I'm sure this has probably been asked before & I just can't find a thread in search, but here it goes:
Is the S2000 more aerodynamically efficient with the top up or top down (top down is assuming the cover is in place)?
I would normally assume top-up, but after driving in a light rain with the top down and watching how the drops traveled differently, I'm not so sure.
Enlighten me please

 

Top up makes a huge difference, reducing drag and making the car substantially faster. The coefficient of drag is poor with the top up, but horrible with it down, demonstrated with faster straight speeds at the track when you sit in the shade.

 

And I understand there is even less drag with the optional hardtop installed.