# KMC Digital Chain Checker



## unobtainium (Feb 28, 2005)

I just got the new KMC Digital Chain Checker. It’s the only digital chain checker I am aware of. I also have the ProGold Chain Gauge which is marked at 50, 75, and 100% wear points. The KMCchain on my bike reads about .64 mm worn (.8 is considered worn out) while the ProGold shows it to be about 80% worn, essentially the same reading!
So the ProGold is brilliant in its ease of use and simplicity, and low cost while the KMC Digital Chain Checker might be the must have latest tool for gearheads. This is a short video of the KMC by the manufacturer
Digital Chain Checker
I bought my KMC Digital Chain Checker for $46.95 plus shipping from ebikeshop.com


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## tihsepa (Nov 27, 2008)

Get a ruler. Works fine and does more than one thing.


Its like the "Brifter" of tools. :23::9::7:


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## MR_GRUMPY (Aug 21, 2002)

I use THIS and a Park CC-2


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## brucew (Jun 3, 2006)

Unfortunately, all my chains are analog.


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## BunnV (Sep 7, 2005)

brucew said:


> Unfortunately, all my chains are analog.


LOL!!! :lol:

OP, sounds like a cool tool! :thumbsup:


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## looigi (Nov 24, 2010)

A ruler is better and more accurate as it doesn't add in roller wear, which is essentially irrelevant as it doesn't change the pitch of the chain. And, chain gauges that measure inside length between rollers add in twice the roller wear. I've spoken about this with a number of chain gauge manufactures and they agree! Use one of these and you'll be replacing chains far more frequently than necessary.


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## Kontact (Apr 1, 2011)

Roller wear changes the pitch of the chain when you wrap the chain in a curve around a cog. It won't change pitch when the chain is straight and not touching a cog or chainring, but who cares about the chain when it isn't touching anything?


Replacing a one piece metal go/no-go gauge with a digital one seems crazy.


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## looigi (Nov 24, 2010)

Kontact said:


> Roller wear changes the pitch of the chain when you wrap the chain in a curve around a cog.


We disagree.


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## Chainstay (Mar 13, 2004)

The precision this tool gives you is important so that you can replace your chain at exactly the right time to keep the cost of chain replacement down while extending cassette life. There is of course an optimum point of chain wear at which this occurs. That point would be specific to the cost and wear rates of your chains, cassettes and chain rings. Since you bought the tool I assume you know what that optimal wear point is with a high level of precision. What is that value and how do you know it's accurate?

How much money do you expect to save by now making better decisions about chain replacement. Considering the original cost of $48.00 plus shipping and batteries I'm sure this is a wise investment in keeping bike maintenance costs under better control.


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## danl1 (Jul 23, 2005)

Interesting. I have the same head on a digital caliper that I spent $9 on.

If they made the 'arms' a set of equal points( "V" shapes) rather than a set of hooks, extended it by a few inches, and removed the springs, they'd have something that would fairly and accurately measure a chain.


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## Kontact (Apr 1, 2011)

looigi said:


> We disagree.


This isn't an agree or disagree thing, it's a fact of geometry. To have the pitch of the pins match the pitch of the cogs, the rollers can't be larger or smaller than the difference in diameters between pin and cog cuts. Here's a picture from an old thread on this site:











Whether you agree that it causes wear or not is a separate issue.


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## FBinNY (Jan 24, 2009)

Chainstay said:


> The precision this tool gives you is important so that you can replace your chain at exactly the right time to keep the cost of chain replacement down while extending cassette life. There is of course an optimum point of chain wear at which this occurs..


This theory is analogous to buying a digital watch and synchronizing it to the atomic clock in Boulder, so you won't miss a bus that may arrive 2 minutes early or 10 minutes late.

There is no *exact* point at which it's best to replace a chain. Chain/sprocket wear isn't a digital event. It's a progressive process wherein the rate of sprocket wear increases as the chain ages. Experience has shown that replacing chains at roughly 1/2% stretch, or when rollers are worn beyond a certain point extends the life of the sprockets. But that's a guideline only and a bit to either side isn't going to make a material difference. 

You don't pull off the highway and change your oil at exactly 3,000 miles (or whatever number you use), you just schedule it for the nearest convenient time. Likewise you don't replace a chain at exactly 1/2% stretch. Since it's only an approximate replacement point anyway, there's no benefit to measuring it very precisely. (I won't debate whether this tool does that anyway, that's for another time).


