Ask the Mechanic: How do I know that my car needs new tyres?

My car tyres look old and dirty but still move very well. How do I know when my car needs new tyres?

Desire.

Hello Desire, often, one can tell when tyres need to be replaced by their physical condition such as worn out treads (which are crucial for braking and road holding); uneven wear of tyre surface (which affects road handling) or deep cuts or swelling on the tyre side walls, a sign of impending failure or bursting while driving. 

In many cases, car tyres may not have the physical telltale signs that they should be replaced, such as in your case. In this case, you have to rely on the manufacture date to know whether your tyres have expired. Tyres expire after five years and can lead to catastrophic accidents with fatalities when they fail.  Many tyre manufacturers advise car owners to inspect their car tyres after five years.

Leading car manufacturers and technical tyre organisations such as the European Tyre and Rim Technical Organisation (ETRTO) and the UK Tyre Safety Group (TSG) urge customers to replace their car tyres after five years. Used and new tyres with a shelf life of five years or more should not be bought for use on your car. You can tell whether your tyre has reached the expiry date by looking at the mandatory DOT code, which shows the week and year of manufacture. Unfortunately, many car tyre sellers and motorists are not aware that the tyre manufacturers are required to display the date of manufacture.

When tyres expire, they are likely to suffer catastrophic failure such as tread separation, tyre blow out, bulging side walls, tyre cuts or tears and flat tyres. When your tyres fail due to age, while you are driving fast your car will lose traction swerve and lose control causing an accident and possible fatalities.

To appreciate why and how tyres age, we must understand how they are built. Tyres are made up of different layers of rubber and synthetic material with steel belts all bonded together with high heat or vulcanisation. The aging of a tyre results from exposure to extreme temperatures due to quick starts or speeding and stress from carrying weights.

A new tyre that sits on a shelf for six years also suffers exposure to the oxidation aging process. Due to aging, a tyre loses elasticity and becomes dry and brittle. Oxidation increases the ability of bonding materials to separate as the steel belts and rubber or synthetic materials lose their adhesion. This is what causes tread separation and catastrophic failure. It may not be possible to tell the age or expiry of new or well-maintained tyres. The only certain way is to read the DOT code and find out when the tyres were manufactured.

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