How does a differential allow automobile wheels to turn at different speeds?

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A differential gear is a mechanical arrangement that allows a vehicle's driving wheels to rotate at different speeds while still receiving power from the engine.1

When a vehicle travels on a straight road, the wheels rotate at the same speed, and the differential components rotate as a single unit. However, when turning a corner, the outside wheel must travel a longer path than the inside wheel. The differential accommodates this by allowing the side gears—which are attached to the wheel axles—to rotate relative to the differential pinions.1

In this configuration, the ring gear rotates at a speed equal to the mean speed of both wheels, effectively dividing the torque equally between them. While this system is efficient for standard driving, it can cause issues on slippery surfaces where one wheel loses traction; in such cases, a limited-slip differential may be used to maintain better power distribution.1