Once again, SRAM pushes the envelope with their Powerdome X XG-1090 10-Speed Cassette. Light, stiff, quick, and quiet thanks to the ultra-strong, hollow, one-piece design and StealthRing elastomers, this cassette is worthy of even the nicest road machines. SRAM has added elastomer rings between every cog to provide a 'bed' where the plates of the chain interface with the cog. These elastomer StealthRings make for whisper-quiet operation. It's light, too, with the small 11T cog separate, and the remaining 9 cogs milled from a solid block of tool-grade steel pressed onto a single aluminium cog (the largest one). And, to REDuce even more weight, excess material in the space between each cog is milled away.