Tires: Cupping of Tires, Tire Alignment, Wheel Alignment

Question
2004 Tahoe - 4wd - both the original Bridgestones and a replacement set of Michelin Cross Terrains starting showing cupping on the inside and outside of all four tires at around 30,000 miles.  I had the tires regularly rotated and balanced and the front end aligned.  I put around 50,000 miles on the original set and around 85,000 on the Michelins.  Just today put a new set of X radial Michelins on.  What is causing the cupping?

Answer
Jack,

Cupping is caused by misalignment and aggravated by insufficient inflation pressure and insufficient rotation practices.  The fact that it took 30,000 miles to develop the cupping means that the misalignment is slight - probably within tolerance.  I have found that the tolerances for alignment are quite wide.  I think the tolerances ought to be half of the published values.