When is it best time to replace bike chain to prevent any cassette damage?

[Ajax Bay]

how to tell if your cassette is due for replacement.

When you put a bit of power down - just talking a gentle slope here - when the chain slips on one or more sprockets (it'll be the most used ones so middle of the cassette), the cassette (as well as the chain) will need replacing. You cannot tell this by eye, unless you have special(ly developed) powers. Alternatively, run chains till they're just over 0.5% elongated, change (holding on to old chain), and after 3 chains, change both at the same time. Hold onto that pair (no need to clean, clearly labelled with chain distance and cassette distance) - see below. Other protocols are available and have been rehearsed on here on other fellow-travelling threads.
Key lesson/behaviour is to procure and have immediately available a new chain and a new cassette, or have a old but not slipping matched cassette and chain to use while new items are purchased.

 

[cyberknight]

Chains can tend to get worn more quickly at this time of year because of wet salty grit getting flung up onto them by front wheels, unless you have mudguards with big flaps on them. Chains last much longer the other 3 seasons.

PS Curses - beaten to it by @boydj!!!

I think mine is already toast after a month
I will check later when i have cleaned teh biek i intedn to replace the cassette to , i am havind mysterious creask and clunks that i have read could be done to a farked cassette only hapens in one gear , my mash it fast one so im thinking its worn

 

[the snail]

When you put a bit of power down - just talking a gentle slope here - when the chain slips on one or more sprockets (it'll be the most used ones so middle of the cassette), the cassette (as well as the chain) will need replacing. You cannot tell this by eye, unless you have special(ly developed) powers. Alternatively, run chains till they're just over 0.5% elongated, change (holding on to old chain), and after 3 chains, change both at the same time. Hold onto that pair (no need to clean, clearly labelled with chain distance and cassette distance) - see below. Other protocols are available and have been rehearsed on here on other fellow-travelling threads.
Key lesson/behaviour is to procure and have immediately available a new chain and a new cassette, or have a old but not slipping matched cassette and chain to use while new items are purchased.

I don't agree with that. If you wait until the chain slips on the sprockets, then your chain will be well past the wear limit, good chance of damaging your chainrings. Also you can run most chains up to 0.75% wear, although I think 11sp it is recommended to change at 0.5%.
https://www.parktool.com/blog/repair-help/when-to-replace-a-chain-on-a-bicycle

 

[Ajax Bay]

If you wait until the chain slips on the sprockets, then your chain will be well past the wear limit, good chance of damaging your chainrings.

First of all, what is this chain 'wear limit'. Perhaps you could define this? Or are you just grabbing arbitary percentage elongation recommendations here?
Second, I suggest that, because of the geometry of the chain/chainring and chain/sprocket interfaces, and because of rotational speeds say 3 times less, chainrings wear much less than sprockets when a chain is elongated, so the cassette (and the new chain that will go with its replacement) is the limiting factor.
Chainrings do of course wear, and it's the smaller ones which wear first, for the same geometric and chain/tooth interaction frequency reasons, and because the small(er) chainring(s) experience(s) higher peak forces.
Finally, what is the effect of this sort of damage to the chainrings. Do chainrings so damaged cause more wear to the chain than the sprockets?
If a rider has fitted a new casette and chain, and the drivetrain is still slipping, it's likley time to replace the small(est) ring.

 

[faster]

I'm not keen on any of these 'schemes' to save a few quid on chains.

Just change it before it gets to 0.75. It's not worth the risk of it snapping, which might work out okay, but could also end up with your nuts smashing into your top tube, being stranded, losing a few teeth or even ending up under a bus.

The advice to leave it until it slips is poor. I've got no scientific back up, but anecdotally old chains on old cassettes go on for ages without slipping - until the chain snaps. For most of those miles the drive chain will be noisy, inefficient, the shifting will be poor and you'll get more chain suck, which can destroy some frames. It'll ruin your expensive chain rings too and work out more expensive in the end anyway.

