When I bought my ST, it had the original Goodyears on the front, and a brand new set of Westlakes on the rear. They literally mounted the tires, and parked the car on the used car line. After I bought it, the first thing I did was put a brand new set of matching Westlakes on the front. They're asymmetrical. The car tracked straight as an arrow, driving, coasting and accelerating. After I put 6,000 miles on them, I had them rotated, crossing the rears as they moved to the front. It's been pulling left, and trying to take the median during hard acceleration ever since. It's gotten a bit better since they've started to wear, but the tug is still there. The only thing I can attribute it to is an alignment issue on the rear, which has worn one or both of the tires strangely. When it's time for these tires to go, it will also get an alignment.