Originally Posted By: CapriRacer
Here's my assessment:
There ought to be ply cords visible unless the bubble is on top of the ply cords. In that area of the tires, there ought to be 3 layers: Innerliner, ply cords (with rubber layers above and below the ply cord), and sidewall.
We can see 2 different layers, but no ply cords, so I am going with the bubble is within the ply cord layer and is the result of pressurized air getting into the ply cord. That means there ought to be a break somewhere in the innerliner, so the inside of the tire needs to be examined.
Usually a break in the innerliner is the result of mounting damage - but I can not discount a manufacturing defect and/or impact damage.
Good info. Seeing the age of the tire, I figured it was probably impact damage and not mounting damage, but a manuf defect would be something to look out for.