COLUMBUS, Ohio (Dec. 21, 2000)—To the untrained eye, it´s a contraption that would make Rube Goldberg smile.
To its creators and operators, it´s a precision engineering tool.
Either way, the machine—a giant aluminum teeter-totter housed in a lab in a suburb of Columbus, Ohio—could help tip public opinion for or against some of the automobile industry´s most popular and most profitable vehicles.
That´s because the National Highway Traffic Safety Administration is weeks away from issuing the first of its vehicle rollover ratings, and the teeter-totter plays a crucial and controversial role.
The ratings will be based not on handling tests but on a mathematical calculation called the static stability factor. It is determined by dividing half of a vehicle´s track width by the height of the center of gravity.
To NHTSA´s way of thinking, a bigger static stability factor means that a vehicle is more stable and will be awarded more stars on a five-star grading system. A smaller stability factor means just the opposite. And taller, narrower vehicles, such as sport-utilities, are certain to get then worst scores, the agency acknowledges.
Auto makers already are on record with extensive objections to the use of the static stability factor to rate vehicles.
Robert Strassburger, vice president of safety for the Alliance of Automobile Manufacturers, elaborated last week: "Not only does it not take into account all of the factors (in measuring rollover propensity); it does not take into account the more important factors," including tires and suspensions.
A more basic problem for regulators is that the height of a vehicle´s center of gravity—the point where half the vehicle mass is above and half is below—is not easily found. It doesn´t appear on any specification tables.
So NHTSA has contracted with S.E.A. Inc., a subsidiary of FTI/SEA Consulting of Worthington, Ohio, to calculate static stability factors for about 70 vehicles. Each is being done twice, once with only a driver dummy and again with four occupants.
The initial year´s contract amount is for $137,000. NHTSA has an option to extend the work for a second year for another $309,000, an agency spokeswoman said.
Gary Heydinger, project engineer for FTI/SEA Consulting, said measuring track width is a simple thing. But finding the height of the center of gravity requires use of the company´s vehicle inertia measurement facility, the big aluminum scale equipped with precision instruments.
Mr. Heydinger, who worked for NHTSA while in graduate school and who has a doctoral degreeb in mechanical engineering from Ohio State University, said his company is not the first to use devices like the inertia machine. But he said, "We have refined all that work to the state of the art."
It is capable of a variety of measurements, such as weight distribution, and others best understood by physicists and engineers. They include pitch, roll and yaw.
Customers seeking such information have included vehicle designers, independent researchers, computer modelers and racing teams, Mr. Heydinger said. Versions of the inertia machine have been sold to Ford Motor Co. and General Motors, he said.
Vehicle fate in balance
For NHTSA, the height of the center of gravity is the key question. S.E.A. Inc., using rented vehicles, spends about three hours on each one, including setup time and the test.
It works like this: A vehicle is driven onto the aluminum platform. Pylons at the center of each side elevate the platform, and calibrated weights are placed at either end of the platform while computers take measurements and calculate the height of the center of gravity.
S.E.A.´s Mr. Heydinger believes that the static stability factor is meaningful and that his work will lead to safer vehicles. Congress, however, may change the rules.
A bill has been passed by Congress and signed by President Clinton requiring that, within two years, NHTSA come up with a handling test to rate vehicle-rollover tendencies.
Dr. Sue Bailey, NHTSA administrator, said she believes it will be possible to use both the star ratings based on static stability factors and the so-called dynamic testing.
Said Mr. Strassburger of the manufacturers´ group: "How they plan to do that, we don´t know. We are concerned that it could potentially lead to conflicting results."
Mr. Stoffer writes for Automotive News in which this article originally appeared.