At the end of a transition period, any speed symbol denoting a fixed maximum speed capability will be at the end of the service description following the tire marking (illustrated in the second and third examples above). The International Standards Organization (ISO) system currently serves as a worldwide standard for tire markings. Speed symbols may currently be marked on a tire in any of three ways: 245/40ZR18 245/40ZR18 97Y or 245/40R18 97Y. Yokohama defines high-performance tires with a speed symbol of 'H, V, W, Y, (Y)' or 'Z'. Domestically, high-performance tires typically are speed rated. For a tire to be speed rated, it must meet certain minimum industry standards for reaching and sustaining that specified speed. In the U.S., these ratings are based on tire testing in laboratory conditions under simulated loads. Because of the evolution of high-speed passenger car travel, it was necessary to establish a way to rate a tire's high-speed capability. Speed ratings are certified maximum sustained speed designations assigned to passenger car radials and high-performance tires.

Use the following chart to determine the maximum load-carrying capacity based on a tire's load index: Because the maximum tire load-carrying capacity is branded on the tire's sidewall, the load index is used as a quick reference. The load index is a representation of the maximum load each tire is designed to support. These service descriptions contain a two-digit number (load index) and a letter (speed rating). Many tires come with a service description added onto the end of the tire's size.

Tire load index