Ralco RZ ALUMINUM Flywheels are made using the highest quality, most modern materials available. The flywheel itself is made from 6061 T6 billet aluminum. It is CNC machined at a constant surface speed for durability and finish. The friction surface is made from high carbon alloy steel. It is incredibly durable allowing the user to use just about any clutch disc material available from organic to Kevlar and even sintered iron. The friction plate can be machined or replaced as needed. The mass at the center of the flywheel is retained for strength, but the mass at the outside is eliminated for optimum performance.