....? Simply they have created a safety hazard by not reading the actual NON-OEM tires recommended air pressues. I find myself leaving the dealership at 35 psi, when my tires clearly state 50 PSI minimum. If you read the warranty on any tire, you MUST operate the tire within the Manufacter specifications!
Heartland doesn't supply the same exact brand and tire on all their coaches that come off the line. In fact, walking around my local dealer, I noted 4 different makes of tires on the same exact models. Heartland simply makes a generic tire PSI recommendation based on the tire load range requirements of each coach (based on weight) and not the individual tire manufactures recommendations.
The Key to proper tire inflation is to know the weights on the tires. Once you know the operating weight, then read the actual tire recommendations and tire weight ratings. If your loaded coach is close to or near the combined weight rating of all the tires, then you will need to be inflated at or near the max PSI rating of the tire, regardless of what Heartland recommendations indicate.