The frame is also known as the beam. The base of the vehicle, generally consisting of two longitudinal beams and several crossbeams, is supported on the wheels by the suspension, front and rear axles. It has sufficient strength and stiffness to withstand the load of the vehicle and the impact from the wheels.

In order to evaluate the design and construction of a frame, it is important to have a clear understanding of the different forces that the frame is subjected to when the vehicle is in motion. If the frame is not stiff in one way or another, it will not handle well, even with a good suspension system. The frame is exposed to four types of stress in the real world.

Large-beam and load-bearing frames are the dominant form of frame, but they each have significant disadvantages, namely their bulkiness and lack of stiffness. This has led to the emergence in recent years of frame design solutions that combine the best of both worlds.

The frame is made up of a combination of longitudinal beams, cross members, engine mounts, clutch mounts and other accessories. The frames are divided into welded frames, riveted frames and riveted/welded frames according to the different processes. Medium and heavy trucks mainly use riveted frames.

The frame structure can be divided into non-load-bearing, semi-load-bearing and load-bearing according to the force situation.

Non-load bearing vehicles have a rigid frame, also known as a chassis beam frame. The frame is connected to the body by springs or rubber pads for a flexible connection. The engine, part of the drive train, bodywork and other assembly parts are fixed to the frame with suspension devices, which are connected to the wheels by front and rear suspension devices. This non-load-bearing body is relatively bulky, high in mass and height, and is generally used in lorries, buses and off-road jeeps, but also in a small number of high-class cars, as it has better smoothness and safety.

A load-bearing body has no rigid frame, but only a reinforced front, side, rear and floor pan. The engine, front and rear suspension, part of the driveline and other assembly components are assembled in the position required by the design of the body, and the body load is transmitted to the wheels through the suspension unit. In addition to its inherent passenger function, this load-bearing body is also directly subjected to various load forces. After decades of development and refinement, the load-bearing body, whether in terms of safety or stability, has been greatly improved, with a small mass, low height, no suspension device, easy assembly and other advantages, so most of the cars use this body structure.

The body is rigidly connected to the frame by means of screws, riveted or welded connections. In such cases, the car body, in addition to bearing the above-mentioned loads, also helps to reinforce the frame to a certain extent and shares some of the load of the frame.