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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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