Suspension geometry questions

[Ghoste]

What are the proper ways for establishing center of gravity, roll axis, and roll centers?

[motorcitydak]

The center of gravity can be changed by moving weight around the car and using light weight components. You can figure out relatively where it is by having your car weighed and knowing the amount of weight on each tire.

You can only change the roll axis, instant center or roll center if you have a multi link rear suspension. Those terms all refer to figures used in determining proper geometry for a link suspension

[suntech]

To be able to move the roll center you would need a wattslink setup, with  possibility to move centre link up/ down.

[HPP]

Center of gravity height determination requires four wheel scales to calculate its exact location. There are some geometric calculations that are performed and include lifting one end of the car 30" inches and then recalculating everything to nail down its location. I can get you the specifics if your still interested, although it would be easier to recommend a few books for this.

Roll centers are further geometric calculations. The rear is easy, it is mid way between the spring pack and axle center line. Front location requires you find the position of all the suspension pivot points relative to the spindle center height and tire contact point. Again, probably easier to reference a book than explain it all. You then project instant center lines through these points and the resulting intersections create the front roll center. These calculations can be effected by tire height and wheel offset and changing these, alters the geometry intersect points as well.

Roll axis simply goes through the two roll center points. The moment lever arm is the distance between the COG height and the roll axis. the shorter this arm is the less body roll your car will have.

Ball park figures for these; COG is about camshaft height at the rear of the block. Front roll center is usually 4-7 inches up, depending on if you've lowered your car at all and your tire aspect ratio. Rear roll center is around 9-14 inches up, again depending on ride height and tire aspect ratios.

Roll center heights can be changed by things such as spindle height and control arm pivot location for the front, and lowering blocks, spring mounts and spring arch in the back. Both can be altered by tires and wheels.

[HPP]

Anything else?

[Ghoste]

Nope, you have explained it very well and added info I didn't expect.  Mucho thanks.