Originally Posted by Darth Lefty

Let's take the SS for one example. The cog capacity numbers have to do with distance from the pulley to the cassette. At the top cog it can manage a 14T without running too close, and an 11 won't be too far away to shift well. At the bottom, it can manage a 28 without running too close, and a 25 won't be too far away to shift well. With 11-28, the rear takes up 17 teeth of wrap, leaving 33-17=16 teeth difference for the front, matching the 50-34 front rings.