Understanding Numbers and Indicators on Tires

The numbers on a tire sidewall provide various information about the tire’s size, construction, and capabilities. Here’s a breakdown of the most common numbers and what they represent:

1. Tire Width: The first number typically indicates the width of the tire in millimeters from sidewall to sidewall when mounted and inflated to its recommended pressure.
2. Aspect Ratio: The aspect ratio is the ratio of the tire’s height to its width. It’s represented by the second number in the sequence. For example, if the aspect ratio is 60, the tire’s height is 60% of its width.
3. Construction Type: After the aspect ratio, there’s usually a letter indicating the tire’s construction type. The most common ones are:
   • R: Radial construction (the majority of modern tires)
   • D: Diagonal or bias-ply construction (less common nowadays)
4. Wheel Diameter: The next number indicates the diameter of the wheel that the tire is intended to fit, measured in inches.
5. Load Index: This number indicates the maximum load-carrying capacity of the tire when properly inflated. The higher the number, the greater the load the tire can support.
6. Speed Rating: The speed rating indicates the maximum speed at which the tire can carry a load under specified conditions. Common speed ratings include:
   • S: Up to 112 mph
   • T: Up to 118 mph
   • H: Up to 130 mph
   • V: Up to 149 mph
   • W: Up to 168 mph
   • Y: Up to 186 mph
   • Z: Over 149 mph (specific speeds can vary)
7. DOT Code: This is a sequence of numbers and letters issued by the Department of Transportation (DOT) to identify the tire manufacturer, plant code, tire size, and the week and year the tire was manufactured.

Understanding these numbers is essential for ensuring you’re fitting the right tire for your vehicle, considering factors like size, load capacity, and speed rating. Always consult your vehicle’s manual or a tire professional if you’re unsure about which tires to choose.