When altering the suspension of your Mustang, bump steer is an issue that many enthusiasts run into. The geometrical inconsistency due to bump steer can cause your Mustang to handle in an incorrect manner.
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 is steering the car instead of the driver.
Bump steer is the undesirable turning of the wheels when driving over bumps in the road without any input from the steering wheel. This is caused by improper lengths and angles that are associated with suspension and steering linkages.
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 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 bump steer.
In other words, if you plan on lowering your car, you are going to run into this issue. Even with the installation of caster camber plates, that is not enough to fix the problem. Driving with bump steer can be annoying on the street and effect your drivability on the race track. Don't let that keep you from lowering your car! There is a solution. Here at Late Model Restoration we carry plenty options for Mustang bump steer corrections.
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 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.
To fix a bump steer 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 bump steer kit.
Here at Late Model Restoration, we sell a variety of BBK and Steeda Bump steer Kits that have feature spherical ends with tapered shafts. Essentially, a Bump steer Kit includes a modified Tie Rod End that allows for compensation of the geometrical difference by relocating the rack and pinion upward.
Toe: Toe-in or Toe-out describes the alignment of the front wheels relative to each other, the same way you would describe your feet. For example, toe-in means they are closer together at the front than the rear.
Caution! Installing this product requires disassembly of some components of the steering system. If you are not confident you can complete the job safely, have the work performed by a certified technician who is familiar with the front suspension of a Mustang. Failure to install this part properly may lead to serious injury.
If the stock K-member, spindle and balljoints are used, the best position is more likely to be with the rod-end at the middle to top of the stud (more spacers at the bottom).
If the Steeda X2 balljoint is used, the best position is most likely to be with the rod-end nearer the bottom of the stud (more spacers at the top). Caster angle settings affect bump steer. Increasing caster with caster/camber plates raises the outer tie-rod. The more caster is added, the more the spacers will be needed above the rod-end to compensate.