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This IMCA dirt Modified utilized a Z-link rear suspension. Note there are two holes for the coilover mount on the lower arm. Moving the mount changes the motion ratio of the arm and the spring rate that is felt by the chassis. Using a 200-pounds per inch (ppi) rated spring, the front hole would yield a net spring rate of about 110 pounds. Moving the spring to the back hole would increase the net spring rate by 20 pounds to about 130 ppi.