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Motor Accident & Safety
Friday, February 1, 2002
Tread carefully

Tyres are one of the most important components on any vehicle, and more often than not the most neglected, says Volkswagon. They contribute to the vehicle’s ability to handle and brake efficiently and safely under various road and weather conditions.
New tyres. All tyres fitted at the factory are tubeless. Tubeless tyres are fitted because they are safer in terms of reaction to puncturing. New tyres do not give maximum grip straight away and should therefore be run-in at moderate speeds for approximately the first 300 kms. Avoid hard braking, acceleration and cornering as far as is possible — especially during the run-in period This also contributes to longer tyre life.
Tyre pressure. Over- or under-inflation shortens the life of the tyre: over-inflation results in excessive wear in the centre of the tread; under-inflation results in excessive wear on both shoulders of the tyre. And this also has a detrimental effect on a vehicle’s handling and performance, and increases fuel consumption.
More seriously, vehicles driven at high speed with under inflated tyres result in the tyres flexing more than normal causing excessive heat build-up. This could result in possible blowout or tread separation.
When a vehicle is driven fully laden, the tyre pressures must be increased. Refer to the Owners Instruction Manual, the fuel flap, or the driver’s door inner panel for the correct pressures.
Tyre pressures should be checked and corrected, preferably when filling the petrol tank or before any long journey when the tyres are still cold. Once every two weeks is recommended. Don’t forget the spare wheel.
However, if the check is made when the tyres are hot, they should be inflated to at least 30 kPa above the recommended pressure for normal operating conditions.
Never adjust the pressures of hot tyres to the recommended (cold) pressures. Pressure increases during running, and may reach or even exceed 20% of normal — this is allowed for in the design of the tyre.
Spare wheel. Certain vehicles are equipped with a ‘space saving’ temporary spare wheel. The advantage of these spare wheels is that they take up less space in the boot than a normal spare wheel and are also con¬siderably lighter. It is important that the pressure of the temporary spare wheel is maintained at 420 kPa and must be checked regularly.
When using a temporary spare wheel, note the following points:
• This spare wheel is only for temporary use for short periods in emergencies. When it is fitted because a wheel has a flat tyre it must be replaced by the normal wheel as soon as possible.
• The vehicle must not be driven faster than 80 km/hr when the emergency spare is fitted. Full throttle acceleration, hard braking and fast cornering should also be avoided.
• The emergency spare has been developed specifically for the vehicle model and must not be used on other models. Emergency spares from other vehicle models must not be used in its place.
• No other type of tyre should be fitted on the emergency spare wheel hub.
• Never use two or more emergency spare wheels at the same time.

Tyres must be checked for damage such as cuts or any foreign bodies embedded in the tread on a weekly basis (more frequently when driving on secondary roads).
Repairs. Tubeless plug repairs must never be considered permanent. The tyre must be removed from the rim and examined for possible inter¬nal damage. If no internal damage exists, a proper vulcanized repair must be effected and this must include a suitable patch on the inner liner. Fitting an inner tube to seal a damaged tubeless tyre should not permitted.
Rotation. Tyre rotation is recommended at 7 500 km intervals. Most vehicle Owner’s Hand Books carry details for your specific vehcile. The advantage of this is that all the tyres will then last for about the same mileage. When the wheels have been rotated it may be necessary to have them balanced again. Maximum grip will not be attained until more or less 300km after rotation. This should be kept in mind when braking and cornering.
Tyre wear indicators. Tyres are equipped with minimum tread depth indicators at the bot¬tom of the tread. When there is no tread left at these points the tyre should be replaced as soon as possible. When the depth is down to 1 mm, measured at any point on the tread, the official permissible minimum tread depth has been exceeded. It is not recommended to let tyres wear down to this extent as tyres with treads in this condition cannot disperse water properly when driving on wet roads.
Various factors can cause tyres to wear. Here are some of the most common:
• Fast cornering can cause excessive wear on the outer shoulders of tyres.
• Locking wheels when braking can cause flat spots on tyres result¬ing in vibrations.
• Incorrect wheel alignment, for example, too much toe-in or toe-out causes excessive wear on the inner or outer shoulder of the tyre which can be identified at an early stage by feathering of the tread..
• Incorrect camber causes uneven wear across the full width of the tyre from the inner or outer shoulder.
• Tyre imbalance, worn suspension joints or worn shock-absorbers will cause flat spotting of tyres in places. The cause of this must be attended to immediately.
• Diagonal wear across the tread of the tyre can be attributed to excessive toe-in or a fault in the tyre manufacture. This can also be detected by a slight vibration or noise from the rear suspension.
Note: Unevenly worn tyres will maintain their wear pattern even though suspension settings have been corrected, nothing can be done about this.
Speed ratings. Tyres are manufactured to cope with various speeds. The speed rat¬ing is marked on the tyre and can be identified as follows:

S Maximum speed of 180 km/h
H Maximum speed of 210 km/h
V Maximum speed of 240 km/h
Z Above 240km/h.

It is of importance to observe these speed ratings when replacing your tyres, so that you use the same grade on all wheels of the vehicle..
Other markings on the tyre are usually noted in the following order, for example:

195/70 R 14 91 H
195 Tyre width in mm
70 Height of the sidewall, expressed as a percentage of the width
R Design (in this case, ‘Radial’)
14 Rim diameter in inches
91 Load carrying capacity index
H Speed rating
*The load carrying capacity is an index figure that corresponds to a table giving the maximum pressure.

Replacement. For safety reasons tyres should be replaced in pairs (on one axle) and not singly. When replacing, new tubeless rubber valves should be fitted for safety reasons. Observe the tyre speed rating as explained above, and nor should you mix different tyre design either, for example, steel belt and textile tyres.
Wheel balancing. Tyre and rim combinations should always be maintained in a state of static and dynamic balance. During normal vehicle operation, tyres may suffer from creep (relative movement between tyre and rim), and hence the wheel assemblies require periodic checking and rebalancing.
Unbalanced wheels increase steering, suspension and tyre wear. For this reason the wheels should be re-balanced as soon as possible. Furthermore, whenever a tyre has been removed for repairs or new tyres have been fitted, the wheel should be rebalanced.
Wheel alignment. Incorrect wheel alignment is one of the most common causes of irregular tyre wear. Besides irregular tyre-wear, it can also have the following adverse effects:
• Increased fuel consumption
• Affect handling or cause the vehicle to pull to one side
• Increase steering effort.

There are many factors that can disturb the wheel alignment, for example: driving techniques such as rapid starts and stops; and hitting potholes and kerbs. It is necessary to have the adjustment checked when any of the above symptoms are noticed. The checking and adjustment of wheel alignment is excluded from the vehicle warranty.

Copyright © Insurance Times and Investments® Vol:15.1 1st February, 2002
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