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This paper examines the directional handling characteristics of several vehicles in their original condition, then examines modifications to a few of these vehicles to determine if the handling characteristics can be made more forgiving of normal operators without sacrificing utility and without substantial increases in cost. These analyses of vehicles are made in the context of what normal operators are capable of performing with regards to steering response.

Rear axle tramp can be excited by rough roads or cyclic vertical inputs from tire failure. If the excitation frequency is at or above the natural frequency of the axle/tire spring-mass system, the response can be sufficient to cause loss of control due to axle tramp, which will cause decreased lateral friction of the rear tires resulting in oversteer. Recognition of this problem led to this study of the mechanics of the rear axle motion during controlled cyclic inputs. Tramp response to cyclic impacts or imbalance is analyzed theoretically and compared to measured responses on a vehicle. The effects of axle moment of inertia, spring stiffness and placement, and shock stiffness and placement are discussed. Testing of a vehicle with a controlled vertical impact to the rear axle was conducted in an SAE J266 circle maneuver to determine the effects of tramp magnitudes and frequency to the understeer characteristic of the vehicle and reported in a previous paper [1].

Typically the roll propensity of a vehicle is calculated from the assumption that the vehicle is a rigid body and that its roll propensity can be determined by taking the ratio of the track width and the center of gravity height. However, a passenger vehicle is not a rigid body; it is at least two rigid bodies connected through links and springs and shock absorbers. The objective of this paper is to derive a new second order rollover metric, which will predict whether a vehicle may be susceptible to rollover from simple physical measurements of the vehicle. The validation of the derived metric using a stock and modified vehicle configuration will be presented. Further validation with several vehicles is planned and will be reported in later papers.

Occupants of off-road vehicles are very susceptible to the effects of vertical accelerations. Root mean square values normally accepted are 0.25 g's for longer duration and 0.4 g's for a shorter duration (up to two hours per day) (ref. 1). Typical off-road vehicles stiffen the suspension in order to prevent bottoming of the vehicle. This causes the ride to be extremely rough, meaning the vertical accelerations are at the limit of the human endurance. The speed of the vehicle is then limited by the endurance of the individual. By lengthening the suspension travel and tuning the spring stiffness and damping coefficients, a smooth and controllable ride is achieved thus increasing the natural limit speed. “Whoop-de-doos” are referred to by off-road drivers as a set of evenly spaced waves in the path of travel. These are often caused by repeated traffic over a soft surface. These bumps are sinusoidal in nature and are usually spaced 6 meters apart and 0.2 meters high.

This paper describes a modeling method whereby the occupant impacts during rollover collisions may be predicted with sufficient accuracy to predict their injury level. By using MADYMO to reconstruct the vehicle motions during a rollover collision and the subsequent vehicle accelerations, the model may also be used to calculate occupant impact accelerations if reasonable estimates of interior surface stiffnesses are used.