[RACER X #99]

427,
Those two days of track time is what caused most of the tire wear. I have to assume the the track you ran was in a clockwise direction and that is why you are seeing the wear on the inside of the left rear. I wear out the left rear much faster than the right simply because the majority of the turns are right handed and you are working the left side tires harder than the right.
I have thrown out a half dozen left rear tires that look exactly like the ones in your photo (minus the grooving).
I'm gonna look for pictures of my car doing hard right handers and you will be able to see what I am talking about.
I'll post here when I find them.

X