Cheating the Wind With Pickups - Car and Driver Magazine

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 CD were measurable, though not profound. For instance, with a 2002 F**d F-150 Crewcab, its tailgate-up CD was measured at 0.5304. Tailgate down, it was 0.5425; tailgate off, 0.5596.

Indeed, there was one case, a 2001 F**d F-150 standard cab, where lowering the tailgate actually improved CD, 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.

 

This is very interesting and helps supports the conclusion that I had already come to several years ago. On a vacation trip, I tested my gas mileage: with the tailgate up and with the tailgate down. I never really believed any of it, but gave the benefit of doubt to what people were saying.

Sure enough, during my 1800 mile roundtrip, not one spec of difference in gas mileage.

Even with the tonneau cover, you still get that wake behind the cab, that they talk about. You can see this effect, when the truck is wet, by the water pattern that is left on top of cover.

Interesting article.

 

So the covers will help some then thats good.

 

That's all fine and good, but the reason most guys take them off at the track is for weight. Keep in mind this also. Those numbers are fractional at best. Adding a bed cover may help drag, but will add to the weight. This probably negates any effect that the lessened drag will help in racing. Now open road driving is a different matter. Best thing to do...fabricate an aluminum cover for the track.

 

Get a soft cover that fits between the bed rails and take the tailgate off.

 

I got a soft cover on mine and seen a definite improvement in gas mileage over 70 on the hiway of I think 1.5MPG !!! Thats alot if you ask me. 17MPG to 18.5MPG...Zed

P.S. I noticed on the ECSB and ECLB that the aerodynamics are different than on my RCSB by noticing where the air hits the cover on all three trucks. On mine the air pushes down the most after the last bow right before the tailgate. And on the others it was in the middle of the bed. By having the cover on it it deflects the air off right before it catches the tailgate. That is my observation...Zed

 

I have done my own tests and have found that I have knocked .2 off of my quarter mile times by JUST taking the tailgate off. I dont believe that .01 of drag is really going to hurt your quarter mile times. I believe less weight would still be quicker in my opinion.

 

A few guys with 4x4 have found it better to take off the gate because the weight you lose is better than the aerodynamics you gain. In my experience I need to leave the gate and my hard tonneau on just to get half decent 60' times.

 

yep the tail gate comes off because of the wieght issue, and not for aerodynamics..

 

yes.. the weight is an issue in drag racing, but then you are loosing the weight in the rear of the truck, where you need traction the most... but i have heard that taking it off helps due to less overall weight and better times.

good article though, I know that leaving the gate up or down doesn't really affect gas mileage.