The following is a is a tech letter by Gary Whisler. It explaines what hub rings are used for. I hope this answers some questions soem of you.
THE VITAL ROLE OF THE HUBRING DURING INSTALLATION
by Gary Whisler
Hub rings serve no purpose after installation, their entire job is to hold your wheel perfectly centered while the lug nuts are being installed.
The hub rings sole responsibility is to take up the space between the center bore of the wheel and the hub of the car. For example: the center bore of all 4x100mm and 5x100mm wheels is 64mm. However, the hub diameter of the Honda is 56.1mm. Therefore to take up the space between 64mm and 56.1mm a hub ring is used.
All wheels are classified as being either "Hub Centric", or "Lug Centric." The term Centric refers to the way a wheel is centered. In other words a hub centric wheel centers on the hub of the car, if you put the wheel on the car without lug nuts the wheel would be perfectly centered. On a lug centric wheel, the wheels are centered by the lugs as they are tightened down. Manufacturers build wheels lug centric to allow the wheel to fit a wider selection of vehicles.
I cannot stress enough how essential it is for you to be certain that the installer of your Performance Wheel has used the correct hubring. Statistics show that the most common cause of a car vibration is a wheel that is off center slightly. For example, with lug centric wheels vibrations commonly occur when an installer tightens the lug nuts incorrectly, such as when they tighten one side before the other the wheel can be "pulled" to one side. This common problem could be prevented if the correct hubring was used during installation."