Here is a drag table from Hucho's book showing the effectiveness of the roof-mounted air deflector
Here you can see the actual flow being influenced by the deflector
This image I found online this morning,showing a pickup with deflector
Here's a tow vehicle under crosswind conditions
Here's box truck under crosswind conditions.Notice the leeward jet blasting out from the gap.This can be 16% or so of the drag on a rig.
Here's Hucho showing us the enormous fuel-robbing wake
Like a parachute added to an otherwise 'clean' form
