Install a 42-tooth Sprocket on a 10-speed Cassette

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One Up Components 42 Tooth Sprocket:

This is designed for SRAM and Shimano’s 10-speed drivetrains, which use 11t-36t cassettes.

42-tooth Sprocket for 10-speed SRAM or Shimano Cassette

For this particular you will need a chain whip, cassette tool, phillips head screwdriver, and a 5mm allen wrench.

The first thing you are going to do is shift into the smallest cog and release the clutch mechanism on the rear derailleur. Using a 5mm allen, remove the axle and drop the wheel out of the dropouts. Next, secure the cassette with the chain whip and use the cassette tool to back off the cassette lockring.

Remove Cassette Lockring with Chain Whip and Cassette Tool

In order to make room for the 42 tooth sprocket, you need to remove the 17 tooth cog from the middle of the cassette. Depending on what brand cassette you’re using, the provided spacer will either go on the front or back side of the one up sprocket.

For a Shimano cassette, place the spacer on the back side of the sprocket against the hub. Just like any hub, line up the thick spline with the thickest groove on the free hub body. Next, reinstall the rest of the cassette without the 17 tooth sprocket and its spacer. Next, reinstall the lockring, then reinstall the rear wheel.

Remove the 17-tooth Sprocket to Make Room for 42-tooth Sprocket, then Reinstall

Because this rear derailleur is set up to work with a 36 tooth cassette, we will need to readjust the b-tension screw to accommodate the larger diameter. With the b=tension adjusted all the way in, it gives just enough clearance to have it jump up on the 42 tooth sprocket with no problems.