It's one of the oldest tricks in the book, but according to tire manufacturers, it's still effective. Place a penny between the treads of a tire. If Lincoln's head is covered, you still have an adequate amount of tread remaining.

"If not, maybe it's time to, as they say, 're-tire," says Ray Bourgoin, manager, national accounts, for Michelin North America Inc.

Checking tire treads is part of what the tire manufacturers say is a simple but very important way to reduce tire wear: regular preventive maintenance.

Bourgoin says preventive maintenance includes regular checking of tire air pressure.

"You should certainly do it no less than once a month and possibly as frequently as once a week," Bourgoin said. Checking for the proper tread depth is equally important, he says.

According to the laws in most states, Bourgoin says, if a passenger car or light truck tire has 1/16 of an inch of tread remaining, it is considered worn out. That is about the same distance between the top of Lincolns' head to the end of the coin, he said.

Don Kolmodin, assistant vice president of merchandising for Pep Boys, says rotating tires and maintaining proper air pressure are the best two ways to prevent tire wear.

"A lot of people say you should check your tires at the beginning of summer and the beginning of winter," Kolmodin said. "We as a company recommend you check your air pressure not as often as you put gas in your car, but at least once a month."

5 Points to Check for Longer Tire Life

Keeping your tires in good shape can increase your gas mileage and decrease wear and tear to your tires and the car. Here are five points to check regularly, according to the American Automobile Association.

1.      Inflation: Check air pressure when the tires are cold, when the car has been sitting for at least three hours, or has been driven less than a mile.

2.      Tread: Tires should be replaced when less than 1/16 inch of tread is left. Remember that front tires of a front-wheel-drive vehicle will wear more quickly than those on the rear axle.

3.      Road damage: Remove foreign objects imbedded in the tire. Glass, gravel, and other debris can work deeper into the tread and cause a flat. But if you find a nail or other sharp object deeply imbedded in the tire, have a professional remove it, and seal the puncture.

4.      Valve and rim: Each valve stem should have a cap to keep out moisture and dirt and to keep the valve core from being accidentally depressed and leaking air. Also check valve stems for cuts and scrapes, which could cause leaks. Check the rim for dents and rust, which can lead to leaks or blowouts.

5.      Spare tire and tools: Be sure the spare is properly inflated. The temporary tire should not be used at speeds of more than 50 miles per hour, and its tread life is only about 3,000 miles. Be sure all the parts for your jack are in place and you know how to use them.

Fleet mangers interviewed for this article said they follow regular preventive maintenance to extend tire life.

Janet Springler, fleet manager for The Purdue Frederick Company in Norwalk, CT, has a simple plan for preventing tire wear. "We rotate the tires every 10,000 miles, and every 5,000-mile oil change, we always have the tires checked," she said.

Lois Woolum, fleet administrator for Michigan Millers Mutual Insurance in Lansing, Mi, said company drivers are told to keep the tires properly inflated and rotate them every 10,000 miles.

Beth Sanchez, fleet manager for Buckman Laboratories Inc. in Memphis, TN, says her company does not have tire policies, other than reimbursing drivers for snow tires where they are needed.

Sanchez said the only other tire policy is: "We ask the drivers to follow the owner's manual" in regard to tire rotation.

Karl Schmitt, fleet administrator for Time Warner Inc., takes a different approach. "Our leasing company, ARI, handles our tires and all other maintenance."

What Are the Different Types of Tire Wear?

Kolmodin described two types of tire wear: The first is normal wear, which is caused simply by day-to-day driving.

"The rubber starts to wear out and you start getting less tread depth," he said. "The higher the quality of tire, the longer it's going to last."

The other type is abnormal wear, which is caused from other factors, Kolmodin said. One of those factors is under inflation.

"That's probably the biggest cause of abnormal wear," he said. "The tires will wear out on the inside and outside of the tread, you will get a spongy ride, your handling characteristics diminish, and the car becomes less dependable."

Another factor causing abnormal wear is over inflation.

"A lot of people say that with more air pressure, although the car might not handle as well, they get better gas mileage," Kolmodin said. "That's probably a true statement, but you will probably wear out the center of the tire a lot faster, and your vehicle may not handle as crisply and may not hold the road as well because the tire is less forgiving."

Bourgoin has his own term for abnormal wear, calling it "mechanical wear."

"If you have a worn shock, for example, the tire bounces, so it ends up cupping the face of the tread," Bourgoin said. If a tire is misaligned, it causes a toe-in or toe-out condition, which means the tire is pointing in or out and not straight ahead when driving, he said.

Bougoin said most tires are manufactured with wear bar indicators. When the tire is new, you can see a groove between each rib as you look across the tire. At the bottom of the groove, at various points around the tire, is a raised portion of rubber. As the tread wears down to the indicator, the indicator fills the void.

"It's a quick visual for fleet [drivers]," Bourgoin said. "If you see the wear bar indicator, it's time to replace the tire."

Bourgoin and Kolmodin differ on when tires should be rotated. "When people buy tires from us, we recommend they have them rotated every 6,000 miles," Kolmodin said. Bourgoin says tires should be rotated only when absolutely necessary.

"They should be checked no less than every 6,000 miles," Bourgoin said. "You should check for a difference in wear rate from front to rear every second oil change or 6,000 miles, whichever comes first. You're really looking for a difference in tread depth between the front and rear tires that's normal wear and not caused from a mechanical condition." Goodyear recommends checking the vehicle owner's manual for the proper tire rotation schedule. If no rotation period is specified, Goodyear recommends rotation every 6,000 to 8,000 miles.

How to Tell What's Causing Tire Wear

According to Goodyear, the location of tire wear can indicate what is causing it. If you have wear on both outside edges, this is caused by under inflation. Under inflation also generates excessive heat, which reduces tire durability. And it reduces fuel economy by increasing rolling resistance.

Where Should You Check for Proper Air Pressure?

The sidewalk of tires shows a specified tire air pressure. The information on the driver's side door shows a different air pressure. Which one should drivers follow?

Kolmodin of Pep Boys says the driver's side door (or the owner's manual or on the inside of the glove box door) is the place to check for the recommended tire pressure. "The door jamb will tell you what the manufacturer recommends to be what they consider the ultimate. That is their specification, and if you maintain that tire at that air pressure, you'll have a combination of comfort, long wear, handling, and it holds that extra load you might put in the vehicle." The information on the side of the tire, on the other hand, only tells the maximum air pressure the tire will take.