The automotive chassis system primarily refers to the frame and axles. Wheels are mounted at both ends of the axles; the wheel hub is the main load-bearing component and one of the key safety components. Wheel hub bearings include single-row tapered roller bearings (typically used in pairs), first-generation wheel hub bearings, second-generation wheel hub bearings, and third-generation wheel hub bearings, which are widely used in heavy-duty trucks, passenger cars, and commercial vehicles.