The Reserve Rack II provides a simple, aerodynamic solution to carrying water and inflation devices. It mounts behind the saddle for enhanced aerodynamics, and if used only for water, it can hold up to two bottles with the included Rib Cage II bottle cages. And if used with our Sitero Wing, it's capable of holding one bottle and a CO2 inflation device. Say goodbye to sacrificing aero performance for the sake of carrying your essentials.