I know this is an old thread but I did wonder why the back left wheel kept falling off. This has happened twice in the last two years, once with the wife driving vthe other myself. Both times thankfully it was at low speed. Both involved replacing the left brake assembly and a new rim. I have since got rid of my alloy time and replaced them with steel. Over all it makes me nervous when I hear or feel anything out of place when I drive.
Still not sure what the real issue is that causes this.