Previously we wrote about LED light bar aerodynamics and specifically studied the effects of an LED bar mounted on the windshield of a truck (a 2014 Ford F150 in this case). We recently received a comment on the article asking about LED bars on a Sport Bar style rack behind the cabin of the truck, so we thought it would make for an interesting comparison.

Side view of air flow over the roof of an f150 pickup truck with an LED bar above the roof behind the cab on a sport bar type mount.
This comparison of flow trajectories of the three difference scenarios shows that the LED bar on top of the windshield creates the most disturbance, this seems to be a very critical point because up till then, the air is still really smooth, and fast. The LED bar behind the cab on a sport bar mount shows similar levels of air disturbance as the scenario without an LED bar, however it does divert some of the airflow down into the bed which generates some more drag, but not as much as one might think due to the relatively smooth flow inside the bed that is able to rejoin the rest of the airflow near the tailgate.

In summary, the LED bar behind the cab on a sport bar mount didn’t effect the drag force as much as I expected. This analysis showed that the fuel efficiency would go down by just 2% (from 18.5mpg, to 18.1 mpg) as a result of this mounting approach, while the windshield mounted LED reduced efficiency by 7% and brought the fuel consumption down to 17.4mpg. Although the fuel efficiency is better with the rear mounting of the LED, you may find that the light pattern may be a bit of a draw back; with the LED that far back, the roof will block all the low light angles, and as a result the setup will illuminate mainly out in the distance rather than right in front of the truck. This is a great mounting location for “laser” light led’s which have a very narrow beam pattern, and would be great to combine with some powerful fog lights in the bumper which would illuminate the trail directly in front of the truck.

If you are curious about specific details of how the analysis is set up, go check out the article linked above. Hope you enjoy the rest of the led light bar aerodynamics analysis below.

First things first, we need to adjust the mesh so it focuses in on the aft portion of the cabin.

FEA Aerodynamics mesh for LED Bar behind truck cab on a Sport Bar
The mesh was adjusted to refine the area around the back of the cab where the LED bar was relocated to
Side view of a pressure cut plot for truck aerodynamics with LED bar behind the cab on a sport bar.
Side view of a pressure cut plot for truck aerodynamics with LED bar behind the cab on a sport bar. The LED bar does create a bit more of a low pressure zone behind the cab.
Isometric view of a pressure cut plot for truck aerodynamics with LED bar behind the cab
Isometric view of a pressure cut plot for truck aerodynamics with LED bar behind the cab on a sport bar.
Isometric view of air flow over the roof of an f150 pickup truck with an LED bar above the roof behind the cab on a sport bar type mount
Isometric view of air flow over the roof of an f150 pickup truck with an LED bar above the roof behind the cab on a sport bar type mount.
Side view of air flow over the roof of an f150 pickup truck with an LED bar above the roof behind the cab on a sport bar type mount.
As you can see, while the LED bar does introduce some disturbance, it diverts some of the airflow down, which actually makes the scenario not quite so bad as it allows the lower airflow rejoin the upper flow somewhat smoothly after the tailgate.
Top view of air flow over the roof of an f150 pickup truck with an LED bar above the roof behind the cab on a sport bar type mount.
Top view of air flow showing a bit more of what the air being pushed into the bed is doing.
Side view of air flow over the roof of an f150 pickup truck with an LED bar above the roof behind the cab on a sport bar type mount.
Closer view of the airflow that makes its way into the bed of the truck as a result of the LED bar. The vorticity is relatively low so the airflow stays somewhat smooth as it rejoins the rest of the flow.
Side view vorticity plot of the roof of an f150 pickup truck with an LED bar above the roof behind the cab on a sport bar type mount.
This side cut plot of the air vorticity shows that the LED bar behind the cab does generate some disturbance which seems to affect the region above the back of the cab