OneUp 42t cog

Looks kinda cool if you ask me. The jumps are noticeable.
Looks kinda cool if you ask me. The jumps are noticeable.

My fatbike has a 26t front ring and an 11 x 36t (10spd) rear cassette.  The biggest middle ring for the Surly O.D crank is a 26 but that’s not a bad thing for me.  Most of the time when fatbiking I’m always looking for a lower granny gear to keep momentum and smooth pedaling to keep traction and a straight line, especially on soft snow.  So when I saw the OneUp 42 aftermarket cog for Shimano or SRAM cassettes I had to give it a try.  (Wolf Tooth Components also has one.)  This is how it works. You remove your 17t cog and put the new 42t behind the 36t, with the supplied small spacer either in front of or in back of the 42 (depending on whether you have a Shimano or SRAM cassette).  This is an XT so I put it in back, put on the 42, then put on the rest of the cassette.

keep or leave out the B-limit washer depending on how it shifts
keep or leave out the B-limit washer depending on how it shifts

Once it’s on your wheel, you have to tighten the B-tension screw until the upper pulley clears the 42, which is quite a few turns.  If it still doesn’t shift up there you will have to remove the plastic washer that limits the B-limit screw.  I took mine out and added another turn of the screw before deciding that was good enough clearance and good enough shifting.  It’s a bit slower shifting across the entire cassette if you leave the clutch on but with the clutch off it’s pretty regular and you hardly notice the 2 new bigger jumps.

that's pushing the range
that’s pushing the range

While riding, I did notice the jump where the 17t cog was removed.  But the jump to the 42 feels natural, probably because when you need that extra low gear the easier the better.  I tested it out up the road and i can definitely say that if i hadn’t installed the 42 i would have turned around almost immediately because I wouldn’t have been able to pedal easy enough to stay afloat.  As it was, it was slow going in the 4-6″ of wet Sierra cement on top of…cement, but with 3psi in the Lou/Bud combo…i was just able to stay afloat and pedal in the 26×42.  I’m pretty sold on these for converting an existing 1×10 setup to a cassette with more range.

Robinson Flat
Robinson Flat

2 thoughts on “OneUp 42t cog

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  1. Good to hear some rider feedback on one of these. I’m curious, but don’t currently use a 10sp drivetrain. I am hoping either SRAM or Shimano choose to bring some wide range 1x systems to market for 10/9sp systems, especially at the XT/SLX and X9/X7 price point.

    Any chance you think this will work with a 9sp cassette, including some spacer adjustments? In theory, a thumb shifter and a 9sp cassette with a 30T ring and an 11-42 might actually allow me to go 1x on a mountain touring bike like the Krampus, etc. For me, 11-36 isn;t enough unless I choose a super small chainring, but I’d prefer to keep some higher gears.

    However, I’ll also be exploring 29+ on the Mukluk, which leaves all kinds of room for extra gears.

    I am really enjoying the blog. In fact, it is my current favorite, especially with all the new fatbike and 29+ ideas coming through. Thanks!


  2. Thanks Nicholas! I’m humbled to hear my blog is your current fav.

    I would bet others are wondering the same thing as you about putting a 42t on a 9spd cassette. I don’t see why not, it would just be a matter of putting a very slim spacer between the 42 and the biggest cog on the cassette. The OneUp ring comes with such a spacer (maybe 1mm wide, i didn’t measure) so maybe they’d send you two if you asked? But i bet you could run a 10spd chain on the 9spd cassette with the 42 and get fine shifting. I’m not sure what ring i’d take off, maybe the 16 on a 9spd?

    I know what you mean about going 1x on a touring rig. I had my 29+ set up with a 28t ring and a 10spd 11×36 and although it was doable unloaded it was too hard a gear on very steep stuff especially with gear. With the 42, i bet it’d be much better, but your “big ring” wouldn’t be that big for the flats and downhills. Always a tradeoff but i think for being able to run Knards it’s worth it. Because of that I’m making myself a new 29+ that’ll become my touring rig and use the Rohloff and Dually rims. Super psyched to get that up and running for the summer.

    I’d be surprised if Shimano doesn’t come out with a wide-range cassette to match SRAM’s 11-spd offerings, but i would be surprised if anyone offered a 9 or even 10spd equivalent. OneUp and Wolf Tooth would be good to talk to about such conversions, I’m sure they’ve tried it all.

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