But even on track day, lower air resistance will help to get higher speeds and it is bit like putting more power to engine, so I would not say that aero work would be wasted effort. Speeds nearing 100mph, then lower cd starts really working.
Recently I had to overtake one unreliable driver, first overtaking after aeromodding my car, I did overtake as before, however car did pick up more speed, so that I was doing 10 more than normally, at higher speeds even small mods seem to help much.
Of course with competition regulations one can easily do things that are wasted effort, but there is quite often modified class which would make racing possible with mods.
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