Originally Posted by Art Zarate Jr.
I thought that for "good handling" the car needed to be stiff
A stiff suspension works (sort-of) on a Mustangs because if the car's poor geometry. The front end on the car is practically zero camber gain in roll (which is needed to keep the contact patch flat on the road's surface.) So one way of dealing with it is to dial in a lot of static camber (so as the top of the tire moves ourward in a turn, the tire gets more vertical and the contact patch gets bigger.) Limiting the movement of the suspension also helps with this.
And this would work great if the track were prefectly smooth. Indeed, karts do very well with no suspension at all because they are very light and the tracks are smooth. (The only compliance in a kart's suspension is in the tires.)
But we don't drive on smooth spreets or tracks, so we need the suspension to be able to move to absorb the bumps and keep the tires planted firmly on the track surface. this is not an easy thing to do and find ing the tight amount of compliance versyus stiff ness is a black art and may take years of trial-and error to get just right -- for a particular track. Go to another track and all that changes and you have to start all over again.
So you want a suspension that is stiff enough such that the tire's movements are restricted enough that the contact patch remains as large as possible, but compliant enough to absorb the bumps and keep the tire planted as firmly as possible to the surface.
This is not easy, and if you have a suspenion geometry that is correct, you can allow the tire to move around more, making it easier to go with a softer suspension which plants the tires better.
So stiffer is not necessarily better from a handling perspective.
Body lean is a function of roll stiffness. It is partly determined by the stiffness of the suspension (springs and anti-roll bars,) and partly determined by the geometry (roll centers and the location of the genter of gravity.) If you have a stiff setup to keep the tires in a nice, contact-patch-friendly location, you'll have less body roll. If you have a good geometry that lets the tires move around more while keeping the contact patch happy, you will have more body roll, and it's not such a bad thing (although your center of gravity will move around slightly more with more body roll. This may or may not be a bad thing.)
It's interesting to note though that some body roll is a good thing. drivers seem to be able to driv4e better at the limit with at least a little body roll. Apparently the brain uses this to determine lateral acceleration. Part of what makes a Formula-1 car so difficult to drive fast is that there is little, if any, body roll, the suspension is so stiff (for a different reason, F1 cars have to maintain a very consistant gap between the track surface and the under tray for the aerodynamics to work. Their suspension moves less than an inch, typically.)