just for experimenting sake after you pack the bike give it a shake to see how much the contents in the bags and the bags wiggle around. Then loop a bungie from the bottom part of the rack up over the pannier to the top rails and see if it is more solid. Take it for a ride either way and see how shimmy or out of the saddle riding is affected. One thing though is to make sure the bungies cannot come undone as the last thing you want after hitting a big bump is for the bungie to unhook and get caught in the wheels.