While your car’s contact with the road is through the tread of its tires, your vehicle is actually riding on the cushion of air inside them. The pressure in your tires is of vital importance: for starters, it’s what keeps your tires on their rims.

“The bead is the part of the tire that holds the tire on the wheel,” says Orazio Mastracchio, quality product manager for Canada at Pirelli Tire.

“There is a groove in the wheel, which is called a hump. Once the tire is inflated, the bead sits in the hump, keeping the air in the tire hermetically sealed.”

A tire has to be extremely low on air before it separates from the rim, but even a few pounds of pressure too low or high can be detrimental. If a tire is low, it creates more rolling resistance, which in turn wastes fuel — as much as two weeks’ worth over the course of a year. The tire also runs hotter, which can reduce its lifespan. If the pressure is too high, the tire will wear unevenly and produce a harsher ride. Both over- and under-inflated tires can also affect the car’s steering, braking and stability control.

 

Many cars now have tire pressure monitoring systems, which continuously measure each tire’s pressure electronically and flash a warning if one gets too low. However, these are primarily for safety and only notify you when a tire is 25 per cent below its recommended level. You could still be wasting fuel due to a tire that’s low on air but not enough to trigger the warning.

Tire pressure should be checked once a month, Mastracchio says, and before leaving on long trips, when carrying heavy loads, or when towing a trailer. Tire gauges are inexpensive and can help save you considerably on your fuel bills.

The recommended pressure varies by vehicle and tire. It’s found in the owner’s manual or on a sticker found in the driver’s door jamb, on the glovebox door, or inside the fuel filler door.

Don’t go by the number molded into the tire, which is the maximum it can hold. To check it, remove the small cap on the tire’s valve stem, press the gauge firmly onto it, and then check the number on the gauge. Add air at a service station if the tire is low.

Gauge accuracy can sometimes be problematic, Mastracchio says, especially if the gauge is old or has been dropped.

“Have one that you use as a reference, and another that you use to check the pressure,” he says.

“This way, you will always know where you stand with your pressure.”

All-season vs Winter tires

All-season tires have inferior grip to winter tires when the temperature reaches 7C, even on dry roads. Switching to winter tires vastly improves handling and stopping distances.

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