Quick Q. When I measure 12 chain links with a ruler, at what amount of stretch should I:

a) Change the chain
b) Change the chain, cassette and front ring
c) Change the chain, cassette and front ring, and tell myself off for being a very bad boy

?

The drop-in tools measure wear at 0.75% and 1% overall values.

At 0.75% you can usually get away with just changing the chain and keeping the cassette, if they are the first of both.

At 1% you usually need to change the chain and cassette.

I'd only worry about changing the front ring if the teeth are looking hooked or if front ring shifting is suffering – somewhere between 5 and 10 chains is pretty normal for rings as long as you're sensible with your gear changes (i.e. ease off the pressure a little when changing).

So 0.75% = 12.1"ish
And 1% = 12.12"

: P

I think 12 full links is 12" so work out how much longer your chain is. 0.75% stretch is usually considered to be the point to change the chain, if it's gone beyond 1% stretch it's likely to be new cassette etc. as well.

Oh and go and buy a chain checking tool, less than a tenner much more accurate and much easier to use than measuring with a ruler. It'll save you money in the long run.

Ok thanks all. I only have a single ring up front so front shifting is not an issue!

i change my rings and cassette with chain suck and chain slip respectively. I await any indepenent research re having to replain rings/casettes and them not taking new /old chains BS to generate sales IMHO. I have a chain stretched to about 2 % at a guess that works fine with new rings – my hack bike – that is a 7 speed chain with 9 speed rings as well. I have put a new chain on it as well to see if it worked and it did.
I think some of this is to get us to buy stuff we dont really need. Basically if it is actually broken I will replace it if it still works why replace?
I do check chain and replace at about 1% wear mind on my expensive MTB.

There will always be a few chumps who will ride kit into the ground and claim that it works fine but the reason that people like KMC, who make some of the best chains in the world, specify wear parameters is so that people know when you're using the chains within those parameters they will be as reliable as they're designed to be.

Like with just about every other component, of course you can cover it in gritty crap, abuse it and never lube it and if you're lucky it might keep working for a long time. But it's not meant to work that way and you can't then whine about how unreliable or poor quality a brand is if you haven't looked after it.

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Sheldon Brown, he say change before you hit 12" and one eighth, or you gonna have to buy whole new drivetrain baby.

I also just use a steel ruler and a chain under tension. Measureing between pins.

I'm sure I've thrown away plenty of chains with some life left in them and some cassettes that could have lasted longer if I'd got a new chain sooner. Then I bought that park measuring tool. I know it's expensive but I suspect you'd fail to find someone that regretted buying one.

There will always be a few chumps who will ride kit into the ground and claim that it works fine but the reason that people like KMC, who make some of the best chains in the world, specify wear parameters is so that people know when you're using the chains within those parameters they will be as reliable as they're designed to be

I asked for independent research. INot like it is hard to think of a reason why chain manufactirers and component makers would ask us to change things more often now is it?
As for chump persuade me with some research not insults
I only speak of experience with components/drive train myself, I am not convinced and nothing you said changed my mind. I have yet to have catastophic failure by mixing parts despite what makers claim.

the Park drop in chain checker is only about 6 or 7 quid. Get it. It'll save the guesswork.

I have a chain stretched to about 2 % at a guess that works fine with new rings

How do you guess the stretch of a chain?!

Chain rings and cassettes don't generally wear out unless the chain has stretched, once the chain has stretched the teeth don't take an even share of the load, and become elongated and hooked to match the chain. Change the chain before its stretched too much, and the rings and cassettes can last years.

I think everyone on here will have had the experience of buying a new chain, only to find it skips under load on their old rings. Last week I lent some tools to a colleague, his hack bike was worn out, big ring had pointy spikes instead of teeth, and so did the bottom half of the rear cassette. Worked fine in those gears, if he needed lower gears for big hills the chain wouldn't even sit properly due to the amount of stretch.

If you've left it too late and your new chain skips, then yeh, you might as well stick the old chain back on and keeping riding til its totally knackered, but otherwise, a few quid on a chain every now and then to save the rest of the drivetrain is money well spent.

I don't think many of us would go out and buy a whole new drivetrain just on the off-chance the old one is knackered, you change a part, if it slips, you change another bit, etc etc, until either the whole lot has been renewed, or it stops slipping.

I still don't see why you need anything other than a ruler – I mean just how hard is it to use a ruler accurately? I always follow what Sheldon Brown actually says and change the chain at 12 1/16" (which is near as makes no difference 0.5% wear) – if you let it go to 12 1/8" you'll also be wearing the sprockets and need to replace those. The thing with chain wear is that the outer surface of a chain is a lot harder, so once you've worn that off (which you have by 0.5% "stretch") the wear is a lot quicker, so you don't actually gain yourself as much as you might think by waiting, and in the process destroying your sprockets.

http://www.sheldonbrown.com/chains.html#wear

I have a chain checker which pronounced a chain used once as dead. I use a ruler now, or the chain checker with a pinch of salt.

BTW chains don't stretch, they wear (net result the same, just being pedantic).

They do stretch. But the stretching is almost insignificant compared the wear. 😉

wear it into the ground! im a chump! works out cheaper if using standard parts such as deore cassetes and rings and lets face it, thats all you need, you'd have to change the chain frequently every month, depending how much you ride! otherwise , shifting will still be ok as the middle ring chain and cassette (jockey wheels) will all wear together untill you start getting chain suck, and thats only because the middle ring has burred from wear and at that point either change them 3 parts or if moneys tight just file burrs down to get a bit longer out of it!

BTW a drop-in chain checker like this is usually accurate:

whereas the dial sort of tools are usually no good:

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They do stretch.

Permanently?

How do you guess the stretch of a chain?!

you use your chain tool and see that it is massively over the stretch limit and then you guess at the percentage for an internet forum.