I have a 05 a4 ultra-sport and i put a set of tsw donington 18" wheels on it. I've been having a really hard time getting the car to balance. the tire company has been very helpful and has upgraded my tires twice and replaced the all the rims and i still get a vibration around 50-60mph, and again at 80-90mph. I brought the car into the dealer to see if they could check out the car and see if something else was the problem and they said the hub-centric rings weren't the right size. so i got those swapped out and i still have the same problem. Does anybody know what else could make my car wobble like it is?