On your example P235/70R15 tire, the P designates it as a standard passenger-car tire, 235 is the section width, 70 is the aspect ratio, R means the tire is of radial construction, and 15 is the ...

There are two major size designations commonly used for passenger car tires, called P-metric and Metric sizing. If you see a "P" in front of the tire size displayed on a tire's sidewall it is a P ...