What is the primary function of a differential in a vehicle?

The primary function of a differential in a vehicle is to allow the wheels to rotate at different speeds while turning. This capability is crucial because during a turn, the outside wheels travel a greater distance than the inside wheels. If both wheels were forced to turn at the same speed, the vehicle would experience excessive tire wear, potential loss of traction, and reduced handling performance. The differential achieves this by using a set of gears that enables one wheel to rotate faster than the other, effectively distributing the engine's torque to both wheels while accommodating the differences in wheel speed required for smooth and stable turns.

The other options do not pertain to the differential's function. For example, increasing engine power is related to engine components rather than the drivetrain. The air conditioning system is a separate component altogether, and while fuel efficiency can be influenced by drivetrain dynamics, it is not the fundamental role of the differential.