How to Check Tyre Pressure

Watch our video guide on how to check the tyre pressure on your car, below.

Tyre Pressure Tips

Tyre pressure should really be checked every few weeks to ensure your vehicle is still safe to drive and sufficiently inflated.

The correct tyre pressure is important for two key reasons:

  1. Safety - poor tyre pressure can lead to the higher risk of over/understeering, increased braking distances and aquaplaning.
  2. Cost reduction - tyres with incorrect pressure will have a reduced life span and increase fuel consumption.

Let’s dive into some extra tips around how to check your tyre pressure, and how to manage low tyre pressures. Or check out our tyre safety video game to test your tyre knowledge.

Checking tyre pressure

Halfords recommend checking tyre pressures (including the spare tyre) every few weeks and before any long trip. Tyres should be checked regularly as they are susceptible to drops in pressure which can be caused by:

  • Natural leakage of air through the walls of the tyre
  • Drops in ambient temperature
  • Slow puncture

Tyre pressures should be checked cold - meaning either your tyres should not have been run for at least two hours, or that they’ve been run for less than two miles at low speed. If tyre pressures are checked hot, add 4 to 5psi (0.3 bar) to the recommended pressures. Correct the tyre pressures if they no longer correspond to the pressures recommended by the vehicle manufacturer.

Information on the recommended tyre pressures can be found in the vehicle documentation, and often on a sticker fixed to the vehicle, for example on the door jamb or on the fuel filler cap.

In case of unusual pressure loss, have the internal and external condition of the tyre checked, as well as the condition of the wheel and valve.

Low pressure affects the balance of the vehicle

  • A reduction in pressure on the front axle will tend to increase the chances of understeer.
  • A reduction in pressure on the rear axle will tend to increase the chances of oversteer.
low tyre pressure causing understeer

Understeer: The car turns less than expected

high tyre pressure causing oversteer

Oversteer: The car turns more than expected

Low tyre pressure and the affect on aquaplaning

Michelin conducted tests to see how much of the tyre is in contact with the ground when it was progressively deflated by driving a car through a fluorescent dye on a toughened glass window and photographed the results. As you can see below, the lower the pressure, the less the tyre is in contact with the road. This will dramatically increase the chances of aquaplaning in wet weather.

If the tyre with correct pressures has a nominal surface contact area of 100% then the progressive reduction in contact can be seen.

2 bar tyre pressure

Pressure = 2 bar
Surface contact = 100%

1.5 bar tyre pressure

Pressure = 1.5 bar
Surface contact = 50%

1 bar tyre pressure

Pressure = 1 Bar
Surface contact = 25%

Low tyre pressure and the risk of rapid deflation

Prolonged running at reduced pressure causes a buildup of excess heat in the tyre, and in exceptional cases, can cause the tyre to fail and cause a rapid deflation.

Low tyre pressure and the effect on tyre life

A tyre that is under-inflated by 20% will have a reduction in life of just over 20% (depending on use). This could mean changing the tyres up to 5,000 times sooner than normal.

Conversely, over-inflation will also increase the incidences of abnormal wear and these will be particularly accentuated in the middle of the tyre.

Low tyre pressure and the effect on your fuel efficiency

A set of under-inflated tyres will cause the engine to work harder and this will increase your fuel consumption. A set of tyres that is 10psi under-inflated will have the same effect as increasing the cost of fuel by 4.5p per litre (based on £1.50 per litre). This could lead to needing an extra tank of fuel per year.

What is the correct tyre pressure for my car?

You can usually find out the recommended tyre pressure by checking your car handbook or by checking with your manufacturer. Other places this can be found on your vehicle, though, include:

  • Your vehicle’s handbook
  • Stamped into the sill of the driver’s side door
  • Inside the fuel cap

Effectively checking your tyre pressure

To ensure you get an even reading of your tyre pressure you need to ensure both that your vehicle is on a flat surface and that your tyres are cold as this will produce more accurate results.

From there, you can either use a home tyre pressure gauge or visit a petrol station (which will typically have an air station), and the operator will be able to show you the pressure for each tyre.

Don’t forget to inspect your spare tyre too. This tyre can lose pressure even when it isn’t being used. If you’ve identified a flat tyre, check out our tips on how to inflate your car tyres.

Are tyre pressures checked in an MOT?

Tyre pressures are not checked within a standard MOT test, however if your vehicle is fitted with TPMS (tyre pressure monitoring system) and a fault is detected, this will result in a failed MOT, having switched from a minor to a major category in 2018. A TPMS fault can be a result of many reasons including battery failure or a damaged sensor. Check our guide on what a TPMS is and how they work here.

Halfords Autocentre recommend that you check tyre pressures weekly, or at the very least, monthly.

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