[Richard]

Bearings and shocks should be checked as Jeff said.

I based my guess on the number of tag bushings that I have seen that are kaput and allow the tire to go out of alignment. So the tire is being dragged down the road. Lower air pressures make the tag edge dig in causing the scallop.

Some enterprising fellow ran an experiment once to lower the tag pressure to the minimum because that was still above the weight on the tire. 500 mile later the tag looked exactly like the one in the picture. Needless to say the inflation was increased right then and there.