We always start with the assumption you have a vehicle rated for the tires. Because if you use tires for a heavy load beyond the vehicle original design, and current condition you will still have a bad tow, even if the tires are inflated to Max for their design max load. So if you have a vehicle in condition that is the same as the new design specifications then use the design specification rated tires or better rating, never less than original design. So the weight being at max for vehicle may be the same as the vehicle or better. That higher rated tire can't be loaded beyond the vehicle design load. So if you are at max vehicle load, then depending on the tire inflate to make the tire tread surface pushing on the pavement all the way across the tread evenly. That is done in a static,(non moving and level),measurement with trailer and tow vehicle no more than 4 inches up or down from level to each other. The trailer should have 60% of the load in front of the trailer axle or center of axles, so tongue weight is enough to keep the trailer from wagging the rear of itself. Assuming that has been done, then the tongue weight should be checked to see if it exceeds the manufactures design and current condition of the hitch and towing weight of the tow vehicle. That is done by jacking the trailer off the hitch of the tow vehicle until the load is off the tow vehicle, always keeping safety in mind, blocking the wheels so nothing moves. Always then return the trailer to the seated position of the hitch and lock them together. That being done and within specifications then finally the tires can be inflated to the loads you have determined, never more than max design of the tire and possibly slightly less as the weight is in proportion to the design of the tow vehicle, which can be less than the design of the tires if you used over rated tires beyond the tow vehicles specification. You want stability, not hard ride at rear of the tow vehicle, as then the weight will be transferred to the front end of the tow vehicle making steering plow due to turning wheels up front having pressure on sidewalls greater than the rear tires that for the most part going straight. Top heavy loaded trailers will also cause instability as loads shift as pavement slope changes side to side. Always inflate the tires of the trailer to the maximum weighted side, as determined by a scale designed for side readings. That eliminates the shifting weight factor in dynamic,( moving) conditions. An experienced tower knows the correct feel for the proper inflation and many times can tell by looking at the tires and how they come down to the pavement on the sides. Others know from wear if the tires are being over inflated, as they wear on the center, and under inflated wear on the outsides. Remember max inflation at cold tire is set so that when it's hot it has enough air to keep it touching the pavement. Hot tires read higher pressure so always check when cold, or use the manufactures calculators which require temperature readings at the surface of the tire to convert what you need. This is Physics and if you ever paid attention to a NASCAR race you always hear the drivers saying how the vehicle is handling the track, and do pit stops for suspension and inflation adjustments to get maximum handling so they can win.
