Differential is a mechanical device used between rear wheels of a four-wheeler vehicles. Typically 4-wheelers are rear wheel driven i.e. power is given to rear wheels . When a vehicle takes a turn it’s inner wheels have to undergo less number of revolutions whereas outer wheels have to undergo more number of revolutions. Now as front wheels are free (not powered) to revolve, they can suit themselves to required number of revolutions. But that is not the case with rear wheels. They are powered, hence their number of revolutions are controlled. A differential is a unit which governs the number of revolutions of both the rear wheels in order to take a turn without skidding. i.e. it provides more revolutions to outer wheel whereas less number of revolutions to inner wheel. Also it provides same speed to both the rear wheels when vehicle is travelling straight.