DEVELOPMENT OF MAXIMUM ALLOWABLE HITCH LOAD BOUNDARIES FOR TRAILER TOWING

This paper presents an analytically based approach to specifying a maximum allowable hitch load for passenger cars pulling trailers. The change in tow car steady-state directional stability, i.e., understeer, is the basis for the specification. This handling parameter is a function of hitch load, lateral acceleration, tow car to trailer weight ratio, and the amount of load leveling applied by a Class III hitch. Using these variables an allowable hitch load range was defined as that which would insure positive tow car understeer up to and including 0.3 g cornering. Over 50 combination-vehicle configurations (using three tow car sizes and eight trailers) were then tested in order to validate and revise the analytical boundaries. Based on these results a tow car stability criterion derived from maximum hitch load considerations appears a valid format for the trailer user and/or manufacturer.