What allows the steering wheel to change the direction the vehicle is traveling?

The steering linkage is the correct answer because it is the system of components that connects the steering wheel, which the driver turns, to the wheels of the vehicle. When the driver turns the steering wheel, the steering linkage translates that motion to the steering mechanism that pivots the wheels to change the direction of the vehicle.

The steering linkage typically consists of various parts including tie rods and ball joints that work together to ensure that the wheels respond accurately to the driver's input. This connection is crucial for vehicle maneuverability, as it directly affects how sharply and quickly a vehicle can turn.

In contrast, while other components play important roles in the steering system, they do not directly facilitate the change in direction of the vehicle. The steering axis refers to the imaginary line around which the wheels turn, steering knuckles connect the steering linkage to the wheels, and steering ratio gears help determine how much the wheels turn in response to the steering wheel's rotation, but they do not directly change the direction the vehicle travels like the steering linkage does.