A Comprehensive Guide To Tyres

Given that the tyres are one of the most important parts of any motor vehicle, it is quite surprising how few drivers have more than a basic understanding of them. The tyres on your vehicle enable you to change direction, start moving, stop moving again… every single command the driver sends through the engine is actually carried out by the tyres. Your car cannot go without a functional set of tyres, regardless of the power of the engine or the luxury of the interior. With that in mind, it becomes a bit more apparent just how much we rely on our tyres and how we should make a point of becoming more educated about them. If nothing else, it will reassure you that you’re not being ripped off next time you need to buy a new set.

Components of a tyre

A standard tyre consists of between 19 and 25 components and up to 200 raw materials – they’re not as simply constructed as you may think. These components include:

  • An inner liner which helps the tyre to hold its shape and keeps the air in
  • Fabric belts connected to beads, which work together to keep the tyre and wheel together
  • Steel belts above the fabric belts. These provide the tyre’s stability and keep the tread pattern as flat as possible
  • The sidewall of the tyre determines the shock absorption, cornering and sharp steering abilities of the tyre. As a rule, tall and soft sidewalls are best for absorbing impact, while shorter, stiffer sidewalls provide better cornering and sharp steering.
  • The tread of a tyre is the surface which comes into contact with the road – this is why it is important for the steel belts to keep it as flat as possible. By law, tyres must be replaced once the tread has been worn to under the minimum depth of 1.6mm. Tread depth is the distance between the external tread pattern and the fabric and steel belts contained beneath it. If a tyre becomes too worn down, the belts will come into contact with the surface, with potentially disastrous consequences.
  • The grooves in the tread pattern are designed to channel water away from the tyre and maintain maximum grip on wet surfaces. Different rubber compounds and patterns are used to make them suitable for different vehicles and surfaces. The most well-known example of this is the various types of tyres used over the course of a F1 race.

Tyre treads and the law

As we mentioned above, there is a legal minimum tyre tread depth of 1.6mm for most vehicles. Tyres which are out of this level pose a significant risk both to the driver and passengers in the vehicle, drivers and passengers in other vehicles on the road and to pedestrians. Should a tyre blow due to excessive wear, it is likely that injury will be caused.

According to UK law, tyres must:

  • Have a minimum tread depth of 1.6mm
  • Inflated in accordance with the manufacturer’s guidelines
  • Be of the same construction type on both sides of an axle. That is, you are not permitted to have one radial tyre and one cross-ply tyre on the front or back axle of a vehicle. Tyres produced by different manufacturers can be combined, depending on the specifications

Choosing the right tyres

When shopping for new tyres, there are several factors which should be taken into consideration. Choosing the wrong tyres may be an expensive and uncomfortable mistake to rectify but, more importantly, may reduce the safety of your vehicle.

  • Size - While it may be tempting to switch to low profile tyres for better looks, it is generally advisable to stick as closely to the original specifications as possible. Choosing your tyres on the basis of vanity may have a significant adverse effect on the braking, handling, fuel consumption and other aspects of your vehicle.
  • Climate – Most tyres are designed to withstand a wide range of weather conditions, after all, we experience a very varied range here in the UK, but you should bear in mind that your tyres and driving style will need to be adapted for particularly cold, hot or wet conditions.
  • 4 Wheel Drive – If your vehicle is a 4x4, it is strongly recommended that four identical tyres are used at all times. By that, we mean that the model, manufacturer, size, pattern, load index and speed symbol should all match. The only exception to this is where the manufacturer’s handbook specifically states that different front and rear tyres should be used.
  • EnvironmentThe roads on which you most regularly drive will also affect your choice of tyre. City driving calls for tyres with greater longevity due to the numerous stops and starts they will be subjected to, whereas drivers who travel mainly on motorways should opt for comfort, minimal noise and vibration and good braking distance when travelling at speed.

Tyre markings

The letters and numbers on the sidewall of tyres are there to help you to choose the most suitable replacement. The code relates to the tyre’s size, composition and capabilities. The printing is not always immediately obvious as it may be quite small but, if you keep looking, you will find it!

