...the carbon fiber plastic ones assplode.

When the shifting settings are correct does my bike shift properly? Yes? For me chain is OK. It's only when I start to experience some unsolvable issues that I check my chain. I use the Park Tool. Recently, I reached a point of an insolvable adjusting issue and checking the chain with the Park Tool revealed the chain was quite worn with both the .5 and .75 both easily fitting in between the links. Put a new chain on and shifting is perfect. Checking the new chain with the Park Tool and it says everything is cool.

Even a worn chain works significantly longer if you always keep it clean along with the overall drivetrain. I wipe my chain thoroughly after each ride.

https://cimg3.ibsrv.net/gimg/bikefor...7258bbfe3a.jpg
https://cimg8.ibsrv.net/gimg/bikefor...b26c05f0d2.jpg
A tape measure works fine.
Just don't use the hook end since they can be inaccurate.
I'll use the 2 or 3" mark and check at the 38 or 39" mark.

I measure a 3' section to give me 3X the resolution over checking a 1' section.
I also use the end of the side plate instead of the pin. I think it lines up with the "ruler" better.

...might not have mentioned it, but the chain needs to be slightly under tension when you measure. That's why there are a couple of chain checking tools that are "more"accurate, because they have a couple of hooks that put a small part of the chain under tension before you insert the final checking doohickey. But just hanging the thing from a nail, or even measuring on the bike (which limits how much length you can measure) is sufficient for our purposes.

Point taken, but the only error would be in favor of changing the chain, with preserves at the cassette and the chain Rings which is my reason for checking chain wear.

Using my system, I replaced seven chains at about 2000 to 3000 miles before I had to replace the cassette and chainrings.

Chains is cheap, cassettes and chainrings are not.

For what it's worth, basic chain checkers are pretty useful as a quick, casual check. When they measure worn, go ahead and recheck with a ruler. If you want something that isolates for roller wear, Shimano TL-CN41 is still go/no-go but eliminates roller wear, as does PEDRO'S CHAIN CHECKER PLUS II which is a similar design.

It seems that the original question has been ignored and the thread has evolved into a discussion of how to measure a chain. Let's go back. To the OP: I think most here would agree that measuring chain stretch by whatever method is preferable than using mileage. Mileage will vary based on a lot of factors. I've gotten > 3,500 miles from some chains and half-that from others. So yes, do your measurements periodically and replace the chain when you reach whatever stretch limit you've decided on.

My two bikes are pretty good at letting me know when the chain is near the end. I am a perfectionist when it comes to clean shifting and I start looking for causes early. My Trek road bike starts to stumble at the .5 setting on the park tool.

$40 for a new chain every couple years doesn't even move the needle on the cost of our sport.

Read the manual. From the Park Tool website on the CC-3.2 Chain Checker:

The mileages are only a range. If you want to get more life out of the cassette which is the more expensive part of the drivetrain, replace the chain more often. Sure you could run a chain for 5,000 or 10,000 miles but you’ll have to replace the cassette with each chain because a new chain will skip on an cassette that has had a chain on it for that long.

I can’t find a manual on the KMC chain checker but I think you are reading it wrong. If it is anything like the Park Tool, that’s not “75% of life” but 0.75% of elongation. In other words, the chain is 0.75% longer than it was new. It’s not much.

If chain checkers were made by Big Chain, you might have a point. However I’ve seen few chain checkers that are made by companies that sell chains. Perhaps Park Tool gets residuals for every chain that is “checked” with it’s tool but I rather doubt it.

For the “use a ruler” people, you do realize that using a ruler has it’s own problems. There’s the ruler used and the way it is read. No measurement is “exact”. Most people probably couldn’t use a ruler properly and most people don’t have access to a steel rule. A tape measure probably isn’t much better than a chain checker tools and the chain checker tool is easier to use.

A chain checker is good enough and quicker.

Regarding ruler material: We have two metal rulers in the bike shop we use for measuring chains. One is a steel ruler, the other a Park aluminum ruler (in blue). I like the aluminum one from Park, it's a little bigger (wider), the numbers are embossed instead of printed, and it's easier to read. So I like an aluminum ruler for chain checking....Just trying to be contrarian, but I do prefer that Park aluminum ruler for checking chains.

I know WHAT it's supposed to read.
I related what mine ACTUALLY reads.

If you want to argue, you need to pay attention first!

Apologies. I read your post wrong. In my experience, however, most people don’t know what the readings on the Park chain checker mean. I’ve also found that replacing a chain that is showing past 0.75% on the Park checker will usually skip on anything but a new cassette.

