To achieve the perfect balance of performance, durability and cost, Zipp hubs are machined to the closest tolerances possible and are supplied standard with steel bearings of the highest grade available.But, for cyclists looking for that extra advantage, Zipp has partnered with CeramicSpeed to create specific ceramic upgrade bearing kits for use in all Zipp hubs and free hub driver bodies. These kits are all available now, and offer the following:- Lowest resistance hybrid ceramic (ceramic balls and steel cages) available.- Measurable wattage savings between 1.5 and 9 watts per bearing set, depending on the level and condition of your existing bearings.Available in convenient two-packs for Zipp front hubs, rear hubs and free hub driver bodies.