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I have a Shimano 8 speed 11-34 cassette (one of those "mega range" ones). If I change my cassette to a different one, say an 11-32, will I need to change or otherwise modify my chain? I just got the chain replaced and now it's slipping on the old cassette. I'm not the biggest fan of the mega range, so I wouldn't mind changing it out to something different.

  • Your symptoms are similar to what you'd get with a stretched chain on a new cassette. You might want to check the amount of stretch in your chain and replace it. – RoboKaren Jun 30 '17 at 18:23
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    The OP says the chain has just been replaced so chain stretch is likely not the cause. I'd be replacing the cassette if the chain is indeed new but slipping over the cassette. – Bikebum Jul 2 '17 at 16:39
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    That is correct. I took it to LBS yesterday, they put a new cassette on it, and it's working fantastically. I had initially thought that the cassette wasn't worn, but the mechanic showed me that I had practically worn away about 1/2 of the material on the teeth of the gears I used most often. It's sort of cool, actually :-) – Michael Stachowsky Jul 4 '17 at 13:02
  • Thanks for all the information .l will do a few adjustments – Creighton Oct 2 '18 at 1:58
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As the smallest cog is the same and the largest cog is smaller, the gear range is a subset of the old one. The old chain length should give you no problems at all. If you were going the other way a longer chain might be needed.

  • Thanks. Would my cable tension need to be adjusted as well, or does the same thing apply? – Michael Stachowsky Jun 30 '17 at 12:55
  • That should be the same too. If I changed the cassette and the cable tension flt like it needed changing I'd check everything had gone together properly before adjusting (also the limit screws). I've replaced a whole wheel without the need to adjust the rear derailleur at all. – Chris H Jun 30 '17 at 12:57
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Theoretically, you could shorten your chain to accommodate the smaller (largest gear) cassette. However, I never install a new cassette unless I install a new chain as well. Cassettes and chains tend to "wear" to one another and one can sometimes encounter difficulty if you don't.

That "could" be the issue with your new chain. If the old chain was run past it's proper service life and damaged the cassette, no new chain is going to work well with it. Depending how many miles/hours you put on the new chain, if you put a new cassette on your rig and leave the "new" chain, it could be fine.

However, there are many other issues that could cause slippage. A stiff link in the new chain if it was twisted/damaged during installation would be a prime example.

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    I feel that it is probably the cassette for the following reasons: 1. the jump only happens in the two gears that I used most often. 2. the jump happens no matter which chainring I'm in. 3. The old chain was the original chain, and the bike has several thousand km on it. The chain was not well cared for, and I suspect there was a ton of wear – Michael Stachowsky Jun 30 '17 at 14:54
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    @MichaelStachowsky that sounds like the answer then. I'd replace the cassette immediately before the new chain wears to it prematurely and is ruined as well. – Deleted User Jun 30 '17 at 14:56
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    Chain wear is dependent on a number of factors including, but not limited to , power applied, lube, riding conditions, amount of shifting, and condition of the rest of the drive train components. I wouldn't do it with my new chain. Other people might. – Deleted User Jun 30 '17 at 15:45
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    I have changed the cassette after putting a few tens of km on a new chain (on a 3x8 system) and I didn't have any trouble. Any increase in wear was so small as to not be noticeable. – Chris H Jun 30 '17 at 15:54
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    If you can't change it before your ride this weekend, I would try to stay off those two gears that skip. – Noah Sutherland Jun 30 '17 at 16:01
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As there is only 2 tooth difference on the top end and the same number of teeth on the bottom end, you should not need a new chain or adjustment. There is some room in the derailleur to adjust the length (between 11 teeth and 34 teeth). Your new range of 11-32 is within the 11-34 so there should be no problems.

The one thing you would have to make sure is that the chain and cassette are compatible, correct width, size, shape. So if you are using Shimano, your new set should also be Shimano of the same groupset if you want to make sure it will work.

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Generally Yes you have to change your chain. The only time you might get away without changing chain is if its JUST been replaced. That is, under a hundred km of riding or in the last ~week.

Running an elongated chain on a new cassette dramatically increases wear on the cassette.

It really depends on how long/far since "it was jut replaced"

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