The MTX TrunkBag uses a unique material process to provide our largest, stiffest, and most weather resistant MTX series bag. In addition to the expandable top section and rear water bottle holder, the side panels expand to full panniers maximizing capacity. Compatible with all MTX QuickTrackâ„¢ racks with attachable side frames. MTX Dual Side Frames are required when using panniers on MTX BeamRacks.