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Old 07-31-11, 05:44 PM   #1
Mr. T.
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Should this Cassette be replaced?

I bought a new chain to install and the LBS said I should get a new cassette because they wear together, which I have heard but I know you don't have to change the cassette everytime you change a chain. Can I get an expert opinion on whether this 105 cassette should be replaced?

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Old 07-31-11, 05:50 PM   #2
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That's not something that can be evaluated from a photo. If you want to try a new chain on it, then find a safe place to exert a lot of torque and carefully try each cog with heavy torque to see whether any of them result in skipping. Best to do this while seated, in case it cuts loose on you.
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Old 07-31-11, 06:05 PM   #3
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Originally Posted by mechBgon View Post
That's not something that can be evaluated from a photo. If you want to try a new chain on it, then find a safe place to exert a lot of torque and carefully try each cog with heavy torque to see whether any of them result in skipping. Best to do this while seated, in case it cuts loose on you.
When you say skipping, do you mean the chain skips when heavy torque is applied without shifting?

If you can't tell by looking at it, when do you determine that it is time to change a cassette? Is it just when you experience this skipping issue, or are there other signs?
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Old 07-31-11, 06:08 PM   #4
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peened or mushroomed cassette teeth can be checked in a photo. by that time the cassette is toast
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Old 07-31-11, 06:09 PM   #5
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If a chain is allowed to wear it becomes stretched too much it causes the cassette cogs to wear excessively, the teeth wear to match the extended chain. When this happens a new chain does not mesh properly with the worn cogs causing the chain to skip.
This problem can be avoided by measuring your chain often with a good steel ruler. A chain should be replaced by the time any one foot interval of chain has elongated to 12 1/16 inches.
A good cassette should out last at least 3 chains.
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Old 07-31-11, 06:18 PM   #6
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There is this tool for checking cassette wear: http://www.rohloff.de/en/products/hg_ig_check/

But is is simpler to just put on a new chain. If it skips on certain cogs, then the cassette is toast and needs to be replaced.
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Old 07-31-11, 06:38 PM   #7
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Mr. T: You can get a clue by measuring the old chain. If 12 links measure less than 12 1/16 inches you may or may not need a new cassette, depending on its history. If they measure 12 1/8 or more you definitely need an new cassette.
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Old 07-31-11, 06:48 PM   #8
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There is this tool for checking cassette wear: http://www.rohloff.de/en/products/hg_ig_check/
That tool is from the 7-speed era. Too bad they don't work on the size of cogs used on mountain bikes these days. Rohloff holds the amusing opinion that cogs larger than this tool was designed to measure, wouldn't be likely to wear out:

Quote:

Sprockets with more than 21 teeth are rarely worn out, so they
should not cause any problems while in use. Therefore, a check up
is normally not necessary.


Riiiiiight. And monkeys might fly out-- well, we won't go there. Ok, done with my little rant now

My own general preference is to wear out both at once, then replace both at once. When I gamble on adding a new chain to my old cassette, sometimes I have chain skip in cogs I use a lot, and sometimes that only shows up at the worst possible moment, whether it's climbing a hill in a race, or trying to blast across an intersection where I got stuck waiting to turn across oncoming traffic. If you want to roll the dice, then just do the best high-torque reality check you can in every cog.
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Old 07-31-11, 08:26 PM   #9
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A good cassette should out last at least 3 chains.
Although I had to replace a 16t SS freewheel after 5k miles and the chain was fine. 1/8" chains rule!
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Old 07-31-11, 09:45 PM   #10
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I have the new chain on. I also measured the old chain which appeared to be within the 1/16" tolerance. Will try the high torque test tomorrow.

Just to clarify, let me ask what you mean by skipping. I assume this means that the chain stays on the same gear but suddenly lurches forward as it has skipped grabbing one or more teeth on the cog. Is this correct?


BTW, this cassette came on the bike, is about 4 years old and has had several chains replaced on it through ~10K miles. I've never noticed chain skipping up to now.
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Old 07-31-11, 09:55 PM   #11
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Only if the chain skips would I change the cog. Mr.T. thats correct the chain will skip or slide over the teeth of it's cog. You'll easily hear and feel it, if it skips.
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Old 08-01-11, 12:25 PM   #12
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Skipping feels like the chain just slipped off the cog and moved forward set of teeth. For me, it usually happens with the smaller cogs, and happens when you're exerting a decent amount of force. You'll definitelly notice it if it happens.

To test for it, I go up a decent incline while seated.
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Old 08-01-11, 01:44 PM   #13
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Quote:
Originally Posted by Mr. T. View Post
I have the new chain on. I also measured the old chain which appeared to be within the 1/16" tolerance. Will try the high torque test tomorrow.

Just to clarify, let me ask what you mean by skipping. I assume this means that the chain stays on the same gear but suddenly lurches forward as it has skipped grabbing one or more teeth on the cog. Is this correct?


BTW, this cassette came on the bike, is about 4 years old and has had several chains replaced on it through ~10K miles. I've never noticed chain skipping up to now.
You'll know when it skips. If it's not skipping you're good to go.
FYI, chain skip can also be caused by the shift cable being out of adjustment. But this kind of skip is caused by the chain trying to make an unwanted shift to another cog (auto-shifting). A cable tension adjustment should correct this condition.
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Old 08-02-11, 05:34 PM   #14
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Final Report

New chain on.
Shift indexing adjusted.
Performed high torque test.
No skipping.

Thanks for all the great info.
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Old 08-02-11, 05:51 PM   #15
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Originally Posted by Mr. T. View Post
New chain on.
Shift indexing adjusted.
Performed high torque test.
No skipping.

Thanks for all the great info.
Great, you changed the chain in time. As mentioned, the smaller cogs are the most skip-prone since they are used the most and have the fewest teeth to share the load.

MechBgon annoyance at Rholoff's statement that cogs over 21T rarely wear out is justified for MTB use and some road bikes use but, in general, Rohloff is correct. The largest cogs see little use as far as total miles go and have more teeth to spread the wear over.
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Old 08-02-11, 06:41 PM   #16
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http://www.sheldonbrown.com/brandt/chain-care.html
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