As a Driver, Pressure Is on You to Keep the Tires Properly Inflated

Ken Zeller lives and breathes cars.

By day, he is head of engineering for B&M; Racing & Performance Products, a venerable Chatsworth-based aftermarket company. Nights and weekends, when Zeller’s not helping his wife take care of their two young daughters, he tinkers in his well-equipped garage, downing root beer and coming up with go-fast parts for his Ducati racing motorcycles. His supercharged, roll-cage-equipped yellow Corvette has been on the cover of Hot Rod magazine.

So how often does Zeller, who is as comfortable with a laptop computer as he is with a torque wrench, check tire pressure on the Geo Tracker and Jeep Grand Cherokee his family uses as daily transportation?

About every two months--even though “it should be every two weeks, four weeks, tops,” Zeller said with a chuckle.

He is not alone in his lackadaisical approach to tire inflation.

The Car Care Council, an Ohio-based organization that sponsors National Car Care Month, routinely finds that 18% to 33% of the vehicles inspected at its affiliated garages during the October promotion have under-inflated tires.

But the Aug. 9 recall by Bridgestone/Firestone Inc. of 6.5 million Firestone light-truck tires, prompted by a National Highway Traffic Safety Administration investigation into at least 148 deaths linked to the tires, should hammer home the point that under-inflation and the subsequent overheating of tire rubber is anything but benign neglect.

Under-inflation and vehicle overloading are the major culprits in tire failures, according to the Tire Industry Safety Council.

The official drill on tire inflation (available at the council’s Web site, https://tmn.com/tisc/) is:

* Check the tires when they are cold.

* Check inflation at least once a month and always before long trips (and don’t forget the spare, which may call for higher pressure).

* Follow the recommendations of the auto manufacturer, which will list its inflation specifications in the owner’s manual and on a special sticker, often placed on the door or doorjamb or under the trunk lid or hood. Multiple pressures may be called for, depending on how the vehicle is loaded.

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But potential for confusion arises when the conscientious motorist rolls up his or her sleeves to do the deed.

For instance, what exactly is a “cold” tire?

The Tire Industry Safety Council’s guide for auto and recreational vehicle tires defines cold as “before they have been run a mile.”

But a tire engineer for Michelin--a brand that earns J.D. Power & Associates’ highest customer-satisfaction rating among car and light-truck owners when replacing their tires--says that a vehicle can be driven a few miles to a nearby service station for checking.

The ambient temperature also is crucial, experts say. Tires can lose pressure at the rate of about a pound per square inch a month, even more in warmer climates. Every 10-degree Fahrenheit change in temperature results in a corresponding fluctuation of about 1 psi.

Tire-pressure recommendations assume an ambient temperature of 68 degrees. That means, for example, that if you inflate your tires to 26 psi during a summer day when the mercury hits 98 degrees, they’ll be inflated at only 23 psi that night if the temperature falls to 68. And because the tires are under-inflated at that point, they will be prone to overheating when they hit the road. Over time, in the worst case, you may experience a catastrophic tire failure.

Pressure readings are only as good as the gauge and the people doing the checking. So we decided to conduct a real-world exercise.

We took a 1995 Buick Regal to a San Jose-area location of a major national tire chain. We asked for a tire rotation and made a point of requesting that the inflation be checked. When we returned a few hours later, the cheery counterman reported that the tires had been “set at 32, all the way around.”

Problem No. 1: The pressure recommended by Buick is 30 psi, front and rear, not 32. (Note that it’s not unusual for vehicle manufacturers to call for different front and rear pressures.)

Problem No. 2: When we got back home and checked the pressure with our own gauge, not only were the tires not at 32 pounds, but the pressure was different for each one. The front-left tire was a real wild card: 37.6 psi.

We conducted our tests with an Intercomp TP700 digital air-pressure gauge, factory-certified to be accurate to within 0.1 psi.

At $295 list, it’s not an item for everyone, but we needed a credible instrument. We also used the company’s $39 2.5-inch air gauge and found that its readings--zero to 60 psi on a glow-in-the-dark face--were consistent with those of the more expensive model.

There’s even debate about which pressure to run.

Most of the experts we interviewed said the correct pressure is that recommended by the vehicle maker, not the maximum pressure indicated on the tire’s sidewall. But Mark Ewing Sr., a 23-year veteran of the tire business in Indianapolis, will have none of that.

“You’re going to have a different view from different dealers, but the way I look at it, the tire will perform the best if it’s at the maximum pressure,” Ewing said. “If you think about it, sometimes you have one person in the car, sometimes you have four. You can’t fluctuate your air pressure. The best thing to do is run the maximum air pressure.”

Which is what Ewing does, unless the customer requests a different inflation pressure.

Keeping tire pressure between 38 and 40 psi, he said, helps him get 65,000 miles out of tires that are supposed to last 40,000 miles.

Ewing’s bottom line: “A tire has to be standing up straight if it’s going to get the wear the manufacturer built into it.”

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Then there’s the high-tech route.

Some vehicles, such as the Chevrolet Corvette, have tire-pressure monitors built in. Or you can opt for an aftermarket pressure-temperature warning system such as those from SmarTire Systems, which start at $299 installed.

The recently passed federal Transportation Recall Enhancement, Accountability and Documentation Act, or TREAD, has jump-started such moves by requiring that new vehicles sold by Nov. 1, 2003, have on-board systems that will warn the driver when a tire is significantly under-inflated.

So the fallout from the massive Bridgestone/Firestone recall does have a bright side, tire-industry observers say.

“If there’s one positive thing that has come out of all these recalls and concerns about tires, it’s this idea that tires are not infallible,” said David E. Zielasko, editor of Tire Business. An informal nationwide survey the trade magazine conducted in October found that nearly three in every four vehicles were operating with at least one tire under-inflated.

“Tire dealers are always reminding customers to air up their tires,” Zielasko said, “and consumers have just taken their tires for granted.”

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Jeff Yip is a Silicon Valley-based journalist. He can be reached at jeff@cyberspeed.com.