Inflation pressure isn't the same as running pressure! Once a vehicle is loaded the air pressure of the tires can go up substantially relative to what they're

Inflation pressure isn't the same as running pressure! Once a vehicle is loaded the air pressure of the tires can go up substantially relative to what they're inflated to. Like you said, action and reaction. That's why under-inflated tires will have a very large contact patch; increasing the contact patch increases the area in the area * pressure equation. But it also reduces the volume of air inside the tire/tube and that raises the pressure, also.