On my most used bike, I don't bother measuring now and just change every 1,800 miles (which results in just under 0.75% of stretch for me). Chainrings and cassettes last ages with a bit of care.

I realise though, that some bikes (especially the 1x ones with little tiny front chain rings that are becoming fashionable these days) will destroy a chain and cassette in no time. These might get quite expensive to run!

 

[davidphilips]

Agree with the snail,(most chains up to 0.75% wear, although I think 11sp it is recommended to change at 0.5%.) Far as i know single speed chains can go to 1.0% plus i change the cassette every 3rd chain

 

[HLaB]

I've found the Park Chain measuring tool too premature; I've had 4,500 out of a chain and replaced it no skip. I usual replace around 3000miles and at the same time by a cassette if needed but if it doesn't skip I keep it for the next time. (There's been exceptions, like for my LEJOG, when I didn't wait to see if its skips and just replaced both). It also helps that I don't put big power through a chain and the roads down here are comparatively clean. When I lived up north IIRC I changed chains around 1,500 miles.

 

[Notafettler]

Get a Rohloff 25000 kilometres at least. Same chain, sprocket, chainwheel. Might have to take a link out or and turn the sprocket and chainwheel round but other than that no maintenance.

 

[Blue Hills]

At 0.75% chain elongation (NB not 'stretch': nothing's stretching), you have left it too late to change it and expect the cassette to be content with the new chain.
Your best approach is to leave the matched chain and cassette to happily grow old together. Very likely you'll get another 1000 similar type riding miles. Then the chain will slip on the most used (and therefore worn) sprockets. Well before then, you will have bought a new chain and a new cassette, spreading the cost over to months if needs be (you haven't shared what speed your drivetrain is). When you get the slippage, change both chain and cassette at the same time. If the cassette is expensive, then resolve to measure more often, with care and accuracy, and change the chain once it gets to 0.5%. That way you'll get likely 3 chains per cassette (this is in line with @slowmotion 's advice/observation). The more expensive the cassette the more attractive this is, from an economic PoV.

No need to change at 0.5 for 9 speed.
Chain checkers for 9 speed (or predating 10) don't even have a 0.5 marker). Don't think the OP said how many speeds their bike was.

 

[Blue Hills]

One thing that I've always wondered about is how to tell if your cassette is due for replacement. Does anybody know?
Thanks.

Do start a new thread, though i fear the answer is "it's damn hard/almost impossible to tell" for mere mortals.

 

[Blue Hills]

Oh that's easy, when you fit a new chain and it jumps on the rear sprocket. If however you've saved an old chain or 3 they'll run fine on the slightly worn out bits.

Agree that if a new chain skips you need to change the cassette but if you put an old chain back on to cure this won't you be risking accelerated wear on the chainrings?

 

[Notafettler]

Agree that if a new chain skips you need to change the cassette but if you put an old chain back on to cure this won't you be risking accelerated wear on the chainrings?

Not if it fits. I am running out of turns on elliptical bottom bracket, a nobber I know insists I should replace the chain as opposed to removing a link. As if a new chain would fit a worn (but still plenty of life) sprocket and chainring? Mind it's been so long since I have used deraillures that I could be talking bollocks!

 

[gbb]

No need (IMHO) to over analyse what, why and when...just buy a new chain, fit it, if it doesnt present any problems, ride on happy. Simples.

 

[MontyVeda]

How's about not buying a new chain, ever!

Just let the chain, cassette and chain rings all wear out in unison... over several/many years, then change the lot when the teeth are so worn that they don't look like teeth anymore

 

[Blue Hills]

How's about not buying a new chain, ever!

Just let the chain, cassette and chain rings all wear out in unison... over several/many years, then change the lot when the teeth are so worn that they don't look like teeth anymore

Ok on hack/pub bike, keeps things simple, but not on any bike you want a nice day ride on I fear.