XTD Flywheels are made using the highest quality, most modern materials available. XTD could achieve manufacturing its original flywheels about 200% more strength compared with normal flywheels. It was forged using Chrome-molybdenum steel. The power of inertia rotation can be decreased by reducing the excess weight, and therefore, its strength directly passed through to the high response. The XTD light weight flywheel is made from the optimal weight and optimal form which were set up for each type of a car from the chrome forge material. By shaving all circumference of the chrome forge material, the variation in weight and the deviation of balance are pressed down to the minimum. Processing for raising wear durability and heat treatment etc... is performed in the surface. Various know-how for realizing lightness, strength, and high balance is condensed to the XTD light weight flywheel. If a flywheel is made light, it is said that an engine response improves. In case of revolving thing like a flywheel, the power (inertia power) which is always going to continue fixed rotation occurs. When an accelerator is stepped on in from an idling state, a flywheel tends to keep an idling state according to its inertia power, although engine is going to raise rotations. When inertia power becomes large, much time is needed for going up rotation. In the case of the XTD lightweight flywheel, since weight (especially flywheel perimeter part) is light, there is little inertia power of influencing rotation of engine. Since time to go up rotation is shortened, the response of engine to a accelerator becomes quick (a response improves).