This is what I found. Has any one else had this problem w/ there tires??
Just like wheels, tires can have excessive radial and lateral runout. Again too much and it will present as a vibration even when they are perfectly balanced. I am sure you can understand how this works just like the wheels and I will not go into it again.
There is another defect in tires that can cause a vibration called loaded road force variance. The tires and pass a visual inspection, a radial and lateral runout test, be perfectly balanced, but still cause a vibration. This is due to the internal defects in the tire. All tires have variances in the stiffness of the sidewalls. As the tires roll with a load on them and they roll onto a soft section of the sidewall the truck will settle slightly down toward the road. As it rolls to a stiffer part the truck will be raised up slightly. When the sidewall variances are the same on both sides this causes an up and down motion in the truck. When the sidewall stiffness is different from right and left side when the tire is viewed on edge, then this can induce a side-to-side movement called a lateral variance.
If these variances in sidewall stiffness get to be too much you will feel it as a vibration. There are other things that add to this like the way the tire casing is constructed and if it has seems or not, but it all ends up causing the same problem. The problem is how can you measure for this and correct it? Until recently you really could not, but there is hope. There is a new type of balance machine on the market called a road force balancer and Hunter makes it.
Road force balancing works well. Discount tire calls it "ride matching" and they were the only ones who got rid of my shimmy. Recently I had my Armada in to get the brakes fixed (again). Before the repair, no shimmy. Dealer touches my truck, and the shimmy is back. WTF?
I guess it's back to Discount to see what they can do.
Just got back from Discount and 1 tire had bad RFV. All 4 tires were way of balance. The dealer had counter waited 2 to 3 sides. Discount also told me that the stock Continental tires were not very good to start with. Anyway they were able to get all balanced and $62 later - no more shimmy.