WickWerks makes a 38/24, a 36/22 and a 33/22 chainring set designed for a 3x to 2×9 or 2×10 conversion. The 2 new rings replace the 2 smaller rings of a typical mountain bike triple. The large ring is replaced by either a bash guard or some finger tip ends that cover the open spot on the outside where the large ring was.
Quick Instruction Overview:
1) With the new rings mounted, install the crank and check for frame clearance. Most frames are just fine, but depending on specific frame geometry, one of the 2.5mm spacers from the non-drive side of the BB can be moved to the drive side so the new 36t, or 38t ring will move outward, away from the frame, to clear the chainstay.
2) Next, shorten the chain. (We recommend a new chain with a new set of rings.) Set it properly for big ring to big cassette cog and the rest will be okay. The long cage rear derailleur designed for the mountain triple works fine. If building a new bike, you might choose use a medium length rear derailleur, but it’s not necessary.
3) To complete the change, adjust the front derailleur. It will need to be moved vertically for position to the new rings, then adjust the stops to lock-out the unused stroke where the big ring used to be. Some cable adjustment will also need to be done, and the conversion to 2x is complete.