Confused About Tyre Pressures?

Car tires have to be capable to handling a number of conflicting requirements to achieve optimum use of the available performance of the modern vehicle.

The tyres should be stronger to resist and cushion impacts and yet be flexible. It should respond accurately to steering inputs and not be deflected by ridges in the road. On the safety aspects, tyres have to provide good grip and traction during acceleration, cornering and braking, and they must do all these things under all weather conditions, and on wet and dry surface. From the layman’s point of view, the tyres must run quietly, give a comfortable ride and have a long tread life. Modern tyres are tough and hard wearing with built-in safety features that enable to withstand and hold the stresses of latest motoring conditions. However, there are several factors which will affect and also the rate of tread wear such as cornering, braking, hard acceleration, speed, wheel alignment, road surfaces, climatic conditions and tyre pressures.


The tyre pressures are determined by three factors:

  1. The type and size of tyre being used.
  2. The load the tyre is subjected to.
  3. The speed at which the tyre is to be operated.

Correct tyre pressure is the basis of tyre care. It is the air in the tyre, not the tyre itself, that carries the weight and load of the vehicle.

Incorrect tyre pressure has a marked effect on the rate of the tread wear and vehicle handling characteristics. It is very important to ensure that the tyre pressure is maintained with the use of a reliable and accurate gauge. Do not trust a gauge which is unfamiliar to you. It is always better to carry your own tyre pressure gauge of a good brand. The accuracy may be wanting but it is the consistency that matters, as long as you are aware of how much your gauge is over or under reading. Determination of the actual pressure appears to be complex but there are basic principles which, if adhered to, make the determination easier.

The first step is to establish the size and type of tyre on your car. This can be done by observing the sidewall of the tyre where the size and type of tyre on your car. This can be done by observing the sidewall of the tyre where the size and tyre, such as 7.50-14 or 185 SR14, will be moulded.

The second step is to consider your type of motoring requirements which may be:

  1. Normal motoring-which is usually with 2 or 3 passengers and speeds up to 100km/h
  2. Heavy load condition-which is more than 2 or 3 passengers plus luggage
  3. High speed motoring-which is continuous high speed in excess of 100km/h.

The third step is to refer to your owner’s manual. In it are recommendations for the pressure to be used under the motoring conditions you have decided upon.

If none of these sources is available then it is necessary to contact the vehicle dealer or tyre dealer to quote the:

  1. Size and type of tyres and
  2. The type of motoring that most adequately describe your driving requirements.

Always remember that all tyre pressures quoted are absolute minimum figures and can be increased by 2 or 3 psi (14 or 21 kPa) for optimum handling and tyre life.It must also be remembered that there are limits to be observed and you should not exceed these pressures:

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 a smaller figure.