You've seen them advertised and maybe you've already purchased and installed a lightened flywheel for your street, street/strip or full-race car. The clutch company offered a lightened flywheel, so you decided to get one with your new clutch. Did you make the right decision? In most cases, you may have gone in the right direction. In some cases, the stock, a slightly heavier or a slightly lighter flywheel may have been optimum for your application. Understanding exactly how a flywheel works will ensure that you get the best flywheel for your performance combination.

Flywheel: The Friction Surface
One purpose of the flywheel is to serve as a friction surface for the clutch disc. As the clutch is disengaged (when you release the clutch pedal from the floor), the clutch disc begins to be pressed against the flywheel by the pressure ring of the clutch cover (a.k.a. pressure plate). Friction between the clutch disc and the flywheel will cause the clutch disc to be accelerated. Once the clutch is fully disengaged (your foot is off the clutch pedal), the pressure ring will have clamped the clutch disc against the flywheel and the input shaft of the transmission will now be at the same speed as the engine. At this point the clutch disc has also been accelerated from a dead stop to the speed of the engine.

The important aspect of the flywheel as a friction surface is that the flywheel must have a surface that is compatible with the material used on the clutch disc itself. We have seen some aluminum flywheels that use steel inserts that do not fair well with many of the more-popular metallic disc compounds. In most cases, non-metallic, organic clutch discs will be the most compatible to the different materials used on flywheel friction surfaces. The metallic compound clutch discs will be the most difficult to find compatible flywheels friction surfaces. For any application uses a metallic clutch disk, it is a good idea to purchase the flywheel from the clutch manufacturer or be sure to ask the flywheel manufacturer if the flywheel will be compatible with the clutch disc material that you will be using.

When you teardown your clutch for inspection, you should not see deep grooves or gouges in the friction surface of the flywheel. If you do, you should seek a different flywheel to work better with your specific clutch disc.

Flywheel: The Energy Storage Device
So if the purpose of the flywheel is to just serve as a friction surface why do people care about the weight of the flywheel? A flywheel actually serves an additional purpose besides acting as a friction surface. The flywheel also serves as an energy storage device for your vehicle.

When your engine is running, potential energy is stored in your flywheel. Two factors influence the amount of energy stored in the flywheel: 1) the weight of the flywheel and 2) the speed at which the flywheel is being rotated (engine rpm).

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