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## looigi (Nov 24, 2010)

Kontact said:


> This isn't an agree or disagree thing, it's a fact of geometry...
> Whether you agree that it causes wear or not is a separate issue.


I think your illustration of the geometry is wrong.


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## Kontact (Apr 1, 2011)

looigi said:


> I think your illustration of the geometry is wrong.


The geometry is very simple. If you have a circle that is 10 inches in circumference, a tape exactly 10 inches long will fit around it perfectly. If you reduce the radius of the circle, then the circumference gets smaller, and now the belt is too long.

Correctly sized rollers make sure the pins stay at the correct radius from the center of the circle. If the rollers are thin, that effectively reduces the radius, and then the pins will attempt to descend to that new radius and the cog circumference and chain length are a mismatch. That is what the diagram illustrates.


Anyway, if you think something is wrong, you can actually say what geometry is right. That diagram has been around for awhile, and you're the first person to say it isn't exactly what it looks like.


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## Hughsdad (Jan 21, 2011)

danl1 said:


> Interesting. I have the same head on a digital caliper that I spent $9 on.


So KMC gives us just one more example of how absurd pricing can be for cycling-specific stuff.


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## wim (Feb 28, 2005)

Kontact said:


> That diagram has been around for awhile, and you're the first person to say it isn't exactly what it looks like.


It's fine to illustrate most of the points made here, but is a simplified view. For example, links "elongate" on a short-long-short pattern, with every other link not taking part in this. This Rohloff illustration of a worn chain-worn cog condition goes into more detail (admittedly excessive for this discussion).

Dimensions in mm. Light circle = high pedal force. Bold circle = light pedal forces. Arrows = force vectors and magnitudes.


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## Kontact (Apr 1, 2011)

wim said:


> It's fine to illustrate most of the points made here, but is a simplified view. For example, links "elongate" on a short-long-short pattern, with every other link not taking part in this. This Rohloff illustration of a worn chain-worn cog condition goes into more detail (admittedly excessive for this discussion).
> 
> Dimensions in mm. Light circle = high pedal force. Bold circle = light pedal forces. Arrows = force vectors and magnitudes.


Neat diagram.

The one I posted just illustrates roller wear on an otherwise unstretched chain. Elongated links just make the roller wear problem worse.


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## wim (Feb 28, 2005)

Kontact said:


> Elongated links just make the roller wear problem worse.


Absolutely. Here's the new cog-worn chain combo.


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## wim (Feb 28, 2005)

And last one: new chain on a worn cog.


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## wim (Feb 28, 2005)

If you can stand it, one more. This is really the last one. New chain, new cog. The 120-degree or so sector labeled _Nutzbarer Bereich..... _ is the "Area of effective ("usable") chain force transfer."


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## looigi (Nov 24, 2010)

Looking for an accurate diagram of new cog, non-elogated chain, worn rollers.


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## FBinNY (Jan 24, 2009)

Looigi,

Skip the diagram for a moment, and make a picture in your head. 

As the rollers wear they allow the pins to move inward closer to the center of the sprocket. That means that the radius of the circle formed by the pins is smaller. A smaller radius means a shorter circumference, so the same pitch (or pin-to-pin distance) is now too long for the sprocket.

If you can't see this, go down to the local pub and take a good look at the dartboard. You'll see that the segments get narrower as you move toward the bulls eye. use two fingers to walk segment to segment and you'll see that you have to widen or narrow the gap as you move in or out.

Now buy yourself a brew or two while you contemplate how chains and sprockets interact.


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## Kontact (Apr 1, 2011)

looigi said:


> Looking for an accurate diagram of new cog, non-elogated chain, worn rollers.


It is accurate. And FBinNY and I have both given you perfectly reasonable and understandable explanations about why it is accurate. You haven't even raised a logical objection to anything.


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## FBinNY (Jan 24, 2009)

Kontact said:


> It is accurate. And FBinNY and I have both given you perfectly reasonable and understandable explanations about why it is accurate. .....


You're being a bit unfair when you say we both gave him good explanations here. My explanation was in response to the request for a better diagram, so he couldn't have read it when he posted the request.


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## JCavilia (Sep 12, 2005)

looigi said:


> Looking for an accurate diagram of new cog, non-elogated chain, worn rollers.


