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Longjohn

What would you do?

Question

I have many thousands of miles on my nine speed chain.  It still checks out ok using a chain checker and the teeth on the cassette all look good.  I asked my LBS owner what he thought about replacing the chain now rather than wait until it shows signs of wear and he suggested I let it go and when I replace the chain put on a new cassette at the same time.  I was thinking by changing it now I could avoid having to change the cassette.  He says sometimes even when the cassette looks good a new chain will skip on a used cassette.  Anyhow I am changing the chain anyway and see what happens.  I really respect this LBS guy and he knows way more about bikes than I do.

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I have always heard that a chain and cassette should be changed at the same time, since they "wear together" but I can't really corroborate that.  That never really made sense to me, as even on the smallest cogs there are a minimum of 5-6 teeth engaged in the chain.  Are they all going to slip at the same time and cause the chain to skip?  I am probably making some incorrect baseline assumption, but the "replace chain and cassette together" line sounds like something the Chain And Cassette Industry might propagate.

I wouldn't bother changing anything if I was not having any problems - but I am a cheap bastard.

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If you want to be sure not to miss any rides, have a new cassette on standby as you will most likely need it.  I've replaced more than a few chains, and only the very newest chains (replaced due to breaking, not wear) were I able to reuse the cassette.  It will be fine for normal spinning, but try to stand up and mash?  Annoying and dangerous skipping.

 

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FYI (from Sheldon Brown's site):

Quote

Sprockets do not change pitch when they wear, only their tooth form changes. The number of teeth and base circle remain unchanged by normal sprocket wear. What changes is the diameter at which the worn and lengthened chain bears on the sprockets, making wear indentations at a larger diameter than a new chain requires. In practice, this amounts to a change of pitch, since the chain will no longer ride in the original valleys between the sprocket teeth.

A new chain often will not freely engage a worn rear sprocket under load even though its root diameter has the same pitch as the chain. This occurs because the previous (worn and elongated) chain formed pockets higher on each tooth (a larger pitch diameter) than an in pitch chain describes. This wear occurs because a worn chain rides high on the teeth. A chain with correct pitch cannot enter the pockets when its previous roller bears the previous tooth, because the pocket has an overhang that prevents entry.

Without a strong chain tensioner or a non derailleur bicycle, the chain has insufficient force on its slack run to engage a driven sprocket. In contrast, engagement of a driving sprocket, the crank sprocket, generally succeeds even with substantial tooth wear, because the drive tension forces engagement.

However, worn teeth on a driving sprocket cause "chain suck", the failure of the chain to disengage. This occurs more easily with a long-arm derailleur, common to most MTB's: that is one reason this occurs less with road racing bicycles, which experience a noisy disengagement instead.

http://www.sheldonbrown.com/brandt/chain-care.html

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1 hour ago, Reverend_Maynard said:

FYI (from Sheldon Brown's site):

http://www.sheldonbrown.com/brandt/chain-care.html

That's the most detail I've seen on the subject - thanks.  I'm not going to dispute Sheldon Brown's opinion, may he RIP.

Thinking back - one of my worst crashes happened when I was standing on the pedals and the chain slipped.  I veered back and forth a few times and I thought I was going to save it but then the front wheel taco'd and I went over onto a concrete roadway (maybe asphalt would have ripped me up more).  I limped two miles home (literally), wheeling the bike with one hand and carrying the wheel in the other.  

I cobbled that bike together from all sorts of old parts - surely this was part of the problem.  So don't mess around with this stuff! 

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Ha, I just noticed I never got back to this thread to say what happened. My chain checker tool said my chain was still good so I figured a new chain would prevent the cassette from wearing. I installed a new chain and climbing steep hills the chain would skip in some gears. I went back and changed the cassette and all was good. Sometimes these guys that have been doing this stuff all their lives know what they are talking about. I wonder how long I could have gone on that old chain?

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5 hours ago, RalphWaldoMooseworth said:

Well sheesh, I was just getting ready to replace my chain, but now you bastards have scared me!

I have replaced them before without an issue. I really thought it would work. The chain checked out good on the chain checker tool and the cassette looked good too. I couldn't see any wear looking at it. The only reason I changed it was I knew that chain had a lot of hard miles on it riding dirt roads and trails. I'm thinking the chain had over 5,000 miles on it.

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