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This SAE Information Report presents the background and rationale for SAE J1574-1. The motor vehicle industry is working toward a more complete understanding of the factors affecting the motions of vehicles on the roadway, by using a variety of techniques that predict responses to road and operator inputs. The capability to predict responses is desirable so that vehicles can be designed for optimum safety and utility. In addition to the force and moment properties of the pneumatic tires, a number of vehicle and suspension parameters affect the response of the vehicle; these include weight, center-of-gravity location, moments of inertia, suspension ride and roll rates, suspension kinematic and compliance properties, and shock absorber characteristics. These parameters must be quantified in order to predict vehicle responses. Measurement of most of these parameters will be limited to determining their values in the linear range for use in directional control simulations.

This SAE Information Report presents the background and rationale for SAE J1574-1. The motor vehicle industry is working toward a more complete understanding of the factors affecting the motions of vehicles on the roadway, by using a variety of techniques that predict responses to road and operator inputs. The capability to predict responses is desirable so that vehicles can be designed for optimum safety and utility. In addition to the force and moment properties of the pneumatic tires, a number of vehicle and suspension parameters affect the response of the vehicle; these include weight, center-of-gravity location, moments of inertia, suspension ride and roll rates, suspension kinematic and compliance properties, and shock absorber characteristics. These parameters must be quantified in order to predict vehicle responses. Measurement of most of these parameters will be limited to determining their values in the linear range for use in directional control simulations.

The parameters measured according to this SAE Recommended Practice will generally be used in simulating directional control performance in the linear range. (The “linear range” is the steady-state lateral acceleration below which steering wheel angle can generally be considered to be linearly related to lateral acceleration.) But they may be used for certain other simulations (such as primary ride motions), vehicle and suspension characterization and comparison, suspension development and optimization, and processing of road test data. This document is intended to apply to passenger cars, light trucks, and on-highway recreational and commercial vehicles, both non-articulated and articulated. Measurement techniques are intended to apply to these vehicles, with alterations primarily in the scale of facilities required.

The parameters measured according to this SAE Recommended Practice will generally be used in simulating directional control performance in the linear range. (The “linear range” is the steady-state lateral acceleration below which steering wheel angle can generally be considered to be linearly related to lateral acceleration.) But they may be used for certain other simulations (such as primary ride motions), vehicle and suspension characterization and comparison, suspension development and optimization, and processing of road test data. This document is intended to apply to passenger cars, light trucks, and on-highway recreational and commercial vehicles, both non-articulated and articulated. Measurement techniques are intended to apply to these vehicles, with alterations primarily in the scale of facilities required.

The vehicle dynamics terminology presented herein pertains to passenger cars and light trucks with two axles and to those vehicles pulling single-axle trailers. The terminology presents symbols and definitions covering the following subjects: axis systems, vehicle bodies, suspension and steering systems, brakes, tires and wheels, operating states and modes, control and disturbance inputs, vehicle responses, and vehicle characterizing descriptors. The scope does not include terms relating to the human perception of vehicle response.

The vehicle dynamics terminology presented herein pertains to passenger cars and light trucks with two axles and to those vehicles pulling single-axle trailers. The terminology presents symbols and definitions covering the following subjects: axis systems, vehicle bodies, suspension and steering systems, brakes, tires and wheels, operating states and modes, control and disturbance inputs, vehicle responses, and vehicle characterizing descriptors. The scope does not include terms relating to the human perception of vehicle response.

This SAE Recommended Practice establishes consistent test procedures for determination of steady-state directional control properties for passenger cars and light trucks with single axles. These properties include the gradients with respect to lateral acceleration of steering wheel angle, understeer/ oversteer, sideslip, roll angle, and steering wheel torque; the gains with respect to steering wheel angle of yaw velocity, lateral acceleration, and sideslip; the characteristic speed or critical speed; and the total, steering, and tire compliances at the front and rear wheels.

This SAE Recommended Practice establishes consistent test procedures for determination of steady-state directional control properties for passenger cars and light trucks with two axles. These properties include the steering-wheel angle gradient, reference steer angle gradient, sideslip angle gradient, vehicle roll angle gradient, and steering-wheel torque gradient with respect to lateral acceleration. They also include the yaw velocity gain, lateral acceleration gain, and sideslip angle gain with respect to steering-wheel angle. Additionally, the characteristic or critical speed and the front and rear wheel steer compliances may be determined.