improve aero by making underside smoother

BMW i3 Forum

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Aug 7, 2017
The i3 is not as smooth as you would expect underneath.
Most notable is the big space where the engine would be if my BEV were are REX.
If this space had was covered, I wonder how much more efficient the car would be at highway speeds.
The triangular opening just behind the battery pack was first noticed in 2014 and discussed by i3 owners. As much work as BMW put into lowering the i3's aerodynamic drag, it was difficult to imagine why BMW would leave this opening, especially in a BEV, if it didn't serve a purpose and if it really increased aerodynamic drag significantly. No one could explain the purpose of this opening (transaxle cooling?), and as far as I know, no one covered this opening and reported the results.

if you decide to cover this opening, please report whether aerodynamic drag is reduced and if overheating of the transaxle occurs in hot weather.
I assume the Wokeby trunk extension somehow covers the void. Has anyone with trunk extension seen a change in efficiency?
No. The Wokeby tapers down to the dimensions of the foam block that houses the inflator and tow hook. Pretty small compared to the overall size of the opening. There's still plenty of open area in that cavity.

A simple experiment might be a piece of yarn and a GoPro to check for airflow at highway speeds.