The main function of the car surround is to reduce the reverse airflow generated during driving, while increasing the downward pressure on the car, making it smoother to drive, thereby improving the car's fuel economy and reducing fuel consumption.

The scientific name for the car bumper is the external body diffuser, which originated from racing and was used to improve the impact of airflow around the body on the stability of the vehicle during movement. The large bumper usually includes the front bumper, side bumper, and rear bumper, as well as parts such as wheel arches, mudguards, and door trims on certain models.

In addition, the use of a large bumper is not limited to racing cars. Some car owners, for visual effects reasons, may also modify the large bumper for their beloved car to increase the vehicle's sportiness and personalization. There are various materials available for large enclosures on the market, including ABS plastic PU plastic PPS plastic materials, resin fiber materials, etc., each have its own advantages and disadvantages. For example, although resin fiber materials are prone to local damage, they have high hardness and can be repaired; PU plastic is less prone to damage, but may deform due to prolonged storage or high temperatures. Overall, the role of a large surround involves both aerodynamics and exterior design, aiming to enhance the performance and appearance of a car.