Understanding Tire Hieroglyphics
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 tires side its own user manual.
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 than 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 tires section height with the tires section width. For example, this aspect ratio of 55 means that the tires section height is 55% of the tires 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 74 – 150 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 U.S. 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 max speed of 112 mph. Even though a tire can perform at this speed, we do not advocate exceeding legal speed limits.
|Speed Symbol||Speed (km/h)||Speed (mph)|
|(Y)||Above 300||Above 186|
DOT Serial Number
The “DOT” symbol certifies the tire manufacturer’s compliance with the U.S. Department of Transportation tire safety standards.
Below is a description of the serial number. Starting with the year 2000, four numbers are used for the Date of Manufactuer, first two numbers identify the week and the last two numbers identify the year of manufacture.
Prior to year 2000 three numbers are used for the Date of manufacture, first two numbers identify the week and the last number identifies the year of manufacture. To identify tires manufactured in the 90’s a decade symbol (a triangle on its side) is located at the end of the DOT serial number.