On a Z-link four bar type of rear suspension, there is an indexing effect as the chassis travels that will tend to rotate the birdcage and, along with it, cause changes in the height of the bottom of the spring mount. In this example, as the chassis moves down, the arms straighten out and that causes the birdcage to rotate. When the spring is mounted behind the axle tube, the indexing stiffens the rate felt by the chassis on that side. You can mount the spring in front of or behind the axle for different effects. If the RR spring is mounted to the rear of the axle, then as the car goes into the turns, crossweight will be reduced because load will increase for the LF and RR tires. Mounting the spring in front of the axle will increase bite, or left rear weight.