How to Correct Bumpsteer
As we found out, bumpsteer can be a serious problem on some modified vintage Mustangs. Here's how to fix it.
What is bumpsteer?
As we learned the hard way, bumpsteer is a condition you want to avoid. In fact, for a car to drive and feel right, it needs to be eliminated totally. Generally, bumpsteer is caused by an incompatibility between the steering system's tie rods and the front suspension's upper and lower control arms. As the suspension cycles, the path or arc followed by the outer tie rods in relation to the control arms and spindles are different. Since something has to give, there is a toe change (the wheels toe in or out) as the suspension moves up and down. This occurs every time the suspension moves.
While bumpsteer is a factory design flaw every Mustang has to varying degrees, it becomes noticeable when the car is lowered or modified with other suspension improvements that make the car more responsive to steering input. Better tires also make bumpsteer more noticeable. When experienced, the car twitches or darts around on bumpy or undulating roads and can also be twitchy on heavy braking. The car might also pull to one side or another when braking.
Bumpsteer is eliminated from a Mustang by ensuring the tie-rod (steering linkage) pivot point matches the travel of the spindle. Match these curves by either raising the inner tie rod or lowering the outer tie-rod mounting point. Since the location of the inner tie rods and steering center link is under the oil pan, this option isn't practical. Fabrication of a spacer block to relocate and lower the outer tie-rod from its location on the spindle is easy. The Pro-Motorsports' bumpsteer corrector kit accomplishes exactly that. It repositions the outer tie rod 1-inch lower, 1-inch forward, and 1/4-inch outboard from its stock location. The 1-inch drop is for the bumpsteer, the 1-inch forward move quickens the steering the same way the longer idler and Pitman arms did on '65 Shelbys, and the 1/4-inch outboard move reduces (but doesn't eliminate) the Ackermann Angle, a toe-out condition that is designed to occur during turning. While helpful for street cars driven at low speeds, it's less desirable in racing or high-performance situations where high lateral cornering loads are present.