Instead of a pannier that doubles as a backpack, I have just used the backpack on the bike carrier rack and works fine. Use bungee cords to hold it on. I don't think I'd leave panniers on the bike when parked (especially after having the bike stolen last week from job site). To make the back pack fit, you have to fold down the top 1/3 and tuck under. Be sure to tuck in and secure any straps from the backpack so they don't get churned into the wheel or chain.