In a previous one of these columns I made the point that simply going stiffer with the suspension's springs and sway bars (where installed) was more likely to be detrimental to grip than beneficial, even if the stiffer settings felt better.
However, beyond ensuring they're not so stiff that they cause overall grip to be lost (or so soft that it causes other issues), you can also use the spring and sway bar rates (how soft or firm they are) to adjust a vehicle's tendency to have oversteer or understeer in various circumstances.
So, if a vehicle is suffering serious understeer, and the front is already soft enough, one of the ways you can address this behaviour is to increase the rate (stiffness) of the rear sway bar.
'But you said going stiffer would be more likely to hurt grip' I hear you thinking. I did. And I still do. But it also improves the grip a little bit at the opposite end. You're sacrificing something at one end to gain a bit (and possibly not as much) at the other.
Therefore, if a vehicle has too much oversteer, and the rear is soft enough already (ie. going any softer will unload the inside rear too much and make things worse instead of better), then you can address that oversteer with a stiffer front sway bar rate.
The springs have an influence on this too (especially in designs that don't bother with a sway bar). Stiffer rear springs improve front grip a bit but also sacrifice some at the rear. Stiffer front springs improve rear grip a bit but also sacrifice some at the front.
One extreme example of this that I became aware of recently was when Bertrand Gachot said in an interview for Formula 1's Beyond the Grid podcast that they had a breakthrough with the setup of the Jordan 191 F1 car in 1991 when he asked his engineer to put the front springs in the back and the back springs in the front.
Gachot said the car used to have epic understeer because that's how his teammate and team test driver Andrea de Cesaris preferred it (understeer is certainly less twitchy and makes a vehicle easier to keep on the road for a whole race), but this seemingly unconventional change saw Gachot produce the fastest lap of the race in the 1991 Hungarian Grand Prix and declare to his team they'd take the pole at the next race in Spa.
That wasn't to be with Gachot blindsided by a court case in the UK that put him in prison for two months (thinking the incident wasn't serious he was only anticipating a slap on the wrist), but his temporary replacement Michael Schumacher certainly didn't find the car to be slow in his first F1 appearance (although the clutch failed almost immediately in the race so he did find it unreliable, but that's a very separate issue).
Suffice to say, just changing the spring rates at both ends was enough to make the car much more suited to Gachot's driving style (and undoubted skill), helping him significantly improve his lap times.
As for the sway bars, in race cars that have them it's not only desirable for them to be adjustable, but for the driver to be able to adjust them mid-lap. The driver can then use them to tweak the car's oversteer-understeer balance as the tyres wear (depending on the vehicle the fronts or rears may begin to lose performance before the other pair does) or as the fuel load comes down (and therefore the weight distribution changes a little).
If the driver is really hard working, they may even change a sway bar setting back and forth for different corners. I've seen tin-top drivers do this at the Paperclip (Queensland Raceway) to have one setting for attacking the first few fast corners and another setting for the differing needs of the slower corners.
One thing to bear in mind throughout all of this when contemplating vehicle setup (and design) is that suspension travel distance is also important.
We can go into more detail another time, but for now we'll just make the point that the springs must never become uncaptured, which can happen when lowered springs are mismatched with stock shocks (a common mistake by novice vehicle modders).
Insufficient bump (compression) travel is also problematic. Put simply, bottoming out and hitting the bump stops is bad, and makes the vehicle very difficult to control.