So, been biking for little over two years now and when to replace my chain is getting more confusing as I try. I started with a KMC 10.93 ten speed chain and I replaced this at 3/32 inch elongation based on using a metal one foot ruler I have had in my tool box for years. I actually went to long based on the ruler. On my second chain I used the Shimano CN-HG95 10 speed chain and purchased the Park CC-3.2 chain checker:

https://www.parktool.com/product/cha...dicator-cc-3-2

So, I used the ruler method and the Park chain checker and when the Park showed .5 wear and the ruler said 1/32 inch elongation, I replaced the chain with Shimano CN-HG95 10 speed.

Now on my third chain I decided to get the Pedro Chain Checker Plus II, which says it takes roller play out of the equation.

https://pedros.com/products/tools/ca...ecker-plus-ii/

And in the process I decided to purchase a new steel 18 inch ruler so that I could measure the elongation more exact then guessing 1/16 inch with the one foot ruler. At this point with around 2200 miles on the chain, the Park tool says worn out at .5, the old metal ruler says 1/32 elongation, the Pedro says still good, and the new 18 inch ruler shows no elongation at all. Huh? So, I compared my old metal to new one and it is off. It is showing short by 1/32 inch for a foot. I checked this against a drafting ruler I have and just a tape measure and my new 18 inch steel is matching both.

Ok, so I ditch the old ruler which I have been using and get my old two chains out of the drawer:

1.) First KMC chain: Pedro shows good, Park shows bad, and new metal ruler says 1/16 inch elongation.

2.) Second Shimano chain: Pedro shows good, Park shows bad, and new metal ruler shows zero elongation.

3.) Third Shimano chain: Pedro shows good, Park shows bad, and new metal ruler shows zero elongation.

Thus, based on the above I replaced my chains to early using a inaccurate ruler and Park tool. And it looks like the Pedro tool is more forgiving as my first chain is elongated by 1/16 inch for sure, but the Pedro says still not worn to .5.

So, based on the above I think I will just go with the ruler as most people have stated on this forum as the best. But I was sure hoping the Pedro checker would be better than the ruler method. I also at this point show cassette wear and that will be replaced after this third chain.

Might be a stupid question, but are you putting tension on the chain when you measure with the ruler? Doesn't take much, but probably more than a derailleur pulley cage spring will provide. If you take them off and hang them, their own weight will do it. A finishing nail in the wall works fine.

Chain checker tools put some tension on the chain automatically.

Chain checkers are valuable because they reduce human error--they are less precise than a literal measuring of length of a tensioned chain can potentially be, but in a shop environment in particular mechanics should check chains on literally every used bike they touch, and speeding up that process is critical. Measuring with a ruler accurately takes a steady hand, a good eye, and a solid moment of concentration. Your Pedro's tool, along with the Shimano chain checkers, are the most accurate.

At work I use a Rohloff chain checker. I've never seen it underestimate wear, but the majority of the time its results are sufficiently accurate. I do double check with a ruler when the result is borderline, particularly when considering whether a cassette of freewheel is likely to need replacement due to excessive wear.

A nice thing about an your new 18-inch rule is that you can start your measurement at the 1-inch mark and measure to 13; this is easier to do precisely than to line up to the end of a rule. This is how the old 3-sided drafters' scales worked.

The park tool is junk.

Just use a ruler.

Your problem is using a "ruler". A ruler is a person in charge of some where. A thing that measures is a "scale". Sorry, I'm a machinist and if I called it a "ruler" instead of a "scale" I'd get crucified. Methinks too many people worry needlessly about chain "stretch" and other nonsense. Also, get a precision scale such as Starrett or Browne and Sharpe, not the local Harbor Freight special. Sure you'll pay more but quality costs.
Just my 2 cents worth.
Jon

I bought the Pedros tool and it seems to do the job.
I bought the Rohloff years ago and after a while used it until it showed the chain was shot and then went to the tape measure.

Scale it is! Just like saddle, it took me a while to switch from seat. And the Starrett or Brown and Sharpe, are very nice. Brown and Sharpe are in my budget.

Chains don't cross an imaginary line of being worn out, its a big wide gray area. All of these measures are useful information. Scales/rulers are useful if your objective is exactly 1% elongation, which is still in the gray area.

And there is... https://www.rohloff.de/en/shop/wear-indicators/ + a digital read out chain wear checker from KMC..

The problem with "gray area" is that too many wait for a part to be completely worn out and wind up getting stuck on the side of the road when things break.

That's the purpose of a spec, to prevent people from running stuff down to the point where it breaks.


-Tim-

Virtually all of these instruments err on the safe side. The complaints generally are that they err on the too safe side and result in changing the chain before the "magic" 1% elongation number.

And chains generally don't break for being worn out - they break because they're damaged somehow. So your point is valid for a lot of stuff, but doesn't really apply to chain checkers.


Full disclosure - I use the Park tool - it's really handy. I know the limitations, and I'm fine with them.