Fuel Savings Guide

How Better Aerodynamics Lead to Fuel Savings

Side skirts, boat tails and other devices reduce wind resistance, but how much can they save your trucking fleet on fuel?

Improving the aerodynamics of tractor-trailers has become a big issue in recent years. This is because heavy trucks burn a lot of diesel as they push up against air resistance. When an 18-wheeler travels on the highway, more than 50% of its fuel use goes toward reducing aerodynamic “drag.”

Cutting the drag on trucks will also cut down fuel consumption. Lawrence Livermore National Laboratory in California is studying ways to improve the fuel economy of tractor-trailers. In 2017, the lab and truck manufacturer Navistar designed a SuperTruck prototype that gets 13 miles per gallon and has 104% improved fuel efficiency. Nearly half of the truck’s fuel consumption improvements come from aerodynamic enhancements.

Lawrence Livermore researchers believe that aerodynamics developed in its partnership with Navistar could save the trucking industry 21 billion gallons of diesel fuel per year.

Streamlining Your Fleet

What this means for your fleet is that adding the right aerodynamic devices can generate significant savings at the pump. Not all devices are equal in making the air smoother around a Class 8 rig as it barrels down the interstate. It is important to know what improvements reduce the most drag—and save the most fuel.

Four areas create the most aerodynamic drag on a tractor-trailer: the front of the tractor, the gap between the tractor and the trailer, the under-body of the trailer and the back of the trailer. Trucking companies added streamlined shields to the tops of truck cabs to save on gas after the oil embargos of the 1970s. In recent years, “side skirts” that reduce the air flow under trailers have become a common sight on the highway. Some trucking companies are now experimenting with devices that cut drag in the tractor-trailer gap and in the rear of the trailer.

Proven Methods

Here are the most effective steps you can take to make your trucks more aerodynamic and fuel efficient, according to industry experts:
  • Narrow the Gap. Research shows that a gap of 18 inches or more between the tractor and trailer could lead to increased air resistance. Devices that completely cover the gap can reduce aerodynamic drag by as much as 6%. Several gap-fairing products on the market advertise fuel savings of 2% by narrowing the gap.
  • “Skirt” the Issue. Many trucking companies have adopted side skirts. By reducing the air underneath trailers, fuel savings of between 4% and 7% have been reported by side skirt manufacturers.
  • Reduce Tail Winds. Wind tunnel and road tests show that adding a 24- to 32-inch “boat tail” can reduce turbulence behind a trailer’s square rear end. According to manufacturers, boat tails can save more than 6% on fuel for tractor-trailers traveling at 65 miles per hour.

Other devices like wheel covers, slotted mud flaps and vortex generators lead to modest reductions in drag. These improvements alone do not lead to significant fuel savings.

A Cumulative Effect

Aerodynamic modifications add up to significant fuel savings when they are implemented together. Fleet owners who install gap fairings, side skirts and boat tails on their trucks can increase their fuel efficiency by 14% or more, according to industry sources. The cost of adding these devices is quickly offset by savings at the pump. A company that spends $1 million each year on fuel, for example, could expect to save more than $140,000 a year.

Trucks of the Future

Tesla created waves in 2017 with the unveiling of its electric semi-truck. However, the Tesla Semi won’t go into production until 2019. At a minimum cost of $150,000 per truck, the electric truck will be too pricey for all but the largest trucking fleets.

Fortunately, fleet owners can take advantage of newer truck models that are much less expensive and cut down significantly on fuel consumption. New highway tractors that have 6x2 power configurations—as opposed to the standard 6x4 configuration—have consistently shown a 2.5% increase in miles per gallon. At a time when most tractor-trailers on the road average about 6 miles per gallon, some new trucks now achieve 9 mpg or slightly more. Truck and engine manufacturers continue to develop more streamlined models. Peterbilt and Cummins for example, are collaborating in the U.S. Department of Energy’s SuperTruck II initiative in an effort to meet future emissions standards and increase fuel efficiency.

In the years before electronic and self-driving vehicles become a significant share of the market, the next wave of streamlined semi-trucks could save fleets tens of thousands of dollars in fuel spending.

Sources: The New York Times, Lawrence Livermore National Laboratory, U.S. Environmental Protection Agency, Transport Canada, Walmart, Airflow Truck Co., Peterbilt Motors Co., Cummings Inc.