Happened to my brothers car also 2003 Grand Pirx , seems that he or someone else jacked the car up using the trailing arm (spindle rod ) on both sides. The front tires had almost no wear and the rear tires were junk. Parts were available but had to take shackle off one side do too rust in bushing. Easy fix otherwise.

 

I'd check to make sure all of the suspension parts on both sides appear as they should be and aren't bent or out of alignment. As Jeff said, a lot of people use that stuff to jack up the car when that stuff isn't meant to support the weight of the vehicle and if you bend or budge anything slightly out of place you can mess up the alignment.