Opening the door stiffeners will cause the chassis to deform. There are reinforcing bars in the car door, which play the role of protecting the members of the car in the collision. If the door reinforcing bars are damaged in the collision, sheet metal can not be repaired. At this time, the door needs to be replaced, otherwise the safety of the car will be affected. 

Stiffener A stiffener on a tall web, elbow, or axial profile on the wall of a tubular member. It is mainly used to increase the stability of the structure. Noun explanation in the process of structural design, the structure may appear to hang out too large, or the span is too large, in such a case, the connection surface of the structural part itself can bear the load is limited, then in the common vertical surface of the two combination to increase a strengthening plate, in order to increase the strength of the combined surface.