This is all only a theory, which suddenly hit me while doing research for a term paper on reincarnation. This is for fun and entertainment, and pretending that Haruka *is* a human.
The theory is, that she was once a man. A man who was highly skilled at car racing, and perhaps as a man very skilled at sports too in other lives. Thus, the reason why Haruka is so talented, yet especially for car racing, in the present life. It is rare for souls to reincarnate as another gender, but when they do, traits of their past gender hold so strongly on their present life they continue that gender. If Haruka was a man in the past life, it clearly explains why Haruka cross-dresses. And also the close relationship with Michiru.