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Old 05-23-2011, 05:03 PM   #9 (permalink)
lunarhighway
Master EcoModder
 
Join Date: Feb 2008
Location: belgium
Posts: 663

vectra a - '95 Opel Vectra GLS
90 day: 37.51 mpg (US)
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Quote:
I added an air dam to my VW diesel. My mileage has dropped a mpg over two tanks. I blame the increased frontal area. I am taking it back off.
most air dams that go all the way down like on nascar racers allow the air to escape over the car, but on this setup it seems like the air can only go round the car, and that's gonna add to the wake at the sides. (the front tires add a lot of turbulent flow, so this path is likely aerodynamically even less favorable than the underside)

what you want is full height dams in front of the tires but a raised dam in the center, sending a little air under the car that would otherwise have to take a route of even more resistance.
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