I went to Firestone to change out my General Exclaim tires on my OEM #166s.
They have a Hunter machine, and I wanted to get some high speed balancing.
I now have very strange vibration when I hit 70 mph. I formerly had replica #166s, so I know all about vibration due to hubcentric issues, but this vibration is less violent.

Before I went to Firestone, I had about 6-8 weights on each wheel in various places.
When I got the car back, all of the weights were removed from three wheels, and the weights were untouched on the fourth wheel.

What are the chances that they actually balanced my wheels and tires and that three of the wheels were actually perfectly balanced without any weights (and the fourth needed the original 6 weights)?

Any thoughts on what could have happened here?

Best regards,
Richard

 

You either have a bad tire or tires, or they did a poor balancing job. That happened to me once. I bought four new Goodyear F1s and the car was pretty smooth up to 75 mph. Above that the ride got a little rough. I brought the car back to the tire shop and the re-balanced all four tires which eliminated the problem.
Bring it back and have them re-balance the tires.
Good Luck.