Tyre size and markings explained: how to read a tyre

From sidewall markings to side codes, this guide breaks down everything you need to know to read and understand your tyres with confidence.

Many drivers have a vague idea of what the numbers and letters on a car tyre mean. But do you really know, or does it just seem like a jumble of random characters? This Carwow guide to tyre sizes and markings will explain exactly what they mean, and show you how to read a tyre like a pro.

Remember, you can buy a brand new or used car right here on Carwow. And you can sell your car, too. We’re here to help you through every step of your car-changing journey.

How to read a tyre size

Let’s start with numbers you’ll find on the side of a tyre. These give important information about a tyre’s width, height, and diameter.

Look at the side of any car tyre and you’ll see some numbers and divided by a slash and some spaces, something like: 245/55 R19 91V.

We’ll go through what all these numbers and letters mean. Let’s start with the first set of three numerals…

1. Tyre width

The number ‘245’ refers to the tyre’s width. So, a tyre marking that begins with ‘245’ tells you that the tyre measures 245mm across.

Tyre widths vary from car to car. Small city cars will have narrower tyres than performance cars and SUVs, so expect a higher number on the side of tyres fitted to large and heavy cars.

2. Tyre height or tyre aspect ratio

After the ‘/’ comes the next number (the slash is there to divide the two numbers). In our example the following number is ‘55’. You might think this is the height of the tyre in mm, but it’s not. Instead, this number tells you the height of the tyre as a percentage of the width. So, in this case the tyre height (or aspect ratio) is 55% of the tyre’s width (55% of 245mm).

3. Tyre construction

After these two numbers there will be a small space, followed by a letter and a number.

The letter tells you the tyre’s construction. Almost all tyres these days are radial and will have a capital letter ‘R’ on the side.

Much less common are ‘B’ for bias and ‘D’ for diagonal.

4. Tyre diameter

Immediately after the letter is a number. This gives the tyre’s diameter. Confusingly, although the tyre width is given in millimetres the diameter is given in inches.

This is the tyre’s inner rather than outer diameter, so it corresponds to the diameter of the car’s wheels.

So in our example, ‘R19’ tells you that this radial tyre has an inner diameter of 19 inches.

5. Tyre maximum weight

Now there’s another small space, followed by a number and letter.

The number gives the tyre’s maximum weight (also known as its load rating) in kg. In our example, the tyre displays the number ‘91’, but don’t make the mistake of thinking that means the maximum weight of 91kg – that would be too simple…

These numbers correspond to a load index, so unless you have a photographic memory, you’ll need to refer to a table to find a tyre’s maximum load. The number 91 denotes a maximum load of 615kg for the tyre.

6. Tyre speed rating

You’ll find a letter next to the load index number, in our example a ‘V’. This is the tyre’s speed rating, which is the maximum speed for which the tyre has been approved. A ‘V’ speed rating means the tyre can handle a top speed of 149mph. These speed ratings start with the letter ‘Q’ for 100mph up to ‘(Y)’ for speeds of over 186mph.

How to read tyre markings

Those are the main tyre markings relating to size, speed and load rating – but there are others. These are usually smaller than the main size markings. Here’s what they all mean, and how to read them.

Manufacture date

You’ll see four numbers on the tyre. These show the date of manufacture. The first two of the four tell you the week the tyre was made, the last two give the year. So, ‘2625’ tells you a tyre was made in the 26th week of 2025.

Reinforced types

Reinforced tyres have been designed to handle extra weight. There’s no set marking to denote this, different manufacturers use a different combination of letters. These could be ‘XL’, ‘EXL’, ‘RF’, ‘REINF’, or ‘RFD’.

Run-flat tyres (RFT)

As the name suggests, run-flat tyres are designed to be usable even after a puncture. This type of tyre, popularised by BMW, is now standard fit for a variety of makes and models.

Run flats should last without air pressure for up to 50 miles so long as the car does not exceed 50mph, although it’s best to replace or repair the tyre as soon as possible.

Look out for the letters ‘ROF’, ‘EMT’, ‘RFT’, ‘ZP’, ‘SSR’ or ‘DSST’ on the tyre’s sidewall.

Homologation

Some tyres are designed as original equipment (abbreviated to OE) for particular manufacturers. If this is the case, the tyre’s design and construction has been fine-tuned to meet the carmaker’s requirements.

Various combinations of numbers and letters, or in some cases a symbol, tell you that a tyre is designed for use by a particular manufacturer.

‘B’ is for Bentley while ‘LR’ is for Land Rover. Other designations are less obvious, such as the ‘*’ for BMW and Mini.

Electric vehicle tyres

Electric cars are likely to be equipped with specific tyres. A special ‘HL’ designation was introduced in 2021. This load index code refers to ‘high load’ tyres designed to cope with the high weight of electric cars. A growing number of tyre makers are offering ‘HL’ tyres within their range.

Tyre markings FAQs

How to find tyre size?

To find a tyre’s size, look for the markings on the side of the tyre. You’ll see something like this: 185/65 R16. The first number refers to the tyre’s width in millimetres. The second number gives the aspect ratio (the height of the sidewall as percentage of the width). The letter tells you the type of construction (‘R’ means radial) and the number after the letter gives the tyre’s internal diameter in inches.

What does 91V mean on a tyre?

The number ‘91’ refers to the load index. It tells you that the tyre is approved for loads of up to 615kg. The ‘V’ is the tyre’s speed rating. This letter shows that the tyre is approved for speeds of up to 149mph (240km/h).

What is the M and S marking on tyres?

This means the tyres are designed for use in mud and snow. The manufacturer decides whether to give the tyre a mud and snow marking – it doesn’t have to pass a specific test. A symbol with three mountain peaks and a snowflake (sometimes referred to as the 3PMSF marking) tells you that the tyre has passed official tests and is considered a winter tyre. Many M and S tyres also have the official winter designation, but not all.

Car change? Carwow!

Looking for a new set of wheels? With Carwow you can sell your car quickly and for a fair price – as well as find great offers on your next one. Whether you’re looking to buy a car brand new, are after something used or you want to explore car leasing options, Carwow is your one stop shop for new car deals.

Click here to follow us on WhatsApp, where you can keep up-to-date with all the latest news, reviews, advice guides and videos.