Understanding Your Tyre Pressure

Keeping on top of your tyres is a crucial part of vehicle maintenance. Understanding your tyre pressure will allow you to know when your tyres need air and exactly how much they need. Poorly maintained tyres can lead to serious issues further down the road including flat tyres, breakdowns and worst-case a collision. To stay safe on the roads it is important to look after your tyres and ensure they always have the right pressure.

Types of tyre pressure measurements: PSI, Bar & KPA

PSI

PSI is the most common tyre pressure measurement and is the one motorists are most familiar with, especially here in the UK. PSI stands for Pounds per Square Inch and is a commonly used imperial measurement. It measures how much force the air inside the tyre is exerting and displays the reading in PSI units. The higher the PSI reading, the more pressure inside the tyre. A reading of 30 PSI, would mean there is a force of 30 pounds acting on every square inch of the tyre's internal area. If you live in a country that uses the imperial system, you likely won’t need to convert to Bar or KPA, but just in case you need to know, read on.

Bar

Bar is another way to measure tyre pressure and uses atmospheric pressure - the pressure exerted by the air around us. When measuring tyre pressure, the Bar method measures the amount of force applied by the air inside the tyre. A reading of 2 Bar would mean that the air inside the tyre is exerting a force equivalent to 2 times the atmospheric pressure.

KPA

KPA is another way to measure tyre pressure and stands for Kilopascals, and tells us the amount of air pressure inside the tyre. Think of KPA as a way to understand how much "push" the air inside the tyre is applying. It's similar to how you can feel the pressure when you squeeze a tightly inflated balloon. The more air you put into the balloon, the greater the pressure you feel when you touch it. a reading of 200 KPA, would mean that the air inside the tyre is exerting a force of 200 kilopascals per square centimetre.

How to check tyre pressure

All cars have specific measurement guidelines - whether this be PSI, Bar or KPA. Once you’ve identified the unit of measurement, you’ll need the relevant pressure gauge that uses the same measurement. To use the pressure gauge, follow these simple steps:

1. Unscrew the valve cap from the tyre’s valve stem.
2. Attach the pressure gauge by pressing it firmly into the valve stem - you will hear a hissing sound as the air gets released.
3. A digital gauge will display the reading on the screen. If you’re using a manual gauge, wait until the dial stabilises before you take your reading.
4. Check your vehicle’s recommended pressure - this can be found in your owner’s manual or on your driver’s side door.
5. Compare the reading on your pressure gauge to your vehicle’s recommended pressure.
6. If the reading is lower than your vehicle’s recommended pressure, you’ll need to add air.
7. If the reading is higher than your vehicle’s recommended pressure, you’ll need to release air.
8. Repeat for all 4 tyres.

Bar to PSI Conversion

Most owner’s handbooks will display the recommended tyre pressure in both units, but just in case you need to convert between PSI and Bar, the conversion is pretty simple: 1 Bar = 14.5 PSI

The tyre air machine at fuel stations will display both numbers so you don’t have to convert.

As tyres naturally lose a little air each month, it is important to regularly check your tyre pressure to make sure it is at the recommended measurement. This will keep you safe and out of harm’s way on the roads. If your car is fitted with a TPMS (tyre pressure monitoring system) it will indicate if there is an issue with your tyre pressure by showing a light on your dashboard.