THE SPARE TIRE (WHICH IS MOUNTED BENEATH THE REAR OF THE VEHICLE) FELL OFF DUE TO RUST IN THE MECHANISM WHICH SUSPENDS IT. THE MECHANISM WHICH HOLDS THE SPARE TIRE IS CLEARLY DEFECTIVE (A RELATIVELY THIN METAL BAR ATTACHED TO A METAL CHAIN), AND IT IS CLEAR THAT NORMAL WEAR AND RUST CAUSED IT TO BREAK UNDER THE WEIGHT OF THE SPARE TIRE (WHICH IS A FULL SIZE, FULL WEIGHT TIRE). FORTUNATELY, THE TIRE FELL OFF WHILE THE VEHICLE WAS NOT IN MOTION. HAD IT FALLEN OFF WHILE IN MOTION, THE TIRE COULD HAVE CAUSED SIGNIFICANT DAMAGE TO NEARBY VEHICLES (INCLUDING MY OWN) AND THEIR OCCUPANTS. THE FALLEN TIRE COULD HAVE CAUSED MY VEHICLE OR NEARBY VEHICLES TO FLIP OVER, PARTICULARLY AT HIGHER SPEEDS. NISSAN HAS BEEN INFORMED (BY PHONE) OF THIS DEFECTIVE PART. THEY HAVE REFUSED TO TAKE ACTION. ALL NISSAN XTERRA OWNERS SHOULD BE AWARE-- YOUR SPARE TIRE MAY BE HANGING BY A THREAD. THIS IS A SERIOUS HAZARD WHICH SHOULD BE INVESTIGATED.