Sram XG-1090 X-Dome Red Cassette;

This incredibly innovative design is the most advanced cassette ever made. It is super light, deadly silent, and delivers an undeniable performance advantage. The eight cogs in the middle are machined from a single block of high grade tool steel, increasing stiffness while weighing even less than a titanium cassette. Between each cog in the block is a Stealth Ring elastomer to reduce vibration and noise.