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I have a torque wrench that goes up to 24 N⋅m but as far as I understand a cassette ring should be tightened to about 40 N⋅m. What is the consequence of tightening the cassette ring to 24 N⋅m instead of 40 N⋅m? Will it damage the bicycle or make the bicycle unsafe?

Iwan Aucamp
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    The specific torque really isn’t important. You’ll hear and feel the lock ring start to click as it tightens. Final torque is usually around when the last click takes a pretty hard push (but not a Herculean effort. Don’t step on the wrench or use a cheater bar). – MaplePanda Aug 08 '20 at 17:14
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    Highly doubtful one can get that much torque on the lock ring as the serrations on it and the small cassette cog bind with each other. – Jeff Aug 08 '20 at 17:24
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    @Jeff, you can easily apply over 40Nm. Just keep applying force until you reach whatever torque you want, the 'binding' will actually assist in your endeavour. I guess over a certain torque something will shear and fail, is that what you're suggesting? – Lamar Latrell Aug 08 '20 at 23:01
  • @Lamar Latrell my thinking was the actual torque by threading wouldn't be reached before the serrations bind. I suppose if the torque wrench set at 40 N-m clicks, that's well enough whether it's due to rotational tightness or because the serrations are bound and would take >40 to move further. It's the same result. You're right, the serrations do assist reaching adequate tightness – Jeff Aug 10 '20 at 09:57

1 Answers1

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Assuming your cassette and freehub body are conventional, the cassette sits on a series of splines, and would be free to slide left/right if there were no locknut in the way.

Since the hole in the cassette will be larger than the diameter of the freehub body, a missing or loose lockring will allow the cassette to twist out of the vertical plane parallel with the rim. Effectively this will vary the horizontal position of the teeth over each wheel rotation, more noticeably on the bigger cogs.

However as long as the lockring is done up sufficiently to not back itself out and also tight enough to stop the cassette moving relative to the freehub body, you'll be fine.

I've serviced bikes where the lockring has needed a cheater bar to undo, and others where the lockring was not even finger-tight. These latter ones tended to have poor shifting and/or damage to the freehub body's splines. Since finger-tight is under 3 Nm ( okay 0.1~0.3 Nm or 1.7~2.6 Nm depending on what study you're comparing) then 24 Nm from your torque wrench plus a yank more with a spanner should be close enough.

In full disclosure, I've never used a torque wrench when securing a cassette lockring (new or reused) and I've never had one come off or fail. You develop a feel for a pressure that is tight enough for this application.

  • https://www.ors.org/Transactions/59/PS2--085/1535.html tests .1 to .3 Nm
  • https://en.wiktionary.org/wiki/finger_tight says 1.7~2.6 Nm
Criggie
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    You can get a lot of leverage using typical tools for cassette lockrings, so I agree that a torque wrench isn't vital here - just making it tight should do. I'd just add that because the OP has a 24Nm torque wrench, he can max out that torque wrench to get a feel for what 24Nm is like, then tighten the lockring some more. This may go without saying, but exceeding the maximum torque limit on the wrench will damage the mechanism, so if it's a beam type wrench without a cam-out function, I hope the OP exercises caution. – Weiwen Ng Aug 08 '20 at 13:33
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    I've stopped using my automotive torque wrench for cassette lockrings, in favour of a 12" ratchet handle. With moderate hand force that's plenty, and getting it off again is much easier. I reckon that's 20-30Nm. – Chris H Aug 08 '20 at 17:13