I recently converted from 3x10 to 1x10 on the front of my Trek Fuel EX so I decided to give a 40T cog a try in the back.  It's just not for me so I am back to 11x36.  

This cog has one trip around Sherman (main loop only), but has just enough paint off the tips of the teeth as to be non-returnable.  If anyone has interest and can meet at Sherman for a hand off, I'll take 50 bucks. I live less than 10 min from there. I never could get the arrangement where you replace the 15 and 17 with a 16 to shift just right every time, but if you want to give it a try, I'll include a Shimano 16T for free.  Wolf Tooth and One Up make custom 16T cogs for this arrangement, but I don't know if the results are any better. As far as the 40T, shifting on and off of it was flawless and I did not have to add an extended B screw.

Scoop here: 

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Install is a breeze:  (You need to Login or Register to view media files and links);

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