The Effect of Longitudinal Center of Gravity Position on the Sway Stability of a Small Cargo Trailer

Abstract

Small and mid-sized cargo trailers are often used to transport goods by people with limited experience in loading trailers and driving vehicles with trailers attached. This paper examines the effect of front to rear load position on the stability of a trailer by measuring its dynamic response to a variety of steer inputs at several different highway speeds. Additionally, tests with varying steers and speeds were performed with a simulated suspension malfunction to study the trailer’s dynamic response to this condition. Trailer sway has been a well-documented trailer characteristic for decades. However there are no special driver’s licensing or mandatory training requirements for even large trailers and campers. The trailer chosen for this test was a lightweight double axle cargo trailer commonly rented by people with limited to no towing experience. This consumer is likely to be unfamiliar with the best practices of trailer loading. This consumer is also likely a non-professional driver with little to no towing experience in the event of encountering unexpected trailer sway. Therefore it was the goal of the authors to determine how the stability of this type of trailer varies with different front to rear loading conditions and speeds to see if it is safe to operate on the highways by novice drivers. Trailer sway stability was determined by measuring the trailer sway (articulation) response during repeated, pulse steer tests. The trailer sway damping characteristics were measured, as a “damping ratio”, for six different hitch loads that corresponded to six different longitudinal loading conditions. These conditions, expressed as % load forward of the trailer centerline / % load aft of the trailer centerline were: 65/35, 60/40, 55/45, 50/50, 45/55, and 40/60. These loading conditions were tested per SAE J2664 [1] protocol. The resulting trailer sway characteristics for each loading condition then were compared to published trailer sway stability criteria [2, 3] to determine the suitability of this particular tow vehicle-trailer combination for use by the public in a rental market. The impact of a suspension malfunction on the trailer stability was also studied. This consisted of a detachment of one rear leaf spring hanger.