Ever since I got my new rims installed whenever I'm driving I get this bad vibration. It seems as if they are not balanced... So I went back and they checked it and they said that my tires were perfectly balanced... The guy said some thing about a Centric Hub ring... are you suppose to buy one of those whenever you get a set of after market rims? Or what could b the problem??

I don't know enough about rims to tell you if there is a problem. But if it is vibrating you that bad....switch back to the stock rims & tires just to play it safe for now. Wait until you get the correct answers before putting the new stuff back on. You could be hurting something......

Maybe you could call up the place that you bought the rims from to ask them if you needed something else or not.

A possibility could be that the rims are out-of-round....

Which means you may need them to give you brand new rims because the ones they sold you were warped and not a perfect round, so they wobble.

I used to work at a tire store. Alot of people have issues with there rims for many different reasons, but sometimes rims are made imperfect.

You may want to watch the wheels on the balancing machine.

If it is out-of-round, bent, etc. this will give you the best look at what it does when it spins.

:57:

Check for lumps on the tires too. Hitting a pot hole hard enough will cause enough shock to force out a lump onto the tire. This is also common when you purchase used tires.

If you can, remove the tire from your car and give it a quick roll on an even surface and see if it wobbles or jumps.

this just happened to me.
I recently bought these 18's and the right one was making a tapping noise and sort of vibrating. I took it to a specialty rims shop(the only place where you can find centering rings) they told me that was the problem. They put the rings on, remounted the rims and now the noise is gone and the car looks sweet.