I saw in a video that wind tunnel existed in early versions of the game, but i feel that now it is very necesary, the drag number may tell you your air resistance, but the wind tunnel tells you where the air flows, as some players as me design performance airplanes and cars based purely on drag and airflow, we need to know how the air passes through our vehicles in order to improve them.
I hope you devs re-activate this awesome feature.
https://www.youtube.com/watch?v=clglambOTHA