Why a worn cassette cannot damage a new chain

[Dogtrousers]

Thought about this while riding today, without 'overthinking' it - [ ... ]

I don't think you were entirely successful

 

[Salty seadog]

I don't think you were entirely successful

 

[Spoked Wheels]

@Yellow Saddle, thank you for the opening post.

So if a worn cassette cannot damage a new chain then the opposite must also be true, right? I mean a worn chain cannot damage a new cassette.

 

[Ajax Bay]

worn chain cannot damage a new cassette.

YS's call but I'd be amazed if that's not a 'no, not true'!
Sticking my neck out here , if the chain is worn then the tooth number 12 'o clock will 'feel' (almost) the full tension of the chain. Since the links are elongated the tooth at 11 'o clock might share a bit of the load but the 10, 9 and 8 o'clock ones will take minimal load. The wear on each tooth as it reaches the top 12 'o clock position will experience above normal wear, because it's taking (and then losing) nearly all the load. Compare that with "if the chain and sprocket pitch match perfectly, we could say that these [teeth at 8, 9, 10, 11, 12 o'clock] all share the [chain] load."

 

[silva]

Just trying to give @silva treasure at the bottom of his 'promising' hole, as opposed to a pig in a poke.

My question was based on the statement "It does not wear from the tension induced into the chain by pedaling forces."
That was abit ambiguous, the "hole" I saw.
For the rest, it's not like that I hunt a no wear at all (impossible), I try to minimalize it so that I have less work on the chain. Coming from a once / 3 month replacement, arrived to a once / year replacement. atm I consider to try a type 420 motorcycle chain - from what I've read it should be compatible with the bicycle sprockets.
I it was available at same or reasonable higher cost, I'd try steel chainring, and custom sprockets to fit a chain with again bigger mating surfaces so the force acts on a bigger surface meaning less pressure and less wear, so slower becoming longer under tension.
A wish to minimalize wear doesn't imply a belief in a no wear at all.

 

[Yellow Saddle]

@Yellow Saddle, thank you for the opening post.

So if a worn cassette cannot damage a new chain then the opposite must also be true, right? I mean a worn chain cannot damage a new cassette.

No, the opposite isn't true, I'll explain, but first let's state the opposite to avoid confusion: A worn chain cannot damage a new cassette.

A worn chain has a pitch longer than that of the sprocket. A new sprocket will have a pitch of 1/2 inch and a worn chain a pitch of say, 1/2 and a bit inches. In other words, the chain, when tensioned, will be too long for the row of teeth it has to fit into.
However, it does fit because the chain enters the sprocket from the bottom, on the slack run where it is not tensioned and can compress and fit the sprocket perfectly. It is only when it receives tension, that it starts to mismatch. Because of this, only the last tooth (12 'O clock) takes up all the chain's tension and all the force is concentrated on just that one tooth. Had the chain been shorter (not worn), a few teeth would have shared the load.

Because of that load concentration, a worn chain does damage a new cassette.

I never do a cheap shot and recommend people read my book, but nevertheless, I'll say that in the book I go through all the scenarios and all the variants of the scenarios. There are quite a few scenarios, because bikes without tensioners, such as singlespeed bikes, behave differently from those with tensioners etc.

Edit: I didn't see that Alex also answered the question. His answer is spot-on. Maybe the duplication helps someone to understand. Maybe not.

 

[Spoked Wheels]

YS's call but I'd be amazed if that's not a 'no, not true'!
Sticking my neck out here , if the chain is worn then the tooth number 12 'o clock will 'feel' (almost) the full tension of the chain. Since the links are elongated the tooth at 11 'o clock might share a bit of the load but the 10, 9 and 8 o'clock ones will take minimal load. The wear on each tooth as it reaches the top 12 'o clock position will experience above normal wear, because it's taking (and then losing) nearly all the load. Compare that with "if the chain and sprocket pitch match perfectly, we could say that these [teeth at 8, 9, 10, 11, 12 o'clock] all share the [chain] load."

No, the opposite isn't true, I'll explain, but first let's state the opposite to avoid confusion: A worn chain cannot damage a new cassette.

A worn chain has a pitch longer than that of the sprocket. A new sprocket will have a pitch of 1/2 inch and a worn chain a pitch of say, 1/2 and a bit inches. In other words, the chain, when tensioned, will be too long for the row of teeth it has to fit into.
However, it does fit because the chain enters the sprocket from the bottom, on the slack run where it is not tensioned and can compress and fit the sprocket perfectly. It is only when it receives tension, that it starts to mismatch. Because of this, only the last tooth (12 'O clock) takes up all the chain's tension and all the force is concentrated on just that one tooth. Had the chain been shorter (not worn), a few teeth would have shared the load.

Because of that load concentration, a worn chain does damage a new cassette.

I never do a cheap shot and recommend people read my book, but nevertheless, I'll say that in the book I go through all the scenarios and all the variants of the scenarios. There are quite a few scenarios, because bikes without tensioners, such as singlespeed bikes, behave differently from those with tensioners etc.

Edit: I didn't see that Alex also answered the question. His answer is spot-on. Maybe the duplication helps someone to understand. Maybe not.

Thank you both for the answers.... this is good stuff to know

 

[mickle]

I have an annoying habit of assuming that, because I know a lot, that I know everything. I'm extremely grateful to @Yellow Saddle for his occasional reminders that I don't.

 

[confusedcyclist]

I have an annoying habit of assuming that, because I know a lot, that I know everything. I'm extremely grateful to @Yellow Saddle for his occasional reminders that I don't.

 

[Dogtrousers]

I have a time share in a chalet on the peak of Mt Stupid. I spend as much time there as possible.

 

[Ajax Bay]

Are you in the process of selling it, @Dogtrousers ? Asking for a fellow Falkland islands 1982 veteran who's got a fine to pay and has a chalet on that mountain peak.

 

[Gillstay]

My question was based on the statement "It does not wear from the tension induced into the chain by pedaling forces."
That was abit ambiguous, the "hole" I saw.
For the rest, it's not like that I hunt a no wear at all (impossible), I try to minimalize it so that I have less work on the chain. Coming from a once / 3 month replacement, arrived to a once / year replacement. atm I consider to try a type 420 motorcycle chain - from what I've read it should be compatible with the bicycle sprockets.
I it was available at same or reasonable higher cost, I'd try steel chainring, and custom sprockets to fit a chain with again bigger mating surfaces so the force acts on a bigger surface meaning less pressure and less wear, so slower becoming longer under tension.
A wish to minimalize wear doesn't imply a belief in a no wear at all.

If your after reducing chain wear then I think you would be better going for an enclosed chain set up, rather than motorbike chains

 

[Ajax Bay]

you would be better going for an enclosed chain set up

Pretty sure he has. @silva also advocates not oiling the chain because it picks up too much dirt (I think).