5TH WHEEL SETTINGS

The fifth wheel works in conjunction with the king pin to connect the tractor to the trailer and determine the gap between the two. Some fleets are limiting the travel of sliding fifth wheels to limit the gap when the trailer is in the most rearward position.

There are a number of options for reducing trailer drive height, which can reduce overall drag through the reduction in the profile of the vehicle. Combinations of tire choices and reduced fifth wheel settings can drop the overall trailer roof height.

The biggest influence on drag is the overall frontal area of the vehicle going through the air. Minimizing the fifth wheel height keeps the trailer lower than it otherwise would be, decreasing drag. This effectively lowers the overall height of the vehicle.

Benefits

Eliminating 8” of gap to the trailer is worth about a 1% improvement in fuel economy

Reduction in vehicle profile leads to drag reduction. Air flow should jump from the tractor to the trailer without entering the gap between the two major parts of the vehicle. This is referred to as “laminar air flow”

Challenges

Driver interaction is needed to make adjustments

If the front of the trailer is dipped down but the rear of the trailer is at its standard height, whatever benefit may have been achieved at the tractor-trailer gap may be lost by increased drag on the roof and the trailer wake area

Tractor Aerodynamics

What Fleets Are Saying

“We continue to update our fleet with more fuel efficient post-2014 U.S. Environmental Protection Agency emission compliant engines, install aerodynamic devices on our tractors, and equip our trailers with trailer blades, which all lead to meaningful improvement in fuel efficiency.” — Knight Transportation

“Appearance and detail of our equipment means a lot to our drivers. Drive wheel fairings don’t just save us money, but our drivers like them too.” — Brad Pinchuk, Hirschbach

“Sleeper tractor aerodynamics have been finely tuned by all OEMs. Eliminating various features can add 10% to a fleet’s fuel expense,” — Chief engineer at a major truck builder.

Decision-Making Tools

The Confidence Matrix has been issued to help fleets make decisions about tractor aerodynamic devices.

Conclusions

  • Fleets should use the standard, optimized aerodynamic packages developed by tractor manufacturers and should not remove aerodynamic options that are included in the base model. Depending on the features removed, fleets will see as much as a 10% decrease in fuel efficiency.
  • Tractor and trailer heights should be matched for as many miles driven as possible as the fuel economy reduction from mismatched heights is in excess of 10%.
  • Fleets operating day cab tractors should pursue greater adoption of tractor aerodynamics than is common today, as many day cabs operate at highway speeds during nearly all of their duty cycle, where aerodynamics can offer as much as 13% gain fuel efficiency. Even day cabs operating in start-stop city driving will see savings from certain aerodynamic technologies.
  • Tractor manufacturers should design and make available aerodynamic features for day cab tractors as the industry migration to shorter hauls will likely result in more day cabs seeing significant highway and interstate miles.
  • Aerodynamics have not been fully developed for all day cab configurations, including natural gas, and the tractor manufacturers should develop and release these components.
  • Alternative fueled vehicles including battery electric and hybrid electric are subjected to the same aerodynamic forces as diesel-powered vehicles. Manufacturers need to keep that in mind as they design these alternative fueled vehicles so they are optimized for aerodynamics. In addition, manufacturers of add-on aerodynamic devices need to begin work on adapting their products so they can be used with alternative-fueled tractor.
  • Future EPA and NHTSA Greenhouse Gas regulations will challenge tractor builders to continue to improve the aerodynamic drag of these vehicles in excess of what has been demonstrated in the Department of Energy SuperTruck I and II programs. OEMs should start planning for this today, as the lead time required to design new models is significant and can be costly.

Manufacturers

  • Fontaine
  • Jost
  • SAF-Holland