Alone on a desolate stretch of highway in southern Illinois on a frosty night just before Christmas 2005, Don Amos discovered the value of tire-pressure monitoring systems.

He was nearing the end of a long drive home to Missouri for the holidays from North Carolina, where he works, when the TPMS in his '03 Jeep Grand Cherokee started beeping, accompanied by a flashing light on the dashboard. He'd run over a nail.

For the next several minutes, the vehicle reported the pressure in all four wheels, and Amos watched with dread as the digital readout confirmed air was escaping rapidly from the left rear wheel.

Having driven the route many times before, Amos knew a 24-hour service center was within 10 miles (16 km), and he hoped he could make it there before the tire went completely flat.

The gamble paid off. Amos got to the center before the tire was ruined and installed the spare, glad for the opportunity to frequently warm himself from the bitter cold, rather than changing the tire on the darkened highway.

“I could see the headlines — ‘Man Killed on Highway Changing Tire in Middle of Night,’” Amos says with a chuckle.

Today, Amos embraces TPMS as a technology, and not just because it worked as intended on that frozen highway in 2005. As Continental Tire's manager for industry standards and government regulations in North America, he understands the importance of keeping a tire properly inflated.

Since Sept. 1, 2007, TPMS has been mandatory for every new vehicle sold in the U.S., and Europe is in the process of adopting similar regulations as a way to reduce carbon-dioxide emissions, boost fuel economy and enhance safety. China also is considering similar legislation.

Congress enacted the Transportation, Recall Enhancement, Accountability and Documentation (TREAD) Act on Nov. 1, 2000, after the recall of 6.5 million Firestone ATX, ATX II and Wilderness AT tires used as original equipment on the Ford Explorer, the best-selling SUV at the time.

Treads were peeling off the tires at high speeds, sometimes causing tragic rollovers. At least 271 people died in the crashes, and hundreds more were injured. The defective tires were traced to a Firestone plant in Decatur, IL, which has since closed.

In addition to the tires being defective, Ford Motor Co. had recommended a tire inflation pressure for the Explorer of 26 psi (1.8 bar), which was less than the 30-psi (2-bar) inflation pressure recommended by supplier Bridgestone Firestone.

The lower pressure improves traction, comfort, handling and stability, but it also boosts friction between the tire and road, generating additional heat that can cause a marginal tire to fail.

Compounding the problem was the alarming number of Americans who drive for months at a time without checking the air pressure in their tires.

The National Highway Traffic Safety Admin. inspected nearly 12,000 vehicles in 2001 and discovered about 27% had at least one tire underinflated 25% or more, says Joseph Kanianthra, the former NHTSA associate administrator for vehicle-safety research who was involved in the TPMS research.

At about the same time, Ford began informing its SUV owners and dealers their Firestone tires should be inflated to 30 psi, in line with Bridgestone Firestone's recommendation.

Today, the issue of tire pressure virtually has disappeared from the news in the U.S., but NHTSA has carried out its directive from the TREAD Act to implement a TPMS standard, known as FMVSS 138.

The regulation requires onboard monitors to warn drivers when the air pressure in one or more tires is at least 25% below the auto maker's recommended “placard” cold-inflation pressure.

Following enactment of the TREAD Act in 2005, 20% of every OEM's U.S. fleet had to comply by August 2006 and 70% by August 2007, after which all light vehicles had to meet the code. All OEMs have achieved compliance, NHTSA reports.

Auto makers can decide what technology to deploy in monitoring tire pressure. The vast majority in use are direct systems that place sensors at the base of the valve stem or on the wheel. They signal the driver via radio transmitter when low pressure is detected.

Less popular is an indirect system that monitors wheel rotation as part of antilock braking. An underinflated tire will rotate faster than one properly inflated, thereby triggering a signal to the driver. The '09 Audi A6 is the first vehicle available in the U.S. with such an indirect TPM system.

It's too early to chart the success of FMVSS 138, because relevant crash statistics will not be gathered for several years, NHTSA says.

If not for the TREAD Act, it is doubtful NHTSA would have mandated TPMS, says Kanianthra, the former NHTSA associate administrator.

TPMS “was not cost-effective based on the guidelines NHTSA uses in mandating vehicle-safety standards,” Kanianthra tells Ward's. “When a requirement is mandated, NHTSA promulgates the mandated requirements, even though there is always this concern that the time and effort could have been better spent on higher priority safety problems.”

When TPM systems began appearing on vehicles in higher numbers earlier this decade, some tire retailers were not prepared to deal with the technology and remain so today, Kanianthra says.

He estimates there are about 40 million vehicles on U.S. roads equipped with TPMS, while other sources peg the number closer to 20 million.

“I do not think many tire-dealer mechanics are trained in TPMS yet,” says Kanianthra, who has started a safety consulting company, Active Safety Engineering LLC, since retiring from NHTSA.

Tire technicians accustomed to using brute strength and improper tools to remove old tires can damage the TPM sensor inside, leaving it inactive when new tires are installed.

Kanianthra says it's too early to say whether this problem is widespread, “but it may very well be happening because many consumers and dealers are not largely aware of TPMS.”

One supplier expert interprets the new regulation as prohibiting a vehicle from leaving an automotive service bay if technicians know the TPMS is not functioning.

“We recognized early on the desperate need for education in the industry about TPMS, not just with regard to the sensor…but also to address customer concerns when they come in,” says Ward Randall, sales and portfolio manager for the body and security business of Continental AG's North American automotive unit.

The Tire Industry Assn. reports all major retailers have systems in place to ensure TPMS is functioning after tires are rotated, repaired or replaced.

