eli5: Why can you only learn your proper tire pressure from the car and not from the tires themselves. Wouldn’t different kinds of tires need different pressures on the same car?

Question

Same tires, different cars = different recommended tire pressure

Different tires, same car = same recommended tire pressure

This doesn’t make sense to me. Why is this?

In: Engineering

Answer 1

Truly, any non-OEM tire may require a different pressure. It is generally safe to stick with what is on the car’s door jamb, but different compounds, sidewall types, load ratings can effect the “best” tire pressure. Luckily, passenger cars are forgiving here so 30-35 psi (sorry, freedom units) is just fine for 90% of these vehicles. If you did change wheel size and tire aspect ratio, you’d want to experiment by feel and possibly a “chalk test”. You may even want different alignment settings.