Wheel Imbalance on 2005 Cadillac DeVille DTS

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I replaced the 17 "tires at 60,000 with Yokohamas. The vendor has tried three times to balance them without success. They stillbrate between 60 and 70 mph. Aer defective tires likely to be the cause? They have offerred to replace them.Should I ask for a different tire?
(2) Answers
Have they tried rotating the tires from front to rear and see if the vibration goes away? Yokahama make good tires. Have them spin the tires and see if the tire itself is "true" old tires need to be shaved to make the surface flat (only old timers would remember that, we still do it on old vintage cars). With they wheel off the ground spin the tire and look to see if the rim is weaving in and out of the tire appears to travel up and down, if the tire moves up and down, try dismounting the tire and remounting it.