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## Tailgate Flap

Science brain teasers require understanding of the physical or biological world and the laws that govern it.

 Puzzle ID: #23752 Fun: (2.6) Difficulty: (2.31) Category: Science Submitted By: drussel3 Corrected By: boodler

While buying his new pickup truck, Homer the penny pincher was asked if he wanted to purchase a tonneau cover for the bed of his truck. The salesman told him it would improve his gas mileage with better aerodynamics. While Homer was interested in saving gas, he couldn't see paying all that money for the cover, so he declined.

When Homer got home, he considered the flat vertical tailgate at the back of the bed. By removing this tailgate from his pickup, he surmised, he would reduce the air resistance of the truck, thus giving him better gas mileage without having to buy one of those expensive covers.

Did he make the right choice?

(Note: A tonneau cover is a soft or hard cover that is secured down over the open bed of a pickup truck.)

### Answer

The best fuel economy (aerodynamic) solution is to use a tonneau cover. The next choice would be to drive with your tailgate up, and the least desirable choice would be to drop, or remove your tailgate. Read on below for the explanation.

Logic would leave you to believe that by lowering or removing the tailgate, you would improve the air flow over your pickup truck. But with aerodynamics, logic is not always correct.

Removing or lowering of a tailgate actually increases its aerodynamic drag, and increases its lift. Both of which will decrease its fuel economy. What happens is, air in the bed of the truck will slowly swirl around in the bed of the truck, creating a pillow or bubble of air. The approaching air over the top of the cab will then flow easier over this swirling bubble of air. Thus you would have a more aerodynamic flow over the vehicle.

According to an SAE (Society of Automotive Engineers) paper, the average impact on a truck, based on a vehicle lifetime of 100,000 miles will be (as compared to a truck with its tailgate up):
> Decrease of 122 gallons of gas with the tailgate off
> Increase of 243 gallons of gas with a tonneau cover.

At today's gas prices (\$2.00), that is a difference of \$730, comparing a covered bed versus removing the tailgate.

So, keep your tailgates up, or better yet, buy a tonneau cover. Those cargo nets don't work either.

Safe driving.

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## Comments

 Ozymandias Jun 17, 2005 You obviously did lots of research for this teaser. Good job! annie9698 Jun 17, 2005 Are you by any chance a tonneau cover salesman?? drussel3 Jun 17, 2005 No salesman, just an automotive engineer. PCDguitar Jun 17, 2005 i liked it good job onlyeeyore Jun 17, 2005 Good stuff! Looking forward to a huge "Safe Driving" series. onlyeeyore Jun 17, 2005 Good stuff! Looking forward to a huge "Safe Driving" series. sassy_101 Jun 17, 2005 no offense or anything but who cares? amn22492 Jun 17, 2005 That was very good! curtiss82 Jun 18, 2005 Did anybody notice that you only save 243 gallons or \$486 over 100,000 miles when using the tonneau cover. I use to have a tonneau cover, I can't remember the exact price, but I'm pretty sure it was more than \$500. Searching the internet, I see that some are between \$700-\$800. Thus the tonneau cover is not economical. Even if the cover was around \$486, your better off investing the money and getting a greater rate of return over the life of the vehicle from the interest you earn. My pickup (an F-150) use to get about 14 mpg on the highway (without the cover), doing the math of saving 243 over 100000 miles, that only increases my fuel economy to 14.5 mpg, which is fairly insignificant since the change is less than the variance I seen when checking my fuel economy after every time I filled up. madleon Jun 18, 2005 wow that will get ya thinking good teaser Tammy93 Jun 18, 2005 Very Interesting. drussel3 Jun 20, 2005 The main point of the teaser was to dispell the myth, that the tailgate up is the better option vs. the tailgate down. Tonneau covers are just an added bonus (Fuel Economy speaking). Keep in mind, you get many added bonus' of a tonneau cover, security of storage, things don't get blown around, etc. Fasil Jun 24, 2005 I see what you are saying and agree that it might have some validity. What about the weight of the tailgate though? All in all drag is not a large factor in gas milage. I don't know how much the weight affects the milage, but I would assume weight has more of an impact than drag (more so in the city, and not on the racetrack). So it's still feasible that removing the tailgate could improve mileage more than using the cover. I would like to see this on mith busters. They did it with the airconditioner. puppygirl1213 Jun 29, 2005 You obviously did a lot of reaserch do you have any reaserch suggestions. mxclint68 Jun 30, 2005 Good teaser...information in an easily read format.....I knew the answer, but many will not believe it...the difference the cover makes may be small, but if gas keeps going up (any bets it doesn't?) the difference could become more significant, plus you could make one yourself for very little....just a thought.... mat3 Jul 17, 2005 I had no idea. You had me completely fooled loveshellylove Aug 05, 2005 I enjoyed it. I did'nt know the answer, but I love information. Your answer was wonderful. PatH Nov 19, 2005 Looks like you got your wish, they just tested the tailgate myth on MythBusters (the tonneau cover was not tested). It was made clear, however, that tailgate up is better than tailgate down for gas mileage. rkaaland Dec 10, 2005 Awesome!!! I drive pick-ups quite a bit. I thought the myth was right but through your explaination I have learned something that makes complete sense!!! Thank You Warrior_Poet Jan 12, 2006 Good one, though I thought most people knew that... guess I should learn not to overestimate people. zonarita Jul 30, 2006 My kids all have their tailgate up! We had to reargue this one.

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