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Every Vehicle's Bottom Line: the Tires

Technology: The Firestone crisis has raised awareness of tires and their importance to auto safety. Knowing a little about what they do--and how they are constructed--is a key to proper maintenance.


Steve Mazor was driving home from Burbank on the Santa Ana Freeway three weeks ago when the right-rear tire on his company car blew out at 70 mph.

He backed off the gas, made his way from the fast lane to the right shoulder while decelerating and gently braked to a stop--the proper procedure to follow to avoid loss of control when a tire suddenly loses pressure.

Mazor--chief automotive engineer for the Automobile Club of Southern California--has had a bit of practice at it.

Less than a month earlier, the left-front tire on the same car blew out as it bumped over a Botts dot lane marker as Mazor drove in the fast lane on the Glendale Freeway.

In both cases, the tires were nearly new, mid-priced brand-name replacements for the original-equipment rubber. There was no apparent reason for either blowout.

The car Mazor was driving, a 1981 Toyota Cressida with more than 120,000 miles on the odometer, is serviced at the Auto Club's technical center. The vehicle "is maintained as good as you will ever find a car being maintained, and that includes frequent and regular tire maintenance and inspection," he said.

Still, the tires blew.

"It just happened," Mazor says.

Blowouts, regular flats--even catastrophic tread separations such as those that have plunged Bridgestone/Firestone Inc. and Ford Motor Co. into turmoil recently and made tire safety a topic of dinner-table conversation across the country--do, indeed, just happen with no warning and no identifiable cause.

But many more tire failures are caused by events that car owners and drivers can control, experts say.

And if any public good comes from the Firestone crisis, it's likely to be that it has raised awareness of tires and the importance of regular inspection and proper maintenance.

In the Firestone case, more than 1,000 tires--most of them mounted on Ford sport-utility vehicles and pickup trucks--have disintegrated at high speeds in recent years, leading to several hundred accidents linked to several dozen deaths in the U.S.

Using Your Tires to Read the Road

To really appreciate how important tires are requires an understanding of what they do and how they are constructed.

Simply put, tires are the most critical operating component of a vehicle. Without them, the car or truck--no matter how powerful its engine, how sophisticated its suspension or how luxurious its interior--has to sit, no more useful for transportation than the shade tree in the front yard.

But there's more to the tire than giving mobility to a vehicle.

"It is the tire that gives you all the information you get behind the wheel, the feeling of what the car is doing," says Jacques Couture, chief instructor for the Jim Russell Driving School at Sears Point Raceway in Sonoma, Calif.

"The contact patch--where the rubber meets the road--tells you everything. And when you have to swerve to avoid hitting a child playing in the street, it is the tires that make or break the maneuver. Or when you are driving at 70 miles an hour in a rainstorm, it is the tires--if you have the right ones--that keep you on the road," Couture says.

That contact patch, no more than a few square inches per tire, also is all that sticks the car to the road, all that keeps it upright during cornering and turning maneuvers that create tremendous centrifugal forces that want to pull vehicles off the asphalt and fling them--and their occupants--like a stone shot from a whirling sling.

"The tire is the only part of the car that touches the ground," notes Rick Brennan, director of strategic planning for Yokohama Tire Corp. "Your acceleration, your braking, your steering, your control of the car is only as good as the tires' capabilities."

That, Couture says, is why wheel and tire widths, tire pressures, sidewall stiffness and tread design are so important in the world of high-speed performance driving.

And it is why for most of us, the simple act of walking around our car once or twice a month--visually inspecting the tires for cuts and gouges, checking their pressure with an accurate tire gauge and replacing them before they wear out--is as important as buckling our seat belts.

Tire Pressure Often Neglected

Of all the problems that can affect tire performance and lead to flats and other kinds of tire failure, under-inflation is the most common, tire specialists say.

All tires are marked on the sidewall with a maximum inflation figure, shown in pounds per square inch, or psi. But that's just a guide to keep you and the tire installer from exploding the tire.

Although Ford's recommended inflation for Firestone tires on its Explorer SUVs has raised questions because it is 25% lower than Firestone's own recommendation, tire specialists continue to insist that the vehicle manufacturer's recommended pressure is best.

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