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.
