To correctly read a wheel or tire size chart, it is important that an individual knows what each part of the tire size means. Each tire size has a minimum of five different components: tire type, width, aspect ratio, construction and wheel diameter.
The tire type is the first component and is usually a letter P, which means the tire is for a passenger vehicle, or LT, which means it is for a light truck. Tires without a letter at the beginning are known as Euro metric tires and often have different load capacities. Tire width is the next component and is the first three-digit number on the size chart. This is the width measured in millimeters.
The next two numbers on the size chart indicate the aspect ratio. This is the ratio of the height and width of the tire. For instance, in a tire sized P215/65 R15, the 65 is the aspect ratio and means the height is 65 percent of the width.
The next letter is the construction of the tire and likely is the letter R, which means it is a radial tire. The final number on a tire size chart is the wheel diameter in inches. In the example size of P215/65 R15, an individual would know the tire is 15 inches in diameter.