2006 LEXUS IS 350 Tires Problems

FRONT TIRES ON MY VEHICLE ARE DELAMINATING IN THE TREAD AREA ROUGHLY 1-2 INCHES FROM THE SIDEWALL (BOTH INNER AND OUTER EDGE OF TIRE). TREADWEAR OTHERWISE IS FINE (APPROXIMATELY 29,000 MILES USAGE). *TR

I HAVE MICHELIN PILOT SPORT A/S 225/40 ZR DOT NUMBER 4MCR 002X 4310 ON MY 2006 LEXUS IS 350. I HAD THE FIRST SET INSTALLED IN APRIL 2, 2009 AT 24K MILES AS REPLACEMENT TO MY ORIGINAL TIRES.BY APRIL 09 2011 I HAD TO GET THE TIRES REPLACE BECAUSE OF CHUNKING, LARGE CHUNKS HAD COME OFF AT EITHER SIDE OF THE CENTER LINE. I HAVE THE SAME TIRES IN THE BACK ALBEIT SLIGHTLY WIDER WITH NO PROBLEMS, FEB. 09, 2011 AT 47K MILES THE TIRES WERE REPLACED WITH THE SAME BRAND AND MODEL FOR ASTHETIC PURPOSES AND PERFORMANCE BEHAVIOR ON. AT 57K MILES MARCH 2012 I NOTICED THE TIRES EXHIBITING THE SAME CHUNKING. I WENT TO COSTCO WERE I PURCHASED THE TIRES AND I WAS TOLD THAT MICHELIN SAYS IT IS COMMON AND DOES NOT AFFECT THE PERFORMANCE OF THE TIRE, THE CHUNKS DEPTH ARE OVER A 1/4 OF AN...