Just to be sure we're not all guessing wrong - Peg - what the heck kind of car are you talking about? Maybe I missed it.
If it's a straight axle rear end, there is technically no adjustability designed into the components. However there are special tools available to help adjust in the event that some sort of collision or abuse has caused the rear end to become 'misaligned' or 'bent' in the manner described so eloquently by my good buddy Hissin.
Ford special rear end tool part number BFSH#2995 (BIG F#
[email protected]%ING SLEDGE HAMMER - $29.95) can be used to cause certain percussion adjustments which, if applied repeatedly by the skilled hands of a large and powerful mechanic (often named Bubba) will eventually encourage things back into their proper pre-collision or pre-drifted-into-a-big-arse-curb position.
On a more serious note, I don't know of any solid axle rear ends that have adjustability built in. It takes body shop chassis straighteners or a good alignment mechanic bending things to get one back into shape if it's out of shape. Of course rear IRS is a different animal - but while your initial post wasn't specific, it didn't seem like you were talking about a late model Cobra. Bushings, shocks, improper inflation and separated belts in the tires can cause weird wear patterns as well. Unless you know the car's been hit or run into a curb or something (anything you'd like to tell us that you can't tell your dad?

), I'd rotate the tires (if front and rear are the same size) and check for the wear continuing before I got too concerned about it.