About Rigs

Four Post Rigs.

Four post rigs are used conventionally to apply precise and repeatable prescribed inputs to the vehicle via its tyres with the objective of characterising the dynamic response of the vehicle to road inputs. When appropriate, a constant downforce will be applied to the sprung mass of the vehicle, representing the aerodynamic downforce and downforce distribution that would be applied when the vehicle was travelling at a nominated airspeed. Normally, the chosen airspeed would be appropriate to that of a critical corner.

Inputs to the vehicle are measured using wheel platform accelerometers, and vehicle responses are measured by contact patch load cells, by an accelerometer attached to each hub, and by an accelerometer attached to each "corner" of the spring mass. Measurements are recorded during a "run", and are processed after the run has been completed.

The Multimatic analysis software enables vehicle responses to be characterised graphically by selected frequency response functions (see example) and by time domain trajectories, and expressed numerically by identifying an equivalent linear vehicle model. The overall performance of the vehicle can be quantified by estimating two parameters, a "performance index" and a "comfort rating". The versatile structure of the software allows response anomalies to be explored on an ad hoc basis.

The precision of prescribed input and response measurements means that small differences in response characteristics can be detected and quantified..

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