Suspension 101...

The IC (Instant Center) of any suspension system, is the point where the forces from the rearend housing, apply themselves to the chassis. In the case of single pivot systems, like leaf springs, ladder bars, torque arms, truck arms, etc, that point is where the link connects to the chassis. This is where the rear connects, so it is the ONLY place that force can be applied. The advantage of a 4-bar, is the ability to "project" the IC to a number of different places, because you have more than one pivot point. All vehicles, are trying to "throw" the rearend housing out of the car, when you drop the hammer. Suspension, allows you to control the housing and place the force on the chassis, providing the car with weight transfer. Why do you think leafs wrap up??? because they are pushing on the spring hanger and are not stiff enough to stay straight, is the reason. This is all a Caltrac, or any other leaf spring traction device for that matter, does. It is an attempt to keep the spring straight, so that max force can be applied to the chassis. Where forces are applied, changes how the car reacts. Every car has an "anti squat line". This line extends from the center of gravity, down to the front of the contact patch of the rear tire. If the suspension pickup point, is below the anti-squat line, the car seperates in the rear on launch. If the pickup point is above the anti-squat line, the car squats on launch. If the the pickup point is on the line, the car does neither. Some suspension guys, theorize the IC ON the anti-squat is ideal for any application, because this is where the car has the least wasted movement and applies the most power, but my own testing does not seem to support that. So if you understand how a suspension system really works, it is much easier to understand how various methods of housing control, effect how the car reacts, applies force and what your adjustments are actually doing. Basically, a ladder bar, is like a leaf spring, but the advantage is the ladder bar will not give, plus it moves the IC forward because of bar length. This applies force to the chassis further forward, creating better leverage and increased weight transfer. If you could make your front spring segment dead stiff and move the mounting point out even with the ladder bar, it would be as good as a ladder bar. All this is why link suspensions, be it a 3 or 4 link, is far superior. You can place the IC where it NEEDS to be, to properly apply the force to the chassis, to get the results you desire........Oh, one more thing, if you followed this at all and learned anything about how suspensions work, you can also see why good SHOCKS are critical for a good working car. The whole exercise is about "controlling the housing and applying force". You can have the trickest suspension in the world, but junk shocks render it useless.

Monte