1985 Ford Mustang - 8 Second Crate Motor

Dragstrip ScalingScaling a car is crucial when setting up a four-link rear suspension. Unlike the factory suspension where components are simply bolted on with minimal adjustability, a four-link suspension consists of four tubular bars (links) that are bolted onto the rear housing and front crossmember with brackets that have several mounting points to select from. The lower bars square and center the rearend, and the upper bars are used to set the pinion angle, but making adjustments to both can alter the car's weight bias and the way the suspension reacts. Since there's an infinite amount of adjustability, weighing and setting up a car with corner scales ensures that the weight distribution is where you want it to be. More importantly, it helps avoid unpredictable handling behavior.

The main advantage of a four-link suspension is the ability to infinitely adjust and tune the car's instant center (IC). The IC is an imaginary point where lines extending forward from the upper and lower rear control arms converge. In some cases, they may never converge, in others, the point may be ahead of the car or somewhere between the front and rear wheels. Change the IC and you'll dramatically change the behavior of your chassis. Generally speaking, the farther to the rear the IC is moved, the greater the amount of antisquat the car will display, but as antisquat increases, antidive decreases, which can make the car sensitive under braking. If you have little experience with four-link systems, it's best to have a professional dial in the suspension initially, otherwise you could go in circles and get lost with the infinite amount of adjustability. Jim Sleeper of Sleeper Suspension Development in La Verne, California, dialed in our chassis before we made our first trip to the dragstrip.

By Henry De Los Santos

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