What is my Vehicle's Recommended Tire Inflation Pressure?

Of all the car maintenance checks there is little doubt that the easiest to perform and surely the least expensive involves the verification of tire inflation pressure. The air pressure in the tires support 95% of the car, so maintaining this pressure is essential to ensure a smooth ride.

A  study conducted by Transport Canada has shown that the tires of 23 % of vehicles in Canada are under-inflated by 20 %, and that the tires of 70 % of vehicles are over-inflated by 10 %. This situation puts drivers at risk since over-inflated or under-inflated tires offer a diminished performance. It is also important to know that a correct pressure guarantees a longer tire service life, while also saving money by cutting fuel consumption. Last but not least, properly inflated tires make you and your passengers safer.

Checking the Inflation Pressure

 The first thing you need to know is that there is no universal tire inflation pressure rating. The vehicle manufacturer’s recommended tire pressure appears on a sticker on the driver’s door edge (the standard spot for this sticker), the fuel tank access door or in the vehicle owner’s manual. So the recommended tire inflation pressure IS NOT branded on a tire’s sidewall. The series of numbers marked on the tire’s sidewall only provides data regarding the tire’s manufacturing date, its type and its maximum inflation pressure. In other words, your vehicle sticker provides the recommended tire inflation pressure while the information branded on the tire’s sidewall concerns only the maximum pressure the tire is designed to contain.

The maximum pressure that most car tires are designed to contain ranges between 30 and 35 psi (pounds per square inch). Nonetheless, as mentioned above, the tire’s maximum inflation pressure is not its recommended inflation pressure. Tires inflated at their maximum inflation pressure value are at risk of wearing prematurely because they offer less contact with the road and will wear irregularly, mostly in the middle of the tread surface. The wheel will also tend to bounce on the road. Not only that, but over-inflation increases braking distance and reduces traction. In the case however of under-inflation, the tire’s contact with the road tends to widen beyond the tread. As a consequence, tire sidewalls will wear more rapidly and may cause the tire to blow out entirely, which in turn can lead to rim damage. All in all, braking is negatively affected, tires will offer less grip, service life will decrease exponentially as fuel consumption increases and overall tire performance drops. Under-inflated tires simply put you more at risk of experiencing blowouts because of premature wear and excessive heat buildup issues. In short, over or under-inflated tires will bring about an equal number of problems.

Always check the pressure of all your tires as you never know when a tire is losing air following damage caused by a road hazard. Furthermore, take note that the recommended pressure of front and rear tires is not necessarily the same. Check at all times the vehicle manufacturer’s specifications.

Don’t forget to also check the pressure of your car’s spare tire! A spare tire will lose pressure even when it is not driven on.  

When to Check Tire Pressure?

Ideally you should check the pressure of your tires every 30 days, or whenever a change of temperature of 10 degrees occurs, or before setting off on a long trip. Checking tire pressure on a monthly basis is especially important in winter. When temperatures drop by some 10, 20, 30 degrees, your tires will typically lose 2 psi (tires lose 1 psi by every decrease of 5 degrees Celsius). If the pressure of your tires was already low before a cold spell, you could find yourself driving on dangerously under-inflated tires. So by checking regularly the level of air in your tires, you can discover a minor leak and so avoid an unexpected tire failure.

To ensure that your tires contain the recommended inflation pressure, they should be checked or aired up when cold, i.e. early in the morning before a first drive, or after your vehicle has been parked for a few hours. Driving to a service center a few blocks from your home will not increase tire pressure, but driving for an hour or so on the freeway certainly will. This is because air inside a heated tire expands and increases automatically the inflation pressure, which makes it impossible to measure the real inflation pressure. Also take note that when equipping your vehicle with a new set of tires, inflation pressure remains the same if tire size is unchanged.

Technologies

More recently many cars have been equipped with tire-pressure monitoring systems.  This system features a warning light to report to the driver the under-inflation of one of his tires. Two systems exist to monitor pressure: the indirect and the direct systems. The direct system is integrated to the tire valves and the indirect system detects individual wheel rotational speeds by monitoring ABC sensors, as it is based on the principle that a wheel that is turning more quickly is under-inflated.  This system functions when the car is moving.

 Now that you know where to find the recommended tire pressure ratings for your vehicle, it is also important to have the right tool to obtain a precise inflation pressure reading. A wide selection of tire gauges is available in car accessory centres. Obviously digital tire gauges are the most accurate. Should a tire be overinflated, bleed air from the tire till the digital tire gauge shows the correct inflation pressure. Test pressure a second time to make sure all your tires are inflated to the recommended rating.

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