A hypothetical situation that doesn't really happen in real life. The same factors that cause wear between pins and "bushings" (actually the shaped holes on the inner plates on modern chains) also cause roller wear. If the rollers are worn, the chain will be elongated, at least somewhat. Maybe the relative rates of wear will vary a bit with different designs and materials, but if there's elongation there wll be roller wear, and vice versa.

It seems to me that is a strong argument that the ruler is good enough. Although it only measures pin/bushing wear (which creates elongation) and does not directly measure roller wear, the two phenomena move in parallel, so elongation is a good surrogate for both. There's a lot of expeience that replacing chains at 1/2% elongation maximizes cog life at reasonable cost.


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## Kontact (Apr 1, 2011)

JCavilia said:


> A hypothetical situation that doesn't really happen in real life. The same factors that cause wear between pins and "bushings" (actually the shaped holes on the inner plates on modern chains) also cause roller wear. If the rollers are worn, the chain will be elongated, at least somewhat. Maybe the relative rates of wear will vary a bit with different designs and materials, but if there's elongation there wll be roller wear, and vice versa.
> 
> It seems to me that is a strong argument that the ruler is good enough. Although it only measures pin/bushing wear (which creates elongation) and does not directly measure roller wear, the two phenomena move in parallel, so elongation is a good surrogate for both. There's a lot of expeience that replacing chains at 1/2% elongation maximizes cog life at reasonable cost.


Actually, I don't see how this follows. Rollers can wear from friction alone, while elongation implies a certain amount of torque on the chain. You could have an elongated chain used by a powerful rider that has very little roller wear, and you can have roller wear from a light rider who put on lots of mile with little lube.

One can measure elongation with a ruler or attempt to measure individual roller wear some other way, but chain checkers combine both functions to give an idea of the degree of pitch mis-match between chain and cogs - which is really all anyone cares about.

Chain checkers may be just too conservative, but they do provide a composite check of total chain wear. Maybe a digital chain checker and a table for different brands would be even better, but the basic principle of measuring pitch is sound.


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## FBinNY (Jan 24, 2009)

JCavilia said:


> ...If the rollers are worn, the chain will be elongated, at least somewhat.


I think that this is where some of the confusion may arise. Roller wear will not result in elongation, because it isn't cumulative the way pin wear is. The pitch of the chain is unchanged, but roller wear has the effect of reducing the pitch of the sprocket. Reduced sprocket pitch and increased chain pitch have the same effect.



JCavilia said:


> Maybe the relative rates of wear will vary a bit with different designs and materials, but if there's elongation there wll be roller wear, and vice versa.


There's an assumption here, which may or may not be accurate. The relative wear rate of pins, plates and rollers can change dramatically chain to chain. Part of the difference arises from very narrow, or conical outer surfaces of the formed "bushing" of the inner plate. 



JCavilia said:


> It seems to me that is a strong argument that the ruler is good enough. Although it only measures pin/bushing wear (which creates elongation) and does not directly measure roller wear, the two phenomena move in parallel, so elongation is a good surrogate for both. There's a lot of expeience that replacing chains at 1/2% elongation maximizes cog life at reasonable cost.


Here I agree that in most cases measuring elongation is a good indicator of both wear patterns. The 1/2% guideline is experience based, not theoretical and so the method works to that extent. However, if you're seeing little elongation on a high mileage chain it might make sense to check roller wear and if that's high, adjust your guidelines accordingly.

It's not like we have some magic line at which a chain is suddenly too worn to use, it's more like changing oil in your car. You want to replace it at regular, though not precise, intervals. Use the ruler to check, and some common sense in deciding when it's time to replace the chain.


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## cycocross (Dec 11, 2011)

We have no choice, now that there is a digital gauge we must throw out any and all "old" gauges. It's the only way mankind can hope to evolve to the next level. Ya'll can continue to drag your knuckles as you walk, but I for one am ordering one of these today.


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## JCavilia (Sep 12, 2005)

Quote:
Originally Posted by JCavilia 
...If the rollers are worn, the chain will be elongated, at least somewhat. 




FBinNY said:


> I think that this is where some of the confusion may arise. Roller wear will not result in elongation, because it isn't cumulative the way pin wear is. The pitch of the chain is unchanged, but roller wear has the effect of reducing the pitch of the sprocket. Reduced sprocket pitch and increased chain pitch have the same effect.


