Sometimes a wheel on one side of a vehicle needs to spin faster than the wheel on the other side. While some wheels may spin freely (due to not being attached to an axle), wheels that are driven by the engine need to be on an axle, and this axle needs to allow the wheels to spin at different speeds; the differential allows this to happen. Two axle-mounted gears spin against each other by means of two other gears. The non-axle-mounted gears are attached to an assembly which is turned by the engine power.
Viscous Limited Slip Differentials
In a viscous limited slip differential, fluid is used to resist slip between the left and right wheels.
Torsen Limited Slip Differential
Torsen differentials use a special gearing design to reduce speed differences between wheels.