Proper tire inflation is critical to fuel economy, and to safety. Underinflated tires cause vehicle drag and increase fuel consumption. They also compromise handling ability in turns and in emergency maneuvers. They increase stopping distances and decrease control during braking. Under-inflation puts undue stress on tire sidewalls and also causes rolling tires to build and retain heat rapidly. Stress and heat are prime contributors to tire failure, including blowouts at high speed. Underinflated tires also wear down more quickly.
Properly inflated tires are harder and roll more easily. That helps fuel economy and improves tire life. It allows the treads to grip well in all conditions, including rain and snow. And properly inflated tires are able to work with your vehicle's suspension to provide maximum handling, steering, and braking ability.
An estimated four out of ten vehicles on the road have at least one underinflated tire. Pressure that's 3 pounds per square inch (psi) below the recommended reading may reduce gas mileage by 1.5 percent. Some experts suggest even greater decreases. The Environmental Protection Agency (EPA) warns that running tires at 20 psi or lower can easily cost you a full mile per gallon.
Proper Tire Inflation
Tires can naturally lose up to 1 psi every 30 days, and they will lose pressure more quickly in cold weather. Because cooler air is more dense, pressure drops by about 1 psi for every 10 degrees. A tire inflated to 30 psi at 70 degrees, for example, could drop as low as 26 psi at the freezing point.
The recommended tire pressure is displayed in your vehicle, typically on a sticker inside the glove box door or on one of the doorposts. It's also in your owner's manual. Many vehicles are available with a choice of tire sizes, and each size may have its own recommended inflation pressure.
Match the tire size as listed on the tire sidewall with that on the sticker or in the owner's manual. Note that the inflation number listed on the tire sidewall itself shows the maximum inflation, not the optimal pressure as determined by the tire maker and the manufacturer of your vehicle.
Checking Tire Inflation
Check inflation when the tires are cool. That means they have been driven less than a mile or so. Air expands inside a warm tire, which will give you a false reading.
Tire pressure should be checked at least every 30 days. A tire gauge is the old standby. But federal regulations require that by 2008 all new cars, sports utility vehicles, minivans, and pickup trucks be equipped with an underinflation warning system. Sensors will monitor tire pressure, and if it falls 25 percent below the recommended inflation, a yellow warning light on the dashboard will illuminate.
The system will save an estimated 120 lives and prevent 8,400 injuries annually, according to the National Highway Traffic Safety Administration. NHTSA estimates it will also save drivers up to $35 annually because of longer tread life and decreased fuel costs. Select 2004 and 2005 models already have such a system. For the 2006 model year, 20 percent of new vehicles must have the system, with 70 percent for 2007, and 100 percent for 2008.
Fuel Economy Varies with Tire Type
Those all-terrain or off-road tires with their knobby tread look rough and ready and are designed to get you through rocks and mud. They are not designed to promote high gas mileage.
All-season tires produce less friction and therefore roll more freely to the benefit of fuel economy. They're generally lighter than all-terrain or off-road tires, and less weight means better fuel economy. They also ride more quietly, handle better, and wear longer.