Fuji researched wheel cover drag with respect to their Subaru XT.
*The ventilated flat disc,when taped closed,revealed a delta Cd 0.002,for an overall drag reduction of 0.69% (and no brake cooling).
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John Shinella,of Pontiac styling, researched wheel cover drag in the Lockheed Marietta wind tunnel during development of the Trans Am Firebird of 1982.
*The car,@ Cd 0.32,with no covers
*with ventilated flat discs dropped to Cd 0.296
*TAPING over the vents produced Cd 0.290
*Shinella's ventilated convex covers showed Cd 0.287
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So,taping was good for delta Cd 0.006,which cut overall drag by 2.02% (a 1% increase in mpg @ 55-60 mph).
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The difference between no wheel covers,and Shinella's covers is a 10.31% overall drag reduction.(5% MPG @ 55-60 mph).
A set of MOONs would come in at a little lower drag and mpg increase.
