Auto Trader NZ
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.
| Tyre Construction Type | Description | Advantages | Disadvantages |
|---|---|---|---|
| Radial | Features layers of fabric with cords running at right angles to the tyre’s circumference. | Longer tread life, better fuel efficiency, improved handling. | Stiffer sidewalls, may cause a rougher ride. |
| Bias (or Cross-Ply) | Has layers of fabric with cords running diagonally to the tyre’s circumference, crisscrossing each other. | Smoother ride, better for off-road conditions. | Shorter tread life, less fuel-efficient, less responsive handling. |
| Belted Bias | Combines bias ply construction with belts beneath the tread for added strength. | Better tread stability than bias ply, smoother ride. | Not as durable or fuel-efficient as radial tyres. |
| Run-Flat | Designed to resist the effects of deflation and allow the vehicle to be driven to a safe location after a puncture. | Safety and convenience, no need for a spare tyre. | More expensive, stiffer ride, limited availability. |
| Tubeless | Has no inner tube; the air is contained within the tyre itself. | Easier to repair, safer (less prone to blowouts), lighter. | Requires specific rim designs, can be more difficult to mount. |
| Tubed | Contains an inner tube that holds the air pressure. | Easier to mount and dismount, more versatile for various rim types. | Prone to blowouts, heavier, less efficient. |
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.
Load Index and Speed Rating Table
These examples show different combinations of Load Index and Speed Rating, indicating the tyre’s maximum load capacity and speed capability.
| Load Index | Maximum Load (kg) | Speed Rating | Maximum Speed (km/h) |
|---|---|---|---|
| 85 | 515 | H | 210 |
| 88 | 560 | V | 240 |
| 91 | 615 | W | 270 |
| 94 | 670 | Y | 300 |
| 97 | 730 | ZR | 240+ |
| 100 | 800 | T | 190 |
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 21st 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.
