File:Size nomenclature -- NHTSA The Pneumatic Tire.png

English: USA tire manufacturers participate voluntarily in an organization known as TRA, The Tire and Rim Association, Inc. It establishes and promulgates engineering standards for tires, rims, and allied parts (tubes, valves, etc.) Participation and adherence to these standards assures interchangeability of component parts among different tire manufacturers. “P-metric” sizing was introduced as radial tire usage began to expand in North America in the early 1970s . Size nomenclature can be described as follows (see Figure 1.2). For a P205/70R15 tire, the “P” indicates that it is for a “passenger” car (“T”, temporary; “LT”, light truck). (Note: European tire sizes typically do not utilize the P, T or LT symbols). The “205” is the nominal section width of the inflated, unloaded tire in millimeters. The “70” is the aspect ratio, or “series”. It gives the tire section height as a percentage of the section width. Lower aspect ratio tires, e.g., 45, 50, 55 series tires, are primarily used in high performance applications but are becoming more popular in conjunction with large rim diameters for styling enhancements in larger vehicles. “R” identifies radial construction (“D” for diagonal or bias tires, “B” for belted bias construction). “15” is the rim diameter in inches. Other USA sizing designation system