Good news! You don’t need a physics degree to read a sidewall.
How To Read A Tire Sidewall
When shopping for tires, it’s important to know what all the numbers and letters on the sidewall mean. These numbers and letters are important to finding the right replacement tire for your vehicle. For example let’s look at a Goodyear Eagle, P205/55R16 89H
The manufacturer of the product
The model of the tire
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 which is most often measured in inches.
89 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.
H 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 for one hour. Even though a tire can perform at this speed, we do not advocate exceeding legal speed limits.
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.
Reference Symbol (certifies the tire manufacturer’s compliance with U.S. Department of Transportation tire safety standards
Manufacturer’s Plant Identification Code
Tire Size Code Number
Tire Type Code (coding for type of tire optional by manufacturer
Date of Manufacture - Example 5203 (52nd week of 2003)