Originally posted by InitialD
I don't think there is any difference with regards to how the weight of the car is located with the location of the rear bottom arm. If there is, it's probably very insignificant.
There would be no detectable weight difference when you change the location of the rear lower arm.
When adjusting roll-center, you make small changes with the upper insert, and make large changes with the lower insert.
With the rear upper inserts, when you place the inserts with the holes outward, you use shorter upper arms. This will give more camber change under suspension movement.
When you place the inserts with the holes inward, you use longer upper arms. This will give less camber change under suspension movement.
Roll-center and CG work hand-in-hand.
See the attached pic.
Think of it this way...
* Roll-center (RC) is the point around which the car rolls
* Center-of-Gravity (CG) is where all cornering force is directed
* RC and CG are (ideally) in the middle (left-right middle) of the car
* RC is below CG (for RC cars)
When cornering, centrifugal force is applied to the car's CG, which tends to push the car to the outside of a corner. Cornering force causes the CG to rotate around the RC. Since the RC is below the CG, cornering force causes the car to rotate AWAY from the force... hence the car rolls to the OUTSIDE of the corner.
* When RC is far away from CG (lower RC), when you corner the CG has more 'leverage' on the RC, so the car will roll more.
* When RC is closer to CG (higher RC), when you corner the CG has less 'leverage' on the RC, so the car will roll less.
* If the RC was right on top of the CG, when you corner the CG has no 'leverage' on the RC, so the car would not roll at all.
Depending on what the car is doing, you will want one end or the other to roll more or less. You change the height of the RC accordingly to make it closer or further from the CG (which for all intents is a fixed point).
I hope I didn't muddy the waters even more.