Failure Analysis Associates (FaAA) have experimentally and analytically studied steady-state and transient handling response properties of ATVs, and ATV rider steering control behavior. Two traditional automobile handling tests were adopted, namely, the circle-turn and the J-turn tests. Additionally, serpentine trail testing was used for subjective evaluation as well as identification of ATV dynamics when ridden in an off-road environment. It is well known in the mathematical theory of ground vehicles that "limit oversteer" implies directional instability at speeds exceeding a "critical speed". Yet no evidence of directional instability was found during subjective testing and normal riding of ATVs at speeds above the "critical speed" predicted by the theory. This relative stability of an ATV when compared to the theory is attributed to the fact that the ATV rider can influence the understeer/oversteer of the ATV through his/her body movement, throttle control, and compensatory steering actions. To study the dynamics of an ATV/rider system one of the ATVs involved in the handling tests, a four-wheel ATV, was chosen for repeated serpentine trail runs in which ATV motions in steer and yaw were recorded in real time. A "least square prediction error" method is used for identification of ATV/rider dynamics, and good agreement between the model response and experimental measurements is obtained. Then the "crossover model" theory of manual vehicular control is applied to study the lateral directional dynamics of ATV and rider steering control. The general conclusion is that in the presence of appropriate rider body movement and throttle control, ATV lateral directional response lends itself to effective rider feedback steering control.
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