# How to use ruler to measure chain wear



## fredstaple (Jun 2, 2003)

Great thread on which is best to measure chain wear. Lots like to use a ruler. Can someone explain this in more detail. Where percisely do you measure from and where to (front of the pin to front of pin?). How do you know when the chain is worn out, what should the measurement be? What is it in inches and metric?

I would like to try this meathod, but don't understand how. Thanks


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## looigi (Nov 24, 2010)

http://bicycletutor.com/chain-wear/

This guys measures from the center of the pin. You might find measuring from the left or right edges of the pin easier than estimating their centers. Also, it's easier to be more accurate if you don't start from zero on a ruler. For example, put the first pin at the 1" mark and measure to the 13" mark.


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## C-40 (Feb 4, 2004)

*better way..*

I use a 12 inch precision machinist rule that has an exact overall length of 12 inches. Place the left end on the edge of a pin. The pin at the opposite end of the rule will be completely covered when the chain is new. As the chain wears, the length will increase and the pin that was covered will begin to peek out from the right end of the rule. When you get close to 1/2 the pin's diameter exposed, you've reached .5% elongation.

The bike tutorial guy is wrong about several things. Cogs will wear out, no matter how often the chain is changed. It might take 4-6 chains worth of riding, but eventually you will get new-chain skip. If the difference in the new chain's roller diameter and pitch is not too great from the old one, then chain skip is less likely. A single chain, used until the the elongation is 1% or 1/8 per foot could cause enough cog wear to create chain skip with the second new chain, but it depends on how much the wear is spread among the cogs. If one or two cogs are used heavily, those will be the first to skip. I used to wear out the 19 and 21T cogs when I did a lot of mountain climbing with a triple. The triple's little ring creates more chain than a larger chainring would and that does not help cog life.

I use 3-4 chains in a rotation. Rather than toss a chain when it's half worn, I keep the chain for further use. After all of the chains are half worn, each one can be reused again, until it's truly worn out. I tend to rotate the chains more frequently after their first use.

A completely different form of chain skip will occur if a chain is left in service for so long that it has 1.5-2% elongation. Somewhere in that range a chain will fail to engage the most-worn cogs, even though they are worn-in together. The roller's contact point with the tooth rises as the pitch increases. Eventually, the chain will simply ride right over the top of the teeth and not drive the bike. Cogs always develop a hooked-tooth profile that eventually fouls up the chain's engagement. I've read of people taking a file to the tip of the teeth to remove some of the hook and actually get some more use from a worn cog, but I've never tried that myself.


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## Kerry Irons (Feb 25, 2002)

*Thinking too hard*



fredstaple said:


> Great thread on which is best to measure chain wear. Lots like to use a ruler. Can someone explain this in more detail. Where percisely do you measure from and where to (front of the pin to front of pin?). How do you know when the chain is worn out, what should the measurement be? What is it in inches and metric?
> 
> I would like to try this meathod, but don't understand how.


Bicycle chains are 1/2 inch pitch, meaning that two links equal an inch, and 24 links equals 12 inches. You can measure any point to point as long as you keep the same reference. Front/back/center of pin to pin, leading/trailing edge of side plates, or even the little logos or cutouts that are sometimes stamped into the side plates.

It's usually easiest to measure along the lower run of the chain. While a precision ruler is nice, it's certainly not necessary. You can easily see 1/16 inch even if your ruler has only 1/8 inch gradations. A chain on a 9s or higher drive train should be replaced when it shows 1/16 inch elongation in 24 links (12 inches original length). That is 0.5% elongation.

You can convert these numbers to metric by knowing that there are 25.4 mm per inch.

Rotating chains does extend the life of cassettes, but as C-40 noted, the teeth are wearing whether the chain is new or old and will eventually have to be replaced.


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## bikerjulio (Jan 19, 2010)

> begin to peak out from


It's "peek"

this is where spell check won't help.

once I cudnt even spel enginur. now i are one.


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## fredstaple (Jun 2, 2003)

*Thanks Very Much*

This helps tremendously and also dovetails with the chain slip issue I have experienced.


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