10 March 2020 · Servicing Your Car

What is PSI: Tyre Pressure

Every driver knows how important is to check the engine oil regularly, but few people realise the impact of the tyres on their car’s steering, fuel economy, and safety. Here, we explain the effect of not having the right tyre pressure and how to find the recommended one for your vehicle.

What is PSI and what PSI should Tyres be?

You may wonder what PSI is and what it has to do with the mileage and safety of your car. In scientific terms, PSI is a unit of the Pressure (Don’t panic, please! We are not going to teach you Physics here, but we may mention some scientific facts when necessary).

The Pressure is simply a measure of how much air is inside your pneumatic tyre. For a smooth safe ride and long-lasting tyres, you should ensure that your car tyres are inflated to the right pressure. Knowing the correct PSI for your vehicle is extremely important; Not only does it control the grip and handling of your car but it also deals with your car’s safety and fuel economy.

If your car seems closer to the ground than normal it may be a sign indicating that the pressure of the tyres has been decreased and you need to ask a trusted mechanic to inflate them. Otherwise, you should expect to end up with a flat tyre or the premature wear out (That’s because at a low Pressure the friction between tyres and the road is increased).

On the other hand, filling your car tyres too much is not a good idea. Overinflation of your tyres may give you a temporary superior cornering experience but it dramatically increases the risk of breaking. Too much PSI will also bring you a bouncy ride (When tyres are inflated more than enough, they are too stiff to absorb the shocks of bumps in the road), a poor handling as well as quick tear and wear, and even blowout of tyres!

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You can find the Maximum Cold Pressure of your vehicle somewhere on the sidewall of the tyres, usually just below the name of the manufacturer. For example, you may notice that “Max. Press. 35 PSI” is printed on the tyres. The number tells you that Maximum Cold Pressure of the tyres is 35 PSI. As you see, we mentioned the cold pressure; the reason is that as the tyres roll along the road the heat generated from friction with the road increases both air temperature and pressure. There, the ideal time for filling up your tyres is when your tyres are cold such as early in the morning or after parking in the shade for a few hours.

After finding the number listed on the tyre your job is not finished. Unfortunately, this tells you the maximum pressure that the rubber of the tyre can carry safely without rupture or blowout not the recommended pressure for your car. To maintain your vehicle in the best condition you should find the recommended PSI for your car.

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How to find the recommended PSI for your car?

In the newer cars, you’ll find the optimum or recommended pressure on a sticker inside the driver’s door. If there is no sticker on the door, you could locate the spec in your car’s manual or the manufacturer's website. As an alternative method, you can choose your car manufacture and model on this website and it will show you the recommended PSI. For most passenger cars, the recommended tyre pressure lies somewhere 30-35 PSI.

[recommended PSI for your car]

Regularly check your car’s tyres pressure to ensure that they have inflated to the recommended pressure. Else, it will affect negatively tyres life and vehicle performance as well as how often you need to replace them. As a rule of thumb, check the pressure of the tyres every time you fill up for gas.

Should tires have the same pressure in winter and summer?

We know from physics that as the ambient temperature increases on a hot summer day the air inside the tyres expands and consequently the air pressure rises. The reverse is true for a snowy winter night; both the temperature and pressure of tyres decrease. That explains why several car manufacturer’s manual recommend that the operating pressure of vehicle tyres in winter should be 3-5 PSI higher than the recommended pressure for summer.

The recommended cold pressure is around 32 PSI for a passenger car and around 85 PSI for a heavy vehicle, and for every decrease of 1 degree Celsius in the temperature, air pressure drops around 0.19 PSI. This pressure drop during the winter should be compensated by increasing inflating PSI of the tyres. After all, the best method to find the recommended summer and winter PSI for the tyres is consulting to your car’s owner manual or a mechanic nearby.