The GoatLink 11 is available directly from
Wolf Tooth Components.
The WolfCage derailleur cage is a modified inner derailleur cage (facing the bike) and eccentric upper jockey wheel for Shimano 11 speed rear derailleurs that improves chain wrap and derailleur capacity. This is required for 11-49 cassettes (11-42 cassette + the Wolf Tooth GC 49) and also improves shifting and drivetrain life on other wide range cassettes.
The WolfCage installs in a couple minutes and simply replaces the stock inner cage and upper jockey wheel. You will not need to break your chain or remove your rear derailleur from the bike — much simpler than systems that replace inner and outer cages.