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