[FatKidsCruze]

I disagree the hub rings are generally no more than 25-30 and make larger bore wheels fit "properly" on cars with smaller hub bores. That's not to say you NEED them, but without them you CAN (probably will) experience unnecessary vibrations.

Here is where I have bought my hub rings any size you could ever want:
1010TIRES.COM - Hub Centric Rings (Set of 4)