Wheels and Tires Understanding Tire Markings Laws require tire manufacturers to place standardized information on the sidewall of all tires. This information identifies and describes the fundamental characteristics of the tire. It also provides the tire identification number (TIN) for certification of safety standards, and in case of a recall. 1 Tire category. P indicates that the tire is for passenger vehicles. 2 Tire width. This 3-digit number is the width (in millimeters) of the tire from sidewall edge to sidewall edge. 3 Aspect ratio. This 2-digit number is the sidewall height as a percentage of the tread width. So, if the tread width is 205 mm, and the aspect ratio is 50, the sidewall height is 102 mm. 4 Tire construction. R indicates that the tire is of Radial ply construction. 5 Wheel diameter. This 2-digit number is the diameter of the wheel rim in inches. 6 Load index. This 2 or 3-digit number is the weight each tire can support. This number is not always shown. 208 Model X Owner's Manual