Now you can take advantage of similar gearing of the far more expensive XX1 setup. The Giant Cog is a 42T cog that gives your ten speed cassette a much wider gear range than the standard 11-36 cassette. Available in SRAM and Shimano, the Giant Cog works with XT, XTR and 1030, 1050 and 1070 cassettes. It requires the removal of the 17T cog and spacer. The GC is made in the USA in Minneapolis, MN from the same high quality 7075 T-6 aluminum as Wolf Tooth's front chainrings.
There are tons of reviews for this cog on the interweb but here's mine. Works better than I thought it would. Only issue is with the extreme chain line angle backpedaling more than half a crank rotation kicks the chain down to the 36t. Not an issue since if you are in the 42t you should only be pedaling forward and half a rotation is more than enough to reset the cranks in position to restart if you stop. If not, pick up the rear wheel and pedal forward to spin the chain back on the 42. My setup: full susp 29er 30t narrow wide in front, 11-36 slx cassette in rear. Removed the 11t and added the 42t since the cassette is pinned together in the middle 4 and i don't use the 11 much. Same lock ring worked. XT mid cage clutch rear der. Now I have basically the same granny gear as a 22/36. Also this sold out twice direct from Wolftooth before they emailed me so buy it from here at the same price and have it sooner than later.