Shimano's Dura-Ace Di2 Front Derailleur is the brains of their Di2 electronic shifting system. There's an ultra-compact CPU inside the beautiful carbon body that actually monitors the position of both derailleurs, ensuring that shifting is super fast and incredibly accurate shift after shift. It also creates a front derailleur that moves to maintain clearance between the chain and cage no matter what chainring/cog combination you choose (no rubbing or trimming). Even more impressive and important, this is the quickest shifting front derailleur available meaning you'll never miss a shift again and will hit the right ring faster than ever. Thanks to no cables and housing to stretch, wear, or fail, you'll also love Di2's amazing durability and consistently smooth operation.
Capacity is calculated by subtracting your smallest chainring's tooth count from the largest chainring's tooth count. Example: 46/34/24 chainrings: 46 - 24 = 22-tooth capacity.