AA Car Care: Checking tyre pressures
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Tyre pressure is a crucial factor when it comes to your car’s safety, and it only takes a small amount of time to check. It keeps your vehicle safe, but also improves the driving experience. Another important benefit is improved fuel efficiency, something that is becoming more pertinent as we see petrol prices at record highs.
A study by the National Highway Traffic Safety Administration (NHTSA) in the USA found that under inflation of tyres by 10 per cent increases fuel consumption by 2 per cent.
Tyres lose air pressure naturally at a rate of around 1-2 psi per month, so it’s important to monitor them regularly. The AA recommends checking tyre pressures at least once a month.
What’s the correct pressure for my car?
The tyre pressures specified for your vehicle are agreed to by the vehicle manufacturer and the tyre producer. The psi (pounds per square inch) or kPa (kilopascals) ratings are based on the vehicle’s total weight and size, towing capability and recommended tyre size.
The recommended pressures can usually be found in the vehicle handbook, inside the fuel filler flap, or on the driver's door post. If you can’t find them anywhere, you could ask your local AA Auto Centre, tyre shop or vehicle manufacturer for a recommendation, or use the general rule of 30-32psi in the rear and 32-34psi in the front tyres. These recommended tyre pressures are based on “cold inflation pressure”.
Why do I need to check the cold inflation pressure?
Gas expands when heated and contracts when temperatures decline. This means that you should check tyre pressures in the morning before the ambient temperature rises, before exposure to direct sunlight and of course, before driving the vehicle.
Daily temperatures rise and fall between seasons, which cause tyre pressures to fluctuate - 1.5psi for every 10degC. As temperatures drop in autumn and winter, it’s especially important to check tyre pressures. In some colder areas, tyres could experience a drop of a few psi. Add this to a slow pressure reduction of non-regular inflation checks and you have potential for very under-inflated tyres.
This fluctuation throughout the year is why it is recommended that you check your tyre pressure at the beginning of each month and before long road trips where the additional load may require increased tyre pressures.
Correct tyre pressure is imperative to get the most out of your tyres according to Michelin UK; just a 7psi difference from the recommendation can reduce tyre life by about 8000km.
Likewise, over inflation will also reduce the life of a tyre, focusing wear on the centre.
How to check tyre pressures
- Make sure they’re cool
- Park on a flat surface
- Remove the valve cap and connect a tyre gauge or service station inflator to get the reading
- If the tyre needs air, insert the pump into the tyre valve and fill it to its recommended pressure level
- Once the air has been adjusted to the proper level, replace the cap and check the remaining tyres in the same fashion
Many service stations have a free tyre inflator connected to an air compressor that can display the pressure in psi and kPa. These are electronic and pretty simple to operate, with step-by-step instructions on the front label.
You may also find a traditional tyre inflator gun at your service station. To use this you need to push the filler connector onto the valve and hold it in place; this will display the amount of pressure in the tyre. If it is too high, pressing the trigger about a quarter of the way down will release pressure.
To add pressure, depress the lever completely and release it once again to see the pressure displayed on the inspection glass.
Checking your tyre pressure is a quick and easy process that has many long term benefits. Why not add a reminder in your phone, so you can coordinate with your next charge or petrol fill?