Where is the Chassis Frame of a Sedan Located?
3 Answers
The chassis frame of a sedan is located above the wheels, also known as the vehicle frame, serving as the foundation of the sedan. It consists of two longitudinal beams and several cross beams, supported on the wheels via the suspension system, front axle, and rear axle. Designed with sufficient strength and rigidity, it bears the sedan's load and impacts transmitted from the wheels. A sedan is composed of the engine, chassis, body, and electrical equipment. The engine is categorized into gasoline and diesel engines. The chassis refers to the rigid frame in a body-on-frame structure. The body is divided into unibody and body-on-frame types. The electrical equipment comprises the power supply system, electrical devices, and distribution equipment.
Back when I ran an auto repair shop, people often asked about this. In fact, most sedans nowadays use unibody construction, meaning they don’t have a traditional separate frame. The entire outer shell of the car serves as the load-bearing structure, with one longitudinal beam running front to back on each side of the chassis, positioned right below the doors. These beams are made from high-strength stamped steel. Together with the transverse subframes, they form the entire chassis skeleton. If you want to see them, you’ll need to lift the car—you can clearly spot two robust beam structures in the middle of the underside, which bear the weight of the engine and driving impacts. This design makes sedans lighter and more fuel-efficient, though their torsional rigidity is weaker compared to off-road vehicles with separate frames.
I've repaired cars for thirty years. Old-style trucks indeed had exposed frame rails, but modern sedans are different. Their frame rails are integrated into the underbody - specifically the two parallel main longitudinal beams running from front to rear on the chassis. The thickest part of the chassis you can feel directly below the door sill is the longitudinal beam, approximately 10-15cm wide. These beams are designed to crumple and absorb energy during collisions to protect the passenger compartment. When changing oil, observe the central underbody area - you'll see two raised metal beams with anti-rust coating, which form the core skeletal structure of the sedan.
