Tire Pressure Monitors Required by 2003

July 27, 2001 -- When was the last time you checked the air pressure in your car's tires? Chances are, not lately.

"We're constantly finding that tires are worn, improperly inflated, sometimes under-inflated, sometimes over-inflated," says mechanic David Schaffer.

And there is little doubt that improperly inflated tires are the source of many vehicular problems. For example, under-inflated Firestone tires are being blamed for many of the 203 deaths involving Ford Explorers last year.

Those tragic accidental deaths — and the subsequent industry-wide recall of 6.5 million Firestone tires — has prompted the National Highway Traffic Safety Administration to mandate that all vehicles made after 2003 to come with so-called tire pressure monitors.

The Way the Wheel Turns

There are two major kinds of tire pressure monitoring systems (TPMSs) currently available: indirect and direct.

An indirect TPMS, the cheaper and more common option, uses the wheel-speed sensors of the car's existing anti-lock brake system (ABS) to keep track of each wheel's rotation. An under-inflated tire has a smaller radius and therefore spins faster than the other properly inflated tires. When the indirect TPMS system detects such anomolies, it alerts the driver that they need to check their wheels.

Indirect TPMS systems are simple and highly affordable. In fact, NHTSA estimates that installation in a car with ABS would cost less than $13.

But indirect systems have some limitations. Since it relies on the rotational speed of the wheels, indirect monitoring systems may not be able to detect slight changes in tire pressure.What's more, they won't detect a problem at all if all four tires lose similar amounts of pressure.

A more accurate TPMS relies on actual pressure sensors installed in all four tires and can accurately measure the pressure in each tire. The readings are sent over radio waves to a wireless receiver mounted in the car and can warn drivers which specific tire needs attention.

Although the sensors are more accurate and informative than indirect systems, they are also more expensive. NHTSA estimates that would add anywhere from $69 to $200 to the sticker price of a 2003 model car.

Ahead of the Curve

Several more advanced options are also emerging, as a number of companies are working on systems that go beyond what the government would require.

The Cycloid Company in Cranberry Township, Pa., is offering a device called the AutoPump. It can not only check each tire's pressure, but maintains proper inflation by automatically pumping air into those that need a boost.

In Finland, Nokian Tyres has developed a system that provides the driver with updates on tire condition via mobile phone.

The system would be housed entirely in a tiny chip mounted on the tire. If it detects any change in pressure, it would send an alert to the driver's cell phone using a new wireless radio standard called Bluetooth.

Driven to Action

While it may be years before consumers see such an advanced tire pressure system in the United States, the good news is that many automakers aren't waiting.

General Motors claims that since 1987, it has sold more than 2 million cars equipped with tire pressure monitors.

"We've demonstrated we can do it," says GM spokesman Greg Martin. "The hardware is there; the software is there. It's a matter of matching it up to consumer demand."

Other companies are also stepping up their efforts. Chrysler has announced that its 2002 Jeep Grand Cherokee, available this summer, will become the first sport utility vehicle to feature a tire pressure monitoring system. Ford expects to equip all of its SUVs, including the Explorer, with low tire pressure warning systems by the 2003 model year.

NHTSA estimates that if all 2003 model cars come equipped with tire monitoring systems, some 80 deaths and more than 10,000 injuries may be avoided per year.

ABCNEWS' Lisa Stark contributed to this report.