The side inner brace is a co-tightening type of body reinforcement part that bolts on directly to the front side frame. Since it reinforces the undercarriage and engine mounts, it effectively prevents body sagging such as threading and distortion against movements such as acceleration, braking, and cornering in the behavior of the car. It is a reinforcing part from the front monocoque to the engine compartment. The installation is co-tightened to the door mounting hinge at the bottom of the A-pillar, and the undercarriage mounting part is reinforced with an inner brace. This part is designed to increase the rigidity around the front, which greatly contributes to the threading of the suspension and body. As a result, the feeling of contact with the tires has been greatly improved, and from braking to cornering, the control performance has been improved, so that you can feel it in your hands under any conditions, from the street to the circuit. It increases the body rigidity near the front suspension, improves the movement of dampers and springs, and improves the contact performance of the tires to improve handling performance. It is a bolt-on installation and a casual body reinforcement part.