What is the plastic under the bumper called? It’s an air dam, front splitter, front lip spoiler, or front valance. Air dams are cool looking. Getting popular in truck commercials shot in California during the summer everybody wanted one. But looks aren’t everything. They do provide a function as well.

Who knew! But specifically, what does an air dam do on a truck and are they absolutely necessary? They are not as popular as they once were, though, they still can add to your truck’s function and styling.

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What Does An Air Dam Do On A Truck?

An air dam is a front spoiler that is designed to press the nose of your vehicle down to maximize traction. The valance does the same thing as a rear spoiler. It is positioned to move air around the vehicle to increase performance. They can even move air to the engine bay to improve engine cooling in certain models.What Does An Air Dam Do On A Truck

Of course, this effect is only achieved at higher speeds. If you never drive your car more than 80 mph (129 kph) then the air dam is purely for looks. Which isn’t a bad thing. They can add a missing piece to your car and get you laid in the process. Win-win baby.

What Is A Front Lip Spoiler?

For cars, a front lip spoiler is also a front valance or air dam. A front lip spoiler is a term used more commonly with on-road cars. They essentially do the same thing, deflect air in a controlled way to increase the downward force on the front of the car to increase traction, control, and acceleration while turning your vehicle.

Cheaper front spoilers are made of plastics while more expensive (and VERY expensive ones) spoilers are made of fiberglass or carbon fiber. These are more for aesthetics because under 60-100 MPH (100-160KPH) the effect is minimal. Around these speeds, the amount of air moving over the front lip spoiler is enough to notice a difference.

Like with flight, an airplane needs to reach a certain speed to be able to have enough air under its wings to achieve flight. The same thing with spoilers.What Does An Air Dam Do On A Truck

Next time you are driving in a car as a passenger stick your hand out the window while accelerating. You will notice that at a stop or low speeds there is almost no resistance. Then as you accelerate you have to hold your hand forward.

If you hold your hand flat you can even move the front edge of your hand up and down and at a certain speed, the wind itself will automatically move your hand up or down with little effort on your part.

Science!

How Do You Create More Downforce?

You can create more downforce by adding body kits to increase the downward force throughout the vehicle and lower the vehicle as well.

Does downforce increase speed? Yes, it does. It provides more traction and better use of the passing air around the vehicle which can be lost going under the car and decreasing downforce and traction i.e. control over your vehicle.

The increased downforce enables the tires to maintain a better grip going into and out of corners giving you more control and faster cornering. In the straightaways, increased drag will reduce overall speed, though it is a common trade-off with race cars to seek a balance of control and performance.

To get a basic understanding compare the following two illustrations to see the way air moves with and without air diffusers:

What Does An Air Dam Do On A Truck
Source: Build Your Own Race Car!
What Does An Air Dam Do On A Truck
Source: Build Your Own Race Car!

Modern race cars use splitters or diffusers to control the amount of downward force they need on a particular race track. How much downforce does a diffuser make? A diffuser can provide up to 1,000 lbs of downward force depending on speed and setup. Though with more downward force you will achieve better cornering and handling, you will at the same time reduce top speeds.

What Is The Most Aerodynamic Shape In The World?

For practical terms, a teardrop provides the aerodynamic shape.What Does An Air Dam Do On A Truck, What Does An Air Dam Do On A Truck?

A teardrop will encounter resistance and thus, a single thin piece of thread, or for argument’s sake, an atom wide string can move through the air with the least resistance becoming the most aerodynamic shape.

A teardrop has a very low breakpoint where the air is moved as the shape passes. And then the air can smoothly slide past the teardrop with its long curving sides and sharp endpoint minimizing any turbulence or “eddy currents” created as a result.

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Why Does Streamlining Reduce Drag?

Streamlining is the smoothing of an object to create as little disturbance to the passing as possible. An egg compared to crumpled pieces of paper with the same weight, is streamlined. With its natural curves and sharper endpoints, it will fall faster than the crumpled up pieces of paper. The paper has lots of ruffled sides that fight and grab the air, thus, increasing drag.

Drag and traction are two opposite fighting forces. With more drag, you can achieve more traction. With less drag, you can maximize gas mileage. So, what does an air dam do on a truck and do you need one? Well with what you know now you can answer with ease.