Bargeboards are pieces of bodywork

Coachwork

Coachwork is the body of a horse-drawn coach or carriage, a motor vehicle , a railroad car or railway carriage. Usually reserved for bodies built on a separate chassis, rather than being of unitary or monocoque construction...

 on open-wheel

Open wheel car

Open-wheel car, formula car, or often single-seater car in British English, describes cars with the wheels outside the car's main body and, in most cases, one seat. Open-wheel cars contrast with street cars, sports cars, stock cars, and touring cars, which have their wheels below the body or fenders...

 racing cars

Auto racing

Auto racing is a motorsport involving the racing of cars for competition. It is one of the world's most watched televised sports.-The beginning of racing:...

, serving a purely aerodynamic (as opposed to structural) function. They are curved vertical planes situated longitudinally, between the front wheels and the sidepods, held away from the chassis at the front on struts or other connectors, and connecting to the sidepods or extensions of the floor at the rear. In general, they are significantly taller at the front than at the rear making them trapezoidal in profile, and they curve outward in plan view, being closer to the centerline of the car at the front, and curving out towards the rear.

Function

Aerodynamically, bargeboards act primarily as flow conditioners

Flow conditioning

Flow conditioning ensures that the “real world” environment closely resembles the “laboratory” environment for proper performance of inferential flowmeters like orifice, turbine, coriolis, ultrasonic etc.- Types of Flow :...

, smoothing and redirecting the turbulent or "dirty" air in the wake of the front wing, the front suspension links, and the rotating front wheels.

Part of their function is to direct the turbulent wakes of the front wing and spinning front wheels away from downstream aerodynamic surfaces. In this capacity, they separate different components of this mixture of flows, and direct them either outside and around the sidepods, or direct flow towards the radiator inlets. As such, the configuration of bargeboards can have significance with respect to cooling. They also help direct flow behind the front wheels, reducing the wake drag created by the wheel profile.

Vortex generators

Another important function of bargeboards is to act as vortex generators, redirecting and energizing airflow. The upper, downward sloping edge can shed a large vortex downstream around the sidepods, where it can interact favorably with flip-ups, or aid in sealing the low pressure underbody flow from the ambient stream. The bottom edge of the bargeboard can also shed vortices that energize the airflow to the underbody, which can help delay flow separation and allow the use of more aggressive diffuser profiles. In recent years, these two edges have acquired relatively large serrations or protruding tabs to enhance this aspect of their performance.

Turning vanes

Smaller, similar structures are often situated further forward, between the front wheels and the monocoque

Monocoque

Monocoque is a construction technique that supports structural load by using an object's external skin, as opposed to using an internal frame or truss that is then covered with a non-load-bearing skin or coachwork...

. These are typically called "turning vanes" rather than bargeboards, and are used in addition to, or sometimes in place of full bargeboards, depending on the aerodynamic approach of the car.

Initially relatively simple in their design, bargeboards and turning vanes became progressively more complex through the 2000s, integrating with the floor, mirror supports, suspension mounts, and other structures in more elaborate ways.