Correct Tyre Pressures – What is the Difference Between PSI, Bar and KPA?

Maintaining the air in your tyres is a vital part of motoring safety! It's an important part of your regular vehicle checks to ensure your car or van is safe and road legal.

It's highly important to keep your tyres inflated to the correct pressures, after all, they're the only point of contact between you and the road! Tyres naturally leak air over time, and they must be kept at the correct pressure to prevent increased rolling resistance, which in turn can affect the acceleration, braking, handling and general comfort. Underinflated tyres also pose a higher cost as they'll wear unevenly on the shoulders and require replacement sooner than tyres kept at the correct pressures.

While checking tyre pressures, you may have noticed different units of measurement, either on the pump you're using or on the sticker located in your door seal. Although they all represent the pressure of air in your tyre, they have different meanings, and it can sometimes help to know exactly what these measurements correspond to.

What different measurements are there?

PSI – the most commonly used measurement in the UK – stands for "pounds per square inch". This is the pressure that results when a 1-pound force is applied to 1-square inch. A force of 34 pounds on 1 square inch of your tyre would give a reading of 34PSI. It is the imperial unit of measurement for pressure.

Bar – this is the metric unit of pressure, commonly found in Europe and other countries that use the metric system. 1 bar is roughly equal to the pressure of the earth's atmosphere at sea level. A tyre with a pressure of 3 bar would have 3 times the atmospheric pressure of the earth.

KPA – otherwise known as kilopascal, is more commonly seen in scientific or engineering applications. It is the pressure of 1 newton per square meter. These are rarely used for tyre inflation.

What Does The Tyre Pressure Information Mean?

Your manufacturer will provide you with a recommended tyre pressure in both PSI and bar. In this case they both mean the exact same amount of pressure in tyres. It's important to know the difference between which pressure value corresponds to what unit of measurement.

For example, occasionally our customers will read "4.1" on the front tyres of this van and interpret it as 41psi. If you look below 4.1, you'll see 59.3 which is the PSI measurement. A very different pressure to 41psi!

Always check what unit of measurement is displayed on the pump you're using. Most petrol station pumps have settings which allow you to change the unit between PSI and Bar.

If you have any concerns about the pressure of your tyres, or if you want a free service check, give Hometyre a call on 0333 444 5454 or book online!