One of the most common problems I have found which are manifested by excess vibration in the area of tire/wheel that is not cured by rebalancing has to do with the condition of the tire. If a tire that is out-of-round is balanced, the out-of-round condition is not cured. What that means is that, while the balancing ensures that the tire/wheel assembly will not deviate abnormally from the forward/backward plane as you drive(side-to-side), there exists nothing to prevent its up-and-down movement due to its shape(oval or ellipsoid). Another common problem, potentially dangerous, is tire separation. Should a tire begin to separate, that separation may not be readily apparent without a road-test, at which time it will be noticed that the steering wheel shakes violently when certain road speeds are reached. To locate the offending tire, it is advisable to move the front tires, one at a time, to the rear of the car. In so doing, you should notice a distinct difference in the car's behavior when driven once the culprit is moved from the front. Note: If you have just had your tires replaced and the wheels balanced, there may be another explanation for the problem, assuming it did not exist prior to this: The stub-end of an old tire-valve trapped inside the tire. I have encountered this problem at various times; and, what happens is this: The tire purchase is made, and the tire man pulls your wheels off of your car. The wheel/tire assembly is put onto the tire machine, and the valve core is removed from the valve, letting the air escape so that the tire may be dismounted. The tire is then removed from the wheel. A new tire is now chosen and mounted onto the wheel. Next up is a new valve. The replacing tool is screwed onto the old valve, which is then pulled free from the wheel, out of its hole. Most of these do not come out whole. The "bottom"? Well, that falls innocently away. A new tire valve is now installed, being pulled into place with the same tool used to remove the old one. The tire is then aired-up, sealing the bead, and is moved to the balancing machine, where it is spun by computer-control and indexed for weights to be attached.