Originally Posted by Bacciagalupe

What is he supposed to do, carry a torque wrench during a time trial?

It's not his job to keep the drivetrain tuned, they have professional mechanics for that. He's also using a different bike than last year, different drivetrain, and almost certainly a different mechanic. It's merely a coincidence that he dropped a chain at a somewhat critical moment last year and at an all-but inconsequential moment this week.

Also in this type of situation, it's faster (and smarter) to just hop on a spare bike than to try and fix the drivetrain.