Especially now that checkers that work the "right" way, i.e. compensating for roller wear, are available from several sources (Park CC-4, Pedros Chain Checker Plus II, Shimano). Slightly harder to use than the old style but not too bad.

Adequate precision.

Durability.

Availability.

Affordability.

Stanley tape measures are steel, easy to find (Any hardware store), not very expensive and work just fine. (I measure from 10" to 22"; never from the hook.)

Edit: Oh, the other reason for steel rulers/tape measures. They will heat and contract at the same rate as the steel chain, giving you accurate measures in both the Sahara and the South Pole. Aluminum will be affected quite differently as will wood. (Wood also has humidity issues.).

Ben

This thread has become amusing. Not many familiar with precision measurement. In a machine shop, the least accurate way to measure something is with the most precise ruler that you can buy - a thin steel rule, with .010 inch increments, but for some jobs, it's good enough.

You don't even need to read the markings, when measuring a chain, since it's precisely 12 inches long. Just lay one end on the edge of a pin and see how much of the pin at the opposite end is exposed. If it's less than half, the elongation is still under .5%. The rule is made thin, so the markings that most people need to use can be placed close to the item being measured, to minimize error. Tape measures are worthless.

Here's an adequate rule that's cheap:

https://www.amazon.com/General-Tools.../dp/B00004T7SR

It doesn't. In fact a plastic architect's scale is nice because it's longer than 12" and you can actually measure the extra bit in stretch.

https://images-na.ssl-images-amazon....eL._SX425_.jpg

I use this only if my chain checker says more than .75%, because chain checkers are so fast and easy and I understand measurement error.

I replace my Campagnolo (C8, C9, and now C10) chains after 4000-4500 miles when shifts onto my big ring get sluggish due to increased flexibility from excessive side plate wear although they've only elongated 1/32", and expect to replace my cassette with the next one now that it has 25,000 miles on it. Probably not coincidentally, when I've checked using my dial calipers this was just a little more or a little less than the distance between rollers Campagnolo recommends as the wear limit.

I ran one off brand chain in the Pacific Northwest that was approaching 1/8" after 2000 miles. Your mileage may vary.

Use a $1 ruler or $30 Shimano TL-CN42 because every chain checker that measures between rollers is inaccurate.

Put tension on the chain, measure between the same point on pins which should be 11" apart, and replace at 11 1/16" (1/2%).

That will omit roller wear which doesn't increase pitch and therefore impact cog life.

Usually people use 12", although 11" means you'll have fractional marks to line up with the end on a standard ruler.

Replacing at 0.56% elongation instead of 0.52% is a 0.0048 inch difference that's too small to matter.

Yeah it always seemed kind of contradictory to me to get a ruler that precisely measures 12", then end up having to eyeball the extra stretch, which is the measurement you actually want precision in. The other problem I've had is how easy it it for the 0" end of the rule to slip on you while you're lining up the 12" end and trying to get a reading. It only has to move like 1/32" to throw off the decision between worn out or not. I guess if you have an extremely steady hand and eyesight that's good enough to see both ends of a 12" scale to <1/32" resolution, this won't be a problem. I can sort of do it with good glasses, but don't have a very steady hand. So I mostly use a chain checker also.

I check my chains when they are clean and off the bike, so I can lay them out on a table. That makes it easy to lay a rule on top and not have to worry about movement. The .5% figure is arbitrary. A campy chain may show far less, but be shot due to roller wear or excessive side clearance (after 5000 miles). If several chains are used in a rotation, they can be used longer and you'll never get chain skip. Tossing chains prematurely to prevent new-chain skip results in more money spent on chains than necessary.

Not all chains are cheap throw a ways. High quality chains cost more but last longer.

I guess we Americans are lucky to have inch rulers handy. I imagine they are rare in other countries.

I'm not unfamiliar with accuracy and precision...they aren't the same thing. I'm also familiar with when something needs to be very precise and when it can be just good enough. Chain checking tools, in my experience, are good enough. On the other hand, putting a chain on a 12" rule and estimating how far off the rule the chain hangs off isn't all that "precise" nor accurate. It's an estimate.

I would also point out that no one in this entire thread has said what the value one is supposed to be looking for with a 12" rule. 0.5% wear is 1/16" and 0.75% wear is slightly less than 3/32". For the rest of the world, that's 1.6mm and 2.3mm over 30.48 cm. But those are only estimates as well.

Aw, hell, I'll just use the chain checker and buy cheap chains. It won't matter that much in the end. A more expensive chain wears out at about the same rate as a cheap one.

...don't come crying when you're using that one day and it asplodes while you're measuring and dumps you on the ground.