Twenty6 40T Cog ShimanoWhen SRAM launched it’s original one by specific drivetrain, it not only inspired 2x loyalists to give up their front derailleurs, it also opened the eyes of long time 1x devotees to the wonders of a wider gear range.

Unfortunately, even with the release of slightly cheaper 11 speed drivetrain, the technology still remains out of reach for the average consumer. Luckily, the aftermarket has been quick to find a solution to the poor mans first world problems. Companies like Twenty6 are now offering a cassette adapter that will allow you to swap out a lesser used gear for a 40 or 42T granny gear.

At $95, plus the price of the cassette, the cassette adapter is the only option (for well) under a thousand dollars that gives you the performance benefits of an 11-42T cassette. So how does it work? Shift past the break to find out..

Twenty6 40T Cog Details

Twenty6 Products is a small company based out of Montana. They’re famous in the cycling arena for wild anodization, high end platform pedals, and our favorite aftermarket brake levers. In addition to their bicycle product division, their machine shop also manufacturers products for local and national engineering firms, and all of their products are built here in the United Sates.

Twenty6 40T Cog RidgesFor the past five months, the company has been developing their new 40T and 42T cogs. The first four weeks were spent creating different revisions, making design changes, and doing subtle tweaks until the cog worked perfectly.

Each cog is machined on a US built Haas CNC machine out of Kaiser brand 7075 aluminum plate. They started with such high grade aluminum because it has excellent strength, stiffness, and wear resistant properties.

One of the areas the company experimented with was shifting ramps, before ultimately settling on five. They found that the more shifting ramps you added, the weaker the overall cog became due to the quantity of material that had to be removed.

Twenty6 40T Rear Cog

One of the other unique features of this product is that the thickness of the cog has been stepped down, starting from the center and moving outwards in 1/4mm increments.

Both Shimano and SRAM drivetrains are fairly similar, so the Twenty6 cog is compatible with either drivetrain via the inclusion or exclusion of a spacer. For SRAM cassettes, you simply use the included spacer to push the cog out from the cassette body.

The rational behind this approach, rather than making two drivetrain specific models, is that this doesn’t force retailers to stock two different items. The one caveat, is that the 40T cog works best for Shimano drivetrains, while SRAM will easily accept either a 40 or 42T.Twenty6 40T Cog Weight

Claimed weight for the 40T was 68 g, although our pretty blue cog was two grams lighter at 66 g. The claimed weight for the larger 42T is 80 g. Shimano B-Tension Screw

In addition to the cog and spacer, each kit comes with an extra long b-tensioner screw. Our demo bike, a GT Sensor, was originally spec’d with a triple. Even though that oudated tech has been replaced with a 1x specific crank, we couldn’t eviscerate all signs of it’s shameful beginnings.

GT Sensor B-Tension clearance with 40T Twenty6 CogTherefore shifting duties are still performed by a long cage XT derailleur, which in this case, did not require the use of the replacement screw. Just for “shifts” though, we used it anyways.

Aside from adjusting the B-tension, the entire setup was fairly painless.
Twenty6 40T Cog MountedThe trade off of for the extra low gear range of the 40T gear is that we had to ditch our 17T. If you look closely, you can see the gap  between the the 15T and 19T on our cassette.

Twenty6 40T Cog Mounted Non Driveside ViewOut on the trail, the increased range is noticeable and makes prolonged steep fireroads less of a chore. Like calculus, you can just plug and chug till you reach your destination.

While Zach experienced some infrequent issues when shifting onto the 42T One Up Cassette Adapter on his fat bike, I did not experience any similar issues with the smaller 40T Twenty6 Cog.

What is noticeable now is the jump between the 15T and 19T when shifting through the cassette. While the stock gearing has a nice gradual step between shifts, removing the 17T left an awkward gap in cadence when hammering on the pedals. It’s not something you could probably learn to live with, but I still find it annoying, and the best solution currently seems to be replacing both the 15 and 17T for an aftermarket 16T.

Small compromises aside, if you’re looking for an alternative to XX1, the Twenty6 cog offers crisp shifting and improved range in a colorful American made package. You can pick yours up in one of ten different colors for $95 here on their website.

Drivetrain Setup:

  • Shimano Deore XT, SL-M780, Rapid Fire Shifter
  • E13 TRS Race Crank
  • E13 Guide Ring M 28T
  • KMC X10 Chain
  • Shimano Deore XT Shadow Plus Long Cage RD
  • Shimano Deore XT, CS-M771-10, 10-Speed, 11-36T
  • Twenty6 40T Cassette Adapter



  1. Replacing both 15 and 17 with any 16 I have come across will not clock properly. A useful kludge is to file the smaller indexing gap in the cog open to be equal is size to the others and then walk the cog around the freehub to get much better clocking and shifting.

  2. Shimano has a new 16t 4th position cog coming that will hopefully take care of that, Mike. I have not seen it yet or the Miche version as they are all vaporware ATM.

  3. One angle that no one else has mentioned to my knowledge is that you could use these with a two by setup and end up with an even bigger gear range. For example, you could use a double crank with a 26t inner ring and a 34t outer one, and end up with a very wide range.

  4. @Rico – I went 32 for my area, and I think 34 would be nigh impossible to push up some of our fire road climbs. Props to you for being able to make it work though!

  5. Hey it doesn’t say what SRAM cassesttes it works with – I have a XO 11-36, and I want to run it as a 11-40 with double on the front.

  6. LilJoe, I have an 18t Miche cog I also fiddled with to turn a 6700 12-30 into a 13-30 (yeah, old guy, virtually no need for fast gears!). This one shifts fine.

  7. I have been using a different make 40t and love it! I opted to replace my 15 and 17 cog with a 16. This makes my step go from 13 -> 16 -> 19. It works really well for my cadence desire.

  8. … ok, another piece of colored aluminium (for 100 bucks). But why? We need correct, entire, black or silver 11-40/11-42 cassettes! 🙂

    SRAM X* and Shimano XTR, thanks but we need cheaper cassettes. I wont pay $$$$$ for piece of Alu as for Francium or Lawrecium 🙂 Dont need CNC either. Common sense? It is not a part of STS-132 (Shuttle)… It is just a piece of ordinary metal.

    Still and still the only one correct, cheap and decent (I have one on my Spesh Camber 2013) 11-40/11-42 cassette around:

  9. i run 30 x 11-36. great low gear, and i never spin out. i used to but after some bad crashes i’ve given up on that, ha ha.

  10. OneUp Components has been throwing in a free 16T when you purchase the 42T. You remove the 15T along with the 17T which yields a smaller 16-19 instead of 15-19 gap.

  11. Why is this item needed?

    32×11 at 110 cadence = 31.1mph
    32×36 at 50 cadence = 4.2mph
    (650b wheels)

    If you need to go faster than 31mph in the woods your a better man than I am…
    Slower than 4mph? Run! (or walk)

  12. “It’s not something you could probably learn to live with”

    You mean “It’s something you could… live with”

What do you think?