- The Washington Times - Friday, August 8, 2008

One fuel-saver that doesn’t get much press is the “rolling resistance” of your tires. Rolling resistance is the force that must be overcome to move the tires forward.

This is what happens: With every turn of the wheel, tires adapt their shape to follow the road.

They flatten out and then bounce back continuously.

That causes the tire’s components to become heated and use energy.

The engine delivers fuel to move the vehicle/tires forward, which means that rolling resistance is directly proportional to fuel economy.

High rolling resistance means fewer miles per gallon; low rolling resistance means higher miles per gallon.

Here’s something: rolling resistance increases when your tires are underinflated. Every pound of air you’re underinflated costs you about one mpg. When your tires are underinflated as they flatten out to conform to the road, they flatten out too much and expend more energy.

Underinflation also reduces the life of your tire and makes the tires hotter.

Make sure your tire pressure matches the recommendation written on the label that adheres to the driver’s doorjamb. Don’t try to overinflate your tires to improve fuel economy. Overinflating can change the handling characteristics of your vehicle.

The U.S. Department of Transportation estimates that if every vehicle on the road had properly inflated tires, the U.S. would save 4 million gallons of gasoline a day, every day. At today’s prices, that’s over $16 million dollars a day! Well, I wonder if the guy at DOT who crunched those numbers checks his tire pressure once a month.

The message is clear: Maintain your tires.

Michelin, the tire company, says that for passenger cars, up to 20 percent of the fuel burned is directly due to your tires overcoming rolling resistance. That means about one in five tanks of the gas you’re paying $4-plus for is burned because your tires are overcoming rolling resistance.

Not all tires are created rolling-resistance equal. Rolling resistance is influenced by design, dimensions and tread compounds. Different tire brands of the same size and type to equip the same vehicle can differ by up to 50 percent in rolling resistance or fuel efficiency performance.

“Rolling resistance is effected mostly by tread compound (the types and formulations of rubber used) and tread depth,” says Mike Wischhusen, director of industry standards and government regulations for Michelin North America.

Does that mean that low rolling resistance tires have less grip and wear faster? As a rule, tire companies balance the characteristics and try not to compromise performance in the key areas: wear life, braking distance, wet handling and grip. But performance tires, off-road tires, mud tires and winter tires, for sure, have a higher RR than green tires. Advancements in the development of tire compounds are allowing tire companies to maintain performance in all key areas. Michelin’s X Ice Xi2s, for example are Green X tires, Michelin’s low rolling resistance designation.

Can consumers really choose a tire for its low rolling resistance? Yes they can.

“Consumers should ask for tires with low rolling resistance/good fuel economy that maintain excellent performance in other key areas - particularly long wear life and good wet handling/wet braking ability.

The short cut to low RR is to give up other performances, especially wear and braking. Make sure you get a tire that does it all. Good fuel economy with half the wear life doesn’t save anybody,” says Wischhusen.

Buyers should compare the total package of performance and wear life when purchasing tires. Ask about high fuel-efficient tires. Make sure you’re getting well-rounded performance.

Tires that improve fuel economy but last only half as long won’t be a good value in the long run (for your pocketbook or the environment).

Too bad tires are not labeled with fuel economy performance.

Legislation at the U.S. federal and California state levels are pending. The National Highway Traffic Safety Administration is working on rule making to roll out legislation in the “next few years”, which in Washington probably means a decade or more.

LOAD COMMENTS ()

 

Click to Read More

Click to Hide