After 4,863 miles of shifting nirvana (5,217 total miles on my Di2 drivetrain), today I had a bad shift. I’ve grown so accustomed to absolutely perfect shifting with Ultegra Di2 that this was a rather soul-wrenching experience. The reason I don’t have 5,217 perfect miles is that it took me a little over 300 miles in the beginning to figure out that Di2 is less forgiving of lateral chain sway than a conventional drivetrain. Once that was solved, Di2 has been a dream. What follows is the reason my record of perfect shifting ended today.