Not 100% sure on this, but I believe it has to do with when you hit a bump and the tire like to "steer" or turn a little. Essentially, when you hit a bump and the suspension goes up, the front wheels like to change their toe angle. I can't think of any way to word that better. The kit eliminates that. I always thought it was a new type of steering system until someone explained it to me .
It's a spherical rod bearing to help the tie-rod end on lowered cars. You'll want to get the X2 balljoints first though, that will help the most.
Look underneath the front of your [lowered] car, youll notice how the outside end of your A arms angles upward, and notice the angle of the tie rods, how they are not in line with the steering rack itself. Stock, everything is perfectly lateral.
Stay away from offset rack bushings and the bumpsteer kit until you get the X2 balljoints or something equal (you're just looking for the longer stud).
Bump-steer is a change in toe* angle caused by the suspension moving up or down. Bump-steer is built into the geometry of the suspension and steering system, and has nothing to do with turning the steering wheel. The effect of bump-steer is for the wheel to toe-in or toe-out when the suspension moves up or down. This toe change or "steering" occurs any time the suspension moves, whether it is from body roll, brake-dive, or hitting a bump in the road. Bump steer is undesirable because the suspension is steering the car instead of the driver.
The front wheels do not move directly straight up or down when the car hits a bump. Instead, the wheel follows an arc, or curving path, that pushes the wheel slightly inward (towards the centerline of the car) or outward (away from the car) in response to vertical wheel movement. The outer tie-rod (which connects the steering rack to the wheel) also moves in-and-out in an arc as it moves up and down. If the rate which the outer tie-rod arcs in or out does not match the rate the wheel moves in or out, the wheel will be turned by the tie-rod. This is bumpsteer.
The center point of the arc traveled by the wheel (known as the instant-center) is controlled by the location and angle of the moving suspension links. This point moves as the ride height changes. In contrast, the arc of the outer tie-rod is controlled by the position of the steering rack, which is fixed. In order to eliminate bumpsteer, both the length and the center point of the two arcs must be the same. However, since the instant center moves with ride height, bumpsteer cannot be eliminated throughout the entire range of suspension travel. Therefore suspension designers concentrate on minimizing bumpsteer within the range of movement closest to factory ride height. Changing the ride height or other suspension components may move the suspension outside this narrow "optimized" window.