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KMC's digital chain checker looks like a modified digital caliper. Looking at their website showing this item I notice it doesn't give you a true length but just a .030 mm and up to a value of .080 mm and probably a little over that. With the value given it tells you if your chain is a go or no-go.

I have searched the internet and I know that a 12" machinist ruler between pins is good as it gets but these chain tools are go or no-go's and I want to know that measurement they are telling me is a go or no-go.

My question is what is that true distance they are measuring? What is the "go" chain measurement and what is the "no-go" measurement?


Chain checkers - Extras - Products - KMC Chain
 

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It looks like it fits between pins 4 full links apart. that's about 100 mm. Presumably it's measuring elongation from the nominal new-chain dimension. It suggests replacing the chain somewhere between .4mm and .8mm. The traditional ruler rule is to consider replacement at 1/16" over 12" (.5%), and definitely before 1/8" (1%). So the digital tool is pointing at about the same range: .4 to .8 percent.

The ruler is pretty easy to use, IME.
 

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The ancient rule is "no more than 0.1 mm per link." But that's a math constant to be used over a number of links since only every other link of a chain elongates with wear, not each one. The 12" ruler rules. :)
 

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Any tool that measures between the rollers, adds roller wear to the true elongation and delivers an incorrect reading. A Shimano or KC chain may measure .25% elongation when new, even though that's totally wrong.

If you want to measure elongation accurately, use a 12" machinists rule. Place one end on edge of a pin. When new, the pin at the opposite end will be completely covered by the rule. When the elongation increase to the point when the covered pin is almost 1/2 exposed, you've reached .5% elongation.
 

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My question is what is that true distance they are measuring? What is the "go" chain measurement and what is the "no-go" measurement?
Go/No-go is a joke. It's like "your chain is OK when it's 0.495% elongated but no good when it's 0.5%." This is just another reason why chain checkers are pointless compared to just about any ruler. You don't need a machinist ruler unless you completely lack the ability to see where the pin is in the 1/16" gradation. You can estimate pretty accurately (or at least accurately enough) even with a ruler that has 1/8" gradations.
 

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Read and understand the above page. Then run out and get a nice steel machinists rule.
Rulers don't cut it in a bike shop. I used the ruler method for showing people why their chain needed to be replaced for the first year or two of business. Their eyes just glazed over. Then I got the Park chain checker. I still check it with a ruler, but use the chain checker to show customers why they need a chain. Chain sales improved a lot.
 

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Rulers don't cut it in a bike shop. I used the ruler method for showing people why their chain needed to be replaced for the first year or two of business. Their eyes just glazed over. Then I got the Park chain checker. I still check it with a ruler, but use the chain checker to show customers why they need a chain. Chain sales improved a lot.
My car dealership uses other forms of motivational aids to sell me things - oil additives, paint, upholstery and theft protection, oil changes, etcetera. I'm old school - I ignore almost all of their blather and measure oil changes by the calendar and bike chain wear with a ruler.
 

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Any tool that measures between the rollers, adds roller wear to the true elongation and delivers an incorrect reading. A Shimano or KC chain may measure .25% elongation when new, even though that's totally wrong.

If you want to measure elongation accurately, use a 12" machinists rule. Place one end on edge of a pin. When new, the pin at the opposite end will be completely covered by the rule. When the elongation increase to the point when the covered pin is almost 1/2 exposed, you've reached .5% elongation.
Why is measureing roller wear a problem? I'm not really looking to get a true reading of "elongation" but a reading of then the chain needs to be replaced. I would think roller wear would factor into that. No? My thought is that the teeth on cogs and rings can't tell the difference between roller wear and true elongation and only know how far apart the contact surface of the chain (roller) is?
 

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Why is measureing roller wear a problem? I'm not really looking to get a true reading of "elongation" but a reading of then the chain needs to be replaced. I would think roller wear would factor into that. No? My thought is that the teeth on cogs and rings can't tell the difference between roller wear and true elongation and only know how far apart the contact surface of the chain (roller) is?
Thank you for asking the obvious, but never asked, question!
 

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Thank you for asking the obvious, but never asked, question!

The wear between the pins and bushing that cause elongtation is very small, compared to roller wear. At .5% elongation, each pin/bushing pair only has about .0025 inch of wear. A pair of rollers can easily have 10 times that amount of wear. Mixing the two totally different wear rates creates a mix that can report a chain to have twice the elongation that is actually does.

Roller wear is important however. A Campy chain can have .15% elongation after 4-6,000 miles, but the space between the rollers may have increased from .200 inch to .240, which is a very large amount of wear. If you leave a single chain in use with a cassette for that long, the most-used cogs are virtually guaranteed to suffer from new-chain skip, when a second new chain is installed.

Since I know that my Campy chains will never reach .5% elongation, I use calipers to monitor only the roller wear. I also alternate the use of at least 3 chains, so I never encounger new-chain skip and get more use from each chain because I don't trash them prematurely, to protect the cassette from new-chain skip.
 

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The wear between the pins and bushing that cause elongtation is very small, compared to roller wear. At .5% elongation, each pin/bushing pair only has about .0025 inch of wear. A pair of rollers can easily have 10 times that amount of wear. Mixing the two totally different wear rates creates a mix that can report a chain to have twice the elongation that is actually does.

Roller wear is important however. A Campy chain can have .15% elongation after 4-6,000 miles, but the space between the rollers may have increased from .200 inch to .240, which is a very large amount of wear. If you leave a single chain in use with a cassette for that long, the most-used cogs are virtually guaranteed to suffer from new-chain skip, when a second new chain is installed.

Since I know that my Campy chains will never reach .5% elongation, I use calipers to monitor only the roller wear. I also alternate the use of at least 3 chains, so I never encounger new-chain skip and get more use from each chain because I don't trash them prematurely, to protect the cassette from new-chain skip.

Are you a politician by chance? I appreciate the detailed answer but don't see how how the question about why measuring roller wear would be a problem. Or as you put it "incorrect reading".
 

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I would think roller wear would factor into that.
It doesn't factor into it because roller wear does not affect chain spacing. Rollers wear on their inside surfaces, so the outside diameters of the rollers do not change. Worn rollers will slop around on the bushing and could eventually break if they get thin enough. But since their outside diameters remain the same, they can't affect chain spacing. Even if a worn roller shifts over a bit on its bushings in one direction, the next worn roller in line will shift the same amount in the same direction, so spacing never changes.
 

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Rulers don't cut it in a bike shop. ....
Sure. They're great for selling new chains, long before they are in fact needed. IMO, using one of the many common chain checkers that are basically measuring roller wear instead of chain elongation to sell a customer a new chain should be considered a deceptive practice...perhaps even fraud.
 

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Sure. They're great for selling new chains, long before they are in fact needed. IMO, using one of the many common chain checkers that are basically measuring roller wear instead of chain elongation to sell a customer a new chain should be considered a deceptive practice...perhaps even fraud.
I had one of the original Park chain-checkers and it could be made to read "fail" on a brand new chain. Let's hope the e-bay winner doesn't own a bike shop. It's the 12" rule for me and it's never let me down.
 

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Sure. They're great for selling new chains, long before they are in fact needed. IMO, using one of the many common chain checkers that are basically measuring roller wear instead of chain elongation to sell a customer a new chain should be considered a deceptive practice...perhaps even fraud.
As I said, I check it with a ruler. I use the tool to illustrate the wear to the customer. If anything, I let chains go too long before I try to sell a new one.
 
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