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Tyres

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The comfort and safety of you, your passengers and other road users depend to a large extent on the condition and quality of your car’s tyres, which must be capable of satisfying a number of conflicting requirements.

• Tyres must be flexible, yet strong enough to resist and cushion impact damage.
• They must respond accurately to steering and not be deflected by bumps in the road.
• They must provide good grip for accelerating, cornering and braking, and they must do all these things in all weathers and on all surfaces without overheating.
• There are tyres that are best suited to particular requirements and it would be unreasonable to expect a universal tyre to suit all purposes.
• All tyres are a compromise solution to a complex series of problems.
• Modern tyres are hard wearing with built in strength and safety factors, enabling them to withstand the stresses of modern motoring conditions.
• There are many issues that can affect the rate of tread wear and tread life, such as speed, cornering, braking, accelerating, wheel alignment, road surface and terrain, climatic conditions and most importantly of all inflation pressures.

Inflation

Inflation pressures are determined by three factors:

• The type and size of the tyre being used.
• The load being carried.
• The speed at which the tyre is operated.
• Correct inflation pressure is essential to good tyre maintenance and performance, as it is the air in the tyre not the tyre itself, that carries the weight of the vehicle and its load.
• Incorrect pressure, whether over or under, has a marked effect on the rate of tread wear and vehicle handling characteristics.
• It is essential in maintaining tyre pressures to use a reliable and accurate gauge. Do not trust a gauge that is unfamiliar to you.
• Determining tyre pressure - most inflation pressures quoted are absolute minimum pressures, with the tyres in a cold condition, and that more air is needed to meet heavy load and / or fast driving conditions.
  • Consider your usual driving style.
  • Normal motoring is usually two or three occupants including the driver, carried at speeds up to 100 km per hour.
  • Heavy load conditions are more than two or three occupants plus luggage, or if towing a trailer, caravan or boat.
  • High speed motoring is continuous high speeds over some distance in excess of 100 km per hour.
  • If your driving habits include frequent variations from normal to heavy load conditions or low to high speed driving, assume the most severe type of motoring as your type and adjust the inflation pressure to suit. This will avoid necessary inflation adjustment, which might easily be forgotten, or be inconvenient at the time when the greater stress is being applied to the tyres.
  • Establish the type and size of tyre on your vehicle. This will be stamped on the sidewall of the tyre.
  • Consult your owner’s manual for the manufacturer’s recommendation. Later model vehicles have a tyre placard attached to the bodywork with the manufacturer’s recommendation.
• Remember that all inflation pressures quoted will be minimums and can be increased by two to three psi (14 to 21 kPa) for optimum performance. But do not exceed:
  • 32 psi (221 kPa) for 4 ply rating bias tyres.
  • 36 psi (248 kPa) for 6 ply rating bias tyres.
  • 40 psi (276 kPa) for 8 ply rating bias tyres.
  • 40 psi (276 kPa) for all radial ply tyres.
  • Or the maximum pressure stamped on some tyres, which may be less.
  • All inflation pressures quoted are cold and a tyre that has been driven two to three km is no longer cold.
• Do not bleed air from a hot tyre that has been correctly inflated when cold – the rise in pressure due to heat is allowed for and reducing the pressure generates more heat again.
• If your tyre pressures are consistently rising above the original cold pressure by more than 10% when hot, it may be that you have the wrong tyres fitted or that the cold inflation pressure is too low.
• Consult a tyre specialist for advice.
• Do not exceed the maximum load indicated on the tyre.
• Check your vehicle's spare tyre regularly.

Performance identification

Code letters are used to identify the performance rating of tyres and are as follows for differing construction:

Construction identification

• It is important for safety and legal reasons to identify the type of tyre construction.
  • R designates radial ply construction.
  • B designates bias belted construction.
• No specific code marking is used to identify Australian made bias ply tyres.
• Follow the advice of Australian design Rule 4, which states - All tyres fitted to a vehicle shall be of the same type of carcass construction.
• The correct metric expression for tyre pressure is kilopascals (kPa) a few imported vehicles and gauges show tyre pressure in kilograms per square centimetre (kg/cm²), while some are yet to be converted from pounds per square inch (psi).
• We have converted psi and kg/cm² to kPa in the following chart: