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Semi Truck Aerodynamics & Fuel Economy

2010 prostar exterior

How Do Semi-Truck Aerodynamics Affect Fuel Economy?

Whether you drive a used truck or own a fleet, chances are you’re looking for ways to maximize fuel economy. Besides choosing an efficient engine, one of the easiest ways to improve fuel efficiency is to reduce drag by making the vehicle more aerodynamic. When you do a fuel economy side by side comparison with a truck that is less aerodynamic, the differences are too great to ignore. International Used Truck Centers has some suggestions for aerodynamic enhancements that’ll save you thousands per year on fuel fill-ups.

Basic Aerodynamics of Trucks

Aerodynamic drag is the force that opposes an object’s motion. When a vehicle — no matter the size — is designed to allow air to move fluidly over its body, aerodynamic drag will have less of an impact on its performance and fuel economy. Heavy trucks burn a significant amount of fuel as they power through air resistance. In fact, more than 50% of an 18-wheeler’s fuel is spent reducing aerodynamic drag on the highways.

Aerodynamic Semi-Truck Design Features

International trucks are designed with aerodynamics in mind, so you don’t have to spend a considerable amount of time and money on parts and accessories to help make your semi-truck more efficient. The ProStar, for example, boasts smooth radius edges and a sloped hood that not only make it look more streamlined but improve semi-truck aerodynamics.

And that’s not all. Its A-pillar design and windshield radius were developed after extensive wind tunnel testing, while the cab-to-sleeper and cab extenders cut down turbulence. Set-back front axles simplify loading while creating an airflow region along the front wheels, allowing the air from the engine compartment to travel through the front grille.

Drive Fenders

The front fender is at the forefront of your truck’s battle against wind resistance. Installing a more aerodynamic fender will reduce drag while boosting your vehicle’s top speed and fuel efficiency.

Chassis Skirts

Chassis skirts reduce air turbulence near the front fender extensions, battery box, fuel tank, quarter fenders, and frame access steps. You can purchase chassis skirts in different sizes, i.e. cab-length skirts that span the length of the day cab/sleeper cab or full-length skirts that run to the rear wheel.

Side Extenders

You can use side extenders to reduce airflow between the tractor and trailer where there’s often a larger gap. Even if the trailer isn’t at full height, side extenders help keep trailer gaps at a minimum and promote adequate swing clearance.


Panels (or fairings) can be added to exterior areas of your truck like the undercarriage, body, or roof to increase fuel efficiency by as much as 15% percent. Some types of fairings are easy to detach, so you don’t have to work around them while loading or unloading your cargo.

Wheel Covers

With their large middle indentations, bumps, and ridges, most semi-truck wheels aren’t the perfect picture of aerodynamic design—and in fact, air easily gets into their crevices and slows your truck down. With wheel covers, you can close any gaps, saving you a bundle at fuel stations.

Fifth Wheel Placement

Fifth wheel placement is a crucial part of semi-truck aerodynamics. Typically, the trailer gap should be no wider than 36 inches and the fifth wheel — be it sliding or fixed — should be installed so the trailer can swing back and forth without touching the cab, trailer landing legs, or side extenders.

Boat Tails

Installing a boat tail that measures around 24 to 32 inches can decrease turbulence at the rear end of the trailer. Properly installed, boat tails can save you around 6% on fuel if you’re traveling at 65 mph.

Vented Mud Flaps

Simple but effective truck accessories, vented mud flaps allow air to pass through and decrease resistance while catching mud, dirt, etc.

Optimizing Semi-Truck Aerodynamics Through Testing

Engineers at International are always at work trying to build a more aerodynamic semi-truck. To become the industry leader in semi-truck aerodynamics, International leverages different types of testing to understand the true effect of aerodynamic drag in various types of conditions:

Computational Fluid Dynamics (CFD): Engineers use computer modeling to gain insight into airflow under, around, and through the vehicle.

1/8 Scale Wind Tunnel: Designers sculpt and re-sculpt the basic shapes of the vehicle—such as the curvature of the fenders and hood—until the desired combination of appearance and performance is achieved.

Full-Scale Wind Tunnel: Using a complete tractor and trailer, engineers can turn the vehicle 360 degrees to see how it is impacted by crosswinds. This is important because wind direction is random and unpredictable, and the average wind in North America at any given time is 7 mph.

Coast Down: With this test, engineers can get an accurate depiction of conditions out on the open road.

Over the Road Testing: Finally, the vehicle leaves the lab and is tested in real-world conditions. International Trucks engineers are rigorous in performing these tests, ensuring the same conditions between tests and removing as many variables as possible. What’s more, the testing process is governed either by SAE Type II or TMC Type IV, which regulate every element—from test vehicle mileage, vehicle drivers, trailers, routes, and more.

Learn More About Truck Maintenance with International Used Truck Centers

Tires are just as important to fuel economy as semi-truck aerodynamics! Check out our semi-truck tire selection and maintenance guide for more information on choosing the best tires for your truck and application. If you have any questions about semi-truck aerodynamics or want to learn more about some of the most fuel-efficient used trucks we have for sale, all you have to do is let us know!

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International Used Truck Centers 41.776180, -88.200918.