Tyre sizes and markings: How to read your tyre

Most manufacturers follow an industry-standard method of indicating tyre size with a series of letters and numbers, so you’ll be glad to hear that no matter which manufacturer made your tyre, its size can be found embossed or printed on the tyre sidewall. These numbers indicate the size, type, and performance of the tyre.

Now you’ve located the series of letters and numbers on the side of your tyre, let’s read it together using the image above as our example.
The tyre size is: 225/45 ZR17 94Y.

The first number represents the width of the tyre in millimetres from one sidewall to the other, meaning this tyre’s radial width is 225mm.

After the slash is the height/profile ratio as a percentage of the width of the tyre. In this case it would be 45. This number is calculated by dividing the tyre’s section height by the tyre’s section width, so if the tyre has an aspect ratio of 45, the tyre’s height is 45% of its width.

Next are the letters ‘ZR’ which indicates the type of tyre dependent on how it was constructed. The 'Z' before the 'R' just means that this tyre has been adapted for speeds above 149mph. On this occasion, the ‘R’ specifically refers to the tyre being a radial type, which is generally the most common type of tyre you’ll see on the roads these days. However, alternative letters can be used to indicate other types of tyres - B (Bias-ply) and D (Diagonal construction).

Following the letter ‘R’ is the number ‘17’, which tells us the size of the wheel rim diameter stated in inches. Therefore for our example, the tyre will fit over a rim that is 17 inches.

The ‘94’ indicates the load index, which is the maximum load that the tyre can support when inflated properly.

Ending the sequence is the letter ‘Y’ which relates to the tyre speed rating. In our example, the speed rating indicates a maximum speed of 186 MPH (300 kilometres per hour).

On electric vehicle tyres, the HL load index code may appear at the beginning of the tyre marking. These letters are specific to electric vehicle tyres and signify that the tyre can support a higher load index. The HL marking was introduced in 2021, and more tyre brands are incorporating these into their product lines.

The sidewall of the tyre indicates the company brand, the maximum allowable operating inflation pressure, the maximum load-carrying capacity, and the model type.
Tyres from international manufacturers include additional information required by domestic regulatory authorities.

Your tyre sidewall should have a four-digit number, which represents the tyre’s manufacturing date. The first two digits show the week, and the last two digits show the year. For example, 2423 means the tyre was made in the 24th week of 2023.

Reinforced tyres are designed to support additional weight. These tyres have markings to indicate reinforcement, which can differ among manufacturers. Common markings include XL, EXL, RF, REINF, or RFD.

With run flat tyres, you can drive for a short duration if there is a loss of pressure or a puncture, giving you time to reach a safe location. Run flat tyres are designed to function without pressure for approximately 50 miles but should not be driven at speeds exceeding 50mph. The markings for run flat tyres can vary between manufacturers and may appear as ROF, EMT, RFT, ZP, SSR, or DSST.