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Tyre pressure: what you need to know

It may seem like quite the hassle, but making sure you have the right tyre pressure can improve how your car drives and save you some money at the pumps

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Whether you have just got home from a long day at work or the school run, or you are getting the caravan ready for a long weekend away, checking your car’s tyre pressure is likely to be the last thing on your mind.

However, making sure you have the correct tyre pressure is very important for safety, as well as providing your car with the best combination of performance and fuel economy. Keeping tabs on tyre pressure can also extend the life of your tyres, saving you the potential cost of replacing them.

In this article, we explain when and how to check your tyre pressure, how to find out what the correct tyre pressure reading should be for your car, as well as the drawbacks of driving with under-inflated or over-inflated tyres.

How to check what the correct tyre pressure reading should be for your car

More often than not, the owner’s manual will tell you what your tyre pressure should be – it will give you a figure in pounds per square inch (PSI). Most manufacturers recommend a tyre pressure of 32 to 35 PSI for the average passenger car.

The manual may also give you the recommended pressure reading in a BAR figure. If so, you can use this handy converter from Which? to get a PSI figure from the listed BAR recommendation.

If you can’t find the car’s manual, some passenger cars have tyre pressure information markings in the driver’s door pillar or inside the petrol flap. Still no luck? Not to worry – type your registration number into Kwik-Fit’s free tyre pressure search tool to get accurate tyre pressure recommendations for a number of different tyre sizes.

You can also contact the customer services team of your chosen car manufacturer to find out the correct tyre pressure for your car. For this, you will need the size of the tyres fitted to your car, which is marked on the sidewalls of your tyres, and your car’s registration number.

Please also note that if you are travelling with heavy luggage in the rear, or towing a trailer or caravan, it is wise to slightly increase the pressure in your rear tyres to avoid oversteer.

When and how often should you inspect your tyres

Recommended tyre pressure figures always refer to ‘cold’ tyres that haven’t been on the move for a few hours. Driving around town causes your tyres to heat up, which increases the pressure in your tyres, so checking your tyre pressure just after driving will give you a false reading.

Therefore, if you are driving to a garage or petrol station to inspect your tyres, it is best to choose a location that is only a short drive away.

Tyre manufacturers generally recommend that you check your tyre pressure on a monthly basis, as passenger cars typically lose around one PSI of pressure every month through natural causes, and even more in the winter months.

How to check your tyre pressure

Once you have found your recommended PSI reading, you are ready to check your tyre pressure.

Checking tyre pressure at a petrol station

Most petrol station forecourts have their own pressure gauge and air pump that you can use for a small fee. Some of these tyre pump machines allow you to pay with coins, and others require a token purchased from the petrol station counter.

It usually costs about 50p to use the pump for four minutes, which should give you enough time to check all four tyres. When safely parked in front of the machine:

  1. Find the valve caps on each of your tyres, which jut out between the spokes of the alloys, and remove them (but keep them safe!)
  2. Insert the payment or required token, and then select the tyre pressure in PSI you would like using the +/- buttons on the air pump
  3. Connect the pump’s air hose to the tyre valve where the valve cap used to sit, and the machine should then show you a current pressure reading for the tyre.
  4. The pump will then inflate or deflate the tyre to match your chosen PSI value, and will start beeping when it is done.
  5. Repeat these steps for the other three tyres
  6. Remember to screw the tyre valve caps back on before you set off

In some cases there will be a PSI reading marked on the tyre, but do not mistake this figure as the recommended tyre pressure for your car – this is usually the maximum pressure that the tyre can take before popping.

Checking tyre pressure at home

If you prefer to check your tyres at home, you will need a reliable pressure gauge, a screwdriver and tyre pump or air compressor. You can pick up a pressure gauge for around £10, while a quality tyre pump usually costs between £15 to £30. With your recommend PSI pressure reading in mind:

  1. Remove the valve cap from one tyre
  2. Press the pressure gauge onto the tyre valve until the hissing sound stops and the gauge gives you a reading
  3. If the tyre is over-inflated, press the small metal pin inside the valve with a screwdriver to let air out of the tyre
  4. If the tyre is underinflated, press the tyre pump or air compressor hose onto the valve and fill the tyre with air
  5. Check the tyre once again with the pressure gauge to see if you have the correct tyre pressure
  6. Repeat these steps for the other three tyres
  7. Remember to screw the tyre valve caps back on

Alternatively, you can take your car to a garage to ask a mechanic to check your tyre pressure – some garage chains, like Kwikfit, offer tyre pressure checks free of charge.

As well as the tyres you have fitted, remember to check the pressure of your spare tyre every once in a while – you never know when you might need it.

The benefits of having the correct tyre pressure

It will usually cost you 50p at most if you are checking your tyre pressure monthly at the petrol station, but that will save you £s every month at the petrol pumps – breakdown cover provider RAC asserts that driving with correctly-inflated tyres can improve your mileage per tank by up to 3%.

Getting your tyre pressure right will improve how quickly you can brake and how accurate your car is when steering. Keeping your tyres at the correct pressure can also greatly extend the lifespan of your tyres, and for the eco-conscious among us, it is better for the environment.

As properly-inflated tyres also help to reduce punctures, cuts and tire failures, checking your tyre pressure on a regular basis can make your car safer to drive, as you will read below…

The drawbacks and dangers of under-inflated tyres

It may seem more comfortable to drive with low-pressure tyres, but an under-inflated tyre is too flexible, which makes it uncontrollable. The centre of a low-pressure tyre does not make as much contact with the road as the outside edges, meaning at the edges of your tyre wear out faster, reducing the lifespan of your tyre and making your car more prone to breakdowns and road accidents.

Tyre manufacturer Michelin says that a difference of just seven PSI under or over your car’s recommended tyre pressure figure can reduce the life of your tyres by nearly 5,000 miles, and that tyres 14 PSI under the recommendation have an increased braking distance of 11 metres on wet roads.

Underinflated tyres are also prone to overheating, and make your car vulnerable to aquaplaning and other steering problems, which can cause you to start skidding or even spinning on wet surfaces due to a loss of control.

Driving a car with a heavy load while the tyres are under-inflated can also cause the sidewalls of the tyres to bulge and swell under the weight, leading to increased wear and tear, and making sudden tyre blowouts more likely.

The drawbacks and dangers of over-inflated tyres

If your tyres are over-inflated, the centre of the tyre makes more contact with the road than the edges, meaning that the centre of the tyre wears out faster.

This means that you will have to pay for new tyres to pass your MOT more often, as the lifespan of your tyres will be greatly decreased. Tyres with too much pressure also often cause a loss of traction with the road, increasing your stopping distances and making your car more prone to potential collisions.

And of course, the more inflated your tyre is, the more prone it is to rupture in high stress braking scenarios.

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Sean Rees
Sean Rees
Sean is the Deputy Editor at The Car Expert. A enthusiastic fan of motorsport and all things automotive, he is accredited by the Professional Publishers Association, and is now focused on helping those in car-buying need with independent and impartial advice.