First of all, the psi shown on the tire sidewall is NOT the recommended pressure for any & all applications. The definition of the sidewall wording varies a bit depending on tire type, but basically it states the tires maximum load carrying capacity and the psi needed to support that max load.
Second, federal law requires that your vehicle will come with a placard that gives the recommended tire pressure for the OEM tires on that particular vehicle. Generally that recommended pressure (psi) will accommodate the vehicles maximum rated load (if a truck, SUV or RV) or typical passenger loading (passenger cars).
For most purposes you can use the vehicle makers recommended tire psi and feel safe. However, the psi may be more than is really necessary or even desirable, so it is often possible to optimize the psi on front & rear tires for that particular vehicle and load. To do that, you would need actual vehicle loading (weight) and the tire manufacturers load/inflation table, which shows the minimum pressure needed for a given weight on the tire. Actual weights need to be axle by axle, or (better yet) tire by tire. If you have axle weights you can come up with a pretty good estimate for tire loads, but with individual tire weights you know exactly what you need.
Tire experts recommend that the inflation be somewhat greater than the minimum for the estimated load, but you will hear all kinds of theories about how much more is desirable. I'll leave that subject for a later debate.
), then search "Goodyear ABC123 inflation table" and you should find the info you need. The table will be broken down by weight ranges, and give you the PSI that should be apply. If you weigh the axles and not the individual corners, then just do the math appropriately and divide by the number of tires on any given axle to find your approximate numbers.
