This bag is bad ass. I've rode thousand's of miles with this bag and never had a problem with it coming loose, it's seen over 120mph and triple digits several times. It is a two piece bag, a large bag for traveling and a small bag for every day use. Lots of pockets for cell phones or anything else you can stuff into it. Both bags have map pockets. To change the bags you unzip a bag from the base and attach the other bag. The base is held on by four large suction cups, so it will attach to any smooth surface. As I said it will never come loose unless you remove it which takes seconds, and attaches in seconds. This bag is in like new condition and I paid $130 for it new. I'm asking $50 for it plus shipping.