I did not perhaps state my case so clearly there. I know that roller wear does not result in elongation. My point was that if there is roller wear there will also be pin/bushing wear, which will result in elongation. But you make a valid point that it is an asssumption that the rates will track.

As for kontact's point about torque affecting pin but not roller wear, I'm not sure. pins and bushings are worn by friction just as the rollers are, and while friction wear is higher if the chain is under greater stress, that may be true of the rollers as well.

I like your bottom line FB: use the ruler unless it seems not to be working.


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## FBinNY (Jan 24, 2009)

the problem in these chain wear debates is that folks try to make a precise science out of what are essentially only guidelines. 

Decades ago when chains had bushings we mostly used 1% stretch as the replacement point, or considered it a limit and replaced as we approached it. the system served well and our freewheels survived about as well as cassettes do today.

These days conventional _wisdom_ is that 1/2% is the replacement point. the change might reflect an adjustment for faster comparative roller wear in bushingless chains, softer, thinner sprockets, or other mechanical factors such as the use of 11 and 12t sprockets. It might also be the result of a change in the relative cost of chains and sprockets making folks more conservative.

The fact it the 1/2% like the old 1% guidelines are only rules of thumb based on cumulative experience. A little bit either way won't end the world, so there's no need for any degree of precision.

OTOH, most of the chain checkers tend to exaggerate the wear. Many of the checkers I checked, showed a new chain to have 1/4% stretch and showed the 1/2% mark way too soon. If the goal is to get the best total dollar value out of drive train components replacing chains too soon can be as wasteful as replacing them too late.


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## Chainstay (Mar 13, 2004)

That was my point, but I guess the sarcasm is easy to miss


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## looigi (Nov 24, 2010)

A chain elongates from wear between the pins and inner surfaces of the bushing formed from the inner plates. This increase the pitch of the chain which makes it ride further out on the teeth of sprockets. Roller wear does not change the pitch of the chain.


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## Kontact (Apr 1, 2011)

looigi said:


> A chain elongates from wear between the pins and inner surfaces of the bushing formed from the inner plates. This increase the pitch of the chain which makes it ride further out on the teeth of sprockets. Roller wear does not change the pitch of the chain.


How many times do you have to say this before it becomes true?


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## danl1 (Jul 23, 2005)

looigi said:


> A chain elongates from wear between the pins and inner surfaces of the bushing formed from the inner plates. This increase the pitch of the chain which makes it ride further out on the teeth of sprockets. Roller wear does not change the pitch of the chain.


That is a true statement, but an incomplete analysis with respect to wear.

Roller wear doesn't increase the linear pitch of the chain, but it does increase the effective pitch when wrapped around a cog. Or, think of it as FB and wim have described it. As the rollers outer surfaces engage the cog, we can think of them as 'part' of the cog, and the inner pins as the 'chain' itself. Worn rollers effectively make the same kind of mismatch as having a new chain on a worn cog. And that scenario is just as bad as a worn chain on a new cog.

We replace chains to minimize mismatches between cog and chain, because those mismatches accelerate wear on both parts. 

But FB's 'guidelines' commentary are most useful part of the thread. There's a lot of precision being described for a fairly inexact replacement schedule. My take: While the normal sort of chain-checker does mathematically overstate wear, that's only a calibration issue. It just means that we understand the effect and take it into account, replacing slightly later than that style of measurement says we ought. Why not just use a ruler? No good reason, save that it's slightly more convenient.


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## Kontact (Apr 1, 2011)

danl1 said:


> That is a true statement, but an incomplete analysis with respect to wear.
> 
> Roller wear doesn't increase the linear pitch of the chain, but it does increase the effective pitch when wrapped around a cog. Or, think of it as FB and wim have described it. As the rollers outer surfaces engage the cog, we can think of them as 'part' of the cog, and the inner pins as the 'chain' itself. Worn rollers effectively make the same kind of mismatch as having a new chain on a worn cog. And that scenario is just as bad as a worn chain on a new cog.
> 
> ...


Why differentiate between linear pitch and wrapped around the cog? When is linear pitch ever important?

My problem with a ruler is that it is not directly measuring chain pitch - it measures one factor that _partially_ controls pitch, so it is an indirect measure. How the chain actually engages the cog is the actual pitch, and that engagement happens at the rollers, not pins.


