ARLINGTON, Va. (June 7, 2004) — When it comes to altering the height of a customer's vehicle, “How high is too high?”
That's the question posed recently by the American Association of Motor Vehicle Administrators (AAMVA), an association of U.S. and Canadian motor vehicle and law enforcement officials, which is warning motorists that aftermarket oversized tires and lift kits have a potentially deadly effect on the rollover propensity and braking performance of motor vehicles.
In a study conducted last year and released recently, the AAMVA showed that braking performance in a light truck equipped with a 4-inch lift kit and oversized tires worsened by 20 to 25 percent. At the same time, the vehicle's propensity to roll over doubled with the lift kit and an extreme tire changeover, and the retrofit created a potentially dangerous bumper height mismatch with traditional passenger cars.
The AAMVA claims its study is the country's first to examine the effect lift kits and oversized tires have on used motor vehicles, particularly light trucks.
“The crash involvement of raised vehicles has been difficult to quantify because there is no standard for law enforcement officers to use in recording these tragedies,” said Linda R. Lewis, president and CEO of the AAMVA. “But sadly, their tracks are permanently etched in the shattered lives of families nationwide.”
While the AAMVA study shows a deterioration in braking effectiveness, the Specialty Equipment Market Association (SEMA) pointed out that since the study involves only one vehicle—a 1992 Ford F-150 pickup—the association does not believe the test “offers sufficient data or support by itself to warrant revising the current AAMVA model standard.”
In a written statement to the AAMVA, Steve McDonald, senior director for government affairs at SEMA, pointed out that SEMA does not oppose regulations on height-altered vehicles, provided they are “well-targeted regulations which can be enforced in a practical way.”
SEMA presented technical input and suggestions that helped shape the AAMVA's existing regulations on altered height vehicles, developed in 1988, Mr. McDonald wrote.
“SEMA still believes that the current AAMVA model can achieve the important goal of eliminating unreasonable vehicle elevation while allowing a level of modification which is useful,” Mr. McDonald wrote. “The model regulation was intended to address the question of how much is 'too much' and lays down very specific limits on frame height and bumper height for classes based on gross vehicle weight rating (GVWR).”
SEMA supports the existing AAMVA model because it was founded on comprehensive OEM engineering analysis and data and because it allows a reasonable opportunity for utility- and performance-enhancing modifications, the SEMA executive wrote. The AAMVA model prohibits unreasonable height modifications, including the type of “monster truck” modifications about which state regulators have complained.
In its commentary accompanying the release of the study, the AAMVA said it is revisiting this area of its coverage because of two factors: experts note that when such cars crash with light trucks, fatalities are greater for the car occupants; and light trucks now represent more than half of new vehicle sales, increasing the potential impact on the first factor.
“Our study shows that raised vehicles can be harder to control,” said Dave McAllister, crash investigation team leader, Virginia Commonwealth University and a member of the AAMVA working group that conducted the study.
“When all factors are combined, raised vehicles that go out of control and then strike other vehicles outside their bumper's range simply compound the severity of such collisions,” Mr. McAllister said.
The association said it will explore developing model legislation with uniform inspection guidelines for inspecting vehicles outfitted with aftermarket body and suspension lift kits and/or oversized tires.
To this end, the AAMVA contacted a number of additional highway safety organizations to involve them in its decision-making process. Among them are:
c National Transportation Safety Board—to conduct a study to understand the cause/effect relationship between oversized tires and the crash involvement of raised vehicles.
c Society of Automotive Engineers—to identify safe practices and guidelines to communicate what must be considered when installing replacement tires on light trucks.
c SEMA—to distribute warning messages to raise end users' awareness of the effects oversized tires could have on the handling characteristics of light trucks.
c National Highway Traffic Safety Administration—to examine collision data to establish a problem size assessment associated with light trucks whose ride heights have been raised excessively by aftermarket body and lift kits and oversized tires.
Regarding oversized tires, SEMA's Mr. McDonald pointed out the existing AAMVA model allows a maximum of four inches of body lift, which prevents unreasonable tire sizes because of the limited amount of space under the wheel well opening.
“Because tire size will affect both bumper height and frame height, we believe bumper and frame limits can effectively regulate against inappropriate tire size,” Mr. McDonald wrote.