Alloy 5 beam spider carrier with 3 alloy, 5 titanium & 4 Chromoly sprockets make this a lightweight, stiff & durable 12-speed Micro Spline MTB cassette. Hyperglide+ sprockets have a new computer designed tooth configuration with contoured shift gates, resulting in 1/3 faster shift time than current HG cassettes providing seamless, smooth operation even under load. Each of the sprockets are cut away extensively & drilled to further reduce weight without reducing rigidity; they also use a hard anodizing & nickel-plated finish for added durability & resistance to corrosion. The 10-45T allows a more efficient use of energy through finer cadence control in ever changing trail conditions while the 10-51T offers the ultimate wide ratio range of gears.