The aftermarket cassette cog. Its like XX1 but for people with a real-world income and can't afford to drop $425 on a cassette and $300 on a derailleur while keeping the lights on at home. I call them the Working Man's XX1.
I bought the Wolftooth GC (Giant Cog) 40 this summer to squeeze some more gear range out of my 1x10 setup. Wolftooth offers models in 40 and 42 tooth that are machined to match the shift ramps or either Shimano cassettes or Sram. It works by being placed onto your freehub body before your cassette, then remove the 17t cog when assembling the rest of your cassette. Easy peasy.
The GC40 shifts smoothly and looks to be wearing well, although it is a bail-out gear for me that only sees use a couple of times on a typical ride. Its top notch machining quality and looks like it should last longer than the cassette itself. Your mileage may vary though, especially if you use the 40 (or42) tooth gear regularly. In conjunction with my Race Face Narrow-Wide 30t chainring and Zee short cage rear derailleur its the near perfect driveline setup. It would be nice to remove not only the 17 tooth from the cassette but also the 15 and replace it with 16 to give a nicer spread (I see that One-Up components now has a 16t cog that ships with their product).
To me, its worth the $80 to have a bail out gear that will hopefully last a few cassettes. Climbing on the fatbike while tired can be a taxing ordeal, so its nice to know that the 40t is there..... IF I need it. And its made in the USA, so your supporting North American workers when you buy.
I'll give it 4.5/5 stars. It would get the full 5 if it shipped with the 16 tooth like its competitor One-Up.
As always, these product(s) where purchased with my own money. I have not been paid or bribed to review this product. Comments whether positive or negative are purely my opinion only.
The Bric...._ mountain biker, road rider, heavyweight gear abuser. Built like a brick sh*thouse. No bike is safe.