It seems that a common arrangement with midsize cars in the US is that the regular tires are inflated to 35 psi, but the spare (which is smaller), is labeled for something much higher, like 60 psi. Why?
My hypothesis is that it has to do with the force that the air exherts on the vehicle. Large tire * low pressure = ideally rated force. Small tire * high pressure = same ideally rated force, or at least in the ballpark.
Is my basic physics correct? Is this why?