Properly inflated tires are safer, better for environment
Dear EarthTalk: Is it true that driving with soft tires wastes energy and results in more pollution? — Nanci Graham, via e-mail
When tires are not inflated to the pounds per square inch (PSI) rating recommended by manufacturers, they are less “round” and require more energy to begin moving and maintain speed. So underinflated tires do indeed contribute to pollution and increase fuel costs.
An informal study by students at Carnegie Mellon University found that the majority of cars on U.S. roads are operating on tires inflated to only 80 percent of capacity.
According to the Web site fueleconomy.gov, inflating tires to their proper pressure can improve mileage by about 3.3 percent; leaving them under-inflated can lower mileage by 0.4 percent for every one PSI drop in pressure of all four tires.
That means the average person who drives 12,000 miles yearly on underinflated tires uses about 144 extra gallons of gas, at a cost of $300-$500 a year. And each time one of those gallons of gas is burned, 20 pounds of carbon dioxide is added to the atmosphere as the carbons in the gas are released and combine with the oxygen in the air. As such, any vehicle running on soft tires is contributing as much as 1.5 extra tons (2,880 pounds) of greenhouse gases to the environment annually.
Properly inflated tires are also safer and less likely to fail at high speeds. Underinflated tires make for longer stopping distances and will skid longer on wet surfaces. Analysts point to underinflated tires as a likely cause of many SUV rollover accidents. Properly inflated tires also wear more evenly and will last longer.
Mechanics advise drivers to check their tire pressure monthly, if not more frequently. The correct air pressure for tires that come with new vehicles can be found either in the owner’s manual or inside the driver-side door. Beware, though, that replacement tires may carry a different PSI rating than the originals that came with the car.
Tire pressure should be checked when tires are cold, as internal pressure increases when the car has been on the road for a while, but then drops when the tires cool back down.
Congress has mandated that automakers install tire pressure monitoring systems on all new cars, pickups and SUVs beginning in 2008. To comply with the regulation, automakers will be required to attach tiny sensors to each wheel that will signal if a tire falls 25 percent below its recommended PSI rating. Car makers will likely spend as much as $70 per vehicle to install these sensors, a cost that will no doubt be passed along to consumers. However, according to the National Highway Traffic Safety Administration, some 120 lives a year will be saved once all new vehicles are equipped with such systems.
Contacts: Carnegie Mellon Today, “Save Gas, Money and the Environment with Properly Inflated Tires,” www.cmu.edu/cmnews/extra///050921_tire.html; FuelEconomy.gov, “Keeping Your Car in Shape,” www.fueleconomy.org/feg/maintain.shtml.
Got an environmental question? Send it to: EarthTalk, c/o E/The Environmental Magazine, P.O. Box 5098, Westport, CT 06881; submit it at: www.emagazine.com/earthtalk/thisweek/, or e-mail: earthtalk@emagazine.com. Read past columns at: www.emagazine.com/earthtalk/archives.php.
