Camper Shell Impact on MPG

[Master Blaster]

Adding the front angle in a vacuum area above the cab is probably doing nothing. The majority of your drag is probably coming from the enlarged eddy currents behind the vehicle. Maybe add some slightly-angled sheets to the back top and sides behind the tailgate, moving the eddy currents further back. Getting the eddy currents away from touching the body should make a noticeable difference.

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[Gomav]

Adding the front angle in a vacuum area above the cab is probably doing nothing. The majority of your drag is probably coming from the enlarged eddy currents behind the vehicle. Maybe add some slightly-angled sheets to the back top and sides behind the tailgate, moving the eddy currents further back. Getting the eddy currents away from touching the body should make a noticeable difference.

You are correct. My latest development is adding a box to the rear door. Both simulation and road tests confirmed the effectiveness. Before, MPG loss was about 5-8, now about 0-4 (depending on wind). The height of the cap makes no difference though, from 20" to 16".