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A mobile dynamometer for measuring the longitudinal force acting at the fifth wheel connection between a tractor and a semitrailer has been developed. The use of this dynamometer for testing retarders installed in tractors is described and example results are presented. Computational methods for predicting total retardation of various vehicles equipped with retarders are discussed.

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.

Driver-vehicle tests were performed in which the deceleration/pedal-force ratio (i.e., gain), pedal-displacement level, speed, surface-tire friction, and driver characteristics were systematically varied in order to determine the influence of these variables upon minimum stopping distance and other performance variables. Tests performed on a low coefficent of friction surface showed that high values of deceleration/pedal-force gain result in a greater number of wheel lockups and longer stopping distances compared to results achieved with intermediate or low deceleration/pedal-force gains. Tests performed on the two test surfaces with high and intermediate levels of friction showed that low deceleration/pedal-force gains produced longer stopping distances than were obtained with high gain, even though a high-gain brake system causes higher frequencies of wheel lockup.

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.

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.

Direct impact to the larynx is usually prevented in accidents by the protective nature of the chin. In some situations, the occupant motions leave the larynx unprotected and susceptible to impact by the steering wheel rim or instrument panel. As one of the unpaired vital organs of the body, there is no easy way to provide an alternative for its functions when the larynx is lost or damaged. Information available on the tolerance of the unembalmed human larynx to force is quite limited. This paper describes a multidisciplinary study to determine the response of unembalmed human larynges to blunt mechanical loading and to interpret the response with respect to clinical data. Fresh intact larynges were obtained at autopsy and tested at either static or dynamic loading conditions utilizing special test fixtures in materials-testing machines. Load and deformation data were obtained up to levels sufficient to produce significant fractures in both the thyroid and cricoid cartilages.