Strange failure of a studded tyre

Cycling from work yesterday, I noticed something… well, uneven, on my rear wheel. At the cellar door, the exploration has revealed three places where the sidewall cord of the tyre was torn, two of them longer than 3 cm! Inner tube was buldging out. What a luck that it still got me home and did not explode, say, on half way to work – clear failure of the Murphy’s law!

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Three pictures above show the three openings. All the three go in the direction of the inner cord, i.e. the outer cord threads have failed. All the three are on one (left) side of the wheel. That side shows signs of other places where the cord is weakened, all in the same direction, all directly under groups of two knobs.

I have no idea what can be the cause of such failure.

Even more intriguing: after removing the tyre and inspecting it, I saw that the other (right) side of the tyre also shows signs of the cord wear, but in a different way. Threads were sticking out and tearing around the knobs, which hold the studs! In one or two places this went as far as to leave the hole around the knob:

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This did not bulge (yet) and was not noticeable with the tyre inflated. And only on one side, not on the other – I still have to solve this riddle.

The tyre itself is 3 winters old (meaning more than 5000 km on the rear wheel), rubber is about 1/3 weared out:

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Do not get me as trying to complain about Nokian studded tyres. They are by far the best of what I have tried, currently I have 4 more (in addition to this one) and none shows any similar signs. During all its life, which is over now, this tyre has lost only 2 studs. Long live!

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