Do they Work?

Failures.

Rig tests can fail to improve a vehicle, as the following example will illustrate.

A racing saloon car was tested at Cranfield. As delivered, the vehicle was under-damped at the front, and (very) over-damped at the rear. Overall, the heave mode damping ratio was fairly good, but there was an almost 10:1 ratio of front/rear strut displacement at the heave mode frequency. The vehicle was, apparently, competitive.

The rig was used to balance the suspension set-up, and improve the overall damping of the heave and pitch modes. Ultimately, after setting dampers for several spring combinations, the vehicle was dispatched with the belief that the vehicle would be much improved.

Some time later, the team reported that "rig-based" settings made the vehicle less competitive. Experience suggested that there had to be someting "wrong" with the vehicle, and the team was asked to check the rear geometry. It turned out that rear suspension geometry introduced severe bump steer. This was corrected, and the vehicle then ran (very competitively) with rig-based settings.

The moral of the story is that rig-based suspension settings will not make a poor vehicle competitive, or even necessarily improve the vehicle. However, the rig tests were still useful to the team, since they exposed a previously undiscovered deficiency in the vehicle (sadly, by deduction rather than observation).