How old are your tires? New enough to warranty? I have gotten good support in such a case from my Toyo re-seller once. Especially if you show how you have been trying to solve it. Or old enough to just replace?

 

My buddy changed tires around August and I bought the car from him in end of September. didn't drive the car much but did notice a slight vibration at first. Thought it was just bad balancing from newly replacing tires. Stored the car for the winter. I've had them rebalanced and road force balanced a few times. Tires are bridgestones and probably have about 1500-2000 miles on them so still plenty of tread. Problem is I think they were bought so long ago that warranty wouldn't cover it.

 

try a spare set or wheel/tire or borrow a set?

 

do me a favor and lift the rear, so the tire is of the ground - put one hand at 9 oclock and another hand on 3 oclock and move left to right, put your hand on 12 oclock and 6 oclock and move it up and down, see if have any movement, maybe control arm/s/busings are busted/, should be no movement.

it could be several things, tires, rims, busted bushings, maybe trans is making vibrations or axles. could be busted shock/s

I'm sure alignment is fine, otherwise usually it happens around 60mph's

also best bet would be to borrow 2 rear wheels from a friend and test it. Tires could be bad, do to age, maybe at one point car was for several months.

 

Not too revive an old thread, but I'm having a similar issue. 99 C2. Vibration over 70mph. I've swapped another set of 4 wheels and tires and the vibration stayed with the car, so i was able to eliminate wheels/tires all together as a cause. Any thoughts?