Took the Cobra to the alignment guru yesterday. Told him how the car was following the ruts in the road with the new tires. His first response was that it sounded like excessive toe-in (one of the possibilities mentioned in the Tirerack article). He put the car on the alignment rack and sure enough, it had about twice the specificed amount of toe-in. He made the correction and it made a big difference. He had checked the alignment about two months ago for me and it was fine, and I have been careful not to hit anything, so I was surprised that it needed adjustment. He told me something that I didn't think about but can understand to some degree--the new tires could mean a different overall footprint.
So, lesson learned # 1: In the future, new tires = new alignment, no matter how recent the last one was performed.
Before driving the car this morning I adjusted the tire pressures downward (also recommended in the Tirerack article) to 34 psi F, 31 psi R, from the 37 psi F and 34 psi R I had been running. I'd been experimenting with the higher pressures to try to remedy the problem. The difference with the new tire pressures and alignment is like night and day. There is still a hint of tramlining on really bad road surfaces, but otherwise it is gone, to the point that I don't think I'd even notice it at all now if I hadn't been through this and weren't really looking for it. Another benefit is that the car no longer rides like a lumber truck!
One other thing that my alignment guy told me worthy of passing on: some car and tire combinations, for whatever reason, just don't work well together. Lesson learned #2: Buy your tires from a place that offers a 30-day ride replacement guarentee, especially if changing brands, sizes or models. I bought these BFG's on sale at a military exchange. If I hadn't been able to get them straigtened out I would have had to live with them as they have no ride guarentee, and these were the only tire they carry in my size.
I would now conditionally recommend these tires (condition being that you can swap them out for something else if they don't work on your car). Nice thing about these are that they have a treadwear rating of 400, are all-season and are relatively inexpensive. They are also much quieter than the G-force T/A KDs that had previously been on the car, and are a non-directional tire. I paid $125 apiece for them.
The last thing that you may want to look at is the condition of your front tires. In your original posting you said that you had aligned your car. Somewhere I read of a case where someone was having this problem and it was as a result of a badly worn front tire. Might be worth doing a rotation as a short-term fix if you haven't tried that yet.
