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      11-04-2012, 08:45 PM   #13
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Drives: M3 (E90)
Join Date: Feb 2012
Location: San Francisco

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BMW actually puts real engineering work/R&D/wind-tunnel tests these add-ons prior to marketing. For this and the front splitters, BMW claims that there is additional downforce generated (per original press releases). While probably not noticeable especially at legal speeds, a even a few lbs of downforce or lift reduction is a win, plus you can't beat the OEM quality/looks that you want to retain with a $65+k car.