A door roller comprising: a carriage member comprising a plurality of bores ; and a plurality of roller assemblies connected to the carriage member , each roller assembly of the plurality of roller assemblies comprising a pivot bearing rotatably disposed within a bore of the plurality of bores and a pair of rollers coupled to the pivot bearing , wherein the plurality of roller assemblies comprises an upper roller assembly configured to roll upon a topside of a roller track and a lower roller assembly configured to roll upon an underside of the roller track , characterized in that : the carriage member comprises a plurality of slots formed through walls of the bores and each bore of the carriage member is coupled to two slots of the plurality of slots ; and each roller assembly of the plurality of roller assemblies comprises a pair of axles , and each axle of the pair of axles extends through one slot of the plurality of slots , wherein each of the plurality of slots has a length and a width dimensioned to allow a corresponding axle to move along the length of the slot so that a central axis of the corresponding roller assembly can pivot about its pivot bearing to allow the central axis to remain parallel with a face of a topside of a roller track when the carriage member pivots about the pivot bearings . a carriage member comprising a plurality of bores ; and a plurality of roller assemblies connected to the carriage member , each roller assembly of the plurality of roller assemblies comprising a pivot bearing rotatably disposed within a bore of the plurality of bores and a pair of rollers coupled to the pivot bearing , wherein the plurality of roller assemblies comprises an upper roller assembly configured to roll upon a topside of a roller track and a lower roller assembly configured to roll upon an underside of the roller track , characterized in that : the carriage member comprises a plurality of slots formed through walls of the bores and each bore of the carriage member is coupled to two slots of the plurality of slots ; and each roller assembly of the plurality of roller assemblies comprises a pair of axles , and each axle of the pair of axles extends through one slot of the plurality of slots , wherein each of the plurality of slots has a length and a width dimensioned to allow a corresponding axle to move along the length of the slot so that a central axis of the corresponding roller assembly can pivot about its pivot bearing to allow the central axis to remain parallel with a face of a topside of a roller track when the carriage member pivots about the pivot bearings . the carriage member comprises a plurality of slots formed through walls of the bores and each bore of the carriage member is coupled to two slots of the plurality of slots ; and each roller assembly of the plurality of roller assemblies comprises a pair of axles , and each axle of the pair of axles extends through one slot of the plurality of slots , wherein each of the plurality of slots has a length and a width dimensioned to allow a corresponding axle to move along the length of the slot so that a central axis of the corresponding roller assembly can pivot about its pivot bearing to allow the central axis to remain parallel with a face of a topside of a roller track when the carriage member pivots about the pivot bearings . <EOS>