The invention relates to an extension guide (1) for mounting a movable furniture part linearly movably along an extension direction (2), comprising a carcass rail (10) which can be fixed to a furniture carcass, a drawer rail (50) which can be fixed to the movable furniture part, a linearly movable center rail (30) arranged between the carcass rail (10) and the drawer rail (50), at least one load-transmitting outer carriage (40) arranged between the center rail (30) and the drawer rail (50), and a synchronizing device (60). Improved wear resistance is achieved in that the synchronizing device (60) is effective between the carcass rail (10) and the outer carriage (40).