Trailer axles can be integral, like a huge barbell, with suspension systems supporting the body at both ends. Therefore, integral trailer axles are usually paired with non independent suspensions; Trailer axles can also be detachable, like two umbrellas inserted on both sides of the vehicle and supported by their respective suspension systems, so detachable trailer axles are paired with independent suspensions.

The structure of the steering bridge is basically the same, consisting of two steering knuckles and a crossbeam. If we compare the crossbeam to the body, the steering knuckle is the head that sways left and right, the neck is what we often call the main pin, and the wheels are mounted on the steering knuckle, as if wearing a straw hat on the head. However, while driving, the straw hat rotates while the head does not, separated by bearings in the middle, and the head only moves left and right. The neck pivot is the axis of rotation of the wheel, which is not perpendicular to the ground and the wheel itself is not perpendicular. We will discuss this in detail in the section on wheel alignment.

The difference between a steering drive axle and a steering axle is that everything is hollow, the crossbeam becomes the axle housing, and the steering knuckle becomes the steering knuckle housing because there is an additional drive shaft inside. This drive shaft has been split into two halves by a differential located in the middle of the axle housing. Two straw hats are not simply worn on the head, they also need to be directly connected to the two half shafts inside. The half shaft has also added a joint - a universal joint - at the "neck" position, so the half shaft has become two parts, the inner half shaft and the outer half shaft.

According to different driving modes, trailer axles are also divided into four types: steering axle, drive axle, steering drive axle, and support axle. Both the steering bridge and the support bridge are passive bridges. Most cars use front rear drive (FR), so the front axle serves as the steering axle and the rear axle serves as the drive axle; For front wheel drive (FF) cars, the front axle serves as the steering drive axle, while the rear axle acts as the support axle.