Quote:
Originally Posted by sdecoman
With the spoiler on, if the road or street is wet, that back window becomes totally unusable within seconds. It happens each and every time whether it is windy or not.
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That's normal and good, as far as reducing drag goes. Bad, as far as rear visibility is concerned.
A "not sharp enough" transition from the roof to rear surface can both increase drag and lift, which is why the trailing edge of nearly every hatchback roof is "sharp" or has a small extension spoiler like yours did.
Same applies to the trunks of most sedans: transitions are getting sharper and sharper (either in the sheet metal, or with lip spoilers added) to promote a clean separation point and smaller/better organized wake behind the vehicle.
Testing is always a good idea, but that spoiler is a relatively small change that may or may not show up in repeated coast-down tests.