@8lackie most aftermarket wheels have a large center hub diameter so the wheels will fit a variety of different vehicles.
Basically, wheels can be centered by the lug nuts or by the center hub. Centering by the center hub is preferred, but if you're careful on how the lug nuts are torqued on, centering with the lug nuts will work pretty good.
The hub-centric rings are designed to fill the gap between the wheel and the vehicles hub to ensure the wheel is perfectly centered. This not only makes installation of the wheels much easier, but will also help eliminate any vibrations you may be encountering by poorly lug nut centered wheels.
Example: Our XXR wheels have a center bore of 73.1 mm, so we installed 73.1 mm OD to 56.1 mm ID hub-centric rings to allow the wheels to be centered on the hub 56.1 Subaru center hub.
Hub rings are sized by using two different numbers that are measured in millimeters (mm). The first number such as 73.1 mm is the diameter of the center bore on the wheel and is the outside diameter of the hub ring. The second number such as 56.1 mm is the diameter of the hub on your vehicle and is the inside diameter of the hub ring.
You can certainly use wheels with a larger center bore, however, it's good practice to then buy hub-centric rings that adapt your wheels to your hub. This better supports the wheels on the hub, and removes any chance of error when torquing down lug nuts, as well as taking the shear forces off of the lug nuts in the theta Z plane.
For example: If your hub bore is 56.1, and you buy wheels with an 80mm hub bore, you need to buy 56.1mm to 80mm hub centric rings.