A Guide to Understanding Your Tyre Size

Vehicle Documentation: Your owner's manual or other vehicle paperwork will specify the recommended tyre size. However, if your car has aftermarket wheels, this information may not be accurate.

 

Vehicle Tyre Placard: Most vehicles have a tyre information placard located in the driver's door jamb, glove compartment, or fuel cap. Again, this information may be inaccurate if the vehicle has non-original wheels.

 

Tyre Sidewall: The tyre size is printed on the sidewall of each tyre. Check all four tyres as they might differ.

Decoding Tyre Size Numbers
Tyre sizes are represented by a series of numbers and letters that provide specific information about the tyre:

• Width: Measured in millimeters, this is the tyre's tread width.

• Aspect Ratio: A percentage indicating the height of the tyre's sidewall relative to its width.

• Construction: Typically "R" for radial construction.

• Rim Diameter: The diameter of the wheel in inches.

• Load Index: Represents the maximum weight a tyre can carry.

• Speed Rating: Indicates the maximum speed the tyre can safely handle.

Tyre Types and Understanding Load Index and Speed Rating

 

Tyre Types
Tyres are designed for specific conditions and vehicle types. Here are some common categories:

• Summer Tyres: Optimised for dry and wet conditions in warmer temperatures. They offer excellent grip and handling but struggle in cold weather.

• Winter Tyres: Designed for snowy and icy conditions. They have a softer rubber compound and tread pattern for better traction.

• All-Season Tyres: A compromise between summer and winter tyres, suitable for moderate climates without extreme weather.

• 4x4 Tyres: Designed for off-road use, with aggressive tread patterns for better traction on various terrains.

• Run-Flat Tyres: Can be driven on for a short distance after a puncture, thanks to reinforced sidewalls.

 

Load Index and Speed Rating

• Load Index: This number indicates the maximum weight a tyre can carry. It's crucial for safety and vehicle performance. You can find a load index chart online to convert the number into weight.

• Speed Rating: This letter represents the maximum speed the tyre can safely handle. It's essential to match the speed rating to your vehicle's capabilities. Common speed ratings include S, T, H, V, W, Y, and Z.

 

Example: A tyre with a size designation of 205/55 R16 91V indicates:

• Tyre width: 205mm

• Aspect ratio: 55%

• Construction: Radial

• Rim diameter: 16 inches

• Load index: 91 (refer to a load index chart for weight capacity)

• Speed rating: V (maximum speed of 240 km/h or 149 mph)

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