Located on the end of the crankshaft, flywheels play a few different roles. On the outer edge of the flywheel you'll find the ring gear which the starter motor gear turns to start the engine. They also store momentum which they release to help the pistons rotate into position. In a manual transmission, flywheels provide a friction surface which helps the clutch do its job. In an automatic transmission, they work to keep the engine’s RPM from falling off too fast when accelerating through the gears. All of these things add up to flywheels helping your car give you a smooth vibration-free ride.