This tire sizing is the automotive nomenclature for tires. For example, 225/30-14: The first number, 225, is the tread width in millimeters. The second number, 30, is what is called the aspect ratio. The aspect ratio is the percent ratio of tread width. The last number, 14, is the size of the wheel/rim that can fit within the tire. This is measured in inches not millimeters. Golf cart tires will be divided into three groupings based on their tread classification. Street / Golf Course Tire provides the smoothest ride on pavement and is the most popular tire for turf usage. All Terrain Tire provides light off-road capabilities, like for use on gravel roads, but this tire is also good on pavement. The Off-Road Tire is popular for agricultural uses as it has an aggressive tread, this tire is designed for muddy or rocky terrain.