I never change the Garmin from Bike 1 to 2 or whatever. Does it make any difference unless you're trying to calculate calories so you need the weight of the bike?

SportTracks is pretty good at guessing the sport (cycling road or cycling trail) based on the speed of the activity. It'll get a little confused when I swap between BC skiing with the ForeRunner and mtbiking with the Edge in the spring, but once I'm only riding it knows whether I'm playing in the dirt or on the pavement based on speed.