Using tyre code 175/65 R14 T as an example, the letters and numbers used can be explained as follows:

175 – The width of the tyre, given in millimetres

65 – The height of the sidewall, given as a percentage of the width. E.g. this particular tyre has a height of 65% of the 175mm width.

R – Radial. All modern tyres are now radial

14 – Diameter of the wheel rim, given in inches

T – Speed rating. This must match or exceed the maximum speed of the vehicle on which the tyre will be used. The T category includes vehicles with a maximum speed of 118mph.

Do I need winter tyres?

UK cars tend to use summer tyres as standard but many drivers choose to switch to winter tyres for the colder months. Your personal preferences and circumstances will dictate whether or not you need to switch.

Winter tyres are designed specifically for use on wet, icy road surfaces and tend to be constructed using softer rubber compounds and deeper tread grooves than those on summer or all-weather tyres. The surface will also be covered with jagged slits, known as sipes.

The features and benefits of winter tyres include:

  • Better grip on cold and wet roads
  • Improved performance in temperatures below 7C
  • Gathering snow in the sipes to improve grip on surfaces covered by loose snow
  • Deep tread grooves are better at dispersing surface water and preventing aquaplaning

Downsides of winter tyres include:

  • Poor grip in dry conditions and temperatures over 7C, when compared to summer or all-weather models
  • It is generally recommended that you invest in a second set of rims to fit your winter tyres to, meaning the change involves quite a significant initial outlay
  • You will need to buy a winter spare as well as four winter tyres
  • Unless you have a particularly roomy shed or garage at home, it is likely you will need to pay for storage for your out of season tyres when not in use. This costs approximately £100 per year

When considering the cost of winter tyres, remember that you won’t actually be doubling the amount of money you spend on tyres. Swapping your summer and winter tyres on and off as required means that your annual wear and tear is divided between the tyres and each set will last longer than they would if used permanently.

While winter tyres are not legally required in the UK, it may be wise to invest in a set if you live in an area which is particularly affected by adverse weather conditions. If you decide to switch, remember not to leave it too late – you’ll have quite a job getting to a garage to have them fitted if you wait for the snow and ice to hit!

It is generally recommended that the switch to winter tyres is made around October.

Alternatives to winter tyres

If you decide against or are unable to switch to winter tyres, some alternatives are available:

  • Tyre socks – These fabric socks wrap around tyres to give more grip on snowy and icy surfaces. If you use tyre socks, remember to take them off once you have moved away from the snow as normal road surfaces will shred them quickly. A pair of tyre socks normally costs around £50.
  • All-season tyres – Rather than having two separate sets of summer and winter tyres, some drivers opt to use all-season tyres year round. While these are more convenient, it is worth bearing in mind that they do not tend to perform as well as either summer or winter tyres do in their respective ideal conditions.

For tips on driving during the winter and making sure you are properly prepared, have a look at our earlier blog post – Top Tips for Safe Winter Driving.

Common tyre problems

While general road hazards such as potholes, shards of glass and loose rocks and stones are mostly unavoidable, most other potential problems can be minimised. Bearing these factors, and their remedies, in mind will help to preserve your tyres and increase their longevity.

  • Incorrect Inflation – Over and under-inflation of tyres can both cause a number of issues. Under-inflating a tyre affects its flexibility, resulting in overheating, increased rolling resistance and quicker wear and tear. On the other hand, over-inflating a tyre can cause irregular wear, shorten the life of the tyre significantly and reduce grip.
  • Speed – The faster you drive, the higher the risk of tyre damage. As well as increasing the impact if a pothole, rock or other debris strikes the tyre, high speeds can cause damage through overheating. Rapid air loss is another consequence of driving at speed. Remember that tyres should be checked regularly for any signs of damage and replaced immediately when required.
  • Load – Overloading your vehicle will also put unnecessarily increased strain on your tyres. Your tyre’s load capacity (specified by its load index) should never be exceeded. Bear in mind that excessive load can also cause damage to the axle.

How to check tyre treads

Given that the tyres are the only part of your vehicle that actually comes into contact with the road surface, it is incredibly important to ensure they are as safe as possible. Following these steps to check the tread depth regularly will help to keep you and those around you safe.

