Really, I just want to know how that door-frame number can really be right for every single tire I could possibly put on the car.

Well, the problem arises when you try and define what is "right".

It depends on what you are trying to accomplish. Are you trying to maximize tire life? Are you trying to get the most comfortable ride? Are you looking for the best adhesion? Do you want the most responsive handling? Maybe you are trying to optimize fuel mileage?

The truth is, no one tire pressure will be best for any more than one of the above requirements. The number posted on your door-frame is the manufacturer's best guess compromise to at least try and satisfy some of them based on the weight of your vehicle.

If you are using the same size tire as recommended by the manufacturer, there will probably not be so much difference in construction from one brand to the next to warrant much concern that tire "A" has inflation requirements different from tire "B".

tanstaafl.