"Peter Dohm" wrote

IMHO, they vary a great deal, and radically sloped windshields and extended
cabs both influence the size, intensity, and placement of the vortex. The
length of the cab will also influence the width of the vortex and crosswinds
will cause an offset.

OTOH, aerodynamic side mirrors (if available), or the presence or absence of
a front air dam, would probably make much more difference than the position
of the tail gate.

There are a lot of aerodynamic tricks, such as belly pans which can make a
huge difference, that just won't work for owners who really use their
trucks.

The underbody aerodynamics is probably the best thing you can do on a truck, but
like you say, then they couldn't work them.

Someone else said, the way you break the wind is not as important as how you
leave the wind. There is a lot of truth in that, but not completely true. A
truck breaks the wind a lot better than a short nosed van, I'll bet.

Still, I think all the above stuff you mentioned is mainly there for styling.
Sure, it helps a little, but to what degree would a slick looking van improve on
a boxy on from the 70's, say? 2%? 5%?

The vortex still has a chance to form, be it a short bed, long bed, slick cab,
boxy cab. How it is shaped is not all that important. It is still a vortex.
All the trucks still have a straight, square drop-off from the cab to the bed.
The vortex just fills in whatever space is left over.
--
Jim in NC