Originally, an axle was defined as a rigid cross-member linking two wheels. In the case of a so-called rigid axle, the wheels are mounted directly on this member and thus connected directly to the car body. Following the modern concept of independent suspension, this link has been removed, which complicates the definition of an axle in automobiles.
We now use the term “axle module” for independent suspension. This module is comprised of the hub carrier and an "axle". In line with this new concept, the definition of the axle is a combination of axle, stabiliser and possibly a driven shaft and steering mechanism. The axle carrier (also called a subframe) is also an essential part of the axle. Its attachment to the body is indirectly ensured by large rubber bearings. In conjunction with the hub carrier connected to it, it guarantees greater driving stability and reduces the transmission of vibrations to the passenger compartment.
The hub carrier consists of the suspension (i.e. spring and shock absorbers and wheel control mechanism) and the brakes. The wheels are mounted directly on the hub carrier via bearings. They are connected to the axle by means of control rods and to the car body by the spring and shock absorbers.