PE 00020: WHILE DRIVING 75MPH VEHICLE STARTED TO VIBRATE. WAS PULLING TO SIDE WHEN A LOUD EXPLOSION WAS HEARD. LOST CONTROL OF VEHICLE, WENT TOWARDS MEDIAN & HIT GUARDRAIL. AIR BAGS FAILED TO DEPLOY. WHEN VEHICLE FINALLY STOPPED, GOT OUT & CHECKED. NOTICED NO TREAD ON LEFT REAR TIRE. NO SERIOUS INJURY. FIRESTONE WILDERNESS, SIZE P235/75R15 WITH 61,000 MILES ON IT. DID NOT HAVE THE TIRE.*AK