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Car Tyres – a comprehensive guide

Good car tyres are crucial for safe and economical driving.  Maintaining and changing your tyres properly and regularily will increase their life span.

This guide covers the following topics:

When to replace tyres

In the UK, for a car to be legal and have a valid MOT, car tyres must have a tread depth of at least 1.6mm across three quarters of the tread width, around the full circumference.

New car tyres have a tread depth of approx 8mm. Tyres should be changed if the tread depth is close to or falls below 1.6mm, if there are cracks, worn patches or a puncture. In wet conditions, tyres wear faster and it is adviseable to change tyres earlier.  Around 2 mm would be a good point of reference.

Tyre tread is also a good guage of tyre health. Car tyres which have a low depth have a higher risk of failure, aquaplaning in wet weather or skidding in winter weather due to less grip.

The Law

  • All tyres must be compatible and in good condition
  • Keep tyres inflated at the recommended level (check with vehicle paperwork/manual/car door jut)
  • Tread depth must be above 1.6mm

How to check tyre depth

An easy to read depth guage can be purchased fr0m motoring shop.  Don’t rely on guessing.

First, check the depth of the main tread grooves all around the tyre using the guage.  There should be tread wear indicators at the base of the main grooves indicating when the tyre is at it’s legal limit.  If the wear is nearly at these indicators or has surpassed these, then the car tyre needs replacing.

 

Which tyres to replace

In an ideal world, all 4 car tyres should be replaced at the same time.  However, this can be costly and so not always viable.

Car tyres also tend to wear at different rates front and rear, generally with the front wearing faster as these are the drive wheels and do the majority of the work on modern vehicles.  When replacing tyres, you put your best tyres at the rear.  If only two are worn and they are at the front, you would move the part worn tyres from the rear to the front and put the new tyres on the rear.  In bad weather or when braking, this helps to control the vehicle and reduce loss of stability.

It is adviseable to swap car tyres front to rear periodically as a rule, regardless of whether you need to buy new ones, to balance wear.

Balancing/tracking

It is important to get your wheels ‘balanced’ when you replace tyres.  (Getting the tracking done).  This is often included in the price of the fitting at most reputable tyre bays.

An unbalanced wheel will cause your car tyres to wear unevenly, generally more so on the inner or outer shoulders of the tyre. This could be because of a misalignment in the suspension.  Another indicator of this would be a feeling of vibration thirough the steering wheel.

Appropriate car tyres

Tyre size and specification for your vehicle should be listed in its handbook.

Most UK cars are fitted with summer tyres or all season tyres as standard.

Summer tyres provide the best performance during summer conditions.  All-season tyres are a generic all season tyre which can be left on the car all year round neither providing the best summer performance, or the best winter performance, but ideal for average fluctuating temperatures without the need to change in spring and autumn.

Some people who drive a considerable amount during the winter months or who live in more rural areas may benefit from fitting winter tyres to their car. Winter tyres are distinguishable by a snowflake or a mountain symbol and are specifically designed to give additional grip on snow and ice and in temperatures below 7C.

Winter tyres

The sidewall size and rating markings will be the same, but they have a deeper tread pattern and slits calls sips.  These combined,  help grip the road on snow due to snow sticking to snow.

During temperatures above 7C however, winter car tyres have significantly less grip on the road than its summer counterparts.

In some parts of Europe where extreme weather is expected for prolonged periods, each and every winter, winter tyres are compulsary, however, in the UK, winter tyres are fitted by choice only.

Ideally, you will need a second set of rims for your winter tyres. Opt for steel, which corrode less after exposure to winter grit and fit them before the bad weather strikes.  Waiting until it is already here, will probably mean that you will be unable to fit them.   Buy 5 as there is still a possibilty of a puncture and it is dangerous, and illegal to mix different types of tyres on the same axel.

Tyre markings

You will find markings on the sidewalls of your car tyres which will help you choose the right replacements for your car.  They will also be written in your car handbook.

The letters and numbers relate to the tyre size (tyre width in mm, height of tyre side and diameter of the wheel rim in inches), composition (all tyres are radial now, but some older car tyres used to be cross-ply) and capabilities ( load index and speed rating).

Example:            205/55 R16 91V

      205 – Tyre width mm
      55 – Tyre height, expressed as a percentage of its width
      R – Radial (composition)16 – Diameter of the wheel rim, in inches
      91 – Load index
      V – Speed rating (must match or exceed max speed of your car..in this case 149mph)

 

      When buying a new set of tyres, you should stick to the same spec as those already fitted.

Car tyre speed ratings

S 112mph
T 118mph
U 125mph
H 130mph
V 149mph
W(ZR) 168mph
Y(ZR) 186mph
ZR Above 149mph

Energy Label

Since Nov 2012, it has been compusary for all car tyres to have a tyre energy label.  This tells the buyer which tyres are the most economical to buy.

