A BIT OF TYRE PRESSURE ADVICE...

Keep tyres at the pressure recommended by the vehicle manufacturer. Incorrect pressures can affect a vehicle’s handling, cause premature tyre wear and damage a tyre irreversibly.

Motorists should be encouraged to check tyre pressures regularly at least once a month, and before every long journey. That includes the spare.

Tyre pressures should be checked when tyres are cold, before the vehicle has travelled any great distance. As they warm, tyres increase in pressure which is quite normal. 

 

THE EFFECTS OF UNDER-INFLATION

Under-inflated tyres will suffer excessively from flexing and get extra hot on a journey which could lead to a dangerous blow-out. They make the vehicle harder to control as the tyre seems to squirm on the wheel. Front tyres that are under-inflated can result in the vehicle under-steering. Rear tyres under-inflated can lead to over-steer. Both situations could be lethal.

Over Steer Under Steer

Despite popular belief, an under-inflated tyre doesn’t sit firmly and snugly on the road. Its edges deflect inward, lifting the centre of the tyre and so reducing the contact area. This affects braking performance and the tyre’s ability to clear surface water, thus increasing the risk of aquaplaning.

Aquaplaning

 

The extra loading on the edges (i.e. the shoulders) of the tyre will cause rapid wear, reducing tyre life. In extreme cases, there could be wear and irreversible damage to the sidewall (C).

Tyre Inflation

 

THE EFFECTS OF OVER-INFLATION

Like under-inflation, over-inflation reduces the area of contact with the road, which can adversely affect vehicle handling and braking, possibly leading to more risk of aquaplaning (B).

It also accelerates wear in the centre of the tread and makes the tyre more vulnerable to impact fracture or other casing failures.

An over-inflated tyre doesn’t absorb road shocks so well, resulting in a much harder ride, which can prove extremely uncomfortable when clocking up the miles.

TYRE PRESSURE MONITORING SYSTEMS (TPMS)

TPMS is a system fitted to a vehicle which constantly monitors the pressures or pressure imbalance in the tyres and provides a warning to the driver if these fall below a certain threshold.

Such is the importance of correct inflation, TPMS is a very useful safety feature. However, TPMS should not be seen as a replacement for regular manual tyre safety checks. Two types of TPMS systems are fitted on cars today. Direct systems use the radio sensors mounted inside of each wheel to measure the tyre inflation pressures. Indirect systems utilise the vehicle's existing ABS sensors to measure and compare the rotational speeds of the tyres, which are affected by their pressures. Both types work with the vehicle's main Electronic Control Unit (ECU) to alert the driver via dashboard warning lights to any pressure loss or variance issues.

TPMS AND THE LAW

Since November 2014, all new passenger vehicles sold in the EU must be equipped with TPMS. Furthermore, with effect from 1st January 2015, all vehicles fitted with TPMS when new will need to have a fully functioning system when undergoing their annual MOT test. Inoperative or faulty TPS systems will result in an MOT failure.

TPMS AND RUNFLAT TYRES

Runflat tyres are designed to provide a limited run-on period following a puncture. These types of tyres can be identified by the "RF" marking found on the tyre sidewall. Runflat tyres are only designed to run for a limited period, at a maximum speed of 50 mph with a limited load-carrying capacity. Due to the nature of runflat tyres, these should only ever be fitted to vehicles equipped with TPMS.

TPMS SERVICING

To ensure your TPMS system continues to operate properly and reduce the likelihood of an MOT failure, it may be necessary to have the system serviced occasionally. TPMS sensors are deisgned to last for many years and miles, however, after a certain period, the sensor's internal battery will run out meaning a replacement is needed. In addition, sensors can become faulty or fail completely as a result of weather damage, corrosion or accidental damage caused when changing tyres. To ensure the sensor remains in good condition, many manufacturers recommend replacement of the valve cap and core components every time a tyre is changed. When replacement TPMS sensors are fitted to your vehicle, your tyre fitter may need to programme the new component to the car using specialist diagnostic equipment.

Related pages

Condition and Faults

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Tread Depth

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Tyre Life

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