Bumpsteer is a change in toe angle (wheel 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. Bumpsteer happens in each wheel, independent of the other wheel, causing excess drag on the car as the wheels steer in differing directions. Bumpsteer worsens when you lowering springs are installed. Only thing is bumpsteer kits last only a couple years and need to be replaced. You'll hear a racket when the spherical rod-ends wear. I have Eibach Pro-Kit, FRPP Bumpsteer kit, Off-Set Rack Bushings, StangSuspension CC plates. I drive with confidence and full control of my Stang. If your use to keeping the car on the road when on screwed up roads, then you don't need them. Me? It has to be perfect. My baby stays straight and true on any road condition. But then again, that's me.