Oneup Components 42-tooth Cog for Ten-Speed Cassettes - Reviewed

Oneup Components makes a CNC-machined 42-tooth cog that retrofits to most Shimano and SRAM ten-speed cassettes. The aluminum cog does not alter the spacing of the original cassette, and Oneup's instructions are quite simple: Unscrew the lock ring, remove the 17-tooth cassette sprocket and its accompanying spacer to make room for the big 42 tooth cog and then reassemble the sprockets. The addition of the 42 gives riders the low gear that is missing from conventional single-ring drivetrains - without having to reduce the chainring size and sacrifice top speed. Oneup Components sells its 42-tooth cog for $100 USD at its webstore.




Tech Info

Oneup's 42-tooth cog will fit any SRAM or Shimano 11 by 36-tooth, ten-speed cassette that has loose cogs from the 11 through the 17. SRAM XO type cassettes, which use a full-width aluminum spider to support the cogs, are not compatible. We used a Shimano XTR cassette and an old-school non-clutch XTR long-cage rear derailleur. SRAM X5 through X9 and Shimano XT and XTR ten-speed rear derailleurs will work in both medium and long cage versions. Oneup Components has a compatibility page that is regularly updated with exact part numbers and gearing ranges should you need further confirmation.



Oneup machined six shift gates into their aluminum sprocket that match up with the gates on Shimano and SRAM's 36-tooth cogs to ensure seamless shifting (Oneup says that there are 12 mathematical shift locations on their 42). The original cassette ratios are: 11-13-15-17-19-21-24-28-32-36, and with the elimination of the 17-tooth sprocket, the wide-range ratio is: 11-13-15-19-21-24-28-32-36-42. We were concerned that the four-tooth jump between the 15 and the 19 would be an issue because it is preceded by a two-tooth jump and followed by a smaller, three-tooth change. In reality, we never noticed the difference, although we are sure that more 'retentive' riders would take notice. On the large end of the cassette, the addition of the 42 creates a logical step from the 36 tooth - just like SRAM's 11-speed XD cassette.



Shimano and SRAM May Be Angry

It should be noted that SRAM and Shimano clearly state that the largest cog that their ten-speed rear derailleurs can handle is a 36 - definitely not a 42. We are sure to get grief from both establishments for posting a story that encourages their customers to force their mechs to handle a 42 - but, because neither have ponied up with a wide-range ten-speed cassette and rear derailleur to give existing ten-speed owners a lower priced wide-range gearing option, we're not concerned if they get their panties in a bunch. So, here's what you have to do to get their derailleurs to shift to the 42:

Most rear derailleurs have a B-tension screw in the body behind the hanger that rocks the derailleur back and away from the largest cassette cog. The function of the B-tension screw is to adjust the position of the upper pulley to ride as close to the largest cog as possible without interfering with shift action, or causing the pulley to rumble on the sprocket teeth. To get the rear derailleur to sit above the big 42-tooth cog, you'll need to run the B-tension screw almost all the way in for Shimano and for some SRAM derailleurs, you may need to remove the plastic thread-locker washer below the screw so you can run the screw in another few millimeters. Rocking the rear derailleur back requires the addition of some chain - as does the addition of the 42. Oneup Components says you'll need two links more, but we added three because the extra length puts the lower derailleur pulley farther back when you are in the big sprocket. This eases the angle that the lower run of chain must take from the pulley to the chainring, which reduces noise and improves shifting.



When you have the rear derailleur shifting properly, it will look completely wrong, but do not worry, because Shimano and SRAM have evolved their mechs to such a high degree, that they will shift marvelously when compromised as such (although, you may hear a different story from them if you ask for warranty instructions). So: Assemble cassette - Check! Crank B-tension screw - Check! Add chain - Check! Ensure shifting is adjusted properly - Check! All that is left is to go ride some hills.


Ride Impressions

We installed the Oneup Compinents 42-tooth conversion on a Shimano XTR-equipped Pivot Mach 5.7 that was previously converted to a one-by using an MRP 32-tooth chainring and chainguide. The conversion took less than an hour including the photos, so anyone with basic skills who has replaced a cassette and adjusted a rear derailleur could crank out the conversion in a half hour. We didn't even have to readjust the shifting, because Oneup's chainring duplicated the location of the original cogs perfectly.

On the dirt, shifting was quick and sure throughout the entire range of the cassette and, as mentioned, there was no discernible leap in resistance when we shifted between the 15 and the 19-tooth cogs, where the 17-tooth cog was removed. Having nearly the equivalent low gear of the Shimano 24 by 36 triple-chainring drivetrain with a single-ring setup was sweet on the steeps and the conversion might allow those who want a slightly taller gear to add a couple of teeth to their one-by chainrings. As far as wear goes, we expect the Oneup 42 to outlast the front sprocket by a considerable margin because it sees less overall use, and also because it has more teeth than any other sprocket in the drivetrain, so each tooth sees less action.


Pinkbike's Take: