Tires are described by an alphanumeric tire code (in American English and Canadian English) or tyre code (in British English, Australian English ), which is generally molded into the sidewall of the tire. This code specifies the dimensions of the tire, and some of 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 ISO Metric tire code consists of a string of letters and numbers, as follows:

An optional letter (or letters) indicating the intended use or vehicle class for the tire:

  • P: Passenger Car
  • LT: Light Truck
  • ST: Special Trailer
  • T: Temporary (restricted usage for "space-saver" spare wheels)

3-digit number: The "nominal section width" of the tire in millimeters; the widest point from both outer edges.

/: Slash character for character separation.

2- or 3-digit number: The "aspect ratio" of the sidewall height as a percentage of the nominal section width of the tire. If the information is omitted, it is assumed to be 82% (if written, it should be like xxx/82). If the number is larger than 200, then this is the diameter of the entire tire in millimeters.

An optional letter indicating construction of the fabric carcass of the tire:

  • B: bias belt
  • D: diagonal
  • R: radial

If omitted, then it is a cross-ply tire.

The speed symbol is made up of a single letter

C means commercial, light truck (185 R14 C).

More Info: en.wikipedia.org