The topeak mtx trunk exp bag with pannier is a super large all in one pannier trunk bag the large capacity mtx trunkbag contains one main divided compartment with two expandable side panels these side panels can be rolled up and zipped away when they are not in use the unique construction process of the bag provides rigidity and water repellency to cope with the british weather the bag is compatible with all mtx quicktrack racks with attached side framesfor a matching frame click here