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## danl1 (Jul 23, 2005)

Kontact said:


> Why differentiate between linear pitch and wrapped around the cog? When is linear pitch ever important?
> 
> My problem with a ruler is that it is not directly measuring chain pitch - it measures one factor that _partially_ controls pitch, so it is an indirect measure. How the chain actually engages the cog is the actual pitch, and that engagement happens at the rollers, not pins.


I agree. I'm only making the arguments in the form that they've been presented. Folks are accustomed to thinking of it in only linear terms, so the differentiation is forced upon those of us trying to change the discussion.

Also, measuring effective pitch relative to a given cog wrap is neither convenient nor especially informative relative to the decision to swap out to a new chain. The straight-line measurement is reasonably accurate, convenient, and measures the wear factor that is generally most impactful and happens quickest. That is, it's the most reasonable proxy we have.


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## FBinNY (Jan 24, 2009)

Kontact said:


> Why differentiate between linear pitch and wrapped around the cog? When is linear pitch ever important?
> 
> How the chain actually engages the cog is the actual pitch, and that engagement happens at the rollers, not pins.


This statement is as inaccurate as the statement that roller wear that roller wear doesn't change pitch, or matter.

Both pin wear and roller wear affect how a chain engages the sprocket to the same effect, though the method is different. 

Pin wear directly increases the chain's pitch beyond the original 1/2" making it greater than the sprocket's.

Roller wear allows the chain to ride closer to the center of a sprocket, effectively reducing the sprocket's pitch to less than the original 1/2" making it too short for the chain.

It doesn't matter whether you lengthen chain pitch, or indirectly reduce sprocket pitch, the effect is the same, the pitches are now mismatched causing added wear, and, if mismatched enough, the chain's ability to climb high enough to disengage under load (skip).


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## Kontact (Apr 1, 2011)

FBinNY said:


> This statement is as inaccurate as the statement that roller wear that roller wear doesn't change pitch, or matter.
> 
> Both pin wear and roller wear affect how a chain engages the sprocket to the same effect, though the method is different.
> 
> ...


I'm not sure what you're saying is inaccurate. If you look at the rest of my posts and the full post you quoted, I'm clear that pin, plates and rollers all affect pitch.

My statement was simply reflecting that where the rollers end up is the only important measurement, since we are only concerned with chain (roller) to cog engagement.

You can wear out a chain without any measurable elongation or roller wear - we see light riders all the time who's chains just don't shift right any more. But they aren't wearing their cassettes riding these chains.


Dan, thanks for clarifying. Same page.


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## Hughsdad (Jan 21, 2011)

This debate between pin/bushing wear and roller wear, how it effects pitch, etc. is interesting. But in the end, if I've understood it at all, I can still use my Park tool to gauge chain wear because if it shows 0.75, this would mean the rollers are no longer meeting well the sprocket teeth (or soon to be such). Is this the case?


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## C-40 (Feb 4, 2004)

*wrong....*



Kontact said:


> Roller wear changes the pitch of the chain when you wrap the chain in a curve around a cog. It won't change pitch when the chain is straight and not touching a cog or chainring, but who cares about the chain when it isn't touching anything?
> 
> 
> Replacing a one piece metal go/no-go gauge with a digital one seems crazy.


Roller wear will add a huge amount to a straight line measurement over a small number of links, as shown with the KMC chain checker, but roller wear never changes the pitch of the chain. Roller wear certainly affects the point of contact with the cogs, but that does not make the the change a change in chain pitch. The rollers rotate about the bushings formed into the inner side plates. As wear occurs, both rollers on a single pair of sideplates, move in the same direction and about the same amount. The result is a pair of rollers, still positioned at the same .500 inch center to center distance as they were, when new.

Chain pitch is the distance between the pin centerlines. Chain pitch will increase as the pins and the ID of the bushings they ride in changes. Chain pitch is most easily measured over the span of many pins. I use a full-length measuring device, so .5% elongation is an easily measured increase of 1/4 inch. 

A chain with an elongation of .5% will have a combined wear .0025 inch on each pin/bushing. If you only measure across five inches, that's .025 inch of total elongation. If calipers are used to measure the space between any two rollers, you'd also find that dimension to have increased by about the same .025 inch. That means that the roller wear may double the reading from one of these flawed gages.

