Tyres are the only part of a car that makes contact with the road, so their condition and pressure have a direct bearing on how the vehicle drives. However, tyre pressure is often overlooked, with many drivers checking it only when a warning light comes on or before a long journey.
Following the carmaker's recommended pressure helps the tyres perform as intended. Here is why it matters, what happens when the pressure is incorrect and how to maintain it.
Reasons to maintain correct tyre pressure
1. Better fuel efficiency
Tyres with insufficient air pressure deform more as they roll, increasing the resistance they create against the road. This is known as rolling resistance, and the engine has to use more energy to overcome it. As a result, the car consumes more fuel. Maintaining the recommended pressure reduces unnecessary rolling resistance, helping the car use fuel more efficiently.
2. Better ride quality
Tyre pressure also affects how a car responds to bumps and uneven road surfaces. When a tyre is overinflated, it becomes stiffer and absorbs less of the impact from road imperfections, which can make the ride harsher.
Underinflated tyres, meanwhile, flex more than intended and can affect the way the car responds to steering inputs. Maintaining the recommended pressure helps the tyres work as designed and contributes to a more consistent ride.
3. Better grip and handling
Correct tyre pressure helps maintain the intended contact between the tyre and the road. This is important for grip, braking and cornering, particularly during sudden manoeuvres or when driving on wet surfaces.
Underinflated tyres can flex excessively, affecting steering response and vehicle stability. Overinflated tyres can reduce the contact area with the road, which may also affect grip and braking. Maintaining the recommended pressure helps the tyres deliver more predictable handling.
What happens when tyre pressure is incorrect?
1. Premature and uneven tyre wear
Incorrect tyre pressure can cause tyres to wear unevenly and reduce their service life. Underinflated tyres tend to wear more along their outer edges, as the tread is pressed harder against the road at the shoulders. Overinflated tyres, on the other hand, tend to wear faster along the centre of the tread. This means tyres may need to be replaced sooner than expected, adding to ownership costs.
2. Increased risk of tyre failure
Underinflated tyres flex more as they rotate, generating excess heat. Prolonged heat build-up can damage the tyre's internal structure and increase the risk of a blowout, particularly at high speeds.
Overinflated tyres are also more vulnerable to damage from potholes and sharp road edges because they have less ability to absorb impacts. Both conditions can compromise safety.
3. Higher fuel consumption
Underinflated tyres create greater rolling resistance, which means the engine needs to work harder to keep the car moving. This increases fuel consumption and can reduce the distance covered per litre. Even if the pressure difference appears small, regularly driving with underinflated tyres can add to fuel costs over time.
When should you reduce tyre pressure?
There are certain off-road situations where lowering tyre pressure can be useful. On soft surfaces such as sand, reducing pressure within the limits recommended for the vehicle and tyres can increase the tyre's contact area with the ground. This can improve traction and help the vehicle move across loose terrain.
However, this is a specialised adjustment and should not be treated as a general rule. The appropriate pressure depends on the vehicle, tyre and terrain. Driving at normal road speeds with reduced pressure can cause excessive heat build-up and tyre damage, so the tyres must be reinflated to the recommended road pressure before returning to paved roads.
For normal driving on snow-covered public roads, do not reduce tyre pressure as a substitute for suitable tyres or snow chains. Lowering pressure can affect steering response, braking and vehicle stability, while increasing tyre flex. Any pressure adjustment for deep-snow off-road driving should follow the vehicle and tyre manufacturer's instructions.
What is TPMS and how useful is it?
A tyre pressure monitoring system (TPMS) alerts the driver when one or more tyres lose pressure. Direct systems use sensors inside the wheels to measure pressure, while indirect systems use ABS wheel-speed sensors to detect changes in rotation that may indicate pressure loss.
However, TPMS is only a warning system and does not replace regular checks. Some systems may not detect gradual pressure loss across all four tyres, so it is important to check pressures manually at regular intervals.
Tips for maintaining correct tyre pressure
- Check when tyres are cold: Check tyre pressure before driving, or after the car has been parked for at least three hours. Tyre pressure rises as the tyres heat up during use, so a reading taken immediately after a drive may be higher than the cold pressure.
- Follow the manufacturer's recommendation: The recommended pressure is usually listed on a sticker inside the driver's door frame, near the fuel filler flap or in the owner's manual. Do not use the maximum pressure printed on the tyre sidewall as the recommended pressure for your car.
- Check before long journeys: Inspect the pressure in all four tyres before a highway trip, particularly if the car will be carrying additional passengers or luggage. Follow the manufacturer's recommended pressure for the relevant load.
- Keep a portable tyre inflator: A portable air compressor can be useful for checking and topping up tyre pressure at home or during a journey. It is also worth keeping a separate pressure gauge to verify the reading.
- Do not forget the spare tyre: Check the spare wheel's pressure as well. A spare with insufficient air may not be usable when needed. Check it at least once a month and before long journeys.