[Gonzalo Bravo]

Aqui esta la explicacion:

What Exactly is Bumpsteer? The technical definition of bumpsteer is a change in toe angle caused by the suspension moving up or down. Bumpsteer is built into the geometry of the suspension and steering system, and has nothing to do with turning the steering wheel. The effect of bumpsteer 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. Bumpsteer is undesirable because the suspension is steering the car instead of the driver.


What is the Cause of Bumpsteer? 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. To fix a bumpsteer problem, you need to alter the height of outer tie-rod relative to the steering rack. Small changes in this relationship can be made with offset rack bushings. Making big changes requires adjustable tie-rod ends, also known as a bumpsteer kit. Many aftermarket companies offer bumpsteer kits such as Baer Brakes, Steeda Autosports, Competition Engineering. When installing a bumpsteer kit, it is highly-recommended that you have a certified technician install the kit. It is required that an alignment rack be used in the installation of the bumpsteer kit. Using an alignment rack allows the technician to monitor the changes in toe with suspension travel and make changes in the bumpsteer kit’s settings.