1987 Porsche Carrera

THE TREAD FROM THE LEFT REAR TIRE, WHICH HAD ABOUT 12,000 MILES ON IT, CAME OFF IN THE FAST LANE ON THE FREEWAY AT ABOUT 70 MPH. TRAFFIC WAS FAIRLY LIGHT AND ALTHOUGH WE FISHTAILED A BIT, I WAS ABLE TO PULL OFF THE FREEWAY. THE TIRES HAVE A "RIM SAVER" FEATURE THAT ALLOWED ME TO DRIVE SLOWLY ON THE REMAINS OF THE TIRE. I HAVE HAD THREE OTHER FAILURES WITH THESE TIRES, TWO OF WHICH WERE UNEXPLAINABLE. I HAD ONE ADDITIONAL BLOWOUT ON THE FREEWAY AT LOWER SPEED, BUT I DON'T KNOW THE CAUSE OF IT. I SPOKE TO FIRESTONE ABOUT THESE INCIDENTS AND THE ASSURED ME THAT THESE TIRES HAD NO HISTORY OF PROBLEMS. AT THIS POINT I'M AFRAID TO KEEP DRIVING ON THEM. I HAVE NO FAITH THAT THEY WILL NOT COME APART OR BLOW OUT AT UNEXPECTED TIMES. WHENEVER I DRIVE OVER BUMPS ON THE ROAD I'M AFRAID I HAVE ANOTHER FLAT. FOUR FLATS IN A YEAR SEEMS A BIT EXCESSIVE. WHEN I READ ABOUT FIRESTONE'S PROBLEMS WITH THE ATX TIRES, IT SOUNDED JUST LIKE MY PROBLEM. IS THIS PROBLEM MORE WIDESPREAD THAN IS BEING REPORTED? I WOULD LIKE THESE TIRES REPLACED BY ANOTHER MANUFACTURER'S TIRES.( DOT NUMBER: TIRE SIZE: 225/50/R16 )