1. The first number (205 in this example) is a three-digit number, which refers to the overall width of the tire, in millimeters.
2. The second number (55) refers to the aspect ratio, which is the relationship between the tire’s height and its width. In this example, the sidewall’s height is about 55% of the tire’s width.
3. The letter following the aspect ratio is usually an “R,” standing for “radial.”
4. The next number indicates the diameter of the wheel rim on which the tire will fit (16 inches, in this example).
5. The final number and letter represent the load index and speed rating. The load index is an assigned number ranging from 0 to 279, corresponding with the load-carrying capacity of the tire; that is, how much weight it is certified to carry at maximum inflation pressure. The rating can be matched against a load index chart to determine corresponding maximum weights.
6. The speed rating tells you the top speed at which the tire can operate. Speed ratings were developed to control the safe performance of tires at standardized speeds. A letter from A to Z symbolizes a tire’s certified speed rating. To maintain the speed capability of a vehicle, use replacement tires with ratings equal to or greater than those of the original tires.

It is important to note that markings do not always appear exactly as they do in this example, as tires can be certified under a variety of designations.