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Common Questions About Tyres Answered

At Kwik Fit, tyres are a key element of our expertise. Here, we look at some of the most common questions we’re asked by customers on a regular basis and give our expert opinion on how to care for your tyres.
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A row of car tyres

What’s my tyre size?

It's important to know which tyre size is correct for your vehicle.

The tyre size can be found on the sidewall of the tyre and is a four-part series of numbers and letters. For example, the most common tyre size in the UK is 205/55R16, though there are many variants.

In this example, we’re going to look at a 225/55R16 tyre.

The tyre width is the first three numbers. This shows the tyre width in millimetres. A 225 tyre measures 225mm across the tread from sidewall to sidewall.

The aspect ratio is the tyre code's fourth and fifth numbers. The profile height or aspect ratio of the tyre sidewall is stated as a percentage of the tyre width. An aspect ratio of 55, for example, means that the tyre's profile height is 55% of its width.

Radial tyres are identified by the letter R. Radial tyres are built with the cord plies at a 90-degree angle to the direction of travel to offer the tyre extra strength. Today, almost every new tyre made is a radial tyre.

The wheel diameter is the following two digits, which indicate the size of the wheel rim on which the tyre may be fitted. It is also the tyre's diameter from bead to bead. For example, a 16-inch tyre will fit on a 16-inch wheel rim.

What does the writing on my tyres mean?


Your tyre also has information about when it was made printed on it. The first eight letters after 'DOT' are essentially a serial number used by the manufacturer to identify the tyre and where it was created.

The last four digits, which are normally shown in a tiny window, will help assist you in determining the age of the tyre.

The first two digits denote the week of the year, ranging from 1 to 52. The year is represented by the last two numbers.

Tyres deteriorate with time. If the manufacturing date on your tyres is more than six years old, we recommend getting them tested to verify they are still roadworthy.

Speed rating

A tyre's speed rating is marked by a letter of the alphabet at the end of the tyre size code which shows the tyre's maximum speed capabilities. Tyres are given a speed rating based on a series of tests that determine the tyre's ability to maintain a constant speed for an extended length of time.

Load index

The load index indicates the maximum weight capability of the tyre. The load index is a numerical code found directly after the tyre size and before the speed rating.


Some tyres are designed expressly for use with specific vehicle models to provide enhanced performance. These tyres are created in close collaboration with the vehicle manufacturer and include a recognised emblem on the sidewall which indicates that the tyre satisfies the manufacturer's strict specifications and has been classified as OE.

Many of the world's major car manufacturers, like BMW, Mercedes, and Audi, have authorised marks, and all tyre manufacturers use the same letters and symbols to signify that the tyre has been particularly made for that vehicle.

How often should you check your tyres?

It is critical to maintain your tyres in order to be safe on the road. We recommend carrying out routine car tyre care and inspecting your tyres regularly or before any long distance journey. 

Tyre pressure

There are three reasons why maintaining proper tyre pressure is essential. The first and most important consideration is safety. Underinflated tyres can overheat, while overinflated tyres can cause poor vehicle control on the road.

The second factor is economic. Over- or under-inflated tyres have a reduced contact patch with the road and, as a result, uneven tread wear. Because of the smaller contact patch, your tyre tread will wear faster, necessitating more frequent replacement. Vehicles with underinflated tyres have higher rolling resistance, requiring more fuel to maintain the same speed.

The environment is the third factor for keeping correct tyre pressure. Correct tyre pressure helps with fuel economy, which can result in fewer CO2 emissions from your vehicle.

Tread depth

Tyre treads are the grooves on your tyres that are meant to collect water from the road, allowing your vehicle to grip the road surface better. Without tyre treads, your vehicle would be difficult to steer since it would become extremely slippery.

The legal limit for the minimum depth of tread on your tyres is 1.6 millimetres, measured across the middle ¾ of the tread circle.

It is suggested that you change your vehicle's tyres before the legal limit is reached. Many car manufacturers recommend a replacement at three millimetres, as stopping distances begin to climb significantly at this depth. In rainy conditions, 1.6 millimetres of tread requires two vehicle lengths (eight metres) more to stop at 50 mph than three millimetres of tread.

External damage

In addition to the minimum tread depth, it’s important to ensure that your tyres are free of any additional faults. Lumps, bumps, and bulges may indicate structural problems, while any cut or tear larger than 25mm, or ten percent of the tyre's width, could suggest your tyres are not road-legal. The same applies if any part of the tyre's ply or cable is visible. If your tyre exhibits any of these signs, you should have it assessed by a trained technician as soon as possible, as this type of deterioration can result in unexpected tyre failure.

