How does one determine best spring rates and alignment specs?

[375instroke]

I see new Challengers and Chargers have 10° positive caster.  The stiffest spring one can tolerate does not equate to better handling.  How does one determine what the rate should be?  It looks like guess work for us.  Same with sway bars.  Now with stiffer springs, the body leans less, so less compensation needs to be built into the suspension to keep the contact patch on the ground.  Am I wrong here?  Does the wheel need to lean away from the turn to keep the contact patch flat on the ground?  Here's what I'm talking about:







In the first two pics, the car leans over very far, thus leaning the tires over with the body.  The outside tire is designed to camber more negatively as it jounces.  Some say the static camber should be negative, with more negative settings if the car is raced.  If the wheel leans when it moves up, why do we need negative camber?  If there is positive caster, the tire will lean into the turn also.  Think of the front wheel of a Chopper motorcycle.  That's an example of extreme positive caster.  Now it's hard to see the angle of the tires on the first two pictures, but on the Pinto, the tires look close to perpendicular to the ground, and the camber was about 1° positive on the left side, and 1° negative on the right, as suggested by a few racers.  That track had more left turns than right.  Two left, and seven right, hence the staggered camber.  The caster was around 2° positive, and the car handled great.  No pulling or wandering at all, and we were doing 130mph at the end of the straightaway.  So, to sum it up, how does one know what torsions, leafs, sway bars, and alignment settings to use, or is it just a crap shoot.  That guy uses this, so I will too?

[HPP]

The answer to that can get pretty complex, but the basic start is intended application; street, autocross, road race, oval track, drag race.

That drives a different set of decision for each application. Concerns within those parameters can come down to analysis of the track, banking, left/right turns, etc.  Obviously if we are competing, class rules and specifications have to be considered as far as what types and kinds of modifications, if any, are allowed. These types of conditions will dictate some component selections and alignment requirements.

Another consideration if the overall weight of the car and then the front/rear weight split, and four corner weight distribution. This will then drive specific spring/ sway bar selections to achieve the right balance of applied wheel rates.

If you doing this with a classic mopar, you also have to figure out the limitations you may have with only a few decent size torsion bars that are available and how you balance that against other component selection.

A general thought to this is you only want to use as stiff a spring as is necessary to accomplish the task. Alignment specs are set to maximize tread contact with the ground. Dynamic suspension movements should also be set up to maximize tread contact and minimize/maximize body roll, again depending on the application. BTW, not all suspension designs create negative cmaber as they compress. For instance, 1st generation Camaros actually go positive as the suspension move up. However, this change can be impacted by the length of the upper and lower control arms as well as the heighth of the spindle. The degree of camber gain you want is directly related to how much body roll you produce, and if used on a track, how much banking is in the turns.

So, are you just asking in general or for something specific?

BTW, the Alfa and Neon could use both a step up in spring and several steps up in sway bar rates. The Pinto is certainly more dialed in. Funny as it may seem, there are actually a lot of performance chassis parts for Pinto/Mustang 2 chassis and they are raced all over the US.