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Flywheel: Function, Design & Importance (Explained)

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The flywheel is a disc-shaped engine part, it stores and releases energy, smoothes power delivery, and ensures the smooth operation of the vehicle’s engine.

This article aims to go over the flywheel and explain its importance, construction, and functionality.

flywheel engine part

Basic Physics of the Flywheel

The function of the flywheel is based on a fundamental physics principle: rotational inertia. This is the resistance of an object to changes in its state of rotation.

A flywheel has its weight concentrated towards the outside edge, meaning it has high rotational inertia, allowing it to efficiently store rotational energy.

Once the fly-wheel gets spinning, it wants to keep spinning, which is key to its function in an engine system.

The rotational energy stored in the flywheel during the power stroke of the engine can be released during the other engine cycles, smoothing out power delivery and helping the engine maintain a consistent speed.

Structure and Materials

Most flywheels are disc-shaped, constructed from durable and dense materials like cast iron or steel that can withstand the immense forces and high temperatures they are exposed to.

They consist of a large outer rim connected to the crankshaft via a central hub.

Recent advancements have led to the use of composite materials that offer improved strength-to-weight ratios.

This leads to lighter and more efficient flywheels that can offer performance improvements, particularly in high-performance vehicles.


The flywheel’s primary role is to store and release energy, but its functions don’t stop there. By working in tandem with the clutch, it allows the transmission to engage smoothly with the engine.

Another function of the flywheel due to its mass is to balance the engine and dampen vibrations, contributing to a smoother and more comfortable ride.

Overall, the flywheel performs the following functions:

  • Stores rotational energy within the powertrain
  • Dampens engine vibrations and shockwaves
  • Allows for smoother gear changes
  • Stabilises the engines RPMs and keeps them steady


The flywheel’s design and role slightly change depending on the type of vehicle and engine. Larger engines or those with fewer cylinders rely more heavily on the flywheel to smooth out power delivery.

In high-performance cars, lightweight flywheels are often used to allow the engine to rev more quickly.

Motorcycles have a small and compact flywheel due to their engine size and configuration, but the basic function is to smooth out the power delivery and ensure consistent engine speed.

Common Problems

Like any component in a vehicle, the flywheel is not immune to wear and tear. Common problems include the following.

  • Warping
  • Heat spots
  • Cracks

These issues can all affect the smooth operation of your vehicle. It’s important to maintain and diagnose potential issues with a vehicles flywheel as part of regular upkeep.

Symptoms of a failing flywheel can range from strange noises and vibrations to clutch slippage. If you experience these, it’s recommended to have a professional inspect the situation.


The flywheel has the main function to ensure the smooth operation of a vehicles engine. It stores and releases rotational energy.

Is a flywheel a clutch?

The flywheel is not the same as a clutch. The clutch connects the flywheel to the gearbox and the rest of the drivetrain, while the flywheel is connected to the engine.

What happens when the flywheel fails?

A damaged flywheel will make it more difficult to change gear as the clutch may not disengage properly. You may also notice more vibration and strange noises.

Will a car still start if the flywheel is broken?

The car may still start if the flywheel is damaged, but it could lead to further engine and gearbox damage. The engine may also run rough, vibrate, and make strange noises.

  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer.He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

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