Swap the two front tires side-to-side and see if it pulls the other way. You're observation is one we use on front-wheel-drive cars to help identify a tire pull vs. An alignment pull. A tire pull will go the other way under acceleration.
If swapping the tires changes the pull, rotate them front-to-back and just leave them that way until two wear out, then just replace those two. General and Uniroyal tires had a real big problem with broken belts in the 1980s and 90s. I don't know if that is still the case but that wouldn't show up in only three weeks. Very often a tire pull is just a characteristic of one pair of tires and it doesn't necessarily mean there is a defect.
Wednesday, April 13th, 2011 AT 1:40 AM