Anti-roll is merely another suspension technique that offers reduced body roll with softer springs for good ride comfort. (and tire contact)
In general the stiffer the springs the less antisway bars needed.
The advantage of stiffer springs with less anti=sway in the inside wheels stay in better contact with the ground though the rougher the ground the more likely the tire doesn't stay in contact the stiffer the spring. (staying in contact means the car is in control; not in contact the car is out of control and no thrust either)
As long as the center of gravity is constant (at rest) physics will easily show you that the higher the centrifugal force (i.e. speed on a radius) the more the vehicle weight is transferred from inside the radius to the outside wheels. As the weight transfers the contact area of the inside tire decreases and only slightly increases on the outside. Cornering power is determined by the coefficient of friction between the tire and ground and the area in contact.
The purpose of the suspension system is first to achieve the maximum area of contact between tires and ground and to maximize the aggregate pressure
on the contact areas. That is a simple statement covering a very complex design situation. That said:
More anti sway is not necessarily a good thing. Stiffer springs is not necessarily a good thing.. Lower center of gravity is not necessarily a good thing.
The optimum combination of those 3 things is a project that drives Cray computers nuts.
First, lower the CG reasonably, taking into ground clearance and ground roughness is paramount.
Second chose springs that match the change in spring lengths per unit time. Shocks are used to assist in that control of spring length changes.
The more change per unit time the softer the spring, the less change the stiffer.
Antisway is a tuning device more than anti-roll. Think of the CG as a line running thru the vehicle front to rear. At the front it is between the front wheels and at the rear between the rear wheels. One is virtually always higher than the other, hence the line tilts, up and down and actually side to side, hence its diagonal to the vehicle. Except on F1 etc designed vehicles it is rarely a horizontal line midway of the car. The purpose of antiroll bars is to make the line more horizontal and midway front to rear. For example on a basically understeering FWD vehicle that line is high and left of center at the front and less higher and more midway at the rear. There needs to be reduced understeer at the front - meaning less antiroll - and more oversteer -more antiroll-at the rear so that if the vehicle slides the front and rear break loose together. And equally. Well as close as possible.
Street FWD cars used on track generally benefit from less antiroll front and more or no less antiroll at the rear. Often the springs are tuned the same way. Softer springs front and stiffer rear to avoid too much or too little spring stiffness.
Really stiff antisway bars may feel great on the street but in competition they will be slower purely because they 'tip' quicker, losing traction, thus sliding around instead of cornering. Don't let ESPN's lurid scenes of sliding dirt trackers fool you. They only do that because they have no traction and are merely balancing all that dirt throwing with thrust in a predicted direction.
Generally we have found a little stiffer spring and no antiroll bar at the front and keping the rear antiroll and spring stiffness along with about 1" lowering is the best combination for both street and track.Thats on more than 30 showroom stock racers in 50 years. And tunable shocks are virtually manitory for fine tuning.
Its not an easy result and usually takes many hours of testing. NASCAR, anyone?
Last edited by mahout : 12-22-2006 at 04:09 PM.
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