The clock is ticking for tire pressure sensors

The United States' regulatory reaction to catastrophic tire accidents may be a boon to suppliers who sell pressure-sensing technology. But they have many problems to solve before adding the systems to millions of U.S. cars and trucks. And they are running out of time.

'The global supplier market right now is still trying to figure out what's happening,' says Philip Headley, chief engineer for Continental Teves Inc. 'There's some planning and a lot of thinking.'

Starting in November 2003, automakers must equip all new vehicles with the sensors. Suppliers fear that the deadline may force automakers to rush prototype testing of tire pressure sensors.

To equip 16 million vehicles a year with sensors, suppliers must build factories and create production controls. But the uncertain U.S. economy has made it difficult for suppliers to estimate likely demand. Moreover, suppliers have little cash to invest in new projects.

unaware of dangers

The National Highway Traffic Safety Administration issued the new rules following intense media coverage of rollover accidents involving Ford Explorers equipped with Firestone tires. Previously, many drivers had been unaware of the importance of proper tire inflation.

In August, a government study of 11,530 vehicles showed 27 percent of cars in the United States had at least one substantially underinflated tire. Light trucks were even worse. Thirty-two percent had at least one underinflated tire.

Any tire that is at least 8 pounds per square inch less than the automaker's recommendation is considered underinflated.

The government must settle two issues before the 2003 deadline. First, regulators must decide who will set tire pressure recommendations. Tire makers such as Goodyear Tire & Rubber Co. suggest that they should set the standards.

But automakers fear that the tire suppliers will limit their tire choices, perhaps mandating harder truck tires for sport-utility vehicles. The automakers insist that they have the expertise to set tire pressure standards because they designed the vehicles.

The other debate concerns the relative reliability of the two major types of air pressure sensors: direct and indirect.

Direct systems require the placement of small radio transmitters inside the tire. These devices relay air pressure readings to a receiver in the cockpit and usually are used with run-flat tires.

Extreme environment

But these battery-powered transmitters must survive in one of the harshest environments on a car - the tire. The sensors must withstand heat, extreme cold, humidity, dirt, oil and shock. It is like designing the sensor to survive a continual earthquake during an oil spill in a rain forest.

By contrast, indirect systems use the vehicle's antilock brakes to count wheel revolutions and compare the spin rate of each tire. A tire that is losing air will spin more frequently than the other tires.

If the sensor detects this discrepancy, it will activate a warning light on the instrument panel.

Indirect sensors cost less and do not rely on vulnerable transmitters in the tires. But they may not be accurate enough to meet federal regulations. 'By their actual rules, the indirect systems would not be able to meet their requirements,' Headley says.

The U.S. government has not said when it will resolve either issue.

Continental produces an indirect pressure monitoring system for its European market and also has developed a direct tire pressure monitor.

Other suppliers, including Lear Corp., Beru AG, TRW Inc., Visteon Corp. and Schrader-Bridgeport International Inc., also produce tire pressure monitors. But volumes are relatively low. Lear claims 800,000 wheels in Europe use its system, a small fraction of the total fleet.

COST factors

There are cost factors as well. The government estimates that vehicles equipped with a tire pressure monitor will cost consumers an extra $31 to $66 per vehicle. Regulators say the devices will save lives, improve fuel efficiency and reduce tire tread wear.

But those cost estimates may be low. Suppliers say costs will increase if automakers design a cockpit display large enough to command the motorist's attention. Moreover, suppliers say the monitors should update its tire pressure information every five seconds, which is the industry's eventual goal.

That would cost more money, too, although the technology already exists. For example, Johnson Controls Inc. sells such a system for $300 system on the aftermarket.

Despite the debates, some suppliers are proposing new cockpit displays to accommodate the tire pressure readouts. One example is Gentex Corp. of Holland, Michigan.

Primarily known for its mirrors, Gentex says automakers could minimize costs by displaying tire pressure information on rear-view mirros. 'Not everybody has a center console,' says Gentex spokesman Craig Piersma. 'Everybody's got a rear-view mirror.'

E-mail writer Tim Moran at

You can reach Tim Moran at

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