Tire pressure issue

Different tires require different pressures. Michelins require different pressures than Goodyears, Goodyears require different pressures than Bridgestones, Bridgestones require different pressures than Toyos, and so forth and so on. That's why each tire manufacturer has a pressure chart. As said, weigh the rig as you would normally travel, and set the pressures according to the tire manufacturer's chart for that tire at that weight.