Feature Article: The Dynamics of Aero

Max Kdvera | December 01, 2009
Truck manufacturers use computers to stimulate how air circulates across surfaces of a model before prototypes are built.


If you want to know whether aerodynamic devices help fuel economy, ask Greg Decker, an owner-operator based in Calgary, Alberta. He’s installed aerodynamic equipment on his 2008 Volvo 780 tractor and 2002 Utility 3000R refrigerated trailer.

Decker, who has meticulously tracked his fuel performance after every tankful for seven years, says his commitment has made a difference. From Aug. 4 to Sept. 30, 2008, he got 6.05 miles per gallon. During the same period this year, his mpg was 6.81. He credits the Windyne Flex Fairings he had installed on his trailer this past summer.

Decker, leased to Caneda Transport, says he previously added aerodynamic mud flaps and airflow tabs to improve handling and curtail road spray, as well as get better fuel economy. “If there were other ways to improve, I would try,” he says.

A combination of higher fuel prices and equipment-altering regulations has the potential of changing how and where truckers will operate. Regulations planned by the California Air Resources Board will eventually require aerodynamic technologies, as well as low-rolling resistance tires, for all trailers that run in the state. All of this stands to change the intensity of owner-operators’ focus on their rigs’ aerodynamics.

Truck aerodynamics got little notice until the oil embargo in the early 1970s led to shortages and sharply higher fuel prices. In 1974 a federally funded study examined wind drag on a cabover with a 45-foot trailer and five add-on devices. Interest waned, however, as oil prices declined.

Beginning in the mid-1980s, truck manufacturers introduced more aerodynamically styled models. Most owner-operators, however, remained loyal to their boxy-hooded vehicles as fuel prices stayed low. More aerodynamic truck models emerged in the 1990s and the first of the trailer components designed to redirect airflow soon followed.

But cheap fuel kept demand weak for the trailer devices, at least until the 2008 summer. “At $1.25 fuel, who wants to save a percent or two [on fuel economy] and spend a couple thousand dollars and have maintenance issues of these things getting banged up?” says Bob Tichelman, president and CEO of Windyne, the maker of sliding trailer fairings used by Decker. “With fuel hitting $5, everybody woke up to the fact that 2 percent of $5 fuel is something.”

Tractor tactics

Smoke stream shows how air flows around a Freightliner truck at Daimler Trucks North America's wind tunnel.

To take advantage of the heightened aerodynamic engineering of the past decade or so, your best move is spec’ing an aerodynamically styled model when you buy new or finding a used aero model.

In designing an aerodynamic model, the primary goal is to reduce air drag around the front, through the radiator and along the sides and roof. Likewise, engineers strive to provide air a smooth transition to the trailer, says Keith Harrington, product marketing manager for Freightliner.

“When you make changes to parts of the truck, it affects the rest of the truck downstream,” says Andy Zehnder, on-highway marketing manager at Kenworth. “When you tweak a bumper or change a headlight, how the air interacts with that component can change the overall interaction.”

Greg Decker can flip up the panels of the Windyne Flex Fairings to access the underside of his trailer.
Greg Decker can flip up the panels of the Windyne Flex Fairings to access the underside of his trailer.

As for retrofit items, at the top of the list are full roof fairings and cab side extenders. Jerry Warmkessel, Mack highway products marketing manager, estimates an aerodynamic package of roof fairings and cab extenders on the tractor could generate a fuel mileage improvement of 8percent to 10 percent and cost about $2,500 to $3,500.

  • Bill J

    I have a very unique problem possibly air flow on my 2006 Ford E350 Super Duty with a Rockport 12 box. I get a fluttering noise that is so annoying. I had the front end done tires even the engine is of while moving you still the noise. Sounds exactly like someone if you car opens up a window but not the other side and you get the pressure sound your ears are screaming for you to open up the other window to balance the pressure. That is the sound but opening my windows on my truck does nothing. Can you help? The sound can be heard from 7MPH and up. 19,000 miles great condition. Would mud flaps help?

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