from SPL's site:
"Subframe bushing spacers are used to tune anti-squat by rotating the instant center of the rear suspension through rotating the subframe or moving the subframe relative to the center of gravity:
For maximum squat (eg. drag racing), rotate the instant center down by installing spacers above front subframe bushings and below rear subframe bushings.
For slightly increased squat, lower the instant center by installing spacers above all subframe bushings.
For slightly increased anti-squat, raise the instant center by installing spacers below all subframe bushings.
For maximum anti-squat (eg. drift), rotate the instant center up by installing spacers below front subframe bushing and above rear subframe bushings.
Note: These spacers cannot be used in conjunction with the collars above, but can be used with our solid aluminum bushings.
Set includes 2 larger and 2 smaller diameter urethane spacers. The larger diameter spacer is usually used above a subframe bushing. "
