Tyre Selection and Safety Tips

Tyre Size Selection

Some may opt to fit mag wheels with different tyre size. The selection of a tyre size should be based on the size originally fitted by the manufacturer.

Compatibility charts are available at most dealers. If not, these would be available from the tyre manufacturer. If the size fitted is incompatible mechanical problems could be experienced.

This is of vital importance on vehicles fitted with ABS braking systems as this system is computer-controlled, based on the rolling circumference of the wheel.

Ensure that the tyre size selected can carry the laden weight of the vehicle. All tyres are marked with a universal load index for this purpose.

The speed rating of the tyre should be in line with the maximum speed of the vehicle. Although we drive a car capable of a speed of 220km/h we may never exceed the legal 120km/h limit and consequently may opt to buy tyres capable of a lower speed.

What would, however, happen in the case of an emergency, when the vehicle may travel at a speed higher than the rating of the tyres?

Trailers or caravans travel less frequently and as a result, people tend to go for the “cheaper” products when kiting them. Remember this tyre must be able to carry the load at the maximum speed at which you intend to travel.

Best Tyre Placement

Many people, particularly those who drive front-wheel drive vehicles, replace two tyres at a time. And these are more often than not, placed on the steering axle. This is a tradition we inherited from our fathers and is totally incorrect. The best tyres regardless of the type of vehicle should be fitted to the rear wheel position.

After having conducted extensive tests, the Swedish Institute of Road Safety found that the majority of tyre-related accidents occur as a result of rear tyre failure. The reasons for this are as follows:

Control: In the event of a blow out the driver will always have control of the front wheels by means of the steering wheel. Much more advanced driving skills will be needed to control the vehicle should a rear tyre blow.
Hydro-pneumatic Trail: A big word which simply means that on a wet road the front tyre leaves, in its wake, a mixture of air and water that has to be absorbed by the rear wheels. This trail is more dangerous than water alone and in the event of worn rear tyres, this could lead to aquaplaning.
Slip Angle: When new vehicles are designed particular attention is given to the vehicle’s ability to negotiate corners. By operating with smooth tyres these design parameters are negated which can lead to loss of control.

Tyre Pressure

A subject on which not enough can be said, as this is the most vital aspect affecting the performance of a tyre.

When going away on holiday, the pressures should be increased to those recommended by the vehicle manufacturers for a laden vehicle. These pressures should be set when the tyres are cold.

Should, for any reason, pressure checks be done on-route, an increase of between 15-20% can be expected, this is normal. Anything higher would indicate that something is wrong and the tyre needs to be checked immediately.

The purchase of your own pressure gauge would be recommended as surveys have in many instances shown inaccurate readings at garage gauges. Should you make use of the line gauges at the service station; prior to inflation, check, blowing air onto your hand; if water or oil residue is evident do not make use of the gauge.

When loading your caravan or trailers, ensure that you do not exceed the gross vehicle mass indicated on the vehicle. If done this could lead to tyre failure.

Tyres and the Law on Tread-Depth

The law states that the minimum tread on a passenger vehicle must be at least 1mm.

If the tread on a vehicle’s tyres is below the minimum it means that the vehicle is unroadworthy and may not drive on public roads.

If a vehicle is involved in an accident and its tyres are not within the lawful specifications, an Insurance Company will not approve any claim even if the vehicle had no blame in the accident or the tyres were not the cause of the accident.

Where there is a Tread Wear Indicator [it indicates a tread of 1.6mm] the tread should not below that mark of 1.6 mm

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Tyre Selection and Safety Tips