New FMCSA research shows impact of tractor-trailer misalignment

WASHINGTON — Insights gained in a comprehensive new alignment study by the Federal Motor Carrier Safety Administration could lead to changes in the design of suspension systems, alignment mechanisms, or even entire truck frames, the agency says.

The project, embarked by FMCSA this year, is one of several performed under the provisions of Section 5117 of the Transportation Equity Act of the 21st Century. The motivation for the study is to show that static commercial vehicle alignment procedures and settings performed both at the factory by OEMs and in the field by maintenance personnel may not be optimal under dynamic conditions-and, in any case, such settings cannot remain optimal under all dynamic moving conditions at varying speeds, loads, and surface geometries

Rear axle misalignment can also cause tractor problems: FMCSA

The study has attempted to identify the impacts that misalignment of commercial vehicles (both tractors, trailers, and in combination) have on the general safety, performance, and functional aspects of commercial vehicles and to identify potential technical solutions and areas of research related to aligning tractor-trailers under dynamic conditions in order to reduce negative consequences of misalignment.

The results from the study — which includes participation of suppliers such as ArvinMeritor, Eaton, and Goodyear, as well as OEMs Freightliner and Volvo — can be used by fleets to help better understand the impacts of misalignment, and by truck OEMs, research organizations, and suspension and steering system manufacturers that may wish to consider pursuing research, of equipment to improve and adjust the alignment of vehicles, states FMCSA.

Misalignment, says FMCSA, can cause a variety of problems, including irregular tire wear, fuel economy loss, and vehicle vibration. Generally, a poorly aligned vehicle can reduce the driver’s level of control, which then adversely affects vehicle stability and has negative consequences for operating costs.

Impacts of misalignment on steer axles (toe, caster, and camber) were examined, as well as “total vehicle alignment” conditions involving thrust and scrub conditions that can occur on drive axles (tractors) and trailer axles.

“Alignment is often thought of in connection with the steer axles only,” the report states “However, it has been recognized for some time that the rear axles on a tractor also must be properly aligned, and that the tractor and trailer units should be aligned with each other (in combination vehicles) for optimal performance.”

The entire study can be read here:

www.fmcsa.dot.gov/facts-research/research-technology/report/report.htm