If you've read How Car Engines Work, you understand how a car's power is generated; and if you've read How Manual Transmissions Work, you understand where the power goes next. This article will explain differentials -- where the power, in most cars, makes its last stop before spinning the wheels.

The differential has three jobs:

  • To aim the engine power at the wheels
  • To act as the final gear reduction in the vehicle, slowing the rotational speed of the transmission one final time before it hits the wheels
  • To transmit the power to the wheels while allowing them to rotate at different speeds (This is the one that earned the differential its name.)

In this edition of HowStuffWorks, you'll learn why your car needs a differential, how it works and what its shortcomings are. We'll also look at several types of positraction, also known as limited slip differentials.