Continental claims to be the No.2 supplier of TPM systems, behind Schrader Electronics Ltd. Continental's customers include Detroit's three auto makers, as well as Mercedes-Benz and Volkswagen vehicles imported to the U.S.

“We determined there's a significant need to educate distributors and jobbers and put on training sessions, and we've made information available to assist them with this product,” Randall says.

Continental Tire's Amos, who still drives the '03 Grand Cherokee and uses the TPM system every day to check the air pressure at all four corners, also has heard occasional complaints about tire technicians mishandling the sensors.

“The systems are too delicate and can be damaged in mounting and dismounting,” Amos says. “But technicians are getting much better at dealing with TPMS.”

He says a number of disputes surfaced when customers brought vehicles in for tire service but did not tell the shop the vehicle was equipped with TPMS.

“Systems have been broken and deactivated, and no one wanted to pay to replace them,” Amos says, referring to both the shopkeeper and vehicle owner. “You can't just do a slam-bang dismount (of a TPM tire). You have to go a bit more carefully because it can be embarrassingly expensive to replace if you don't. Everyone has gotten more acclimated to that idea.”

Amos has been amazed to find some consumers willfully disabling TPM systems.

Some vehicles have five sensors onboard — one for each wheel, plus the spare in the trunk. Tires naturally lose about 1 psi (.068 bar) per month. If consumers do not keep their tires properly inflated, including the spare in certain vehicles, eventually the warning light on the dashboard will trigger.

Some Americans disable the TPM system on their spare tires, altogether, to avoid wrestling with the spare every few months to maintain the air pressure.

The truly creative scofflaws, however, have worked pretty hard to bypass the regulation.

Amos has heard of people who have taken the TPM sensor from their spare and installed it on a much smaller wheelbarrow tire, which easily can be lifted from the trunk every few months so it can be filled with air. The actual spare tire collects dust in the garage, while a useless wheelbarrow tire takes up space in the trunk.

“People will do anything to avoid a little inconvenience,” Amos says. “In my youth, you wouldn't dream of going anywhere without one good spare tire. Vehicles have become so reliable that people don't think about how they would cope if something goes wrong.”

TPMS is not meant to excuse consumers from performing routine maintenance, such as inspecting the tread on their tires and checking air pressure on a regular basis, says Andy Whydell, senior manager-electronics product planning at TRW Automotive, which has supplied TPM systems to Toyota, Honda, Hyundai and Kia vehicles for the U.S. since 2003.

TRW recently took control of the EnTire TPM joint venture it created in 2003 with tire-producer Michelin SA.

“Drivers should look to maintain air pressure for the safety of the vehicle,” Whydell says. “TPM is there to give a warning, if the pressure is going into a potentially unsafe region. The assumption shouldn't be, ‘I don't have to do anything until the warning light comes on.’”

If consumers are uncertain about the proper inflation pressure, they can find that information in every vehicle, as required by federal law. It generally appears on the driver's side door jamb, in the glove box or underneath the lid of the center console.

“What we should tell people is that you will get better gas mileage with tires that are properly filled, and you will have safer travel,” says Tim Hannon, TRW Automotive's global technical sales lead-radio frequency products.

Loads also are a significant factor, Hannon says. A light load in a vehicle consists of one to two occupants, with a full tank of gas. Heavier loads will require additional air pressure in the tires.

In Europe, where drivers generally are more diligent in maintaining their vehicles, governments are debating the performance requirements for TPMS, primarily as a way to boost fuel economy by improving rolling resistance.

Hannon says he expects European countries to begin rolling out the standard in 2012, with 100% compliance by 2014.

Although Europe often leads the U.S. in the adoption of new technology, the process has been reversed in the case of TPMS.

“Europe hasn't had the same kind of issue we saw in North America with the Explorer Firestone (recall) that led to the TREAD Act,” Whydell says. “So Europe hasn't had the single specific event to spur things along.”

TRW estimates about 95% of its TPM devices end up in American vehicles, and all of them are direct-sensing systems. But with its expertise in antilock brakes and electronic stability control, TRW now is developing indirect systems at the behest of European auto makers because of the potential cost savings.

“Our European customers are taking an interest in indirect TPM,” Whydell says. “They are asking all their stability-control suppliers to be able to supply indirect systems in the case that indirect systems will meet the performance requirements.”

NHTSA previously has said TPMS adds between $49 and $69 to the price of a vehicle.

When TPMS was new several years ago, all of TRW's initial systems were “enhanced,” meaning they could provide exact pressure readings for each tire.

“Now with the economic times, the OEMs have been trying to cut back and save money,” Hannon says. “A lot of them have shifted to less-expensive, basic systems.”

Premium vehicles continue to offer enhanced capability, and Hannon pegs that penetration in the U.S. market at about 10%. The vast majority of systems, while meeting NHTSA's performance requirements, provide a basic warning to the driver that at least one tire is losing air pressure.

As a business model, TPMS presents a conundrum to technology suppliers. The extremely high volumes attached to an across-the-board government mandate are good for keeping manufacturing plants operating, but the resulting commodity pricing becomes less attractive.

“The goal is to have a relatively low-cost and simple sensor in each tire,” Whydell says. “TRW is a safety supplier, so TPM is the type of product we believe we need to be involved in.”

Amos believes in TPMS, although he'd like the law to require a warning to the driver earlier, rather than waiting until 25% of air pressure escapes.

The day after his harried ride home to Missouri, Amos took his flat tire to a shop for repair. While waiting, he commiserated with a fellow customer, who, amazingly, had been through the same experience the night before.

Problem is, the other fellow didn't have TPMS on his vehicle. “He lost his driving time, he had to rent a hotel room and he had to buy a new tire,” Amos recalls.

“One night on the interstate sure convinced me it was well worth it,” he says of TPMS.

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