There is a lot of useful information molded into the sidewall of every tire. Included are manufacturer and tire name; section width; aspect ratio; construction; rim diameter; speed rating; load range; tread wear, temperature and traction labeling and other necessary designations.
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All tires sold in the United States must meet the size standards for bead shape, width, diameter and other parameters established by a recognized standardizing organization. World leaders among such organizations are the European Tire and Rim Technical Organization (ETRTO) and the Tire and Rim Association (T&RA). Both use a partially metric based system. Virtually all passenger tires on the market today use the system established by these bodies.
The several tire size designations in use today depend on when a vehicle was manufactured and whether it was domestic or imported. All tire sizing systems used today provide information about a tire's dimensions. Among the most important for proper fitment are height, width and load carrying capacity.
 | P-metric: This is the United States version of a metric sizing system established in 1976. P-Metric passenger car tire sizes begin with "P", which simply means "Passenger". |
| Metric: This European tire sizing system is similar to P-Metric but does not use the "P" designator. |
| Alpha-numeric: This system was established in 1968 and is based on the tire's load carrying capacity, rather than its measurements. The tire's capacity and size are indicated by letter designations from "A" (smallest tire, lowest capacity) to "N" (largest tire, highest capacity). An example of an Alphanumeric tire size is BR78-13. "B" shows size/load, "R" indicates radial construction, "78" is the aspect ratio, and "13" is the wheel size in inches. |
| Numeric: This is the oldest standardized tire sizing system for passenger car tires. When this system was adopted, tire aspect ratios were either 92 or 82. For example, a 7.00-14 tire has a section width of 7 inches, a rim diameter of 14 inches and an aspect ratio of 92. The low profile equivalent size tire with an aspect ratio of 82 would be 7.35-14. |
P Passenger (P-metric/Non-P-metric) - This indicates a passenger car tire. If the first character in the size designation is a "P", the tire is a "PMetric" tire and is engineered to standards set by the T&RA (Tire and Rim Association). If there is no "P", the tire is engineered to ETRTO (European Tire and Rim Technical Organization) standards and is a metric tire. The standards set by T&RA and ETRTO have evolved together and are virtually interchangeable.
215 Section Width - These numerals indicate the tire section width in millimeters. This is the dimension from sidewall to sidewall. A tire's section width will vary depending on the rim to which it is fitted. The section width will be larger on a wide rim and smaller a narrow rim. Therefore, each tire is measured o specific rim width. (To convert millimeters into inches, divide by 25.4.)
65 Aspect Ratio - This two-digit number indicates the tire's aspect ratio. It compares the tire's section height, which is the distance from the bead to the center of tread, to the section width. An aspect ratio of 65 means that the tire's section height is 65% of the tire's section width. For clarity, the section width in millimeters is separated from the aspect ratio by a slash (/).
R Construction -This letter indicates the type of ply construction in the tire's casing or carcass. "R" means radial. "D" means diagonal, referring to bias tires. "B" means belted for belted-bias tires. Never mix radial tires with any other construction on a car.
15 Rim Diameter - The "15" indicates the rim diameter in inches. It is the diameter of the bead seat in the rim. Most tires are built to inch standards for rim diameters. However, some tires are built to millimetric rim dimensions. Always match the tire's rim diameter to the wheel rim diameter.
89 Load Index - Refer to the load index chart of a tire guide and you will find the maximum load carrying capacity of this tire to be 1279 lbs.
H Speed Symbol/Speed Rating - In terms of speed, this tire is designed to go a maximum of 130 mph.
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