The main compartment is divided for storage convenience and features a two-stage expanding top section and side panels, which have a zip opening for easy to the full-size panniers; simply unzip and pull the panniers down for even more storage capacity. Compatible with all MTX QuickTrack racks with the attached side frames. Simple, Secure and Extremely Reliable Storage Thanks to the unique QuickTrack system from Topeak, mounting any QuickTrack equipped bag or basket to a Topeak rear rack is simple, secure and extremely convenient. You simply align the QuickTrack base with the channels on any Topeak rear rack and slide it forward along the guide rails until it clicks into place. No tools are required for this mounting process, no straps needed to hold it in place and since it is so secure there is no need to worry when cycling. When arriving at your destination and its time to remove your cargo, simply push the yellow release button and slide the bag or basket rearward until completely disengaged.