I've measured well-worn Campy chains where the space between two rollers has increased by .040 inch, but the true elongation, measured over the full chain length is only .15%. If you take the rollers off that worn chain and measure the wear, you may find that the OD of each roller is about .005 inch smaller and the ID around .010 inch larger. There's also wear on the inner plate bushing that goes into the total .040 increase in the space between the rollers. Overall, the wear on the rollers is huge, compared to the pins and bushings.


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## Kontact (Apr 1, 2011)

Another poster contacted me about both of quitting trying to argue against the religious beliefs of people who don't like geometry, and now I see that the insults are starting to fly. See ya!


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## C-40 (Feb 4, 2004)

*flawed...*

All tools that measure over a short length and include the wear on a roller at each end produce flawed readings. Even with the exact same chain pitch of .500 inch, different brands will NOT measure the same when new. The reason is that all brands don't use the exact same combination of roller diameter (OD), roller ID and inner plate bushing diameter.

A new Shimano or KMC chain will typically measure .210-.215 inch between the rollers, while a Campy chain may only measure .200-.205 inch. All of those chains will have the same .500 inch pitch and overall length when new, but that chain checker would show them to have different amounts of "wear", even when new. Some tools are calibrated to read zero wear with a Campy chain and may show a new Shimano or KMC chain to have .25% elongation. That is false wear and should be subtracted from future readings. Even then, the reported "elongation" from these chain checkers is exaggerated.

The .5% elongation value that is most often suggested is totally arbitrary. Changing chains at the point may allow the use of only 2 chains for some people and 3-4 for others, before a new chain skips when installed on those worn cogs.

If you want to guarantee that you'll never get new-chain skip, then alternate the use of 3-4 chains with one cassette and never let one become more than half-worn before changing to a new one. Once all of the chains have some use on them, you'll never get chain skip as long as you keep alternating between the chains at reasonable intervals. Each chain can also be used far beyond .5% elongation, if desired.


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## danl1 (Jul 23, 2005)

C-40 said:


> If you want to guarantee that you'll never get new-chain skip, then alternate the use of 3-4 chains with one cassette and never let one become more than half-worn before changing to a new one. Once all of the chains have some use on them, you'll never get chain skip as long as you keep alternating between the chains at reasonable intervals. Each chain can also be used far beyond .5% elongation, if desired.


This is a solid line of thought, of course, and one that you've been holding for years.

It makes me wonder, though - would there be a way to optimize this - for example, is 3-4-5-6 chains per cassette optimal? Staying right on top of chain rotations would be optimal but impractical - could a mileage guideline be developed?

I realize there are far too many variables for there to be a real-world answer, but it's an interesting thing to try to think through.

Plus, angels on the head of a pin and all. It's not as if either chains or cassettes are murderously expensive.


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## FBinNY (Jan 24, 2009)

I use 3 chains for my road bike, and for some reason ended up with 4 for the commuter. I rotate every 1,000 miles or so (based on re-oil schedule, with some adjustment for weather) using reusable connectors which I keep with each chain.

I can't say what's best, probably there's some degree of improvement with more chains, but there's a cost to the chains. Meanwhile both chain and cassette life increase significantly. First because the chains and cassettes remain better matched in condition, and second because I'm freed of having to replace chains at the 1/2% stretch point and can take the entire drive train well past the 1% mark.

Does it work? In my riding career, I've only replaced one freewheel due to sprocket wear. That was on my old road bike with over 50,000 miles on it and that's on the original 2 chainrings (though a Ninja would be proud to own the outer one).


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## C-40 (Feb 4, 2004)

*3-4*

I just decided that with Campy chains, three chains used for 4-5,000 miles each is great life for a cassette. With other chain brands, four chains might be better, since most other brands elongate much faster. Four chains is the most that I would ever use, even with Campy chains. I trash them when the roller spacing reaches .235-.240.

One other factor that's rarely considered is chain tension. If your riding involves a lot of climbing, the average chain tension will be higher. Cog and chain life will suffer. With no chain rotation, I've trashed steel cogs in 6,000 miles and Ti in only 4,000 miles. The Ti cogs had much greater wear, even with far fewer miles. I only weigh 135, so I don't put that much strain on the drivetrain, even while climbing.


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