The special vehicle axle system is connected by the suspension and the frame (or body), the two ends are connected to the wheel. The axle can be integral, like a giant barbell, with two ends supporting the body through the suspension system, so the integral axle is usually fitted with a non-independent suspension. Special vehicle axle can also be broken, like two umbrellas inserted on both sides of the body, and then respectively through the suspension system to support the body, so it is used with independent suspension. According to the different driving modes of special purpose vehicles, the axle is also divided into steering axle, drive axle, steering drive axle and support axle. The steering bridge and the support bridge are both passive Bridges.

Most special purpose vehicles use front and rear drive (FR), so the front axle serves as the steering axle and the rear axle serves as the driving axle. The front axle becomes the steering drive axle and the rear axle ACTS as the support axle. The structure of the steering bridge is basically the same, consisting of two steering knuckles and a beam. If the beam was compared to the body, the knuckle was his head, which swayed from side to side, and the neck was what we used to call the kingpin, and the wheels were mounted on the knuckle as if he had a straw hat on his head. However, when driving, the straw hat turns, but the head does not turn, the middle is separated by a bearing, the head only to shake from side to side. Neck - the kingpin is the axis of the wheel rotation, the axis of the axis is not perpendicular to the ground, the special car wheel itself is not vertical, we will be in the wheel positioning section of the specific discussion. The difference between the steering drive axle and the steering axle is that everything is hollow. The special vehicle beam becomes the axle housing, and the steering knucks become the steering knuck housing, because there are more driving shafts inside. The drive shaft was split in two by a differential located in the middle of the axle housing. The two straw hats were not simply placed over the head, but connected directly to the two shafts inside. There is also an extra joint, the universal joint, at the "neck" position of the car's axle, so that the axle has become two parts, the inner axle and the outer axle.