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Directional performance characteristics of heavy truck combinations are reviewed with respect to the influences of multiple axles and articulation points. The performance characteristics considered include steady turning, directional stability, and forced responses in obstacle avoidance maneuvers. The review provides useful insights to engineers interested in the handling and safety qualities of these types of vehicles.

A method is presented for checking vehicle designs to see if they will meet size and weight rules that may be applicable to vehicles weighing more than 80,000 lb. Then, examples of heavy trucks that have been designed to be productive are used in illustrating analytical evaluations of measures of performance in safety-related maneuvering situations. The paper concludes with the point of view that trucks over 80,000 lb could have design attributes that would allow these heavier vehicles to have levels of intrinsic safety exceeding or comparable to those of current trucks.

A mobile dynamometer has been constructed for measurement of the longitudinal force/slip characteristics of truck tires. The application of this apparatus in testing of a preliminary sample of tires has indicated that the shear force production properties of truck tires differ in many respects from the corresponding behavior of passenger car tires. These differences are discussed in terms of shear force sensitivity to a number of operating variables. The inadequacy of current semi-empirical tire models in representing truck tire traction is noted.