- The Washington Times - Friday, August 13, 2004

Most people have driven around with one or more of their vehicle tires underinflated at one time or another. A federal government study last year estimated that more than one in four cars and one in three sport utility vehicles, vans and pickup trucks have at least one significantly underinflated tire.

Underinflation contributes to tire wear and tear, greater stopping distances and lower fuel economy.

Worse, it can lead to crashes, because over time underinflated tires — with sidewalls flexing and heat building — can be damaged and even fail.

Most drivers recall what tire failures such as tread separations and blowouts did in the Ford Explorer/Bridgestone-Firestone tire crisis of 2000. Deaths totaled more than 270, and the number of injuries passed 700.

Spurred by the Explorer/Firestone brouhaha, federal regulators in June 2003 formally issued a rule mandating new vehicles include electronic tire-pressure monitors as standard equipment for the 2004 model year.

While the National Highway Traffic Safety Administration rule appears to help reduce chances of another Explorer/Firestone crisis, it’s not a panacea. And it most definitely doesn’t let the driver off the hook for overall tire safety.

Here’s why:

The electronic tire-pressure monitors approved as vehicle equipment by NHTSA allow up to 30 percent underinflation, depending on the specific tire-monitor system, before warning of a problem.

They don’t, therefore, help readily gauge the amount of air that puts tires at the pressure recommended by the carmaker.

It is still up to the driver to check the owner’s manual or door label and then get the correct pressure in each tire. One of the easiest, quickest ways to do it is still the simple tire gauge.

Once tires are filled to the recommended pressure, which should be measured at cold inflation pressure, the electronic tire monitors can do their job.

But if a driver fails to put the correct pressure in the tires, the electronic systems won’t necessarily know. When the calibration process occurs, they will simply set the tire pressure that’s available at the time as the reference pressure and measure deviations from there.

A tire gauge is still necessary for checking pressure periodically, to see, for instance, if the pressure is down from the recommended level but not yet down a full 25 percent or 30 percent.

Indeed, some in the U.S. tire industry worry that NHTSA’s seemingly de facto approval of tire underinflation of up to 25 percent could encourage car owners/drivers to be less vigilant about exact tire pressures.

At least three consumer watchdog groups have petitioned for change to NHTSA’s rule, because it gives automakers the right to select from two different tire-monitoring systems.

Public Citizen, New York Public Interest Research Group, and the Center for Auto Safety sued the U.S. Secretary of Transportation last year, saying one of the systems, called the indirect system because it basically piggybacks on a vehicle’s anti-lock braking system, is inferior.

Costs are lower for this kind of system — $13 a vehicle compared with $79 per vehicle for the other system, according to one NHTSA estimate.

ABS is given new algorithms that help it determine that tires are inflated properly by comparing tire rotation speeds via ABS wheel sensors.

This so-called wheel-speed system works because a tire that’s deflated by at least the trigger amount of 30 percent will rotate at a different speed than the other three tires and therefore be noticed by the system.

But in a NHTSA study in 2001, this system was found to be less consistent in its warnings, and not all systems informed the driver when tires had been successfully calibrated, i.e., processed new tire values, after tire rotations and new tire installations.

Because tires have to be rolling for the indirect system to monitor the tires, it also is possible for someone to drive away from a safe location, say a parking lot at work, only to find out a bit down the road that a tire is low.

On the other hand, the indirect system offers the benefit of incorporating ABS, which helps drivers steer around obstacles during hard braking. Batteryless, this indirect system also promises easier maintenance than complex direct tire-pressure monitor systems that require batteries and which are mounted on valve stems and other wheel locations that are exposed to roadway hazards.

Direct systems use radio frequencies to transmit tire pressure to a control unit on the car.

Jim Gill, spokesman at Continental Teves, a global auto supplier that makes both types of tire-pressure monitors, said his company counsels its automaker customers to select systems based on their application.

For example, cars typically have a high reserve and tend to stay within parameters for weight and load. Thus, it may be fine to use an ABS-based system for vehicles such as cars, he said.

But pickups and SUVs, which can have more variable loads, might be better served by direct tire-pressure monitors, Mr. Gill said.

For all this rule-making and debate, drivers still have a lot of tire checking to do on their own — and regularly. You will still need to check your tires for signs of sidewall cracks, depleted tread, uneven tire wear and other tire concerns.


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