tony - Strange blowout.
There is noticeable distortion on the near shoulder. I would guess that this was at least partially caused by a factory defect to begin with. Had it ever been on the road it probably would have failed prematurely
It's possible that the body plies themselves were defective (incomplete coating of the fabric with rubber or dry stock), or the tire builder made bad splices.
I am less inclined to believe it was rusty wire under the tread. It looks more like the sun caused a hot spot right on the top of the tire and the carcass eventually let go.
I guess it might help if a spare is stored in the shade under a trailer rather than mounted in the open in direct sunlight. The cover may block UV rays, but hot and cold temperature extremes still cause expansion and contraction enough to cause stress.
And in this case, that stress, combined with what appears to have been a less than perfect tire, pushed the tire to the breaking point.
Age alone would be my third choice as the root cause of the failure.
