Originally Posted by showcase
What Richard said. Measure the distance from the top of the wheel well to the centerline of the hub (or to the floor). The KW's have a range of something like 1/2" to 2" drop. I wouldn't go lower than 3/4" to start with.
There is a collar adjustment (at least on KW V3's). Your mechanic will raise or lower that collar to adjust the height. Typically, you set it, lower the car so it's sitting on it's suspension, remeasure the height, then lift it back up and adjust the collar to get the final height you want.
If your mechanic is any good, you should only have to say "put these bad boys on and dive me a 3/4" drop."