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
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
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.