Chain checkers.

[Pat "5mph"]

The only chain checker that is reliable is the expensive Shimano model.

All the others measure between a roller pushed to the right and a roller pushed to the left, and are therefore including the amount of roller movement in the result. That's OK if you are using the same chain as the checker manufacturer calibrated the checker against, but if you use a different model of chain you'll get a different answer.
In general, the maker will calibrate against a chain with tight-fitting rollers, because any error just means that you've replaced the chain earlier than need be, whilst if they calibrated against a chain with loose rollers people who had a tight roller chain may find that a new chain slipped despite having replaced at an indicated .75% stretch. This would generate complaints.
In the worst cases, a brand new chain can show as 1% stretched.

The most reliable method of checking chain stretch is to measure between pin centres over about 12 inches using a ruler. Pins on a new chain are 1/2 inch apart, so if the 12" pin on a used chain is at 12 1/8", you've got 1% stretch.

Could we have that in cm and mm?
I just bought a chain tool to play with, uff!

 

[BimblingBee]

http://sheldonbrown.com/chains.html

In metric measurement, 10 links of a new chain are 25.4 cm, or 15 links, 38.1 cm.

If the rivet is up to 25.5 cm or halfway between 38.2 cm and 38.3 cm, all is well.
If the rivet is a little bit past 25.5 cm, or approaching 38.3 cm, you should replace the chain, but the sprockets are probably undamaged.
If the rivet is approaching 25.7 cm or 38.5 cm, you have left it too long, and the sprockets (at least the favorite ones) will be too badly worn. If you replace a chain at this point, without replacing the sprockets, it may run OK and not skip, but the worn sprockets will cause the new chain to wear much faster than it should, until it catches up with the wear state of the sprockets.
More than that, and a new chain will almost certainly skip on the worn sprockets, especially the smaller ones.

 

[02GF74]

The only chain checker that is reliable is the expensive Shimano model.

All the others measure between a roller pushed to the right and a roller pushed to the left, and are therefore including the amount of roller movement in the result. That's OK if you are using the same chain as the checker manufacturer calibrated the checker against, but if you use a different model of chain you'll get a different answer. etc..

do you know that is how the chain wear tool makers callibrate their tools or is it guess work?

if the roller is the same diameter on different chains, and I suspect there is a standard for 1/2 in chain, so it is, then when new, the rollers are tight and I would guess the chain tool makes use a new chain for callibration so it seems quite reasonable to me..

wear takes place in the rollers/chain chain side plate indents so the rollws move further apart so it seems to me quite sensible to measure the distance between them.

 

[Pat "5mph"]

http://sheldonbrown.com/chains.html

In metric measurement, 10 links of a new chain are 25.4 cm, or 15 links, 38.1 cm.

If the rivet is up to 25.5 cm or halfway between 38.2 cm and 38.3 cm, all is well.
If the rivet is a little bit past 25.5 cm, or approaching 38.3 cm, you should replace the chain, but the sprockets are probably undamaged.
If the rivet is approaching 25.7 cm or 38.5 cm, you have left it too long, and the sprockets (at least the favorite ones) will be too badly worn. If you replace a chain at this point, without replacing the sprockets, it may run OK and not skip, but the worn sprockets will cause the new chain to wear much faster than it should, until it catches up with the wear state of the sprockets.
More than that, and a new chain will almost certainly skip on the worn sprockets, especially the smaller ones.

Thanks for that: will compare measurements with the tool when it arrives.

 

[SatNavSaysStraightOn]

I thought I would have a bit of a play with my old chain and a brand new chain which is due to get fitted to my OH's bike later this week just to look at chain wear, lengths and compare measurements verses my chain checker. They are both KMC chains, for 7/8 speed bikes, but not the exact same model.

• As near as I could tell, the new chain was a fraction under 25.4cm for 10 links.
• My old chain came out at 25.6cm for 10 links: a growth of 2mm over the course of 10 links which makes it 0.8% longer when new.
• Both the 0.75% & the 1.0% parts of the chain checker easily fit into the chain but the chain checker is only checking over the course of 5 links not 10.

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• Meauring my chain tool, the 0.75% is 12.3cm in length exactly, 1% is a fraction over 12.3cm but not quite 12.35cm. So that would make 10 links on an imaginary chain checker as just under 25.7cm which would make a 1% increase.
• But the chain tool has measure the old chain as 1% stretch over 5 links when it actually measures 25.6cm at 10 lengths stretched... a 1mm difference which does not sound much until you lay the chains out side my side and can actually see the difference.

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• Hanging the 2 chains alongside each other makes it even more obvious over the course of the 52 links both chains.

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So something is not as accurate as it could be but there is enough to let you know that your chain needs to be replaced using a chain tool which tbh saves time and dirty hands, plus the removal of a chain - I just don't think it can tell you that your cassette should also be replaced and I am dubious about the 0.75% mark as well for chain replacement. My old chain easily fits the 1% mark yet when I tested the new chain against the old cassette on every sprocket (having taken the rear wheel off) it was snug fit all the way around with no gaps at all (see one of the above posts for the link) and after a 45 mile ride I am more than happy that the cassette does not need replacing having used the granny gear on several long uphills with no skipping whatsoever - and I have worn out enough cassettes in the past to know when they do need replacing.

Confused - yep but also left wondering how the manufacturers of the tools can validate a 0.25% difference over 5 chain lengths when they are taking about a difference of 0.5mm at best and probably something like 0.3mm between 0.75% and 1.0%... but I will continue to use the chain tool as a guide not the "law" when it comes to replacing the chain &/or cassette.

For me, it has been a reassuring exercise - if a touch dirty & greasy (! - yep dining room table got it again), my chain did need replacing, my OH's chain can probably go on a touch longer (which given it has only done 1,000km is good news - mine had at least reached 1,900km of winter riding before needing replacing).

 

[Pat "5mph"]

Great informative post, @SatNav