  • Park on a flat and even surface, away from main roads and busy traffic. Make sure you choose a spot where you will be safe while carrying out the checks
  • Switch the engine off, engage the handbrake and put the car into either first gear or park
  • Use a tread gauge to check the depth of the tyre treads. These devices are very cheap and easy to find so don’t cut corners on such an important matter. Using the tool, check the tyre depth at several places across the circumference of the tyre. If any of these show a reading of less than 1.6mm, it is time to purchase replacement tyres. If you can see any of the tyre’s wear indicator markings, tyres should be replaced.
  • If you don’t have a gauge, Tyre Safe’s coin test is another easy way to check your tyres. Insert a 20p coin into one of the grooves on your tyre – if the outer rim of the coin is covered, your tyre is legal. Again, this is should be done at several points around the surface of the tyre.
  • If you are in any doubt as to the condition of your tyres, have them checked by a professional as soon as possible

How to check tyre pressure

As well as checking the tread depth on your tyres, it is also essential that you check the tyre pressure at least once a month. Under-inflated tyres can be dangerous, as well as wearing down quicker and eventually costing you more money. Your vehicle’s handing and safety will be severely impaired if tyres are under-inflated and, if you are pulled over, you could be handed a £2,500 fine per tyre.

  • Consult the manufacturer’s handbook for the correct tyre pressure. If you cannot find the manual, the tyre pressure can sometimes be found printed inside the petrol flap or on the driver’s door pillar. There is also online assistance on the Tyresafe website.
  • There will normally be two ideal tyre pressure figures given; one for a normal load and one for a heavy load. Make sure to take your load into account when inflating the tyres.
  • Use a pressure gauge (these can be found at petrol stations and garages) to check the pressure of each tyre
  • Inflate each tyre to the correct pressure if required

It is also recommended that the total weight of your vehicle (plus any caravan or other towed vehicle) does not exceed 90% of the combined tyre load capacity. This is explained in more depth in our previous article – New Guide for Caravan Tyre Pressures.

Potential consequences of under-inflated tyres

Don’t dismiss tyre pressure checks as a minor task you can put off for “just another few days”. We mentioned earlier that under-inflated tyres can have disastrous consequences – here is more information on some of the risks involved.

  • Under-inflated tyres have poorer road-holding abilities. This could cause problems with steering, particular when turning corners at higher speeds.
  • At 30% below the recommended level, a much higher risk of aquaplaning is present
  • Braking distances can be increased by up to 5 metres at just 1 bar under optimal inflation
  • 1 bar lower than the ideal inflation level can increase fuel consumption by around 6%

Run-flat tyres

Run flat tyres are becoming increasingly popular amongst drivers. If your tyre gets punctured during a journey, run flat tyres are able to support the vehicle’s full weight for up to fifty miles at a maximum speed of 50mph. Run flat tyres should only be used on all four wheels of a vehicle and where a pressure-monitoring system is in place. If you are unsure whether your tyres are run flat tyres, look for the markings DSST, RFT, ROF or RunFL.

EU tyre labelling

Since November 2012, it has been mandatory for all tyres sold to display EU energy labelling. The ratings used on these labels work in a similar way to those found on domestic appliances, enabling consumers to make an informed decision on which option will be most economical.

The labels must include information on the fuel efficiency, wet grip and noise.

  • Fuel efficiency – To measure this particular rating, the tyre’s rolling resistance is tested on a calibrated test rig. The lower the rolling resistance, the better the fuel economy. The fuel efficiency is rated from A to G, with A being the most efficient. Choosing tyres with an A rating could save you 6 litres of fuel every 1000 miles, or approximately £300 over the lifetime of the tyres.
  • Wet gripWhile fuel efficiency is an important factor, it is equally important to make sure that manufacturers don’t compromise the grip to achieve a more impressive efficiency rating. A to G ratings are also used in this category – with braking distance on A rated tyres tending to be around 30% shorter than on G rated models.
  • Noise – The noise produced by the tyres is another very important environmental concern. The exterior noise levels of the tyre are measured using three categories and displayed as curved bars beside a speaker. When compared to the EU maximum 72dB noise level, the ratings are illustrated as follows: [/pink_bullet_list]
    • Very quiet – 3dB less than the EU limit (one black bar on the diagram)
    • Compliant/fairly quiet – In line with the EU noise limit (two black bars on the diagram)
    • Noisiest allowable – Compliant with current limits but not the newly introduced 72dB limit (three black bars on the diagram)

Changing a tyre – step by step guide

This step by step guide to changing a tyre should make it as easy as possible, even for a first attempt.

