[Keith Seymore]

Originally Posted by mels80ga

The car is a 1980 Grand Am (G Body) Ford 9" with stock suspension bolt ons. Trans is TH350. Thanks for your help. I am really trying to learn all I can on tuning my suspension.

TH350 (2.52 gear) x 4.56 rear axle ratio sounds like a lot of first gear. That might be part of the problem.

Nonetheless, here's the deal on suspension:

Alston refers to the relationship between the Instant Center of the rear suspension and the center of gravity as "Percentage of Rise". Some people also describe only the instant center point, in terms of how far forward and up (off the ground) of the rear axle.

You will need to scale the car to determine front end weight and rear end weight. From this you can determine the CG location fore/aft; you can assume the CG height to be the distance of the centerline of your engine camshaft above the ground (it's a good approximation).

You will now also need to measure the suspension attaching points at the front and rear of the rear axle control arms. What you are going to do is "imagine" the control arms extending foward to an intersection point; this is the imaginary point around which the rear suspension rotates as it moves up and down in it's travel.

You can do this by measuring the location of the upper control arm rear attachment and front attachment; plot those as a line (either on a piece of paper, or by duplicating the measurment with string/masking tape on the garage floor). Do this again for the lower control arm (measure the forward attaching point and the rear attaching point, and plot that).

Report back with your findings.

To summarize, what you are going to try to do is move that IC point rearward from it's production location, either by raising the rear of the upper control arm or by dropping the rear of the lower.

K