Dalamar said:
Thank you for the information.
in simple terms, the roll center of the rear, is that the panhard rod to the ground?
That nut is where your rear suspension roll center is. From there to the floor is the distance you want to have anywhere from 7-9 inches.
and how do I determine the roll center of the front end?
That is actually pretty complicated, and you need to measure some dimentions, and sketch this out on the paper, along with the angle your control arms are at. If I remember correctly, you have to draw a line from the balljoint to the bushings on the control arm, and continue it all the way to the end of paper. Then you draw the line through the strut. At the top draw another line which is at 90 degree angle to the strut line, and continue that line until you meet the control arm line. From where they meet, you bring back a third line to the center of your wheel. Then, you draw a line through the center of the car. The point where the tire line and center of the car line meet is your front roll center. This is way too complicated and completely unnecesary to do by hand. A MUCH easier way to know if testing and tuning or asking someone who is running a similar setup.
Edit: I did a quick diagram in paint to help you understand better.
Remember, this applies only to McPherson strut suspension. SLA user upper control arm instead of the 90 degree line from the shock, which is why a properly designed SLA can actually be lowered a lot, and still have good geometry.