Automotive tires are described by several alphanumeric tire codes (in North American English) or tyre codes (in Commonwealth English), which are generally molded into the sidewall of the tire. These codes specify the dimensions of the tire and its key limitations, such as load-bearing ability and maximum speed. Sometimes the inner sidewall contains information not included on the outer sidewall, and vice versa.
The code has grown in complexity over the years, as is evident from the mix of SI and USC units, and ad-hoc extensions to lettering and numbering schemes.
Most passenger car tires sizes are given using either the P Metric tire sizing system or the Metric tire sizing system (which is based on ISO standards but is not to be confused with the ISO metric system). Pickup trucks and SUVs use the Light Truck Numeric or Light Truck High Flotation system. Heavy trucks and commercial vehicles use another system altogether.