A vehicle should track straight on a flat, straight road with the steering wheel centered. To keep it that way it is a good idea to have the alignment checked on an annual basis. The condition of our roads can cause a vehicle to get knocked out of alignment by extremely rough roads or by hitting pot holes and curbs including parking curbs.
If the car pulls to one side, investigate the simplest possible cause first, incorrect tire pressure. If that checks out, look for uneven tread wear. If the wear is uniform, interchange the left front wheel and tire assembly with the one on the right. If the drifting problem disappears or reappears on the opposite side, a tire is the culprit. Otherwise, pulling to one side may be due to incorrect steering caster, which is an alignment angle that can be adjusted with a wheel alignment. The side with the wheel with the most negative caster angle is the side to which the vehicle will pull.
It is a good idea to get a four wheel alignment performed once a year particularly when your vehicle has hit deep ruts, curbs and etc. If you have noticed that your vehicle pulls to the left or right on a straight flat road, it may be time to checked out or aligned. During that alignment inspection a professional can check for loose & worn parts like bushings, tie rod ends, ball joints and etc.
We would also recommend having the alignment checked whenever you have your tires replaced. Keeping the vehicle in proper alignment will help to increase the life and longevity of the tires. Happy Motoring!