It is the ability of the Subaru drive and serpentine belts to transfer the centrifugal motion from one pulley to another that makes it possible to provide power to many auxiliary systems on your vehicle. The drive belts have to be connected to the harmonic balancer that is mounted on the crankshaft to have the ability to provide the required motion for the other components on the front of the Subaru engine to be energized. This is the bottom most pulley in the center of the engine. The construction of the drive and serpentine belts is very similar in the material they use and the shapes expect that the serpentine belt is wider. The material for both is a reinforced polymer that should last for many years. The reason the Subaru drive and serpentine belts wear out is the polymer material they are constructed of tends to dry out and become brittle. This is when cracks and fraying of the belts are formed. If, during an inspection of a drive or serpent belt, cracks, fraying or even splitting of the belts surface are identified, replacement of them is warranted to help keep your Subaru operational. This inspection of the belting system on your vehicle should happen on a regular basis. It is as simple as just looking at them when you are checking the oil. The coolant hoses can also be inspected at this same time. If this inspection of the engine auxiliary components under the hood, including the drive and serpent belts is not done on a regular basis, the owner of the Subaru will not be aware of a problem that is beginning to develop. It is too late to take action if one of the belts or hoses fails when on the road because the vehicle will then be stranded where the failure occurs.