Why is the chassis used in modified cars called the second class chassis? How to distinguish

How are Class I, Class II and Class III chassis divided? A chassis: includes the whole system of the vehicle, that is, the general sense of the whole vehicle; The second type of chassis: the chassis of the car that has been equipped with the engine, transmission, transmission train and cab but no cargo box, is widely used in special vehicle modification, such as: the chassis of the sprinkler, the chassis of the fog cannon, the chassis of the dust suppression car, and so on; Three types of chassis: do not load the body and install the engine and transmission device, front and rear axle, steering gear, suspension device, wheels and tires, braking system and other assembly, can not drive, such as: school bus chassis.
The chassis is composed of four parts: transmission system, driving system, steering system and braking system.

1. The transmission system is mainly composed of clutch, transmission, universal joint, drive shaft and drive axle.

2, the driving system, by the frame, axle, suspension and wheel plate; Spring and shock absorber components.

3. The steering system is composed of a steering wheel, steering gear, steering knuckle, steering knuckle arm, horizontal tie rod, straight tie rod, etc.

4. Brake system, hand brake; The hydraulic brake device is composed of brake pedal, brake master pump, brake sub pump, drum brake and oil pipe, etc. The pneumatic brake device is composed of brake pedal, air compressor, pressure gauge, brake valve, brake chamber, drum brake and gas pipe.