Tyre Codes Explained: What does the writing on a car tyre mean?

Eagle-eyed drivers out there may have noticed that the sidewalls of your car’s tyres feature a strange pattern of letters and numbers. While much of a tyre's sidewall is dedicated to branding, there are also a few essential pieces of information that can help you should you find yourself in a pickle and needing a replacement.

If you’re stranded and need a mobile fitting, you may have to locate and communicate this information, so it’s handy to know what these letters and numbers mean. Buckle up and read on if you want to know exactly what all the writing on your tyres means.

Tyre Width

Here’s an example of a full tyre sequence: 225/55 ZR17 101W

The first element of the sequence tells you the tyre’s width in millimetres. So this tyre is 225 millimetres wide, measured between the inner edges of the tyre, where it meets the wheel.

The width tells you how wide a wheel the tyre will fit. The narrowest car tyres are less than 100mm wide and are fitted to low-powered vintage cars. The widest car tyres measure more than 500mm and are often used on race cars. Most modern cars use tyres between 180mm and 250mm wide.

Tyre Profile

The tyre profile, or aspect ratio, is the height of the tyre’s sidewall compared to its width.

Why does it matter? It impacts both grip and comfort. Low-profile tyres (shorter sidewalls) flex less, giving better grip in corners—perfect for sporty, high-performance cars. On the other hand, higher-profile tyres (taller sidewalls) hold more air, making them better at absorbing bumps for a smoother ride.

Car makers pick tyre profiles to balance grip, comfort, and style, depending on the car and its audience. Plus, some people just love the sleek look of low-profile tyres!

Tyre Speed Rating

The third part of a tyre’s code tells you either its speed rating or how it’s made. The speed rating shows the maximum speed the tyre can handle. For example, a ZR rating means the tyre is good for speeds over 150mph—ideal for high-performance cars. Other tyres use letters like A to Y for speed ratings, which appear at the end of the code.

If you see an R after the aspect ratio, it means the tyre has a radial construction (layers of rubber with metal strands). Almost all modern car tyres are radial, while older cars might use the rarer cross-ply tyres.

Wheel Diameter

The fourth element gives the wheel's diameter (in inches) on which the tyre will fit. In our example, that’s 17 inches. Note that wheels come in a wide range of diameters.

Tyre Weight Rating

This final numerical value reveals the maximum weight that a tyre is constructed to handle; the higher the number, the more weight it can support.

Why Tyre Codes Matter

The sequence of numbers and letters on your tyres isn’t just random—it’s crucial for your car’s safety and performance. Every tyre on your car needs to match this code exactly. Why? Because mismatched tyres can behave differently, and even one tyre with the wrong weight rating or size can throw off your car’s balance, grip, and handling. That’s a risk you don’t want to take.

If you’re unsure about the right tyres for your car, you can easily check online using your car’s make and model or ask a tyre retailer for advice. And when it’s time to order new tyres, you’ll need this code to ensure you’re getting the perfect fit. It’s a small detail that makes a big difference in keeping you safe on the road.