# Light Flywheel vs Heavy Flywheel - Effect of Flywheel Size (Mass) On Engine Performance

Read: What is a Flywheel? Function, Applications

The weight and size of the flywheel depend upon the nature of variation of torque required. In the case of a heavy flywheel, it is hard to change the rotational speed of the engine. As it takes a moment to accelerate the heavy flywheel, the rotational speed of the engine does not rapidly increase even when the accelerator pedal is depressed. The rotational speed of the engine is not lowered quickly when the pedal is released because there is more energy available in the flywheel to run crankshaft. That is, the responsiveness of the engine declines with an increase in weight of the flywheel. This means that acceleration and deceleration are difficult, which cause fuel economy to deteriorate. The heavy flywheel helps RPM recovery, allows the engine not to lug during the gear transmission.

The light flywheels decrease the inertia, so it gives a quick response to acceleration and deceleration. For this reason, light flywheels are used in the sports car. When the clutch disengaged, there is a greater drop of RPM because there is no heavy flywheel to keep the momentum going on. It is not good in normal condition because light flywheels increase the tendency of the engine to die during the gear shifts.

### Flywheel of two strokes and four stroke engine

In a four-stroke engine, there is one power stroke per two revolutions of the crankshaft (720° of crank rotation). The flywheel needs to provide energy to perform remaining three strokes. In a two-stroke engine, there is a power stroke in every revolution of the crank (every 360° of crank rotation) the flywheel of this engine need to provide energy for remaining one stroke. So the flywheel of four-stroke engine is usually designed heavier, and two-stroke engine use the lighter flywheels.

So the size and weight of the flywheel may ultimately depend upon the purpose of the engine.

• The light flywheels are fine, especially when you rarely stop the vehicle. Eg: Sports car