I have not raced since before the patch, but I will be very soon.
Before the patch, I simply used the time trial setup, by pushing the gears up two or three notches, and sometimes dropping the wing one or two notches.
Usually did the trick and give me a competitive car, winning is easy so long as you can avoid the cheaters who purposely crash into you.
Just like time trial, you try something, see if it works, it does then keep it, if not then experiment further, til you find something your comfortable with.