What is swaybar preload?
A swaybar is "preloaded" when it's twisted while the vehicle is at rest on flat, level ground. Any swaybar preload will alter the vehicle's corner weights, which affects handling behavior.
What causes the swaybar to become twisted?
This happens during installation when the second endlink is too short or too long to connect the swaybar to the control arm without forcing the swaybar arm from its relaxed position into a new position. To avoid preloading the swaybar, adjust the length of the second endlink so it can be installed without needing to push the swaybar arm up or down.
Why is it bad if the swaybar is preloaded?
When the swaybar has preload, the twist in it causes vertical forces at each of the endlinks. Those forces are in opposite directions on each side of the car. One side pulls up on the suspension and the other side pushes it down. This changes the corner weights (the amount of weight on each individual tire), which makes the car handle differently in left- and right-hand turns; handling behavior is no longer predictable, symmetrical, or precise.