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Checking the tyre pressureÖ


Itís important to check the air pressure in the tyres every two weeks and maintain the air pressure at a high pressure of 38-40 psi (pounds per square inch) when the tyres are cold for better fuel economy and better handling provided that this pressure is 10 psi less than the maximum allowable air pressure stated on the wall of the tyres in order to allow for a safety margin.  If this high pressure of 38-40 psi when the tyres are cold exceeds the maximum allowable pressure minus a safety margin of 10 psi, then reduce the air pressure until it is 10 psi less than the maximum allowable pressure.  For example, if the maximum allowable pressure stated on the wall of the tyres is 50 psi, the tyres should not be inflated to more than a maximum of 40 psi when the tyres are cold.


Donít overinflate the tyres...

Do not, under any circumstances, exceed the maximum allowable air pressure stated on the walls of the tyres minus a safety margin of 10 psi when the tyres are cold.  One or more of the tyres could suddenly burst when the tyres heat up in use and the air pressure in the tyres subsequently increases, possibly causing you to lose control of the vehicle and have a bad accident.  The higher the speed, the worse the outcome could be.  As the vehicle is driven, the tyres heat up due to the friction between them and the road surface.  The heat generated by the disc and drum brakes during operation is also transferred to the tyres via the wheels.  As the tyres heat up, the pressure of the air inside them increases.  So itís very risky to inflate the tyres to an air pressure thatís close to the maximum allowable air pressure stated on the tyres when the vehicle has not been driven for a while and the tyres are cold.  When the vehicle is driven and the tyres heat up, the air pressure in the tyres could exceed the maximum allowable air pressure stated on the walls of the tyres which could lead to one or more of the tyres bursting.


Relatively high tyre pressure lead to better fuel economy and better handling...

The reason for maintaining relatively high air pressures in the tyres is that the higher the pressure in the tyres, the smaller the surface area of the tyres thatís in contact with the road, so the less rolling resistance there is when the vehicle is in motion, resulting in less energy required to propel the vehicle and hence more favourable fuel economy.  Conversely, tyres with lower air pressures have more surface area of the tyres in contact with the road and offer more rolling resistance so that the deterioration in fuel economy will be noticeable.  Another advantage to maintaining relatively high tyre pressures is that the handling of the vehicle is more sure-footed and the steering is more responsive because the walls of the tyres are more rigid when the air pressure in the tyres is higher.

The tyre pressures stipulated in the ownerís manual of the vehicle are often quite low in order to provide a more comfortable ride.  However, these low pressures, such as 32 psi, wonít result in good fuel economy.  They tend to also result in a spongy ride and an unsatisfying driving experience.


Ensure that the air pressures in the left and right tyres are identical...

Itís very important to ensure that the left and right tyres of the front pair of wheels or the rear pair of wheels have identical air pressures.  If they have air pressures which are different, the handling of the vehicle will be impaired and can become dangerous if the air pressures of the left and right tyres are considerably different.  This impairment of the handling will be most pronounced if itís the front left and right tyres that have different air pressures, since the front tyres are responsible for steering the vehicle.


Checking the tyre pressures with a hot sun on one side of your vehicle will result in mismatched tyre pressures...

Itís important to realise that parking your vehicle outdoors at home in the sun, so that one side of the vehicle faces the sun and heats up more than the other side of the vehicle, will effectively result in different air pressures being delivered to the left and right tyres if you check and adjust the air pressures after your vehicle has been parked in the sun like this for a while.  If you deliver the same tyre pressure to the left and right tyres, as measured by the tyre pressure gauge, after the sun goes down and all the tyres eventually cool to the same temperature, the tyres that were facing the sun will end up with lower air pressures than the tyres that were shielded from the sun.

The tyres that were facing the sun were hotter when they were being checked and will therefore decrease in temperature more than the tyres on the other side that were shielded from the sun.  As a result, their air pressures will decrease more also, since the air pressure of a tyre decreases as its temperature decreases.  The end result is that the air pressures in the left and right tyres will be different when the left and right tyres are at the same temperature which is obviously undesirable.

The solution to this problem is to check the air pressure in the tyres when the sun hasnít been heating one side of the vehicle (such as early in the day before the sun has risen fully or when the vehicle is parked indoors in a garage) and when the tyres are cold on account of the vehicle not being driven for some considerable period of time.


Itís much easier to check the tyre pressures at home than at the service station...

Iíve found that itís more convenient and less time-consuming to check the tyre pressures at home rather than at the service station.  Thereís no waiting around for the air hose to be free and no feeling as though youíre holding up the person behind you when youíre using it.  If you check the tyre pressures every two weeks, it makes sense to check them at home because theyíll require little in the way of added air pressure.

In order to check the tyre pressures at home and top up the air pressure in them as required, youíll need to obtain a foot pump from your local automotive parts shop or from eBay.  For example, Michelin makes a high-quality, double-barrel foot pump which wonít wear out quickly like the cheap ones.  This is the one I use.  I keep it in the back of my vehicle.

Itís worth also obtaining a separate, high-quality, accurate, hand-held tyre pressure gauge from your local automotive parts shop to ensure that you obtain an accurate air pressure reading when you check the tyre pressures.  No matter how good the foot pump, the pressure gauge on it will rarely be as accurate as a separate, purpose-built, high-quality pressure gauge.  Itís worth purchasing one because it will last for ten to twenty years and longer.  Iíve had mine for seventeen years.  You can keep it in the glove compartment or a storage compartment on the dashboard.



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Copyright 2016 Andrew Mackinnon.  All rights reserved.