Step 9: Reap the Benefits
As a note... Yes, I am attaching my bungee to my swing arm. Yes, the distance between the bag and swing arm changes when going over bumps. No, the bag doesn't jump off. I've added a little extra tension to make sure, but the act of the bump will tend to push the bike up and newton's law will tend to keep the bag where it was (at that point, below the rack). No problems thus far riding on the streets (and off the sidewalk curbs) of San Francisco.