How to understand tyre markings

Monday 27th January 2025

Ever wondered what tyre markings mean? Do you need to find out what tyres you need or just curious?

Whether it’s checking your tyre size or learning about your tyre’s ability to perform in winter conditions, you’ll understand what the digits and letters mean by the end of this article.

How to read tyre markings

Raised eyebrows, scratch of the head, quick Internet search? Tyre markings might daunt you at first, but each sign and symbol represents an important piece of information about your tyre.

Tyre marks include:

Numbers

Letters

Symbols

Phrases

What do tyre markings mean?

Your tyre markings can indicate:

Brand

Width

Aspect ratio

Construction

Diameter

Maximum weight (or load capacity)

Speed rating

Date of manufacture

Homologation (or OE marking)

Load index

Usually, the tyre markings follow this order:

How to read tyre size

What do the numbers on tyres mean?

Example: 205 / 45 R 17

This image shows the tyre sidewall markings – the numbers here indicate the size of the tyre, broken down into separate sections:

205 – Width: The first set of numbers. It’s measured in millimetres and accounts for the tyre’s cross-section. This example would be 205mm.

45 – Aspect Ratio: The second set of numbers looks at the tyre’s width to height as a percentage. For example, this tyre’s height is equal to 45% of the tyre’s width. Also, if the tyre has a short sidewall compared to width, this could mean it may be noisier but has better handling and a more stable ride.

R – Construction: This indicates the internal construction of the tyre. This one has a radial construction and is one of the most common. Other tyre constructions include B (bias) and D (diagonal).

17 – Diameter: Measured in inches, this is the inner diameter of the tyre rim and accounts for the wheel that the tyre is designed to fit.

There can often be other alphanumeric sequences, too. These numbers show the Load Index and Speed Rating. For example, 92H means:

Load Index (92): The maximum load each tyre can carry when inflated to its maximum safe pressure. This does not mean the tyre can support 92kg – but that the index is 92. You may also find this information in your vehicle’s manual.
Speed Rating (H): The maximum speed at which the tyre can carry the load safely. These letters largely ascend alphabetically – apart from H – and corresponds to an equivalent of mph.

Other letters you may spot on tyres could refer to the type of vehicle (e.g. P for Passenger Car) or if the tyre is a spare wheel (T for Temporary). If you notice XL (Extra Load) on your tyres, this means the tyre is reinforced to carry heavier loads than the standard tyre with the same dimensions.

Load index

Speed rating

How do I know when to change my tyre?

If your tyres have:

large, deep cuts

have minimal definition or have bald spots

are over or underinflated

tread below 3mm

It may be time to replace them.

Don’t risk driving with illegal tyres, or you’ll face fines as well as needing new tyres.

When you do change your tyres, all 4 tyres should be the same size, tread and brand. However, it isn’t always financially possible to change all tyres at once, so it’s recommended you stick to pairs. It’s critical to know what elements of tyres you can and can’t mix, too.

Need new tyres?

Not sure which tyres are best for your vehicle? Enter your registration to find what you need and get them fitted the same day at your local Formula One Autocentre.