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No you dont have to. They are for 2 diff issues. The ball joints raise the spindle to compensate for a drop, this corrects the front control arm angle, and camber. The bumpsteer kit adjusts the tie rods angle so that it does not pull or push the wheels when going over a bump (simplified version). Having said that, if you have lowered the car, you should use both to correct the geometry of the suspension. When things are at incorrect angles it creates binding and excess wear of the parts, also handling can be affected.