Every label must display:

  • Fuel efficiency:  A measure of rolling resistance.  The lower the rolling resistace, the better the fuel economy.
  • Wet grip: Based on wet braking. Assuming all 4 tyres have the sae rating, the earlier in the alphabet the number, the shorter the stopping distance.
  • Noise: Measured in decibels (dB) and measured in comparison with the new 72dB European max noise level, which will be inroduced in 2016.

One black sound wave = Very Quiet – 3dB less than European limit

Two black sound waves = Fairly Quiet –  already compliant with the limit

Three black sound waves = Compliant now – compliant only with the current European limit, but not the new one

Run-flat car tyres

Run – flat tyres are increasingly popular with new car manufacturers.  A run-fat tyre will support the vehicles weight following a puncture for up to 50 miles allowing you to get to a garage to change your tyre rather tan needing to do it roadside.
Run -flat tyres should only be driven at a maximum speed of 50mph and should not be mixed on a car with traditional tyres….this could affect handling.  It is also not adviseable not to use run-flats when towing or on cars which dont have a pressure-monitoring syste which would tell you if you havd a puncture.
Markings that could indicate your tyre is a run-flat tyre:   DSST, RFT, ROF and RunFL.

 

Part worn car tyres

Part worn or used car tyres are legal providing that they are properly marked and deemed safe by the garage selling them.

Part worn tyres

The Motor Vehicle Tyres (Safety) Regulations 1994:

Part-worn car tyres must not have:

  • Any cuts longer than 25mm which are deep enough to reach the ply or cord
  • Any bulges or tears caused by separation or failure of the tyre’s structure
  • Any puncture damage which isn’t repaired.
  • Any ply exposed (internal or external)

Part worn car tyres must have:

  • Original markings
  • Must state ‘part worn’ in capital letters at least 4mm high
  • If sold on the rim, be thoroughly inspected internally

If part worn tyres are sold privately or by a garage which does not meet these standards then they could have suffered damage and could be dangerous.  Always be particularily careful when buying part worn tyres and buy them from a reputable tyre dealer.

Tyre composition

    • Tread : Rubber compound which makes contact with the road and grips.
    • Steel belt : Rubber – wrapped bundles of steel wire which hold the tread flat to the road and give stability and rigidity.
    • Sidewalls : The side of the tyre – Lower sidewalls help tyre retain shape when cornering.  Higher sidewalls lend themselves to a more comfortable drive.  Sidewalls carry the load.
    • Bead wires : Hold the tyre to the rim.  Ultra strong steel.

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Tyre maintenance

Driving safely and responsibly will increase the lifespan of your tyres.  Harsh braking, rapid cornering and acceleration all put extra wear on tyres and make them work harder.

Check your car tyres regularly for wear.

      • Is the tread wearing evenly?  Uneven tread could be a sign that the wheels are unballanced.
      • Are there any cracks or bulges. This could be an indication that the tyre is damaged.
      • Remove stones or other debris which could damage the tyre.
      • Is the rim scuffed?  If you have hit a pothole or scuffed the curb, this could cause a rough edge which could damage the tyre and cause a blow out.
      • Check your tyre pressure regularily – A tyre which is going flat will cause uneven wear, not just on that tyre but on the others which will compensate.  It will affect the cars hadling ad also the fuel economy as it causes drag.

Tyre pressures

Your vehicles handbook or the inside of your car door will advise of the correct tyre pressures for your car.  This can fluctuate depending on load.  If you have a heavily laden car, you will need slightly higher pressures.

Low pressures mean you will cause drag when driving and therfore use more fuel.   This can also cause the tyres to wear excessively on the edges near the side wall, causing bukges and makes them more likely to fail.  Car tyre pressure which are too high can affect handling and increase the wear along the centre tread.  Over-inflated tyres are more likely to blow-out if you hit a pothole or kerb.

Check car tyre pressure when the vehicle is cold as driving heats the air and slightly increases the pressure.  Inflating your tyres after a long drive will lead to under -inflation.

tyre pressures

Changing a car tyre

With the right tools, it is easy to change a car tyre.
      • Pull over in a safe place as soon as you realise that your tyre is flat or damaged.  Not on an inclined road.
      • Turn your hazard lights on and a warning triangle out.
      • Make sure that any occupants are out of the car and that the handbrake is on.
      • Locate the brace and jack to your vehicle ( usually stowed with your spare wheel).
      • Use the brace to loosen the wheel nuts first (Some cars will have locking wheel nuts – you will need the locking nut).

wheel brace

      • Place the jack under the jacking point for your car (this should be advised in your handbook) and make sure that it is straight with the ground.
      • Jack the car up so that there is room to remove and replace the tyre.

jack

      • Remove the wheel nuts and the damaged tyre.
      • Place the new tyre on and do up the wheel nuts.
      • Lower the jack so that the new tyre is on the road and then tighten all wheel nuts using the brace.
      • Don’t at any point put your head under the car.
If you encounter any difficulties, please consult a qualified mechanic or breakdown service.

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