Tires filled to the correct pressure last longer and they reduce fuel consumption. Tire pressure is so easy to check and so cheap (free) to fix, yet drivers give it so little attention

Tires are one of those critical safety items on our vehicles. We should all check them more frequently. Martin Cousineau, product service manager for Continental Tire Canada, Inc., says checking tire pressure once a month is one of the easiest ways to help improve fuel economy, while also prolonging the life of your tires, and keeping your family safe on the road. Each month three out of four drivers wash their vehicle, but only one out of seven correctly checks their tire pressure, Cousineau says.

Checking tire pressure is an easy task but there are a few things to remember. First, locate the proper inflation pressure for your vehicle. This is typically located on a label on the driver’s door or in the owner’s manual. If you can’t locate it, the dealer can supply the correct specifications for you. If you are loading the vehicle for travel, or pulling a trailer, you may want to increase the inflation pressure a couple pounds per square inch (PSI) as this helps handle the extra load. Never exceed the maximum inflation pressure listed on the tire sidewall or you could have a tire fail as you inflate it, with potentially serious results.

Always check tire pressures when the tires are cool. Air expands when heated. Even driving a kilometre will warm the air in the tire and increase pressures. For every 10C change in air temperature, a tire’s inflation pressure will change by about one pound PSI. An under-inflated tire heats up quickly, so the pressure may show correct if it has been driven, but the tire is actually operating too hot and could fail. Therefore, to measure the correct pressure, always check them when cool.


Most drivers fill their tires with air, but several shops now fill tires with nitrogen gas. Air is about 76 per cent nitrogen, 21 per cent oxygen and three per cent other gases. There are advantages to filling with pure nitrogen. Nitrogen molecules are larger than the oxygen molecules and leak through the rubber membrane of a tire at a slower pace. It takes about three months for a tire filled with nitrogen to lose the same pressure compared to one month for a tire filled with air.

Another advantage of nitrogen is that it is dry. Atmospheric air contains moisture, which expands at a faster rate than dry air or nitrogen. Tire pressures remain more constant when filled with nitrogen. That’s why many race car tires are filled with nitrogen. They need the correct pressure for the best handling.

There are disadvantages to filling tires with nitrogen. One is the cost. Many shops in my area are charging about $8 a tire to fill with nitrogen. Then there is the added cost of having to add nitrogen gas as part of regular tire inflation checks. Even though it leaks less slowly, the gas pressure does change with outside temperatures, so you will need to top them up a few times as temperatures change.

Nitrogen is also inconvenient. If a tire is low, you have to look for a service shop with nitrogen filling equipment, and driving on a low tire is dangerous. If you top up the tire pressure with air, you are losing the benefits of filling with nitrogen, so you might as well as have filled with air in the first place.

You might think that using nitrogen means you only need to check pressures every three months rather than every month. It is still important to check tires at least once a month. You might have punctured a tire in your driving and have a slow leak, or average temperatures might have changed several degrees in a few weeks, so you need to check pressures again.

Filling tires with nitrogen is a good idea, but not a necessary one. Checking tire pressures more often is the best way to maximize tire life and fuel economy and keep the car safe during your travels.

Jim Kerr is an automobile writer based in Saskatoon.

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