I swapped the tires right/left, and sure enough, the problem reversed itself. Now it pulls to the left on the throttle, right on decel. I examined the tires and although they both say "Made in Japan", one of the tires has several additional markings and codes that the other tire does not have. So I'm suspecting they didn't come from the same place and/or batch.

I'm sending Jim our Tire Rack guy an email, since that's where I got these. They still have less than 300 miles on them.

 

The car is very very sensitive to R/L differences in tires. If they are not absolutely identical, the car will pull, sometimes very strongly.

I've experience d this multiple times now when buying used tire.

 

Glad you didn't have to go through a crapload of troubles (alignment, changing control arms, etc).

Make sure your tires are back on properly now!

 

by the way, is there ANY possibilities...that one of your tires was mounted BACKWARDS? some idiot may have reverse mounted it - I believe most tires made for our cars are directional - treads grip harder one direction. You mentioned "additional markings" which I believe some tires have different writings on the inside/outside of the tire...

 

I will double-check the mount direction, and Jim suggested I use a tape measure to find the actual circumference of each tire, so I will do both.

 

Tires are both mounted correctly. Jim correctly pointed out that the tires have different markings on their left and right sidewalls and since they are directional, you see different sidewalls on each side of the car. So the tires actually have the same markings.

However, I measured both tires.

Tire 1 has a circumference of 68 7/8".
Tire 2 has a circumference of 69 1/8".

Unless my math is wrong, that's a difference of ~2.5 revolutions per mile. Waiting to hear back from Jim after sending him that info.

 

my car had the exact same issue.. had brand new kuhmo's do that. replaced both and the issue went away

 

Update:

Tire Rack sent one replacement tire. It matches the smaller of my two existing tires in circumference. Another member PM'd me with the same problem with new Star Specs from Tire Rack, so it sounds like there may be a few bum tires in the current batch of Star Specs. Still, I'm happy with the customer service from Tire Rack and we all know the Star Spec is a good tire otherwise.

 

The tread doesn't "grip harder" in one direction.
Mounting a directional tire backward is not really a big deal, zero difference in dry grip or wet grip, and likely only minor difference in hydroplaning-resistance/water evacuation.
Every test I've seen of directional tires mounted backward in the wet shows zero difference in performance. Fer example:
Tire Rack backwards tire test
From this test of the highly directional Eagle F1 GS-D3:
>>>
Mounted Correctly on a Dry Track
The Eagle F1 GS-D3 tires allowed the car to run 29.387 second average lap times, fast enough to confirm its position in the Max Performance tire category.

Mounted Backward on a Dry Track
With no handling quirks or surprises, the car ran 29.465 second average lap times, within 8/100 of a second of the times turned in with the tires mounted correctly.

Mounted Correctly on a Wet Track
The Eagle F1 GS-D3 performs admirably in wet conditions. For that matter its confidence-inspiring control produced an average lap time of 30.373 seconds in the wet, just one second slower than the lap times it ran in the dry (and about one second faster than the lap times turned in by the best Max Performance dry tires). On the track in the wet, we have found that the Eagle F1 GS-D3 continues to provide predictable handling and enough grip to run the fastest average wet lap times of our Max Performance tires.

Mounted Backward on a Wet Track
This is where we expected to find some noticeable differences since the tires would now be pulling water toward the center of their footprint, reducing the available traction. However, the lap times and drivers’ comments indicated that the wet performance was still there. The Cobra ran average lap times of 30.387 seconds, just 1/100 second different than when the tires were mounted correctly.
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A directional tire mounted backward will not cause a pull to one side. But there could be downsides in terms of a road noise, wear patterns, and definitely a loss of style points...

 

Yep, I'm the other one with a bad Star Spec. Good heads up to you guys buying them currently... Measure them before you mount them. They should all be identical.

My car pulled to the left while accelerating, and pulled right while letting off. Pressures and alignment good. Found the bad one by putting the right rear wheel in the front, and the pull was gone. Tirerack sent my replacement out yesterday. Love their customer service!