Drag coefficient for automobiles

The drag coefficient is a common measure in automotive design as it pertains to aerodynamics. Drag is a force that acts parallel and in the same direction as the airflow. The drag coefficient of an automobile impacts the way the automobile passes through the surrounding air. When automobile companies design a new vehicle they take into consideration the automobile drag coefficient in addition to the other performance characteristics. Aerodynamic drag increases with the square of speed; therefore it becomes critically important at higher speeds. Reducing the drag coefficient in an automobile improves the performance of the vehicle as it pertains to speed and fuel efficiency. There are many different ways to reduce the drag of a vehicle. A common way to measure the drag of the vehicle is through the drag area.
The application of new parts and concepts onto the vehicle design are easier to include when in the design stage of a vehicle, rather than in Aftermarket(automotive) parts, however, the fabrication of these parts assists in the streamlining of the vehicle and can help greatly reduce the drag of the vehicle. Most vehicles with very low Drag coefficients, such as race cars and high efficiency concept cars, apply these ideas to their design.

Wheel covers

When air flows around the wheel wells it gets disturbed by the rims of the vehicles, and forms an area of turbulence around the wheel. In order for the air to flow smoother around the wheel well smooth Wheel covers are often applied. Smooth wheel covers are hub caps with no holes in them for air to pass through. This design reduces drag, however, it may cause the brakes to heat up quicker because the covers prevent airflow around the brake system. This is why this modification is more commonly seen with high efficiency vehicles, rather than sports cars or racing vehicles.

Partial grille block

The front grille of a vehicle is used to direct air directly into the engine compartment. In a streamlined design the air flows around the vehicle rather than through; however, the grille of a vehicle redirects airflow from around the vehicle to through the vehicle, which then increases the drag. In order to reduce this impact a grille block is often used. A grille block covers up a portion, or the entirety of the front grille of a vehicle. In most high efficiency models or vehicles with low drag coefficients there will be a very small grille already built into the design, therefore a grille block is unneeded. The grille in most production vehicles is built generally to have as much air flowing into the engine in order to keep it from overheating. But most commonly there is too much airflow into the engine, preventing it from warming up in a timely manner, so a grille block is used to increase engine performance and reduce the vehicle's drag.

Under tray

The underside of a vehicle often traps air in various places and adds turbulence around the vehicle. In most racing vehicles this is eliminated by covering the entire underside of the vehicle in what is called an under tray. This tray prevents any air from becoming trapped under the vehicle and reduces drag.

Fender skirts

Fender skirts are often made as extensions of the body panels of the vehicles and cover the entire wheel wells. Much like smooth wheel covers this modification reduces the drag of the vehicle by preventing any air from becoming trapped in the wheel well and assists in streamlining the body of the vehicle. Fender skirts are more commonly found on the rear wheel wells of a vehicle because the tires do not turn and the design is much simpler. This is commonly seen in vehicles such as the Honda Insight. Front fender skirts have the same effect on reducing drag as the rear wheel skirts, but must be further offset from the body in order to compensate for the tire sticking out from the body of the vehicle as turns are made.

Modified front bumper

The front bumper is the first part of the vehicle that the air must flow around. Therefore, it plays a crucial role in reducing drag. In order to preserve the teardrop shape of the vehicle a front air dam is often used. A front air dam extends from the very front of the vehicle down to the lowest part of the vehicle. It does this to direct airflow around the vehicle rather than through it. Contoured deflectors, or tire spats, are often made as part of the front bumper in order to direct airflow around the tire without having any increase to the outward flow. With the Sears-Haack body,  body being the best possible aerodynamic shape,the modifications of the front bumper would be ideal to mimic the front of this shape; however, adjustments must be made out of practicality and legality, and more often a tear drop shape is formed by the front of the vehicle, such as in the Dymaxioncar.

Boattails and Kammbacks

A boattail can greatly reduce a vehicle's total drag. Boattails create a teardrop shape that will give the vehicle a more streamlined profile, reducing the occurrence of drag inducing fliw seperation.A kammback is a truncated boattail. It is created as an extension of the rear of the vehicle, moving the rear backward at a slight angle toward the bumper of the car. This can reduce drag as well but a boattail would reduce the vehicles drag more. Nonetheless, for practical and style reasons, a kammback is more commonly seen in racing, high efficiency vehicles, and trucking.

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