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Sometimes as a hobby I repair entry level bikes for myself or for friends and family.

The rear derailleur is working fine (no skipping/ slipping etc..).

But than I discover (with a chain checker), that the chain need to be replaced (almost 1.0 by a Park Tool CC-2). I changed the chain slipping / skipping appears.

The conclusion: probably the cassette also needs to be replaced. So by replacing the chain only, it doesn't improve the situation or even makes it worse.

My question is, in such situation (old entry level bike etc..), if the rear derailleur works fine, is it worth it to replace the chain?

If I leave on an old chain and the cassette is most probably already very worn, can the old chain provide any additional problems?

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    Take a look at my related question: bicycles.stackexchange.com/questions/72287/… – MaplePanda Dec 1 '20 at 19:41
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    This is not a dupe of MaplePanda's link but its strongly related. My answer at bicycles.stackexchange.com/a/72294/19705 is exactly what I'd reply to this question. If the bike is only going to get a little use, there's no point dropping money on it until the new rider commits to riding, – Criggie♦ Dec 1 '20 at 21:38
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    @MaplePanda, it's very relevant. I woudn't post my question if I would find your post before it. In my case the rear cassette is already worn out on some sprockets and when I change chain it become worse. My thougths, that if the front chainring is also worned, for me it definitely doesn't worth to replace all, before new rider doesn't commits to ride. – Michael D Dec 1 '20 at 21:55
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If chain wear is beyond 1% then you are probably looking at a new drivetrain including chainrings. I would just remount the old chain and get the full wear out of everything else.

As far as changing chain only the industry standard is wear between 0.5-0.75% if you change within this range the theory is you will prolong the life of the drivetrain and perhaps never have to change anything except the chain.

The likelihood of snapping a chain is not very high for normal everyday use.

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A very worn chain can break unexpectedly and it’s going to accelerate wear of the cassette, chainring and rear derailleur’s pulley wheels. Shifting, noise and efficiency also get worse, the more worn the chain is.

I guess you can go slightly beyond 1% wear if the components need to be replaced anyway. Especially if reliability and performance are not a priority (e.g. on a bicycle used for short distances within a city and where you are never going to pedal out of the saddle).

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  • By Park Tool CC-2, 1% is maximum. So how I can check if I slightly beyond 1% or not slightly? – Michael D Dec 1 '20 at 21:47
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    @MichaelD: It will feel quite loose and you’ll notice the play. You can also measure with calipers or a ruler. – Michael Dec 2 '20 at 8:33

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