I was scanning the Model 3 thread More efficient to open a window or use the A/C ? about whether it's better to use the AC or open the windows, and started wondering what the impact is of driving a Roadster with the top off. I understand that around town, there is no aerodynamic effect. But what about at freeway speeds? I presume there will be an impact, but how much? Would it matter if the windows were up or down, with the top off?