Pickups aren't exactly R&T's cuppa tea, but certainly a lot of people own them. Each year, the Ford F Series and Chevrolet Silverado vie for the title of best-selling vehicle in the U.S. Hence I see the following as a public service, as well as a neat technical tidbit.

Investigators at the National Research Council of Canada have determined that pickup truck aerodynamics is generally degraded — not improved — by the often-seen practice of lowering or removing the tailgate. Drag is generally greater and, to the detriment of yaw stability, rear lift can be increased by as much as 60 percent. Popular mesh tailgates worsen aerodynamics of these vehicles as well.

The researchers measured drag, lift and yaw behavior of pickup trucks in the same wind tunnel where, years ago, we evaluated Champ-car aerodynamics ("Putting the CART Before the Wind," June 1984). They also performed Computational Flow Dynamics analyses of two simplified pickup shapes. These CFD results agreed with their tunnel findings.


The differences in C<SUB>D</SUB> were measurable, though not profound. For instance, with a 2002 Ford F-150 Crewcab, its tailgate-up C<SUB>D</SUB> was measured at 0.5304. Tailgate down, it was 0.5425; tailgate off, 0.5596.

Indeed, there was one case, a 2001 Ford F-150 standard cab, where lowering the tailgate actually improved C<SUB>D</SUB>, albeit insignificantly, from 0.5230 to 0.5215. (And, yes, pickup trucks are bricks aerodynamically.)

In their report (SAE Paper No. 2004-01-1146), the researchers discussed underlying reasons for the phenomena. In general, there's a wake immediately behind any pickup cab, and this suction is greater without a tailgate in place. True, presence of a tailgate adds a small drag increment; but the cab wake predominates.

A partial tonneau cover helped, lowering the extended-cab F-150's 0.5304 to 0.5072. A full tonneau cover was better, dropping the standard-cab F-150's 0.5230 to 0.4967.