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The influence of degraded steering and suspension components on open-loop vehicle performance at the limits of tire-road frictional coupling is examined in this paper. The major conclusion obtained is that, with the exception of the shock absorber in certain maneuvers, the range of limit performance exhibited by new cars, as derived from design differences, is much larger than the in-use changes in limit performance of individual vehicles deriving from degradation of steering and suspension system components. This result should lead to future studies in which: 1. The influence of steering and suspension system degradation in the nonlimit regime of vehicle operation is examined. 2. Equipment for on-the-vehicle evaluation of suspension damping is investigated. 3. Greater emphasis is placed on the degradation of tires and brakes.

This paper reports the results of a study which had as its aim the determination of braking performance currently achievable by buses, trucks, and tractor-trailers, and the improvement of this performance by use of advanced braking systems. Both vehicle testing and analytical techniques, including dynamic modeling and simulation, were used in the program. Performance qualities essential to braking systems are enumerated, which, when given quantitative definition in the light of performance achievable, can form the basis of rational performance requirements for commercial vehicles.

An engineering analysis of vehicle braking is presented in terms of the utilization of available road friction. Physical relations are derived which allow the determination of optimum brake force distribution on front and rear wheels as a function of axle loading. Ideal braking distribution curves are shown for a typical vehicle in the loaded and unloaded conditions. A technique is suggested for rational design of braking system parameters. It is applied to the case of a two-stage proportioning system, and is validated by experimental data from tests using a specially equipped light truck. It is concluded that a proper design analysis can establish a combination of braking system parameters which results in improved utilization of available friction. A simple, self-adjusting brake proportioning system can be a highly cost-effective safety device for truck use.

About 8,000 pedestrians are killed each year in the United States and probably another 180,000 are injured. This paper reports on an analysis of 1978 and 1979 New York pedestrian accidents to try to find any relationships between vehicle factors and pedestrian injury severity and location. In these data trucks and vans were found to be associated with more severe pedestrian injuries than passenger cars. However, within the passenger car category vehicle weight and injury severity were not clearly related. And few meaningful relationships were found between aspects of the passenger car front end configuration or the past production use of "soft" materials and pedestrian injury severity or location.

Mechanical properties have been obtained from a recent series of truck tire tests using the Highway Safety Research Institute's (HSRI) flat bed tire testing machine. In addition to the vertical and lateral spring rates, a set of three parameters characterizing traction properties of the rolling tire are defined and measured. The influence of tire load and inflation pressure on mechanical properties is found to be significant. Carpet plots of lateral force versus tire operating variables such as camber and slip angle are used to illustrate the effect of changes in ply rating, tread pattern, and wear. Corresponding variations in the mechanical properties are noted. The results of an experiment to determine the relationship between single tire and dual tire force and moment producing capabilities are also described.

An analysis is made of the influence of tire-mechanics characteristics on the behavior of an automobile undergoing maneuvers requiring the tires to produce combined longitudinal and lateral forces. The mathematical model employed to represent the vehicle incorporates wheel rotational degrees of freedom and relationships expressing the longitudinal and lateral tire shear force components as analytical functions of tire normal load, sideslip and inclination angles, and longitudinal slip. The tire shear force relationships, derived by extrapolating from existing theory for the traction mechanics of a freely rolling tire, agree qualitatively with available experimental data. Analog simulation results are examined to assess the influence on vehicle steering/braking response of variations of three parameters: lateral tire stiffness, longitudinal tire stiffness, and the coefficient of friction at the tire/road interface.