Kenworth T680 Aerodynamic Drag Yellow

Increasing Efficiency by Optimizing Truck Drag

For semi-trucks traveling at 55 mph or greater, aerodynamic drag is the largest contributor of fuel consumption. Aerodynamic drag is responsible for 21 percent of a line haul vehicle’s fuel consumption.The faster a truck moves, the harder it is to overcome aerodynamic drag. As the road speed increases, so does the percentage of aerodynamic drag and the horsepower needed to overcome it. Three things to consider:

Account for Variables

Calculating fuel savings accurately can be difficult when considering variable factors, including the environment. For example, a 5 mph crosswind can reduce fuel economy by up to 10 percent when turbulent air is forced under the cab, chassis and through the trailer gap. To mitigate these factors, consider options that reduce turbulence and smooth out air flow, including a reduced trailer gap, fairing extenders and cab to chassis closeout panels.

Another example of environment impact is temperature. For every 10 degree drop in temperature, aerodynamic drag is increased by 2 percent. Altitude can also reduce aerodynamic drag as well as engine efficiency. Wind, temperature and climate variables impact aerodynamics on a daily basis. Keeping this information in mind, you can account for variability and set realistic expectations on the type of fuel economy numbers you’re likely to see.

Good Rules of Thumb

Rule #1
  • Each mph above the road speed of 55 mph is 1/10 of a loss in miles per gallon. Reducing a truck’s speed by 10 mph could save a customer $12,000 annually if the vehicle is driven 120,000 miles per year. Significant savings are reached by decreasing overall road speed of a vehicle.
Rule #2
  • Every 2 percent reduction in aerodynamic drag results in a 1 percent improvement in fuel economy. Adding aerodynamic enhancements to a truck reduces the power required to move the vehicle. 

The relationship between speed and its effects on aerodynamics demonstrates the benefits in spec’ing a vehicle with aerodynamic enhancements, versus without them, especially at even higher speeds.

Kenworth T680 Interior

Additional Aerodynamic Options

T680 Advantage package vs. standard T680 2.5%
Chassis fairings 2-4%
Day cab fairing deflector vs. non with van trailer 18%
Full-height integrated roof vs. mid-roof with van trailer 18%
Mid-height integrated roof vs. full height with flat bed  3-5%
Under-hood air cleaners vs. cowl mounted 1%
Side extenders  2%
Aero mirrors vs. west coast mirrors 1%
Wheel covers 1%
Trailer skirts and trailer tail 8-12%

*Percentages are not cumulative

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