Zinn's article mostly makes sense.

1. He did shift right before the incident. https://www.youtube.com/watch?v=kaLq1yo0hIs Wait for about the 25-second mark when they blow him up in the white circle. Watch his right arm. Then watch the RD.

2. It doesn't look like he moves his left arm, so I don't think it was a big ring/small ring issue.

3. He didn't hit a bump. You can see from the video that the hop in the rear wheel is a result of the chain getting stuck. The front wheel doesn't appear to hit a bump.

I just had a thought. When I had first installed my Rival groupset, the adjustments were just a touch off on the rear shifter cable. It would work fine most of the time but every once in a while, especially on a hill, it would autoshift and pop me out of gear. It wouldn't drop the chain off, but I can see how a powerful person like a pro cyclist could pop a chain off if it decided to autoshift like that.

andy was already given a couple of gifts this tour. no more gifts. it's time to stop whining and start attacking.

erader

Agreed. Since when does the pro tour call 'Time out' when the leader has a problem?