Decoding Vehicle Tyre Numbers and Sizes: A Comprehensive Guide
Vehicle tyre numbers and sizes are crucial for selecting the right tyres for your vehicle. They provide essential information about the tyres specifications, helping you determine the tyres compatibility with your vehicle and its performance characteristics. This guide will break down the meaning of tyre size format, additional markings, and grading systems. By understanding these tyre numbers and sizes, you can ensure safety, performance, and proper compatibility for your vehicle.
Tire Size Format
Tire sizes are typically expressed in a specific format, such as: P215/65R15 95H. Each part of this number conveys important information:
Tire Type (P)
P denotes a passenger vehicle tyre. This letter can also be other symbols such as LT for light truck tyres, or seq_code for special construction vehicles.
Tire Width (215)
The 215 indicates the tyre's width in millimeters from the sidewall to the sidewall. In this example, the tyre is 215 mm wide.
Aspect Ratio (65)
65 represents the tyre's aspect ratio, or the height of the tyre's sidewall as a percentage of its width. For example, a tyre with a 65 aspect ratio means its sidewall height is 65% of its width. If the tyre width is 215 mm, the sidewall height is approximately 139.75 mm (215 mm × 0.65).
Rim Diameter (15)
The 15 signifies the diameter of the wheel rim that the tyre is designed to fit, measured in inches. In this case, the tyre fits a 15-inch rim.
Load Index (95)
The 95 is the load index, indicating the maximum load the tyre can carry when properly inflated. A load index of 95 corresponds to a maximum load of approximately 1,521 pounds (690 kg).
Speed Rating (H)
The H indicates the tyre's speed rating or the maximum speed the tyre can safely maintain under load. In this example, the speed rating is H, which represents a speed capability of at least 210 km/h (130 mph).
Additional Markings
Tires may have other important markings that provide additional information:
DOT Marking
DOT indicates the tyre complies with U.S. Department of Transportation standards. The marking consists of a series of numbers and letters that show compliance with US safety regulations and the tyres serial number for traceability.
Mud and Snow Marking (MS or M/S)
MS or M/S indicates that the tyre is suitable for use in mud and snowy conditions.
Treadwear, Traction, and Temperature Grades
These grades are part of the Uniform Tire Quality Grading (UTQG) system, providing information about the tyre's durability and performance:
Treadwear
The treadwear grade is a comparative rating based on the wear of the tyre compared to a control tyre. A tyre with a grade of 200 would wear twice as long as the control tyre.
Traction Grades
The traction grades are also based on the control tyre and indicate the tyre's ability to stop on wet asphalt surfaces. The grades are AA, A, B, and C, with AA being the highest and C being the lowest.
Temperature Grades
The temperature grades indicate the tyre's resistance to heat and its ability to operate under optimal conditions. The grades are A, B, and C, with A being the highest and C being the worst, meaning the tyre is not capable of operating safely at speeds in excess of those assigned to grade C.
Conclusion
Understanding tyre numbers and sizes is crucial for selecting the right tyres for your vehicle, ensuring safety, performance, and compatibility. Always refer to your vehicle's owner manual or consult a professional when in doubt about tyre specifications.