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"Mythbusters" test tailgate fuel efficiencyMany people believe the fuel efficiency of a pickup truck can be improvedby driving with the tailgate down. The Discovery Channel's "Mythbusters"put it to the test in a recent episode. Driving twin pickups simultaneouslyunder identical conditions, they found the truck with its tailgate uptraveled 30 miles further on a tank of gas than did the truck with itstailgate down. Speaking to truck designers, they found out why. Host JamieHyneman explained, "There's a circular pillow of air that forms behind thecab of the truck when the tailgate is up, known as a 'separated bubble' or'locked-vortex flow'." Using a model, they demonstrated how air rotatesslowly directly behind the cab, seemingly untouched by the high-speed airpassing by. "That nice circular motion of slow-moving air is keepingfast-moving air from contacting the truck," added host Adam Savage. "It'smaking it move right over the truck. When you move the tailgate down, itbreaks down that bubble, and the fast-moving air gets caught and broughtinto the bed of the pickup, producing drag." See for yourself when theepisode repeats at 10 p.m. Sunday.

A few years back, GM built a pick-up for speed trials testing on the Bonneville salt flats. Their best results were with a half tonneau cover. The vortex created actually helped push the truck, achieving a higher top speed. I'm sure MadBill could elaborate on the story with a lot more techno babble. Hey Bro, are you there?

I watched that episode, pretty interesting actually. With tailgate down, the truck ran out of fuel sooner.

Yep, saw it too, and I always thought when i had my truck that you were supposed to get better mileage with the gate down! Imagine all the money I could have wasted! I got an ARE LSII tonneau top shortly after I bought it though.

So what about with a tonneau cover? Is that better than no cover with tailgate up?

I saw that show. It was very interesting.

Quote, originally posted by AndyLT1 »So what about with a tonneau cover? Is that better than no cover with tailgate up?Hard to say, they didn't go that far, but I would imagine it would break up that vortex, but seems like it would make it more like a race-truck at that point. Don't know.

I haven't seen that episode yet, but I love that show. I actually heard about this some where else though. Think about the companies that manufactured the netting that replaced the tailgates. If I recall, didn't they claim the net reduced drag and increase mileage? I wonder if they ever did any testing or just assumed it would and could be a good sales pitch.

when i had my S-10 ZR-2 i did real world tests with tail gate up, down with and with out toneau...the best was tail up and toneau cover. Though the results were all very close to not make all that much deference! maybe 1-2 mpg difference at most.

Mythbusters does some cool stuff. Like finger in a shotgun barrel, that was funny. Or the driveshaft spinning off a rear wheel drive car and catching on a pot hole causing a pole valting effect.

Road & Track published some windtunnel stuff on the same topic a few months ago. They got the same results: better with the tailgate up.