Everything you need to know about tyre pressure

Why should you care about tyre pressure?

This may come as something of a surprise, but it turns out your tyres are pretty important when it comes to driving.

And while we can all understand that damaged tyres can lead to disastrous consequences, a somewhat overlooked aspect of tyre health is tyre pressure.

Short of your tyres being completely flat, many drivers ignore their tyre pressure – as long as they still get you to your destination, there’s no problem, right?

Wrong!

Even a slight deviation in your tyre pressure can have long-lasting consequences, both on your vehicle and on your wallet. And checking and maintaining your tyre pressure is one of the easiest things you can do to look after your vehicle.

Many cars come with the tools you need, and for those that don’t, almost every petrol station in the country has an air pump you can use for (almost) nothing.

Despite this, tyre pressure remains overlooked and underestimated, at least until it is too late and the damage is done. But if you want to know how to check your tyre pressure and avoid these very easy-to-prevent consequences, make sure to read this complete breakdown of tyre pressure, why it’s important, and what happens if you forget to keep on top of it.

Incorrect tyre pressure

If you are an experienced driver, hopefully this is somewhat obvious, but your tyre pressure refers to how much air your tyres have. Overinflated or underinflated tyres will result in incorrect tyre pressure.

What happens if tyre pressure is too low?

Not enough air in your tyres, low pressure or underinflation, means more rubber is in contact with the road, leading to:

• Increased fuel costs – as more force is required to drive the car due to increased friction.
• Poor handling – as the tyres will feel ‘slack’ when turning, making your steering less responsive and heavy.

In extreme cases, such as if the tyre is completely devoid of air, your wheels can be severely damaged, as they are effectively running along the road with no protection!

What happens if tyre pressure is too high?

Again, overinflating your tyres can be dangerous – it effectively lowers the contact of rubber with the road. This means that high tyre pressure leads to:

• Reduced traction – which is particularly dangerous, as you’ll be more likely to skid and your braking distance will increase.
• Uneven tyre wear – as there won’t be uniform contact with the road, parts of your tyre will wear out faster than others, creating weak points in the rubber.

Of course, the most obvious danger of overfilling your tyres is a tyre blowout. Tyres are only designed to withstand so much pressure, meaning that an overinflated tyre could very well burst entirely, especially while you are travelling at high speeds.

Under inflated

Over inflated

Correctly inflated

To prolong a tyre’s life, car owners should regularly monitor their tyre pressure. Check your own specific model for accurate tyre pressure levels.

Why do tyres lose pressure?

Tyres will naturally lose pressure as you drive; this is perfectly normal and is why it is so important to check your tyre pressure periodically to keep on top of this natural loss of air. However, if you find that you are having to fill up one tyre more often than you should, it might be due to a slow puncture.

Slow punctures, much as the name suggests, is where a tyre has a hole, or puncture, but it is extremely small or partially blocked, meaning that air is escaping so slowly that it is not immediately obvious – think a pin-hole trickle of water rather than a balloon deflating.

Now, while the air is escaping gradually, a slow puncture will lose air far quicker than a tyre naturally would, so ignoring a slow puncture can lead to some pretty severe consequences, as mentioned above.

If you suspect one of your tyres has a slow puncture, make sure to get your car to your local Arnold Clark garage for a check-up.

Does cold weather affect tyre pressure?

Cold weather causes air inside tyres to contract, significantly dropping the pressure (about 1-2 PSI for every 10 degrees celcius drop) and often triggering the TPMS light.

It's crucial to check pressures when tyres are cold (before driving) and inflate them to the manufacturer's recommended level to ensure safety and prevent underinflation. Never deflate a warm tyre, as its pressure will be artificially high.

What should my tyre pressure be?

When checking your pressure, the first thing you need to know is what is the correct pressure for your set of wheels. Tyre pressure is measured in pound per square inch, more commonly known as PSI.

Every car has their own ideal pressure range, but you also need to consider the way you use your car. Something as simple as how many people are usually in the car will change what the ideal pressure is.

Where do you find tyre pressure PSI in your car?

Thankfully, it’s incredibly easy to find out your tyre’s correct PSI inflation level. Either check your driver’s manual or find the handy informational sticker that is usually found on the driver’s door frame in your vehicle.

When should tyre pressure be checked?

Most modern cars will tell you when to check your tyre pressure as a tyre pressure warning light will appear on the dashboard.

Tyre pressure can be set using the car's onboard computer system. If the tyre pressure falls below the pre-set pressure, this light will illuminate to alert the driver.

How to check tyre pressure

The easiest way to check your tyre pressure is to use a personal pressure gauge – with the best being a digital calibrated one, though those are only really necessary if you need to be incredibly accurate (such as for performance or sports vehicles).

If you don’t have one, you can find them at most hardware shops or even garages Arnold Clark Autoparts has a nice selection if you’re interested.

Once you have your reading, use a personal pump (we recommend an electrical pump, like the ones you can find on Autoparts) or a petrol station’s air pump to fill it to the correct PSI level, then you’re good to go!

How to check tyre pressure at a petrol station

Most petrol stations have air pumps which you can use to inflate your tyres.

You’ll might need some coins to operate the machine, though most are now fully contactless, making it even easier.

Park next to the air pump and remove the tyre valve caps. Attach the air pump’s hose nozzle to the tyre valve and use the gauge to read the pressure.

Inflate to the recommended level if the reading from the air pump is underinflated, or

release air if the tyre is overinflated. Replace the tyre valve caps and repeat for all tyres.

It’s important to remember that these machines won’t be calibrated for your car, so the readings won’t be pin-point accurate.

They are, however, more than adequate to give you a good idea, plus have the added benefit of being able to fill your tyres there and then.

How to reset tyre pressure

To reset your Tyre Pressure Monitoring System (TPMS) light, first ensure all tyres are inflated to the correct pressure.

The specific reset method varies by car, but it generally involves either pressing a dedicated TPMS button (often near the steering wheel or in the glove box) or selecting the 'Tyre Reset' or 'Initialise' option within the dashboard menu settings.

After performing the reset, drive the car briefly to allow the system to calibrate and switch the light off.

And there you go! Everything you need to keep your tyres in tip-top condition.