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I ran into this claim today about detachable car fins, and was wondering if there is any validity to it:

about a five percent reduction in drag and corresponding five percent boost in fuel efficiency. One of the researchers was so excited by the results that he personally drove the report to Evans from L.A., and exclaimed that car companies “kill” for even just a two percent boost in efficiency.

Will adding these objects to a car realize that large a drag/fuel savings?

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I need to research this a bit more (can't right now, sitting in an airport). Oddly enough, there may be some validity to this (although my initial skeptical senses would say they are exaggerating these claims). Thanks for a good question my old friend. –  Larian LeQuella May 14 '12 at 16:17
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It is just one example, but check out aerocivic.com for an example of crazy improvements in fuel economy by just improving aerodynamics. Of course, it also looks silly. :) –  Sam I Am May 16 '12 at 17:56
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The numbers in the article are all over the map. One sentence says 5% savings. Another says a quarter tank less gas used - which means at least 25% savings, depending on how much gas was actually used. Then it also says you can save $6 a tank. That one's pretty subjective, but if we assume 15 gallons as an average tank, and $4 a gallon for gas, that's 1.5 gallons out of 15, or 10% savings. When a single paragraph implies 5%, 10%, and 25% savings for the same device, I become very skeptical. –  Mark Feb 26 '13 at 0:09
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"five percent reduction in drag and corresponding five percent boost in fuel efficiency" already seems like a dubious claim. Fuel efficiency cannot be so directly correlated to drag. –  denten Feb 26 '13 at 3:31
    
@denten: actually that's the least dubious of the claims in this article. Drag growth is quadratic with speed, while rolling resistance grows linear. At high speeds it's practically only the drag that counts. BTW. if companies would "kill" for that, we'd be all driving fugly cars like Prius ;-) –  vartec Mar 8 '13 at 14:50
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1 Answer

The plethora of fuel savings devices that do not work challenges legitimate products to prove their worth. AeroHance offers the science verifying its claim that making one's vehicle more aerodynamic, by strategically adding GasPods, saves fuel.

AeroHance retained the services of the largest engineering services group to conduct computational fluid dynamic studies (simulated wind tunnel tests) documenting the effect of placing a kit of GasPods on a Volkswagen Golf. This car was chosen because it is among the world's most popular car models, with nearly 30 million built. The "TDI" (diesel) is also highly rated for fuel efficiency, raising the savings bar to contemporary standards. These studies showed a 5.2%-6.7% reduction in the car's drag coefficient.

To make the link to real world fuel savings, AeroHance then invited its clients, previously unknown to AeroHance, to participate as Test Team Members to supplement and verify the computational studies. They were asked to log their fuel purchases over a minimum of 4,000 miles of driving, 2,000 baseline, without GasPods, then 2,000 with GasPods strategically placed on their vehicles. Participants from around the World, driving a broad spectrum of vehicle types responded.

The first Volkswagen Golf TDI driver just filed his reports. G.P., Beacon, NY, increased the fuel efficiency of his 2012 Volkswagen Golf TDI by 5.92%, and comments, "I was skeptical at first when my boss, after hearing that I bought a fuel efficient car, sent me a link to the GasPods.com site and stated that maybe I could save even more fuel. I sort of laughed it off but then when I started reading about it and researched turbulators in general I decided to give them a try. I have to admit I was impressed. After purchasing my car I was attempting to break the 50-MPG average consumption threshold for the full tank and I was coming up shy. You can imagine how ecstatic I was when I easily broke that threshold after mounting the GasPods. The important point here is that I was already trying to get the best fuel economy I could before I even heard of GasPods, then after ordering a set and mounting them to my car I actually experienced further improvement. So to me this validates 100% that GasPods made the difference and not modified driving habits.

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I would love to give you the bounty that is about to expire, but this is an unreferenced answer. :( –  Brightblades Mar 14 '13 at 13:27
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