An axle is a straight shaft that is fixed in location and is use to mount rotating wheels or gears. The wheel or gear can be attached to the axle with a built in bearing or bushing. A bearing or bushing fits inside the center of the wheel and allows it to rotate without affecting the axle itself. The purpose of an axle is to secure the wheels or gears to specific locations relative to other wheels or gears.

Every vehicle with wheels has an axle. To find the axle, look for the wheels and then look underneath the vehicle for a method of securing the wheel in place. Without an axle, the wheels would not remained fixed in position and the force and weight of the vehicle would make the wheel bend flat.

In a vehicle, the axle absorbs braking and acceleration forces, as well as the actual weight of the vehicle. The axle forms a central part of the structural strength of the vehicle. It must be able to absorbs the weight and transfer the forces away from the wheels in order to reduce pressure on the joints of the vehicle. In a modern vehicle, the axle plays a role in the driving, breaking and steering functions. The design of the axle has bee modified over time to accommodate these multiple requirements and to ensure an appropriate level of structural support.

The drive train of a vehicle is the system of transferring the power of the motor into a force that rotates the axle. This rotation, in turn, moves the wheels, which moves the vehicle. When you apply the breaks on a vehicle, the rotation of the axle is slowed by the application of friction to reduce the rate of wheel rotation. The steering wheel is attached to a steering axle, which controls the direction of the front wheels through the attachment to the front wheel axle.

There are three different kinds of axles in vehicles: straight, split and tandem. In a straight axle, there is one shaft connecting the two parallel wheels. The wheels are both secured in place onto the axle. The rotation rate and direction is fixed by the axle. The benefits of this kind of axle are the ability to keep the wheel position consistent and distribute the weight of heavy loads evenly.

A split-axle design occurs when each wheel is attached to a separate shaft. The purpose of this split is to provide a fixed position for the wheel, but to allow each wheel to move independent of the other and is used in passenger cars. In a tandem axle, there are multiple axles located in a relatively close proximity to each other. The purpose of this design is to increase the weight capacity of the vehicle and is most commonly used in large trucks.