When 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 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.
For 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.
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.
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. 
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.
Therefore 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.
The 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.
Out 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
