How To Read Car Tyre Numbers: What do they mean?

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AutoTrader NZ
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Published 30 April 2024

When shopping for new tyres or simply inspecting the ones on your vehicle, you might have noticed a series of markings, numbers and letters imprinted on the sidewall. These aren’t just random markings; they provide crucial information about the tyre’s specifications and its suitability for different vehicles or conditions. Here’s an easy-to-understand guide to what these markings mean, helping you make informed decisions when purchasing tyres and maintaining them properly.

Tyre Type:

The very first letter you see indicates the type of tyre. For example:

  • P stands for Passenger vehicle tyre.
  • LT means Light Truck tyre, suitable for vehicles designed to carry heavy loads or pull trailers.

Tyre Width:

Following the tyre type, a three-digit number gives the tyre’s width from sidewall to sidewall in millimetres. For instance, a marking of “225” indicates that the tyre is 225 mm wide.

Aspect Ratio:

After the tyre width, there’s a slash followed by a two-digit number which shows the aspect ratio. This number represents the height of the tyre’s sidewall as a percentage of the width. A “45” means the sidewall height is 45% of the tyre’s width.

Construction Type:

Next comes a letter, usually R, indicating the tyre’s construction. “R” stands for radial, which means the layers run radially across the tyre, and it’s the most common type of tyre construction.

Wheel Diameter:

This number tells you the size of the wheel that the tyre is designed to fit. It’s provided in inches, so an “18” signifies that the tyre fits an 18-inch wheel.

Load Index and Speed Rating:

The Load Index is a numerical code that specifies how much weight the tyre can carry safely. You’ll need a reference chart to decode the specific weight each number represents. For example, “91” indicates a maximum load of 615kg per tyre.

Following the load index, a letter denotes the tyre’s maximum speed capability under specific service conditions. For example, “V” indicates a maximum speed of 240 km/h, and “Y” indicates a maximum speed of 300 km/h.

Tyre Production Date:

The production date is usually at the end of the DOT code and consists of four digits. The first two digits represent the week of production, and the last two digits indicate the year. For example, a code ending in “2118” means the tyre was manufactured in the 21nd week of 2018.

Additional Markings:

  • DOT Code: Shows that the tyre complies with all applicable safety standards set by the U.S. Department of Transportation, including information about the manufacturing location and date.
  • UTQG: Stands for Uniform Tyre Quality Grading. This rating system, developed by the DOT, provides useful information on the tyre’s treadwear, traction, and temperature capabilities.
  • Special Usage: Some tyres have additional markings like “M+S” (Mud and Snow), indicating that they are suitable for both mud and snow conditions.

Conclusion:

Understanding these markings can significantly influence your decisions about tyre purchases and maintenance. Always ensure that your tyres meet or exceed the specifications listed in your vehicle’s owner manual to ensure safety and optimal performance. Whether you’re dealing with extreme weather or just everyday commuting, knowing your tyre’s capabilities can make a significant difference.