While looking at my tire, I noticed this flexible piece of plastic that I can almost rip off. My tires got rotated a bunch, but I believe this one has been patched before. Is this the other end of a tire patch? Or is this a manufacturing defect? Thanks!
It is a tire plug. At some point a puncture repair was made. This type of plug is shaped like a mushroom. The tire is dismounted from the rim. The "mushroom" stem is inserted into the defect from the inside of the tire. The "mushroom" cap seals the hole from the inside. So it is a patch and plug in one. The advantage of the plug design is the internal pressure keeps the plug in place. The older style "rope plugs" were subject to failure as they were installed from the tread side of the tire. Plugs can only be installed in the tread areas.