Functions of a Rear Spoiler ;

Spoilers generally function by disrupting or diffusing the airflow passing over and around a moving vehicle as it passes around the spoiler. This is accomplished by increasing the amount of turbulence flowing over the shape, "spoiling" the laminar flow and providing a cushion for the laminar boundary layer. Applications are varied, including using body panels, or most typically by adding an extruding attachment.

Occasionally spoilers are added solely for appearance with no thought towards practical purpose.

The Spoilers for automobiles are often incorrectly confused with, or even used interchangeably with, wings. Automotive wings are devices whose intended design is to generate down-force as air passes around them, not simply disrupt existing airflow patterns.

The main design goal of spoilers in passenger vehicles is to reduce drag and increase fuel efficiency . While many often imitate wings and airfoils, these serve mostly decorative purposes. Passenger vehicles can be equipped with front and rear spoilers. Front spoilers , found beneath the bumper, are mainly used to direct air flow away from the tires to the underbody where the drag coefficient is less. Rear spoilers, which modify the transition in shape between the roof and the rear and the trunk and the rear, act to minimize the turbulence at the rear of the vehicle.

Sports cars are most commonly seen with front spoilers  and rear spoilers . Even though these vehicles typically have a more rigid chassis and a stiffer suspension to aid in high speed maneuverability, a spoiler can still be beneficial. This is because many vehicles have a fairly steep downward angle going from the rear edge of the roof down to the trunk or tail of the car. At high speeds, air flowing across the roof tumbles over this edge, causing air flow separation. The flow of air becomes turbulent and a low-pressure zone is created, increasing drag and instability. Adding a rear spoiler makes the air "see" a longer, gentler slope from the roof to the spoiler, which helps to delay flow separation. This decreases drag, increases fuel economy, and helps keep the rear window clean.