What‘s the correct pressure for my tyres?

Checking your tyres regularly, or before a long distance journey, will help you avoid any tyre pressure concerns that can go unnoticed. However, when it comes to determining the correct tyre pressure, there is no 'one size fits all' measurement. With such a wide variety of makes and models, establishing the right tyre pressure for your car could prove difficult.

We offer an online tyre pressure tool at Kwik Fit that was created to alleviate the frustration of having to go through lengthy lists of car makes and models. Simply enter your vehicle's licence plate and we'll calculate the correct tyre pressure for your vehicle.

Why is it important to correctly inflate your tyres?

Your tyres must be properly inflated in order to be safe and efficient on the road. Many aspects of your vehicle's performance may be affected by tyre pressure, including braking distance, tyre longevity, steering precision and fuel efficiency.

When your tyres are underinflated, they make greater contact with the road and wear down faster. Overinflated tyres, on the other hand, have less contact with the road surface and grip poorly, increasing the chance of an accident.

Furthermore, driving with tyres that are less than the required minimum tread depth (1.6mm) might result in a £2,500 fine and three penalty points on your licence. As a result, learning how to properly inflate your tyres is critical to your driving pleasure and safety.

Why do tyres have different tread patterns?

There are hundreds of different tyres, each with its own distinct tread pattern - a collection of channels, sipes, and grooves that give grip, traction, and aquaplaning resistance. Tread patterns will be designed by tyre manufacturers to fulfil specific driving demands such as dry handling, wet braking, and even traction on snow and ice. Each tyre will fall into one of three tread categories: asymmetric, directional, or multi-directional.

Asymmetric tread pattern

Asymmetric tyres effectively combine two separate tread patterns on the tyre's outer and inner edges. The tread pattern on the outside edge has huge tread blocks that are meant to give superior dry grip and handling due to a wider contact area with the road. Meanwhile, the tread block on the inside edge is considerably smaller to give greater wet grip, and there are more grooves to assist disperse water on wet roads and lessen the chance of aquaplaning. The tyre is therefore designed to perform well in both wet and dry circumstances.

Multi-directional tread pattern

Multi-directional tyres, also known as symmetrical tyres, have a tread block that is the same on the inner and outer sides of the tyre. This means that the tyre may spin in any direction and be installed in any location on the vehicle with no performance loss. Because of their simpler tread pattern, multi-directional tyres are often cheaper but less able to adapt to changing road conditions than asymmetric tyres.

Directional tread pattern

Directional tyres often have an arrowhead-like tread pattern, which gives them a highly distinctive appearance. However, directional tyres are more than simply attractive appearances. When creating a tyre that can rotate in either direction, there is an obvious compromise. Asymmetric tyres do just that, which restricts their performance in various ways. Directional tyres are designed to rotate in just one way, providing great wet weather performance and directional stability. Directional tyres function well on snow-covered roads because they provide exceptional traction. That is why many winter tyres have directional tread patterns.

Whereas asymmetrical tyres may be installed on either side of the vehicle, directional tyres can only be rotated vertically (from front to rear), otherwise the tread pattern will rotate in the wrong direction when put on a wheel on the opposite side. The needed direction of travel will be indicated by an arrow printed on the tyre sidewall, which will also match the arrowhead shaped tread pattern.

Can you mix tread patterns?

It is not advisable to mix tread patterns on a single axle. An asymmetric tyre, for example, will not give the same wet and dry handling benefits if its counterpart is not the same kind. For the greatest results, replace tyres with similar tyres to the ones you already have, so that the tread design matches perfectly.

What are run flat tyres and how do they work?

Run flat tyres are designed to stay operational in the event of a puncture or a significant loss of air pressure, allowing you to reach safety and return home or to the nearest tyre repair. Run flat tyres also lessen the possibility of blowouts, which may be dangerous and endanger the driver and other road users if they occur at high speeds.

Run flat tyres feature substantially stronger, reinforced sidewalls, allowing them to be driven on for a limited period of time following a puncture. Even if the air pressure is completely lost, the tyre can briefly keep its form and strength.

Stay safe on the road with Kwik Fit

Don't be alarmed if you find yourself in the regrettable scenario of having a flat or damaged tyre, or even if you're worried about not knowing what tyres you need to get- we're here to help. Visit your nearest Kwik Fit centre to speak with one of our specialists about all things tyres!

If you need to get back on the road more frequently, consider scheduling a free tyre safety check with one of our skilled technicians, who can ensure that your tyres aren't going to slow you down anytime soon.