[aerohead]

The only hard data I have comes from an old article,Road &Track,Sep 1982,Trans Am development.The aspirated wheelcover(which would approximate the Insight aluminum wheel),affected the Cd of the Pontiac by 0.003,as compared to a fully closed-off Moon wheelcover.A second article for the Subaru XT yielded a 2.75%drag difference with a vented cover compared to a Moon.That would be hard to measure at the gas pump but might emerge from the signal-to-noise ratio if tested in quick succession,with and without.---------- Since a full wheelcover can better insure clean flow downstream (ie.for a boat-tail) they would be the preferred choice.If no mods are planned for the aft-body,then maybe the aspirated wheel is just fine.