If your axel in you car was magnetic with copper wire casing would that produce electricity? If so how much? If there is no resistance in that process then there wouldn't be a detrimental effect on the performance (bar added weight of the wire) With the raising popularity of electric cars it would reconvert some of the kenetic energy back into electrical energy. Therefore increase the range? There is probably a easy answer that will shoot this down, or its already in place but though it was a interesting idea.