Manufacturers incorporate tire characteristics, which include size, on the tire's sidewall to adhere to federal safety regulations. The information provides important safety and usage information.
A passenger tire might be branded "P215/75R15," where the "P" indicates the tire is for passenger vehicles, "215" is the tire width, "75" is the aspect ratio, "R" indicates it is a radial tire and "15" denotes the rim size.
The tire size is the width in millimeters from the edge of one sidewall to the edge of the other sidewall. Therefore, a 235 tire is 20 millimeters wider than a 215 tire.
Tire size is important because car manufacturers use it in combination with a vehicle's maximum load limit to determine the tire inflation pressure needed to optimize vehicle performance and safety.
Changing a vehicle's tire size may impact the intended manufacturer performance by altering the gear ratio, which also affects the accuracy of the speedometer.
