Originally Posted by
B. Carfree
Old touring bikes, like my Trek 720, have a little braze-on that holds the chain on the seat stay. That allows one to leave the derailleur on with a bagged bike if one sets it up to rest on the rear drop-out and saddle. The package also gets smaller if one removes the forks.
IMO - the minute you get involved with a bag and partly taking the bike apart to fit it, the entire bike & train dynamic changes. Mainly because you have the question of what to do with the bag.
Of course, one may sew a bag special for this application, using light weight fabric, reinforced with a web strap or two, and roll it up and stow it for the ride. Or you might simply take your chances and stow the bag behind some shrubbery near the station. But it's still not the same as seamlessly hopping on and off a train with your bike.