Schedule—Performance standard for road‑fSchedule—Performance standard for road‑friendly suspension

Schedule—Performance standard for road‑friendly suspension

A suspension system is road‑friendly for the purpose of this legislation if it has the performance and component requirements specified in this Schedule. Performance requirements During free transient low frequency vertical oscillation of the sprung mass above an axle or axle group, the measured frequency and damping with the suspension carrying its maximum legal load must fall within the following limits: (a) the frequency of the sprung mass above the axle or axle group in a free transient vertical oscillation must not be higher than 2.0 Hz; (b) the mean damping ratio must be more than 20% of critical damping (Co) for the suspension in its normal operating condition; (c) the damping ratio of the suspension with all dampers (if fitted) removed or incapacitated must be not more than 50% of the mean damping ratio; (d) in the case of multiple axle groups the static load share between axles in the group must be within 5%. Components Dual tyres must be fitted on the axles except in the case of a six tyred tandem axle group where one axle in the group may have single tyres fitted. Definitions for the purpose of this Schedule

load‑share, in respect of a suspension system on a multi axle group, means a suspension system that:

(a) is built to divide the load between the tyres on the group so that no tyre carries a mass more than 5% greater than the mass it would carry if the load were divided equally; and
(b) has effective damping characteristics on all axles of the group.

frequency and damping:

In this definition a sprung mass “M (kg)” above a driving axle or bogie is considered. The axle or bogie has a total vertical stiffness between the road surface and the sprung mass of K Newtons/metre (N/m) and a total damping coefficient of C Newtons per metre per second (N.s/m). The vertical displacement of the sprung mass is Z. The equation of motion for free oscillation of the sprung mass is: Image unavailable in extracted text The frequency of oscillation of the sprung mass F (rad/sec) is: Image unavailable in extracted text The damping is critical when C = Co where: Image unavailable in extracted text The damping ratio as a fraction of critical damping is C/Co. During free transient oscillation of the sprung mass the vertical motion of the mass will follow a damped sinusoidal path. The frequency can be estimated by measuring the time for as many cycles of oscillation as can be observed. The damping can be estimated by measuring the heights of successive peaks of the oscillation in the same direction. If the peak amplitudes of the first and second cycles of the oscillation are A1 and A2, then the damping ratio D is, where ‘ln’ is the natural logarithm of the amplitude ratio.