Actually, since the steering joint is offset, wouldn't you want the center point to be the axis of rotation?
In simpler terms, place the hub joints at the rotation point for the steering parts. Then, with your wheel model, place everything (your empties and such) at the 0, 0, 0 point and move the wheel the same distance away from 0, 0, 0 as is needs to be to fit neatly inside of the steering section.