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  • Trailer Aerodynamics

    How Semi-Truck Aerodynamics Work

    Tractor-trailer aerodynamics follow the same concepts as other vehicles, but there are more areas where airflow is interrupted. As the truck moves forward, air catches on specific sections of the vehicle's body, effectively slowing the rig and requiring it to compensate with more power. Rigs already aren't particularly fuel-efficient vehicles, and drag can noticeably increase the amount of fuel a tractor needs to use for travel.


    Four sections cause the most significant amount of drag — the front of the tractor, the gap between the tractor and trailer, the back of the trailer and the underbody and length of the sides of the trailer. Overall aerodynamic loss from these sections is 53%. Among these four areas, there are two distinctive types of drag — namely, pressure and skin friction.


    Pressure drag begins with the front of the tractor. As it travels forward, the impact compresses the air particles. Those particles move to the back of the trailer, where they swirl off the end and create turbulent flow. The pressure becomes imbalanced, as the front surfaces of the truck initiate more than the back, which results in drag.

    Skin friction is less about direct impact. It involves the air particles nearest to the surface of the truck colliding with the outer planes and slowing the rig. While tractor-trailers do experience the effects of skin friction drag, they are very minimal. The weight, size and shape of these trucks make them far more susceptible to and affected by pressure drag.

    As an additional detriment, seasons and climate can increase the effects of aerodynamic drag. In cold conditions, the air surrounding the truck is denser, intensifying the friction and decreasing the fuel efficiency. Also, the faster a vehicle travels, the worse the drag gets.

    But how much does it affect big rig fuel efficiency? More than you may think. When faced with strong air resistance, plus rolling resistance and engine inefficiency, heavy trucks are forced to burn through more diesel fuel. Aerodynamics improvements for tractor-trailers can significantly reduce that waste and improve fuel efficiency, saving money and time on refill stops.


    How Truck Manufacturers Are Dealing With Aerodynamic Drag

    Manufacturers are actively creating new and improved solutions to combat aerodynamic drag. They've released installable solutions that attach to various areas of tractor-trailers and are working to improve the base designs as well. As companies continue to study the effects of aerodynamic drag and find new ways to combat them, the tech will keep evolving.


    The current solutions focus on streamlining the airflow around, over and under the entirety of the tractor-trailer body. Some of them deal with the shape and mechanics of vehicles themselves, but others are attachments that apply to any big rig. However, manufacturers are making a concerted effort to improve aerodynamics on semi-trucks, starting at the base of their upgraded models. Some of the more recent design changes include:


    Tractor design: The shape of the tractor creates pressure drag, making it one of the most significant areas for improvement. Appropriately, most enhancements involve the tractor design, such as antennas, bumper valances, roof fairings and chassis configurations. New models focus on airflow direction, channeling it up, over and around the front of the tractor, so it creates less pressure. Every detail of the tractor matters to air resistance — even the side mirrors, which some companies have designed in an elliptical shape to reduce drag. Tractors with several of these upgraded elements yield a significant improvement in fuel economy.

    Narrowing the gap: One area that gets the most attention is the gap between the tractor and trailer. The wider that space is, the more air resistance a truck will experience. Manufacturers suggest the gap between trailer and tractor shouldn't be more than 30 inches, and have been exploring multiple avenues to solve the gap — including minimizing the space in newer models, shifting the fifth wheel forward, producing cab extender fairings and creating a vertical row of vortices called "airtabs" on the body of the cab.

    Altered bumper shapes: Bumpers can significantly change the direction of airflow, depending on how they're shaped. Multiple companies have focused on designing and installing front bumpers that channel air under and around the tractor, creating a smoother stream. The front end of the cab is the first area to produce drag and cut the air, making it one of the most critical sections of the truck in terms of smooth airflow. An aerodynamic bumper sets the direction for the airflow that will travel over the rest of the truck body.

    6x2 power configuration: The standard highway tractor has a 6x4 power configuration. Installing a 6x2 configuration in its place has consistently provided a boost in mileage — a 2.5% increase, comparatively, with improved fuel mileage.

    Fuel efficiency packages: Some companies offer entire factory-installed packages that target multiple areas on the truck, creating a more streamlined model overall. They can include some or all the above solutions as well as other additions, depending on the manufacturer.

    While updated truck models generally have increased overall fuel efficiency, most operators and fleet managers can't afford to purchase entirely new trucks. However, older vehicles are modifiable — manufacturers produce aftermarket accessories that improve 18-wheeler aerodynamics. These solutions are cost-effective, and even though they won't affect the rig on a mechanical level, they'll have a significant impact on fuel efficiency. Trailer skirts are an example of such after-market modifications.


    Purchase Aerodynamic Solutions From Bud and Tony's Truck Parts

    Semi-aerodynamics is an essential science in the trucking industry. It has such a significant impact on tractor-trailer fuel consumption, power efficiency and general expenses. Failing to acknowledge the real effects of drag can cost operators and fleet managers a large sum of money every year. Even small angles and gaps in the truck body that may seem inconsequential — such as holes in the wheels and bumper shapes — can add up to a substantial loss over time.


    With the right tractor-trailer aerodynamic improvements, you'll benefit from multiple gains. The truck won't need to work as hard to combat the effects of drag — meaning, increased fuel efficiency, fewer gas station stops per trip and the potential for less expensive maintenance. Each of these advantages contributes to lower transportation costs overall, and the better the aerodynamics, the more those expenses shrink.


    If you want to improve your rig with aerodynamic solutions, Bud and Tony's Truck Parts has your back. With a focus on customer service and satisfaction, we'll make sure you have everything you need to make your long haul more cost-effective. We provide reliable additions — including wheel covers, fenders, skirts and vented mud flaps — for the top brands in trucking, such as Kenworth, Peterbilt, Volvo, Mack, Sterling, Western Star and more.