Rear spoilers are designed for self installation, and are supplied with full fitting instructions. You should only buy genuine manufacturer accessories, that you can be sure will be an exact match to your vehicle. Providing an excellent fit and ultimately completing the transformation of the vehicle.
The front and rear spoilers are designed to force air under the car. As the air is forced under the car it has to travel faster. By travelling faster it reduces the pressure under the car. The pressure above the car remains constant in relation to the pressure under the car. As the pressure above is greater than that below the car it pushes the car down, or causes down force, sticking the car to the road. The side skirts that also come as part of the kit ensure that the air cannot escape from under the side of the car, so the air is channeled to the back, again increasing the down force.