Proper tire pressure is critical for safe driving and fuel efficiency, but many passenger and light truck vehicles operate with under or over-inflated tires. Ninety-five per cent (95%) of a vehicle’s weight is supported by the tire air pressure, with the tire supporting just 5%, making inflation a critical part of a tire’s ability to perform. Tire inflation also has a strong impact on tread life.

Relying on a sight inspection alone is not an accurate way to measure tire pressure. Tires may be significantly under or over-inflated, yet you may not be able to tell just by looking at them.

The only accurate way to know if your tires need to be inflated is by measuring their pressure with a reliable tire presure gauge. Basic tire gauges are available at most automotive supply and hardware stores. More sophisticated electronic tire monitoring systems are also available at very reasonable costs.

Correct Tire Pressure

Correct tire pressure varies from vehicle to vehicle and wheel to wheel. In fact, the recommended pressure for personal vehicles ranges from 20 to over 50 psi.

The correct tire pressure for your vehicle is listed on the information placard. This placard is normally located on the edge of one of the doors, the inside post of one of vehicle’s doors or inside the glove compartment, trunk, or fuel door. Your owner’s manual should include the correct tire pressure or direct you to the placard’s location on your vehicle.

The pressure listed on the tire sidewall is the maximum tire pressure – or the tire pressure that is required to carry the maximum load of the tire. It is not the manufacturer’s recommended tire pressure, which is a common misperception.

In addition to keeping your tires properly inflated, follow these tire maintenance guidelines.

Under-inflation

Under-inflation is the leading cause of tire failure. Twenty-three per cent (23%) of vehicles have at least one tire under-inflated by more than 20%. Under-inflated tires on your vehicle lead to poor or delayed braking, steering and acceleration. Under-inflated tires may squeal when stopping or cornering even at moderate speeds, particularly on warm pavement.

The Effects of Under Inflation on Tire Wear and Fuel Use

Operating a vehicle with just one tire under-inflated by 20% (8psi) can reduce the life of the tire by 15,000 km and can increase the vehicle’s fuel consumption by 4%. Without enough air, the sides of a tire bend and flex too much. This builds up heat, which can cause serious damage and leads to sudden tire failure. It will also increase rolling resistance, which reduces tread life and increases fuel consumption.

Over-inflation

Over-inflation can be a problem too. An over-inflated tire rides on just the centre portion of the tread. The smaller contact area means reduced grip on the road, leading to a harsh ride, handling issues (such as steering and stopping problems) and increased wear on tires and suspension components. Seventeen per cent (17%) of vehicles in Canada have at least one tire that is over-inflated by 20%.

Measuring Pressure

Tire pressure is affected by temperature and natural permeation. Measure the air pressure of each tire, including the spare, at least once per month or any time there is a temperature change of more than 15 °C. Tires lose pressure in colder weather, so it is important to measure your tire pressure year-round.

Measure your tire pressure when your tires are cold. “Cold” means that a vehicle has been stationary for at least three hours or has not been driven more than 2 km.

To ensure your family’s safety and to reduce the risk of sudden tire failure, be sure to measure tire pressure before heading out on the road for a long trip or when you are carrying a heavy load.

How to Measure Pressure

Step 1:

Find the recommended inflation pressure for your tires on the vehicle information placard. Check the owner’s manual for its exact location. A sight inspection is not an appropriate way to measure the air pressure in your tires.

Step 2:

Only measure pressure when the tires are cold. Tires are cold if they have not been driven for more than 2 km or for at least 3 hours.

Step 3:

Complete tire inflation pressure check: Remove cap from valve on one tire, press tire pressure gauge onto valve and take pressure reading.

Step 4:

Add air to achieve recommended air pressure. If you overfill the tire, release air by pushing on the metal stem in the center of the valve, then re-measure the pressure.

If you have to drive to get air, record the pressure first, drive to the station, take a second reading of the tires pressure (if you have driven more than 2 km) and add the amount of air that was missing from the first reading.

In other words, if the correct pressure for the tires is 35 psi and the first reading was 28 psi, this tire is under-inflated by 7 psi. If you drive 8 km to the fuel station, the tires will have warmed up. A second reading may show that the under-inflated tire is now 30 psi. However, the tire is still 7 psi under-inflated and it should be inflated to 37 psi.

WARNING: Avoid driving on seriously under-inflated tires for your own safety and to prevent damaging the tire.

Step 5:

Replace the valve cap and repeat with each tire, including the spare.