How Do Car Tyres Work?

Jan 19, 2017

How Do Car Tyres Work?

Whenever you’re driving, whatever type of road you’re driving on, it’s a sobering thought that the most important part of the vehicle which ensures that you keep yourself, your passengers, your cargo, and all other road users safe, is the area of roughly 23 to 28 square inches (15,000 to 18,000 square millimetres) at any one time.

This is the amount of your fitted tyre surface which is in direct contact with the road at any one time - that’s no more than the average pair of shoes. But when you consider that this amount of contact is keeping you, your car, your occupants and everything else you’re carrying moving safely at all times, that’s quite a lot of responsibility for four patches of rubber to be carrying.

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Tread Carefully...

Current UK law requires car, van and LCV drivers to have at least 1.6mm of tread across the central three-quarters of the tyre, around its entire circumference.

Tyre treads are designed using highly scientific methods, so as to provide the optimum level of grip to a road surface in all conditions.

Depending on the type of vehicle and the conditions under which it operates, there are six different types of tread pattern. These are listed below, along with their main respective benefits:

  • Rib-shaped: offers lower rolling resistance, so the potential for savings on fuel costs. Generates less heat than other tread designs, so is suitable for sustained, high-speed driving.
  • Lug-shaped: with a groove pattern which runs perpendicular to the direction of travel, this pattern is used on tyres where greater levels of traction are required, along with superior power when driving and braking.
  • Rib-lug shaped: combining the benefits of the two tread types listed above, this combination is regularly used where a good compromise between grip on both paved and dirt roads is required.
  • Block shaped: this is a pattern whereby groups of individual blocks are cut into the cross-section of the tread, and are linked by a number of continuous lines running around the whole circumference of the tyre. This gives good grip on wet or icy roads, but because of the smaller size of the individual tread blocks, the overall tread pattern on such tyres wears more quickly.
  • Asymmetric tread, with different patterns on each side: tyres with such a tread pattern provide increased cornering stability and allow more of the surface to stay in contact with the road at any one time. Such a pattern is well suited to motor sport use.
  • Directional: tread with this type of pattern incorporates lateral grooves on either side of the centre of the tread area. It provides good braking performance, and the tread is designed to effectively disperse water from under it, so giving good performance in wet conditions.

What Is A Tyre Made Of?

You may think there’s one, obvious, answer to this - rubber. While that’s true, the rubber, along with other carefully chosen materials, is formed into several different components, which are detailed below:

  • An inner liner, made of air-tight rubber, which is used on most modern car tyres in place of the old inner tube.
  • A sidewall, which is the outward- and inward-facing parts of the tyre which face sideways. This does the important job of keeping the tyre rigid, and improves the ride for all passengers by absorbing road bumps through being able to expand and compress according to the terrain.
  • The apex. This is designed to minimise distortion of the beads of rubber which comprise the tyre by reduce the effects of impacts on it.
  • The tread. This is self-explanatory, and is the part of the tyre which comes into contact with the road. It has to provide grip and stability when cornering, while also resisting the abrasive forces of contact with the road, fending off cut damage and the effects of impacts with items in the road, as well as withstanding the high temperatures created by the friction between the tyre and the road surface.
  • Beading. This is the bonding which fixes the tyre to the wheel rim, and consists of a length of wire with a rubber core which fits securely to the outer edge of the wheel.
  • There is usually a groove within the tread, which forms a single line, and is designed to keep the tyre, and the vehicle running on it, stable, and so improving its ability to accelerate and brake safely and in a straight line.
  • A belt of steel wire or fabric within the downward-facing wall of the tyre. This helps ensure that the widest possible area of tread is in contact with the road at any time.
  • Shoulder. This is the section from the edge of the tread to the higher part of the tyre sidewall. It plays an important part in dispersing the heat generated by the contact between tyre and road surface.
  • Carcass. An inner mesh of cord which is designed to support the weight of the tyre and spread impact throughout the tyre. Because it is constantly flexing and compressing, it has to be made of a material which can withstand regular high levels of use.
  • Chafer. This part of the inner tyre protects the steel or wire cord mentioned above from coming into contact with the wheel rim. Metal on metal is never good.

Other Features Of A Tyre

One of these with which you should be familiar is the groove, which is the sunken part of the tyre’s tread. The amount and pattern of the grooves directly influence a tyre’s quality, while also having a bearing on the amount of road noise which they create, and on the rate at which the tread wears.

A sipe is a fine groove in a tyre’s tread pattern, which performs several important functions including enhancing braking ability and driving performance, as well as keeping the load which the tyres are supporting stable, and so adding to the driver’s and passengers’ comfort. The sipe on a winter tyre gives valuable extra grip through providing an extra edge for this purpose, while it also helps the driver keep control when braking on a wet road.

What’s The Contribution To A Tyre’s Working Performed By Air?

The air within a tyre produces pressure which performs a handful of valuable functions to keep it working properly and safely.

This pressure helps ensure that every part of the tyre can perform its respective job, as described above. But the air pressure should also be kept at a level which not only keeps the structure of the tyre strong, but also includes some flexibility so that the material in the tyre has some ‘give’ in it to help provide a smoother ride over bumpy surfaces.

That’s part of the reason why it’s so important to keep the right amount of air pressure within a tyre - if the pressure is too high, it raises the tyre slightly off the road surface and so reduces the amount grip available; while too little air pressure within the tyre causes the centre of the tyre to sag under the weight which it has to support, and this also means the tyre cannot grip or stop the car as effectively as it should.

Are Winter Tyres A Worthwhile Investment?

Winter tyres aren’t necessarily the huge-treaded specialist types which you might expect to find on huge pick-up trucks or 4x4s.

More commonly, they are outwardly almost identical to standard all-weather tyres, but according to Which? magazine, “winter tyres are designed specifically to remain supple in colder temperatures and maximise traction when driving on snow and ice.”

The key differences are that they use a softer rubber compound - usually by including more natural rubber in the mix - the surface of the tread blocks is covered with sipes (see earlier for a full description), and they generally have deeper tread grooves than conventional summer tyres.

Modern winter tyres differ from previous incarnations in that they are designed to work effectively in all conditions and temperatures, and have been developed as a compromise between the thick-treaded but hugely unwieldy old-style equivalents, and the standard road tyre which starts to lose effectiveness in heavy snow and ice. These are a much better solution for the conditions which we find most commonly in the UK, which might see a few days of snow or ice, but these only lasting for a few days at a time.

The main differences in a winter tyre won’t be visible until you get close up. Then you’ll notice thousands of tiny sipes, which come into their own in dispersing larger amounts of water more quickly than is possible with a standard tyre.

The negative side to such winter tyres becomes apparent once the temperature rises above 7 degrees C. Because there are so many more grooves between the pieces of tread, this makes the tyre - and hence a vehicle riding on them - less stable. The many extra sipes on these tyres will pick up much more snow between their grooves than standard tyres, and so for driving on hard-packed snow, can offer some benefits of extra grip.

While you might not drive enough miles on slippery winter roads to make the investment in all-weather tyres feasible, they are increasingly being fitted to fleets of trucks and vans which need to keep moving in all conditions, for at least part of the year. But for most standard cars, you have to consider that, due to the extra resistance these tyres create, your fuel consumption will suffer.

As they do such a vital job on your car, or any vehicle, you should be sure to regularly check that your tyres are in good condition. Once your tyres are starting to become less effective at their job, don’t hesitate to register with and shop around for the best prices for buying and fitting new tyres in your area.

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