Will Adding a Spoiler Make My Car More Aerodynamic?

A simple way to answer this question would be with a "yes". However, the science of properly managing airflow to create beneficial automotive aerodynamics is, quite literally, more complicated than meets the eye. The word "aerodynamics" brings to mind visions of a vehicle in a wind tunnel with a smoke wand illustrating how smoothly air flows over it. But true automobile aerodynamics involves a detailed study of how the motion of air interacts with all areas of an automobile. One term that gets the most attention is "coefficient of drag" (Cd), which is an overall measurement of a shape's resistance to airflow.

Modified Sports Car

We've become conditioned to believe a lower Cd number is always better, but that's not completely true. While reducing drag in order to reach higher speeds gets the most attention, aero body modifications such as spoilers are actually intended to resist airflow. For example, all spoilers and wings produce negative lift (known as downforce) and often increase drag in doing so, but the overall result of increased grip on the road is desirable. Since most aftermarket body parts have their roots in body modifications made to racecars, it may be helpful to further explain what we mean by looking at two types of racing to see the goals of each and how vehicles are modified to achieve those goals.

Racing Car At Bonneville Salt Flats

For cars at the Bonneville Salt Flats looking to achieve the highest speed possible in a straight line, modifications are geared completely toward reducing drag. Anything that can interfere with the free flow of air over the vehicle is eliminated. Large front air dams are the primary modification because they achieve the highest level of drag reduction (we'll cover more about how air dams work later in the article). Because grip for cornering and braking won't be needed here to the same extent as on a racetrack, only enough down force to ensure lightweight alloy wheels can maintain traction on the salt is required.

Dirt Track Sprint Car

At the opposite end of the spectrum is the dirt track Sprint car. Because engine power levels are relatively low and loose dirt hampers grip, speeds obtained aren't high enough to be a major issue. What is important is maximizing down force to boost traction and cornering. To do so, exaggerated wings that seem more like roof panels are customarily installed on top of these racecars. Any drag they produce proves inconsequential.

While these forms of automotive competition are extreme examples, just about all other types of racing require a balance of the two when it comes to aerodynamic needs. The right amount of down force is needed for traction and steering, but not so much that excess drag builds up. Conversely, drag must be low enough to allow the vehicle to effectively accelerate and hold higher speeds on straightaways without creating lift that causes instability or forces a driver to slow down in order to handle turns. Different parts provide different effects, and we'll take a closer look at exactly how individual pieces affect your car.

Front Air Dams

Air dams, also known as front valance panels, front spoilers or front lips, are mounted on the front of the car below (or in some case in place of) the bumper. While they vary in size according to vehicle and manufacturer, all of these pieces reduce the amount of air flowing under the car - an effect that's beneficial for two reasons. First, the multitude of parts underneath an average vehicle (exhaust, drivetrain, and suspension) create a lot of friction, so less air flowing underneath means a lot less drag. Secondly, reducing the amount of air going underneath the car forces more of it to travel around to the sides and over the roof. This serves to create a low-pressure area underneath the vehicle, which draws the body closer to the ground top due to a suction effect.

Visually, an air dam will make your vehicle appear more lowered and close to the ground than it actually is. Vigilance will be required when negotiating angled driveways and parking lot barriers, however. We also offer a number of stylish replacement front bumper covers with air dams and lips already integrated into their design.

Front Air Dam By 3D Carbon
The polyurethane Front Air Dam by 3D Carbon. The variation of this product shown here for a late model Volkswagen Jetta is considered more of a lip.
Willpak ABS Plastic Chin Spoiler
The Willpak ABS plastic Chin Spoiler.
Front Splitters
Carbon Creations Front Splitter
The Carbon Creations Front Splitter.
Front Splitter Air Dam Diagram
Close Up View Of RKSport Polyurethane Front Splitter
A close up view of the RKSport polyurethane Front Splitter.

Splitters (like the one shown above) work in conjunction with air dams and are used to create down force on the front of a vehicle. They extend forward horizontally from the bottom of the air dam and create a high-pressure zone in front of the vehicle at high-speeds. As their name implies, splitters separate this high-pressure air from the high velocity air flowing underneath the vehicle. As downward suction is generated from a vacuum that forms underneath the vehicle, downforce is created. Road racecars often have adjustable splitters to fine-tune the amount of down force to maintain an aerodynamic balance under varying conditions.

Canards

Canards are positioned on front bumper corners just ahead of wheel well openings. By scooping up air and redirecting it upward, they create additional down force on the bumper. They're excellent for fine-tuning aerodynamics, especially on front-wheel or all-wheel-drive cars that benefit from additional tire bite at the front.

For Subaru WRX and Mitsubishi Evo models of various vintages, the Duraflex fiberglass canards are available in front and rear applications and come ready to paint in black primer finish. For those who appreciate carbon fiber construction, the ARK Performance C-FX Carbon Fiber Rear Tail Lamp Canards mount atop rear tail lamps to create rear downforce. And if you've got a 1997-on Corvette, RK Sport's urethane canards offer a stylish aero boost for the front of your vehicle.

Duraflex Fiberglass Canards
The Duraflex fiberglass canards.
ARK Performance C-FX carbon fiber Rear Tail Lamp Canards
The ARK Performance C-FX carbon fiber Rear Tail Lamp Canards.
Rear Wings
JKS Custom Trunk-Mounted Wing Rear Spoiler
If you like larger, trunk-mounted wing spoilers, check out the JKS Custom Rear Spoiler shown here from our custom style spoilers section.

