Why Rig Test

Why Use a Four Post Rig?

A competition vehicle suspension performs multiple functions. These include vehicle control, trajectory control, airflow control and driver feedback. The various functions yield conflicting requirements for a vehicle suspension, so that any suspension set-up represents a compromise. An optimum set-up, in terms of lap time, may well vary (a little) between drivers and also from one circuit to another.

A driver will be more sensitive to some of the functions than he will be to others. Therefore suspension settings derived solely from track tests are likely to be biased in favour of driver preferences (feedback and transient vehicle response to steering inputs, in particular) and the overall performance of the vehicle is likely to be sub-optimal.

A four post rig provides a tool that can redress the balance in favour of sprung and unsprung mass control. A four post rig test can also yield quantitative information about the vehicle, and other characteristics that can affect vehicle performance.

Finally, a rig test allows the relative merits of different suspension strategies to be assessed (more).

It is to be noted that a four post rig test carried out in isolation is likely to yield suspension settings that are biased in favour of sprung and unsprung mass control. Taken to an extreme, such settings might mean that a driver would be unwilling or unable to take full advantage of available vehicle performance. it follows that rig and track tests are complementary tools for achieving and maintaining optimal suspension settings.

It is to be expected that the requirements of specific circuits would require minor changes to suspension settings. It is good practice to start with "generic" settings at each new circuit, in order not to drift ever further away from an optimal set-up with each race.

It is worth re-testing a race vehicle periodically during a racing season to check that the properties of the vehicle, its tyres and its suspension components have not changed.