  • Make sure you have the required equipment to hand – jack, cloth, wheel wrench, spare tyre
  • Park the vehicle on a firm, level and non-slippery surface, away from traffic
  • Turn the ignition switch to the lock position
  • Switch on the hazard lights
  • Place blocks both in front of and behind the wheels diagonally opposite the one whose tyre needs to be changed
  • Remove the spare wheel from its storage and have it ready to use
  • To remove the wheel with the flat tyre, remove the wheel cover or centre cap where applicable
  • Loosen all of the wheel nuts by ½ turn each, using the wheel wrench
  • Place the jack under the jacking point nearest to the flat tyre
  • Turn the jack handle clockwise until the flat tyre has been lifted completely off the ground. Check for stability with each movement of the handle.
  • Make sure the jacking point tab is resting in the jack notch
  • Remove all wheel nuts completely and remove the wheel from the car
  • Use the cloth to wipe any dirt or residue from the mounting surface of the wheel
  • Push the spare wheel into position
  • Tighten all the wheel nuts as much as possible with your fingertips
  • Tighten the wheel nuts further, but not completely, using the wrench. Use a criss-cross pattern when switching between wheel nuts
  • Check that the wheel has been securely fastened to the hub
  • Turn the jack handle slowly anti-clockwise to lower the car back to the ground
  • Remove the jack
  • Use the same criss-cross pattern to fully tighten all the wheel nuts on the newly-attached spare wheel
  • Put the flat tyre into the storage area where the spare wheel was kept, making sure to secure it using a wheel nut.
  • Double-check that all nuts and equipment are properly secured before driving off

NEVER

  • Get underneath the vehicle
  • Use a jack or spare tyre from a different car
  • Use the spare wheel permanently – it is only intended to enable you to drive to a garage for a replacement
  • Drive more than fifty miles on a compact spare tyre
  • Drive faster than 50mph on a spare wheel
  • Use snow chains on a spare wheel
  • Use more than one compact spare wheel at a time

Tyre safety FAQs:

Q: How often should tyres be checked?

A: Tyres should be checked regularly and at least once a month

Q: What checks should be carried out?

A: When checking tyres, it is imperative that you check the tread depth and tyre pressure and look out for signs of damage or embedded objects

Q: What is the minimum legal tread depth?

A: The UK limit is 1.6mm across the central three-quarters of the tyre. This is amended to 1mm for trucks and 1mm across one quarter of the tyre’s diameter for motorcycles over 50cc. Motorcycles under 50cc are required to have the original tread pattern still visible

Q: What are the consequences of driving on illegal tyres?

A: As well as the obvious safety risks, a fine of £2,500 per tyre may be applicable

Q: Where can I find the recommended tyre pressure for my vehicle?

A: This can be found in the manufacturer’s handbook and/or inside the fuel cap or on the driver’s door pillar

Q: What causes irregular tyre wear?

A: Scuffing of tyres against kerbs, aggressive driving, misaligned steering, under or over inflated tyres and worn suspension are some of the most common causes of irregular wear.

Q: How long can a deflated run-flat tyre be driven for?

A: Consult the manufacturer’s handbook for advice specific to your tyre type

Q: Do I need winter tyres?

A: Winter tyres are not a legal requirement in the UK but may be a sensible option if you live in an area particularly susceptible to extreme weather.

Q: What do the sidewall markings mean?

A: This has been explained in depth earlier in the article. The markings relate to the size, type and load ratios of the tyre.

Q: What is tyre labelling?

A: Since November 2012, it has been mandatory for all tyres sold to display EU labels. These labels display the fuel efficiency, grip and noise ratings of the tyre. More information can be found earlier in this guide.

Q: Should all four tyres be replaced at once?

A: It is preferable for all tyres to be replaced together but, if this is not possible, both on an axle should be replaced at the same time. Replacing the two rear tyres is best for handling and grip on wet roads.

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