The purpose of this study is to validate a reverse engineering based design method for automotive trunk lid torsion bars (TLTB) in order to determine a free, or unloaded, shape that meets a target closed shape as well as a specified torque. A TLTB is a trunk lid component that uses torsional restoring force to facilitate the lifting open of a trunk lid, as well as to maintain the open position. Bend points and torque of a TLTB at a closed trunk position are specified by a car maker. Conventionally, a TLTB supplier determines bend points of the free shape by rotating the given bend points from a closed position around a certain axis to satisfy the specified torque at the closed position. Bend points of a deformed TLTB shape in the closed position often do not match the target bend points given by a car maker when designed by the conventional method, which can potentially cause interference issues with surrounding components. Therefore, a reverse engineering method based on finite element analysis (FEA) was developed. The bend points of a free TLTB shape are designed as follows: First, the difference between bend points of an FEA closed shape and target closed shape are determined using results from the conventional method. Next, bend points of a new free shape are automatically created by adding the differences to the bend points of the initial free shape with some modification for torque. This process is repeated until the difference reaches an acceptable level. The validity of the method is proven in this paper.