Bump steer generally refers to the change in toe angle that happens to a wheel when the suspension on that side of the vehicle is compressed. Depending on the angle of the tie rod relative to the driving surface, the change in toe can cause abrupt direction changes. Generally this can cause the vehicle to "dart" one way or the other if a bump or dip is encountered mid-turn (this is especially true on lowered vehicles).
Megan Racing Anti-Bump Steer Kits correct the steering arm geometry to improve the tie rod angle and reduce toe change during suspension compression. The resulting "corrected" suspension geometry helps reduce bump steer and keep toe angles much more precise during spirited driving. On lowered vehicles this is especially useful, you will generally notice a much more "composed" feel and precise feedback from your steering system.
