If I replace the chain on a bike can I automatically track the new chain whenever I add the bike to a cycling activity?
No. Currently there is no way to link a piece of gear to another piece of gear.
Thanks. It would be good if you could.
Well, as tmk2 wrote, currently you cannot link gears together, but you can link several gear pieces to the same activity. I do use it in this way. Otherwise, I recommend suggesting the feature to Garmin at Share Ideas | Garmin