Originally Posted by John Wayne
Rather then go by the placard. get each axle weight while loaded for a trip. (each wheel weight is better) Then go to Michelins tire pressure guide and you will have a better ride. If your worried about the pressure until you can get the rig weighed just go by the max pressure on the tire side wall.
Though weighing is always the best, as long as you did not do that, you have to go from GAWR's, assuming this is the maximum allowed by law, and these larger vehicles are not that often overloaded, but realise this is general idea, so can be dangerous.
Then add 10% to that for savetymargin, for R/L unbalance wich is always the case, but also for pressure-loss in time, and or inacurate reading of pressure-device.
If you give that here together with exact specifications of tires, maximum load or loadindex, AT-pressure , and if you can find it speedcode, all can be found on sidewall, I can calculate a save pressure range for you.
The Michelin list given here uses for the large sise you have , the European formula to make the pressure/loadcapacity list, so is saver then American lists.
So you can also do it yourselfes , using that list, but always add 10% , and see how the list is made, Michelin often gives loadcapacity per axle, so 2 or 4 times the tire, or sometimes for dual load ( 4 tires on the axle) per axle-end so for 2 tires.