Mustang Bump Steer Tech
Definition of Bump Steer: 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 steers the car instead of the driver.
Cause of Bump Steer: 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 car's centerline) 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 at 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 Bump Steer.
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. To eliminate Bump Steer, both the length and the center point of the two arcs must be the same. However, since the instant center moves with ride height, Bump Steer cannot be eliminated throughout the entire range of suspension travel. Therefore suspension designers concentrate on minimizing Bump Steer 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.
