How to perform a tyre pressure check
Do you find that your tyres wear out faster than they should do? Perhaps your car is burning through fuel more quickly than it once did, or maybe you’ve started to notice that the handling and braking feel less responsive. While you might assume that the answer to these problems is under the bonnet, the real culprit could be over- or underinflated tyres — and the only way to find out is to perform a tyre pressure check.
Maintaining the correct tyre pressure is an essential part of keeping your car in good shape. It also reduces wear and tear and prolongs their lifespan, while also helping to the overall improve fuel economy of your vehicle. Here, we’ll explain how the pressure in your tyres works, as well as how — and when — to check the pressure level.
- What is tyre pressure?
- What happens if the pressure is too low or high?
- What should my tyre pressure be?
- How to perform a car tyre pressure check
- How do tyre pressure sensors work?
- What should I do if my tyre pressure is too low or high?
- When should tyre pressure be checked?
Tyre pressure is a measurement of the air pressure inside your car tyres. It’s measured in psi, which stands for ‘pound-force per square inch’.
Over time, the pressure in your tyres drops as they gradually become deflated. There are lots of reasons why this might happen: every little jolt, knock, pothole and speedbump you encounter when out on the road contributes to the loss of air. If these are severe, your tyre could even be cracked or punctured, or the bead which seals the rim and the tyre together could be damaged by the impact, resulting in a rapid reduction in tyre pressure. Or, the tyre valve might become damaged or loosened, allowing air to escape.
Temperature changes can also cause the pressure to drop, as the air inside the tyre will contract in cold weather and expand in hot conditions. For instance, if your tyre pressure reads 29 psi (or 2 bar) at 20°C, this reading will drop to 26 psi (1.8 bar) at 0°C. So, even if your tyres aren’t damaged by wear and tear, the pressure will still fluctuate as the seasons change.
It’s perfectly normal for your tyres to lose pressure over time — in fact, the average car tyre deflates at a rate of around 1 psi of pressure per month. But, underinflated tyres can cause serious problems in the long term, so it’s important to keep an eye on things with regular tyre pressure checks, and to adjust the pressure level should it fall under the recommended limit.
Every car has a recommended tyre pressure that will give you the best possible fuel economy, tyre life, and handling. Exactly what this will be varies depending on the make and model of your car, as the pressure is dictated by the weight of the vehicle. If the pressure is allowed to go higher or lower than the range recommended by the manufacturer for a prolonged length of time, then it can lead to serious problems.
When the pressure is low, the contact patch — the part of the tyre that touches the ground — becomes larger, which increases the friction between the road and the tyre. This causes the entire surface of the tyre to wear down more quickly than it would if inflated correctly, and your vehicle’s handling, breaking, and cornering will all be compromised, too. If no action is taken, underinflated tyres can decrease your car’s overall fuel economy, and it could even lead to a burst, cracked, or broken tyre while driving.
When the pressure becomes too high, the tyre is overinflated, which can be just as expensive and damaging. Overinflated tyres will have a narrower contact patch, meaning that less of the tyre is actually resting on the ground. This reduces traction and control and increases braking times, and the central part of the tread will wear out much faster than it would if the tyre was inflated properly. Your car will also bounce around more on the road, which will affect the overall comfort of your ride.
Both under- and overinflated tyres can have serious consequences, and in the worst-case scenario, they can even cause an accident while out on the road. That’s why it’s so important to check your car tyres regularly, and to adjust the pressure or re-inflate them when needed.
It’s easy to find out what the tyre pressure should be for your car: simply look up the information in the manufacturer’s manual. In most modern vehicles, the recommended tyre pressure is usually also displayed on a sticker inside the rim of one of the car doors (usually on the driver’s side). Occasionally, it may also be located in the footwell on the passenger’s side of the car. The recommend tyre pressure for a standard passenger vehicle is usually somewhere between 30–35 psi.
If you don’t have the manual to hand, or you can’t find the sticker, then you should also be able to find out the tyre pressure by contacting the manufacturer directly.
Checking your tyre pressure is simple: all you’ll need is a tyre pressure gauge. There are both digital and traditional tyre gauges available, but both work in essentially the same way.
Before you begin, you should also make sure that the car is parked on a flat, level surface, with the ignition switched off. It’s also important that the tyres are completely cool when you check them, and that the car hasn’t been driven for at least a few hours. This is because the friction between the tyre and the road warms up the air inside the tyre, which can increase the pressure: this will result in a less accurate reading. So, always make sure your car has been parked for a few hours — preferably overnight — before starting the tyre pressure check.
To check the pressure, press the end of the gauge against the tyre valve, and take a reading. The tyre valve can usually be found on the inside of the rim, just inside the trim. If you are using an electronic gauge, then you will need to remember to change the batteries regularly to keep it working correctly.
Most modern vehicles now come with an electronic tyre pressure monitoring system (TPMS) as standard. This is a sensor which monitors the pressure level inside the tyre and automatically sends an alert to the dashboard when it falls too low.
There are two types of TPMS: direct and indirect pressure monitoring systems. Direct TPMS uses a sensor mounted in the wheel to measure the pressure in each tire. If the pressure ever falls far enough below the manufacturer’s recommendations (usually around 25%), then the sensor transmits that information to your car’s internal computer system, and a warning light is displayed on your dashboard.
Indirect TPMS works with your works with your car’s Antilock Braking System (ABS). The ABS uses wheel speed sensors to monitor the rate of acceleration and braking. When the pressure in your tyre falls too low, it will roll at a different speed to the other tires. This information is relayed to your vehicle’s computer, triggering a warning light on the dash.
TPMS systems can be very convenient, as there’s no need to remember to check your tyres regularly using a traditional pressure gauge. And, as they’ll warn you to second your tyre pressure falls too low, you can act immediately to prevent any further damage resulting. However, there’s also the issue of cost to consider: a fault with your TPMS will cause your car to fail an MOT, so you’ll need to pay for repairs should it become damaged.
When the reading on your tyre pressure gauge is lower than the recommended level, you will need to re-inflate the tyre. To do this, you’ll need a tyre inflator or access to an air compressor machine.
Most petrol stations also have air compressors and gauges, although they may charge you for using them. During long journeys, you may also want to keep an emergency tyre reinflation aerosol to hand: can be used to quickly re-inflate and repair tyres if you get a puncture while out on the road.
If the reading is too high, simply unscrew the valve cap and press gently on the valve rod to allow some air to escape. Keep checking the pressure gauge until you reach the recommended reading.
To ensure that your tyres are inflated correctly, it is recommended that you check your tyre pressure at least once a month and make any adjustments to the pressure level as needed. You should also check your tyre pressure before you set off on a long journey, as this will help to reduce the risk of a tyre problem, breakdown or accident later on.
If you accidentally mount the kerb or hit a pothole while driving, it’s sensible to check your tyre pressure as soon as it is safe to do so. Knocks and jolts can cause cracks, punctures, and damage to the seal between the wheel and the rim, but these aren’t always visible to the untrained eye, so it’s best to check your pressure to work out whether your tyre is gradually leaking air.
Every driver should know how to check tyre pressure. Under- or over inflated tyres can cause expensive problems, and they could even lead to an accident, so it’s very important to include this simple check in your car maintenance regime. Remember to check the pressure at least once a month, and you should find that your tyres last longer and that your handling and braking remain responsive.
Here GSF Car Parts, we have a range of wheel and tyre parts, so if you ever need to carry out more extensive repairs, you can find everything you need in our online store. We also have lots more useful advice for repairs and maintenance on our knowledge hub.