Rotational power from the engine's crankshaft is transferred by the 2015 WRX belt to power auxiliary systems like the AC system, alternator, and water pump. It's good to keep tabs on belt wear and look out for abrasions and cracks or damaged ribs, as a broken belt obviously can't transfer this power, potentially making your vehicle undrivable till it is fixed. Check out these replacement 2015 Subaru WRX serpentine belts to determine which is best for you.