Many circle track cars use aluminum axle housing tubes because they are lighter. They also have a greater chance of bending and so the rear wheels need to be checked more often for unwanted toe. You can do a very accurate alignment check on your rearend with strings. Once the rear has been aligned, measure from the front of the axle tubes to specified chassis points so that rechecking the rearend square is quick and easy at the track. A simple rear wheel toe and camber check will tell you if the rear axle housing is bent.