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There are those that say Shimano blew it when they came out with a cassette offering less gear range than SRAM's widely praised 10-42 tooth cassette. At the same time, we'd wager a bet that among those people are people that still prefer the feel of Shimano over SRAM. Well, OneUp has made a product for those people. The new 45 tooth expander sprocket opens up Shimano XT/XTR (M8000/M9000) to a wider range of users when set up with a single chainring by extending the cassette from 11-40 to 11-45 teeth.


While not a huge jump, the 45T expander increases the stock Shimano 11-speed 11-40T cassette range by 12.5%. As a result, you can increase your 1x11 front chainring from a 30 to 34T without losing any low range, or simply keep the same chainring for an easier climbing gear. It's up to you.

Shimano 11-speed mountain bike rear derailleurs do not have the capacity needed to run 2x11 with an extended 11-42T (or 11-45T) cassette, so any 2x bike will come with a 11-40T cassette. Shimano does offer a new 11-42T XT cassette for 1x specific applications, however, though the OneUp expander is not compatible with it.

Ultimately, a modded 11-45T Shimano/OneUp cassette provides very close to the same range as SRAM's 10-42T without the need for a new freehub.


The OneUp 45T tunes the cassette progression into two distinct zones optimized for climbing and descending:

Climbing - (21-45T) 13-15% cassette progression. Smaller jumps to maintain an optimum even climbing cadence.

Descending - (11-18T) 15-20% cassette progression. Larger jumps to reduce double tap shifting and provide faster burst acceleration when mainly pumping not spinning down trails.


OneUp says installation is as easy as the original 42T expander. Remove the stock 17 and 19T sprockets and replace with OneUp's 18 and 45T. Due to the large pulley wheel offset of the latest 11-speed Shimano rear derailleurs, B-Screw adjustment is within the normal operating range and chain wrap is sufficient. The conversion keeps the 40T as the smallest aluminum sprocket.


Product Highlights

  • Price: $90 USD
  • Material: 7075-T6 Aluminum (45T), Nickel plated hardened steel (18T)
  • Weight: 65g more than stock 11-40 cassette
  • Compatibility: For XT/XTR M8000/M9000 11-40T cassettes. 11 speed only. Standard freehub body.
  • Cassette progression:  11-13-15-18-21-24-27-31-35-40-45
  • Increased Range: 12.5%
  • Color: Matched to XTR
  • US Patent 9,011,28

OneUp was recently granted a US patent for their expander sprockets. Whether or not it will have an impact on competing products is yet to be seen.

Visit for more details. OneUp also offers narrow/wide chainrings designed for use with Shimano drivetrains.

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