A flywheel is a rotating mechanical device that is used to store rotational energy. In a vehicle with a manual transmission, the flywheel serves a crucial purpose. It is a thick metal disc, typically made of cast iron, steel, or aluminum, that is firmly bolted to a flange on the transmission side of the crankshaft inside the bell housing. The flywheel has a few different purposes, including:

• Providing mass for rotational inertia to keep the cars engine running. Otherwise, the engine will stall when the driver lets their foot off the accelerator.
• Balancing the engine. A flywheel is specifically weighted to the cars crankshaft to smooth out the rough feeling caused by even a slight imbalance.
• Allowing for an electric starter. The starter motor engages the starter ring on the edge of the flywheel to begin engine rotation.
• Connecting the engine with the transmission via a clutch to transmit power to the wheels.

The flywheel is connected to the crankshaft and is responsible for smoothing out the engines power pulses and storing energy through rotational momentum. It is usually a solid, metal disc thats about an inch thick, a foot in diameter, and around 10 to 40 pounds, depending largely on material, from lightweight aluminum to heavy cast iron. The flywheel also plays a role in inhibiting the supply of mechanical energy and transmitting rotational energy from the piston to the engine parts.