There is a lot to learn from the sidewall of your tire. Although at first glance you may think you stumbled across tire hieroglyphics, you've actually found -- molded into the tire's side -- its own user manual.

Tire Size

Example P205/55R16 91W

P identifies your tire as a Passenger Tire. The P stands for PMetric. If your tire size starts with LT rather than a P then it identifies the tire as a light truck tire.

205 identifies the tire section width, which is the measurement of the tire from sidewall to sidewall in millimeters. This measurement varies depending on the rim to which it is fitted.

(There are 25.4 millimeters per 1 inch.)

55 is the two-figure aspect ratio. This percentage compares the tire's section height with the tire's section width. For example, this aspect ratio of 55 means that the tire's section height is 55% of the tire's section width.

R indicates the construction used within the tires casing. R stands for radial construction. B means belted bias and D stands for diagonal bias construction.

16 The last dimension listed in the size is the diameter of the wheel rim, which is most often measured in inches.

Load Index and Speed Rating

91 The load index and speed rating, or service description, are the numbers that follow the tire size.

The load index tells you how much weight the tire can support when properly inflated. Load indices range from 75 - 105 for passenger tires, with each numeric value corresponding to a certain carrying capacity. The carrying capacity for each value can be found on a load index chart. On each Canadian passenger car tire, the load limit is listed in pounds. European tires have the load limit listed in kilograms and sometimes pounds.

W Speed ratings are represented by letters ranging from A to Z. Each letter coincides to the maximum speed a tire can sustain under its recommended load capacity. For instance, S is equivalent to a maximum speed of 180 km/h. Even though a tire can perform at this speed, Continental Tire does not advocate exceeding legal speed limits.