I disagree with the post about turning the wheel. If done ever so slightly, it can look good from viewing from the rear. But if you do it too much, it looks kind of awkward in my opinion. Here's a thread I started with a few shots of my car, maybe it'll give you some ideas. Somebody mentioned in my thread to pay attention to the reflections coming off the car too.
http://www.thephotoforum.com/forum/photography-beginners-forum-photo-gallery/177195-few-my-car.html
angling the front wheels away from the camera allows you to do the front corner on view that car magazines (and everyone else) love to take. it squares the face of the rim to the camera and you get the nicely filled out wheels well look. Otherwise you wind up seeing tire tread and it just looks awkward.
As an example.....
You can get the very good dead on front/rear/side views in which you'd want to keep your wheels straight, but for the off angle ones, angling the wheels helps pose the car a little more.
This would look like garbage with a wheel poking out..