Busted: Eight myths about car tyres you should know

Tyres may seem simple but they are one of the most important and least understood components of your car.

Some basic rules apply to get the best from your tyres, starting with regular inspection and maintenance to ensure they provide the optimum safety and performance.

Thanks to recent developments in technology and materials, modern tyres – when looked after correctly – offer longer life, and safer and more effective performance, than we've come to expect in past generations.

So rule number one is: Don't take your rubber for granted.

There are a lot of commonly held – and often mistaken – beliefs out there relating to car tyres, especially in relation to wear, tread depth, pressure and replacements.

So let's set the record straight...

Tyre wear is determined by a range of factors including driving style, load and environmental and storage conditions, so it is impossible to predict how long a tyre will last.

However, even if your tyres show no visible signs of damage and the tread remains above the legal limit, most tyre manufacturers and experts recommend replacing them every 10 years at the very least – seven or eight years will be a very good run – as the rubber compounds and bonding in a tyre do slowly degrade over time.

A tyre’s tread grooves are designed to disperse water on wet roads and ensure the maximum contact between the tyre and the road. New tyres have approximately 8mm of tread depth, and for safety, most manufacturers recommend changing tyres when the tread depth is reduced to 3mm.

In Australia, it is a legal requirement that all tread on a tyre must be a minimum of 1.6mm deep. All tyres are fitted with tread wear indicators (TWI) and the location of these is usually marked by a symbol on the tyre sidewall. When any of the indicators are showing, the tyre must be replaced for the car to remain legally roadworthy.

With the variable steering, braking and driving forces placed on each individual tyre, they wear at different rates. Thus, to ensure the longest life and most even wear, most manufacturers recommend rotating your tyres every 10,000km.

For most standard symmetrical tyres, this should be done in a diagonal pattern with the rear left moving to the front right and rear right moving to the front left.

Many modern tyres (especially those fitted to high-performance vehicles) have a unidirectional or asymmetrical tread pattern, with the direction of travel indicated on the tyre sidewall. These should only be rotated front to rear on the same side of the vehicle.

Note some cars also feature different-sized tyres and or wheels (sometimes called 'staggered') on the front and rear. If they use a symmetrical tread pattern, these can be rotated from side to side on the same axle. 'Staggered' asymmetric tyres cannot be rotated.

The front and rear tyres on your car have a different job to do and, generally, the tyres on the driven wheels will wear faster.

However, regardless of whether your car is front-wheel drive, rear-drive or all-wheel drive, you should always fit the newest tyres or those with the greatest tread to the rear as they provide the essential stability to ensure effective braking, steering and traction.

Tyre pressures normally decrease slightly over time through normal use and this is often not visually obvious, thus tyre pressures need to be checked at least once a month.

This should always be done when the tyres are cold and preferably with a good quality pressure gauge as the ones at the local service station are often not as accurate as they should be.

All vehicle manufacturers provide a minimum recommended tyre pressure for each model that is printed on a placard, usually inside the driver’s door jamb, and in the vehicle handbook. If your tyres are inflated to the recommended pressure, they will provide the optimum level of durability, safety, handling, comfort and fuel consumption.

A tyre inflated to less than the pressure recommended by the vehicle manufacturer may have a greater contact area with the road but under-inflation can cause heat build-up and extra stress on the tyre casing.

This can reduce the life and performance of the tyre and increase fuel consumption.

A substantially over-inflated tyre will have a smaller area of contact with the road and therefore lower rolling resistance, but there are significant dangers as it will also mean the tyre can provide less grip, compromised braking, handling and ride comfort. It may also wear unevenly.

Vehicle manufacturers set appropriate tyre pressure recommendations to ensure the maximum tyre life and effectiveness and these should be adhered to. You should only slightly increase tyre pressures to compensate for increased load or regular sustained high-speed driving.

Tyre manufacturers make a huge range of different tyre sizes, but as with all manufacturing there are certain tolerances allowed in the standards. As a result, two tyres from different manufacturers may not be exactly the same size, which could compromise the car’s handling and performance.

At the same time, different types of rubber compounds used by different manufacturers will wear at different rates.

Thus, to ensure the longest tyre life and highest level of safety and performance, it is best to fit matched tyres (size, make and model) when it comes to replacement time.