* Tire Width: The first number in a tire size is the tire's width in millimeters. For example, a tire with a size of 225/50R17 has a width of 225 millimeters.
* Aspect Ratio: The second number in a tire size is the tire's aspect ratio, which is the ratio of the tire's height to its width. For example, a tire with a size of 225/50R17 has an aspect ratio of 50, which means that the tire's height is 50% of its width.
* Radial Construction: The letter "R" in a tire size indicates that the tire is of radial construction. Radial tires have a stronger and more flexible sidewall than bias-ply tires, which results in better handling and fuel economy.
* Rim Diameter: The last number in a tire size is the tire's rim diameter in inches. For example, a tire with a size of 225/50R17 has a rim diameter of 17 inches.
Letters:
* Load Index: The load index is a number that indicates the maximum weight that a tire can support at its maximum inflation pressure. For example, a tire with a load index of 91 can support a maximum weight of 1,354 pounds.
* Speed Rating: The speed rating is a letter that indicates the maximum speed at which a tire can be used safely. For example, a tire with a speed rating of H can be used safely at speeds up to 130 mph.
