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Old 04-06-2012, 02:07 PM   #101 (permalink)
Sven7
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Join Date: Aug 2011
Location: Warren, MI
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Boo Radley - '65 Ford F100
90 day: 13.28 mpg (US)
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I'm going to wager it's increasing drag. The air wouldn't be separating from the roof surface that early, and the spoiler actually ramps up instead of tapering down.

Find someone who owns one without the spoiler, do a tuft test, and see if the air is separating before or after the place where the spoiler is. If it's afterward, the spoiler's probably hurting your FE.

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