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You can change the front or rear roll center by raising or lowering the inner ballstud. A lower roll center (raising the ballstud) will put more weight on the tires during cornering, and increases traction to that end of the car.
Typically, .030″ shims are used to raise the ballstud. If this is too much, you can use thinner shims but be sure that you use the same thickness on both sides of the car.