Tire aging and tire-pressure monitoring systems remain near the top of the National Highway Traffic Safety Administration's rulemaking agenda, according to speakers at the 2004 Society of Automotive Engineers' Government/Industry Meeting, held in Washington May 10-12.
NHTSA is about halfway through its research to determine if it can devise a meaningful tire aging standard for the new tire performance standard mandated by the Transportation Recall Enhancement, Accountability and Documentation (TREAD) Act, said James MacIsaac, project engineer at the agency's East Liberty, Ohio, testing facility.
The agency decided not to include a tire aging test in the final tire testing rule promulgated in June 2003 because of the need for further research on the subject, Mr. MacIsaac noted. At the same time, the average tire on a U.S. vehicle is getting older and older.
``Manufacturers are wringing more and more life out of their tires,'' he said. In just one year, he noted, tires took a substantial leap forward in their average life spans. In 2002, the average was 44,700 miles or 3.7 years; in 2003, it was 46,300 miles or 3.8 years. The lengthening lives of tires, Mr. MacIsaac said, make it all the more important to determine the effects of tire aging and, if possible, develop a meaningful test for it.
Mr. MacIsaac cited the Firestone tire recall of August 2000-the catalyst for the TREAD Act-as an example. ``Only after one to three years on the road did the tire failures start to manifest themselves,'' he said. ``But the Department of Transportation only tests tires that are brand-new. We need to have some way to measure a tire's safety after some years in the field.''
At the start of its testing last year, NHTSA identified 12 tire models it would study, cutting across all makes, models and types of tire, Mr. MacIsaac said. The agency found 60 used examples of each in Maricopa County, Ariz., where the average annual temperature is 73 degrees F.
``Arizona had the highest per capita tread separation rate in the Firestone recall,'' he said.
The agency's goal is to come out with a proposed tire aging test by June 2005, he added. Of six tire aging tests yet developed, NHTSA is analyzing four as possible models-those developed by the American Society for Testing and Materials, Ford Motor Co., Michelin North America Inc. and Continental Tire North America Inc.
The test developed by General Motors Corp. ``is very expensive, and must be performed with the tire on the vehicle,'' Mr. MacIsaac said. Interestingly, the agency also rejected its own test because ``subsequent evaluation showed it to be less effective than others.''
Phase I of the testing, he added, showed that all the tires ``exhibited degradation of performance, some significantly.''
No matter the reason for degradation in performance, a tire-pressure monitoring system is designed to warn motorists of air pressure losses before they become dangerous. Last August, a New York federal appeals court rescinded and remanded NHTSA's first attempt at a tire-pressure monitoring standard, ruling that the indirect monitoring system the agency put forth as its model performed inadequately compared with direct systems.
So it was something of a surprise when a Swedish engineer at the SAE meeting identified the second-generation indirect systems as the most effective kind in terms of saving lives.
``Generation Two indirect systems will fulfill motorists' real-life requirements in real-life situations, with better total reliability than direct systems,'' said Jonas Nilsson, project manager at Linkoping, Sweden-based NIRA Dynamics.
Among other things, second-generation indirect systems aren't dependent on the battery, as are direct systems, and don't have to be calibrated, Mr. Nilsson said. They are cheaper than direct systems and don't rely on transmitters that have to be replaced with the tires. The method of recording tire pressures is more accurate in Generation Two indirect systems than in Generation One, and unlike Generation One they can record pressures in all four tires, rather than just one.
Because they rely on the presence of anti-lock brake systems, they will improve vehicle safety in that area, he said. And unlike direct systems, indirect systems don't have radio signals that can interfere with the operations of the system on another vehicle.
While the appeals court rejected the Generation One indirect systems, it didn't specify the technologies it would accept, Mr. Nilsson noted. ``The court ruled on performance, not technology,'' he said. ``And NHTSA will rule on performance'' in the new final rule it issues, he added, allowing also for changes and innovations in tire- pressure monitoring technology.
Mr. Nilsson also ruffled a few tire industry feathers when he said that 25 percent below the vehicle manufacturer's recommended inflation was a good level for activation of a tire-monitoring system's warning light. Most motorists, he said, would regard setting off the warning at 10 percent below the recommended inflation as a nuisance.
``More sensitive detection will not automatically save lives-rather the opposite,'' he said. But he agreed that having enough load reserves calculated in the recommended inflation was crucial. The Rubber Manufacturers Association is still waiting to hear NHTSA's verdict on its petition for a minimum reserve load requirement.
The new tire pressure monitoring standard probably will be issued at the end of the summer, a NHTSA official said.