As for the Volvo link : only the C30 Drive / coupe version got the belly panels, not the rest of the range.
From personal experience, I doubt very much the - awfully heavy - aerodynamic wheels ever helped its mileage much.
The Hyundai underside shot is bogus, showing the flow to be nicely lengthwise underneath.
It gets pushed out sideways.
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Strayed to the Dark Diesel Side
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