These SRAM BlackBox Ceramic Bearing Pulleys enable you to upgrade your current system to reduce friction, increase stiffness and improve the life of your components. Designed to have a sound dampening effect thanks to AeroGlide technology, for a super-efficient and silent ride experience.AeroGlide Pulleys, with a sound dampening effect,For upgrading your current system to reduce friction and increase stiffness,Can improve the life of your components.