Wheel offset maybe if the wheels you had were different? I ran my 17" RS4 reps for a week as I was gonna refurb my S3 alloys and noticed that I was fighting the camber of the road more as the offset was 35 rather than 32 and the wheel was the same width... gave the impression the steering wheel wasn't aligned
The only other thing I can think of is that a wheel is not on squarely and you are having to compensate by holding the wheel off centre when driving straight..
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