Opposite of the way airplane wings are shaped, automobile aero wings are flat along their top surface and curved on the bottom - because the goal on a racetrack is to create downforce, not lift. Downforce is created because of pressure differences above and below the wing. Air passing underneath is forced to move faster than air on top as it travels around the curvature of the wing, creating a low-pressure vacuum underneath. Higher pressure on top of the wing then pushes down on the wing, and downforce is created.

T5i ABS plastic Custom Style Rear Spoiler With Light
The T5i ABS plastic Custom Style Rear Spoiler With Light features a built-in brake light, and can be ordered pre-painted to match your vehicle's paint code.

Some wings can be angled to increase airflow resistance and create even more downforce. Racecars typically feature this type of wing in order to accommodate a range of conditions and speeds. While most wings increase drag, those that have been integrated into a vehicle's design extremely well will cause little or no drag at all.

Seibon Carbon Rear Spoiler
For those who prefer carbon fiber construction, the Seibon Carbon Rear Spoiler is one of multiple choices available in our "Custom Style" rear spoilers and wings section.
AMI Adjustable Lighted Rear Spoiler
The universal-fitting AMI Adjustable Lighted Rear Spoiler features 4" adjustable risers and is designed to light up in different colors with a remote key fob.
Rear Spoilers
Street Scene Polyurethane Custom Style Spoiler
The Street Scene polyurethane Custom Style Spoiler.

Rear spoilers perform the same basic function as a wing, but for the purposes of our discussion we'll clarify the difference between the two since manufacturers often label them indiscriminately. A "spoiler" mounts to the car's upper rear surface (trunk in most cases) and there is no gap between the spoiler and the body. If there is a gap, the aero piece would be considered a "wing". A spoiler's function and effectiveness are dependent on its size, angle, and shape of the vehicle it's mounted to.

Xenon polyurethane Spoiler
The Xenon polyurethane Spoiler.

If a spoiler's primary function is to provide down force, it will be tilted at a more vertical angle. As such, high-velocity airflow coming off the roof toward the back of the vehicle will be disrupted, reducing its velocity and creating the high-pressure that results in downforce. This downforce aids rear wheel grip, but it can also correct instances where the shape of the vehicle is such that it tends to become unstable at speed due to lift issues.

While downforce spoilers usually increase drag, spoilers can also be fine-tuned to specific vehicles so that they actually reduce drag. When the rear edge of a car's roof drops off sharply, airflow between that point and the trunk lid become choppy and turbulent - increasing drag. A properly designed spoiler can, in effect, make roof slope gentler to reduce drag by preventing airflow separation.

3D Carbon polyurethane Custom Style Rear Lip Spoiler
The 3D Carbon polyurethane Custom Style Rear Lip Spoiler.
Roof-Mounted D2S Custom Style Rear Roofline Spoiler
We also offer a selection of roof-mounted spoilers, such as the D2S Custom Style Rear Roofline Spoiler shown here.
Side Skirts

Side Skirts also work in union with air dams to minimize the amount of air that works it way underneath the car from the sides. In fact, without side skirts, an air dam's effect can be negated because the low-pressure area created under the car by the air dam would cause high-pressure air from the sides to come rushing in. Accordingly, side skirts are more effective when they're closer to the ground. Side skirts also create the visual effect of making your car appear lowered, as if it were "hugging" the pavement.

Xenon Urethane Side Skirts
The Xenon urethane Side Skirts.
VIS Racing Side Skirts
If aggressive side skirt styling is what you're looking for, the VIS Racing Side Skirts are available in fiberglass or urethane, depending on vehicle application.
3d Carbon Urethane Side Skirts
For more conservative looks, the 3d Carbon urethane Side Skirts are just one of many styles you'll find in our Side Skirts section.
Carbon Creations Carbon Fiber Side Skirts
The Carbon Creations Carbon Fiber Side Skirts.
Rear Diffusers
Carbon Creations Carbon Fiber Rear Diffuser
The Carbon Creations Carbon Fiber Rear Diffuser.
IVS urethane Havoc Rear Diffuser
The IVS urethane Havoc Rear Diffuser is available with or without simulated carbon fiber graphics.
Scheme Of Airflow Spreading
This picture allows a look at just how rear diffusers spread and widen airflow as it reaches the rear of a vehicle's underside.

The Rear Diffuser is another component that's dependent on the presence of other parts to function effectively. The rear diffuser works with the air dam and side skirts to create a condition under the car where a low-pressure pocket is caused by high-speed airflow. What the rear diffuser does is redirect this underbody airflow by providing widening channels to expand and decelerate the air. Once it's been slowed down, that air will now be moving at the same speed as the airstream that traveled over and around the vehicle. The transition at the rear goes more smoothly, and turbulence is minimized.

Variety Of Pickup Truck Spoilers
We also offer a variety of Pickup Truck Spoilers that range from discreet to radical. We've even got the Anzo LED Tailgate Spoiler with a built-in light strip that illuminates when brakes are applied.

Browsing through what's available in any of the sections referenced on our website, you'll notice each aero product features one main photo. These lead pictures are not fully indicative of all the variations you'll find from that manufacturer, because designs and materials offered vary from vehicle to vehicle. Be sure to enter your specific year, make, and model vehicle for access to all your options. In the Product Options drop down box, you'll see all the choices available to you for your ride.

Although appearance is an important purchase consideration for spoilers, we hope this article has provided you with equally valuable consideration regarding function versus form. We also urge you to keep in mind that the aerodynamic benefits we've described don't always take effect at lower road speeds. (We encourage you to obey speed limit laws.) Should you have any questions on product specifics, we urge you to contact one of our specialists seven days a week.


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