It looks like you simply wore this tire out. Either that or you skidded the tire at some point. In any case, the rubber was really thin in that spot and it wore through to the cords. I don't think the tar had anything to do with it. The width of the worn strip leads me to believe you use a pretty high tire pressure. Generally, lower tire pressure leads to longer tire lifetime.
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Cat 2 Track, Cat 3 Road.
"If you’re new enough [to racing] that you would ask such question, then i would hazard a guess that if you just made up a workout that sounded hard to do, and did it, you’d probably get faster." --
the tiniest sprinter