Differential gear, in auto mechanics, gear arrangement that allows power from the engine to be transmitted to a pair of traveling wheels, dividing the force equally between them but permitting them to follow paths of different lengths, as when turning a corner or traversing an uneven street. On a straight street the wheels rotate at the same rate; when turning a part the outside wheel has farther to move and can turn faster than the inner wheel if unrestrained.

The elements of the Ever-Power differential are demonstrated in the Figure. The energy from the transmitting is delivered to the bevel ring gear by the drive-shaft pinion, both of which are held in bearings in the rear-axle housing. The case is an open boxlike framework that is bolted to the band gear possesses bearings to support a couple of pairs of diametrically opposite differential bevel pinions. Each wheel axle is attached to a differential side gear, which meshes with the differential pinions. On a directly road the tires and the medial side gears rotate at the same rate, there is no relative motion between the differential part gears and pinions, and they all rotate as a unit with the case and ring gear. If the automobile turns to the left, the right-hand wheel will be forced to rotate faster compared to the left-hand wheel, and the medial side gears and the pinions will rotate in accordance with one another. The ring equipment rotates at a Differential Gear velocity that is add up to the mean speed of the remaining and right wheels. If the wheels are jacked up with the transmission in neutral and among the wheels is turned, the contrary wheel will turn in the opposite path at the same acceleration.

The torque (turning minute) transmitted to the two wheels with the Ever-Power differential may be the same. As a result, if one steering wheel slips, as in ice or mud, the torque to the other steering wheel is decreased. This disadvantage can be overcome relatively by the use of a limited-slip differential. In one edition a clutch connects among the axles and the band gear. When one wheel encounters low traction, its tendency to spin is usually resisted by the clutch, thus providing higher torque for the other wheel.
A differential in its most elementary form comprises two halves of an axle with a gear on each end, linked jointly by a third equipment making up three sides of a square. This is generally supplemented by a fourth gear for added power, completing the square.