A car runs by converting chemical energy (the combination of fuel and air) into mechanical energy. This energy is transferred to the moving parts of the engine through a system of car engine pulleys.
The engine usually has an idler and/or tensioning pulley as well as a few pulleys that use the power of a travelling serpentine belt to drive components such as the alternator or water pump. As this energy transfer is essential to the running of the engine, high quality car engine pulleys are recommended if you need to replace any or all of your car engine pulleys. Show Less