Fan belts, also known as drive belts, are an essential component of a car's engine. They are responsible for transferring power from the engine to other parts of the car, such as the alternator, air conditioning compressor, and power steering pump. The term 'fan belt' comes from the fact that they are often used to drive the fan that cools the engine. The crossword solution for fan belts is 'TIERS, ' referring to the multiple layers of rubber and fabric that make up the belt.