Tractor Gap Devices

The gap between the tractor and trailer has long been a point of known challenges for optimizing aerodynamics.  New solutions are now appearing in the marketplace that are significantly different from past ideas.

Tractor-to-trailer gap closure efforts started with cab extenders, sleeper extenders and most recently added sleeper top extenders to the cab.  Devices for the front of the trailer have been around for years.  Recently new devices have entered the market to deploy at speed to close the gap and then retract as vehicle speed decreases.


Early feedback shows that savings could be as high as 4 to 5% depending on your equipment, weather conditions, time spent deployed and other factors.

Less fuel burned means less engine emissions and less engine wear.

With many fleets having 3 or more trailers for every tractor, implementing solutions on the tractor are more advantageous and affordable than adding devices to the trailers.

Handling and steering become easier if there is no wind buffeting of the trailer.

Use of these systems may allow fleet to run shorter extenders and avoid the cost of damaged extenders.


These systems add at least a minor amount of weight to the vehicle

The system adds electronic controls in addition to the physical components

It isn’t hard to find a tractor with damaged cab extenders so protecting these devices from damage is a challenge unless designed to stay out of the trailer swing path.

Tractor Aerodynamics


  • 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.

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.


AeroWall Dynamics

TruckLabs (formerly Xstream)