If a vehicle is not driving straight when the steering wheel is at center there can be a huge number of reasons. Not only can the steering be out of alignment but the whole vehicle may be as well. This can be caused by an impact on the road with debris or maybe pot hole. Sometimes even after a repair or a modification the alignment may be off from where it should be.
The reason that a vehicle will track incorrectly is because all 4 tires are no longer facing the same direction as they did originally. This can cause the vehicle to pull when driving or it can even cause a condition known as "catapillaring" which is when the direction of travel is not quite the same as the angel of the vehicle. There are some simple fixes for this condition but sometimes it is not so easy. If the issue was caused by a simple alignment issue it will take a mechanic about an hour to fix it. If there is something more than car may need some serious work to get back to proper operation.
