The SS Kit, or Short Stroke kit is essentially a roll centre correction kit. In cars equipped with factory air bag suspension this allows the car to be lowered an additional 50mm from factory. Or if you have an airbag ECU controller then you can go an additional 50mm from the lowest setting on this too. In the rear these kits allow for additional camber of around 10 degrees negative.
Note: 50mm ss kit recommends 20″ wheels or larger.