[AxelPaulsenJr]

Does a convertible with the top down have the same or greater drag than a car with all four windows down?

[Dinsdale]

I'd have to guess. But it would depend on the details of the car design (assuming you mean to compare apples to apples). Do you get better milage with the top up or down?

At highway speeds it is usually more efficent to run the AC vs opening the windows.

But top down is more fun/gallon.