There comes a time when all bicycle mechanics are faced with explaining to a customer why they need a new bicycle chain. The mechanic will explain to the customer that their chain has stretched. The customer, especially if they are a new rider, will look at the mechanic with a look on their face that seems to be saying “You’re pulling my chain.” How can a steel bicycle chain stretch from the weight of just a single rider? Read on to find out.

Do bicycle chains really stretch? The short answer is no, however they do wear in such a way as to cause their maximum length to increase. Mechanics usually refer to this as chain “stretch.” It is the sign of a worn out chain that should be replaced.

Extreme wear on a chain pin

Illustration of extreme wear on a chain pin. Inner links wear groves into the pin.

Chains of Misery

If you take a quick look at a worn out bicycle chain, it might not show obvious signs of wear. The side links might have some inconsequential wear but the real wear happens on the inside of the chain where you can not see it.

Park CC-3 chain wear measuring tool

Tool for measuring chain wear.

Modern chains are made up of inner link plates, outer link plates, bushings, and chain pins. It is the chain pins that show most of the signs of wear. This is not easily visible or measurable, so mechanics will instead use a tool that measures changes in the length of a section of the chain. As the pins wear, it allows the links to be pulled further and further apart. The distance between links of a chain is referred to as “pitch” and this will slowly change over the lifetime of the chain.

On a severely worn chain, groves will be clearly visible in the center of a removed chain pin. This not only changes the pitch, but also causes the chain to have more movement from side to side. This can decrease shifting performance as well.

Chain Reaction

As a chain becomes old and worn, the risk of failure becomes greater. The increased chain “pitch” will begin to wear cogs to match it. This will eventually lead to the freewheel or cassette needing to be replaced along with the chain.

Park CC-3 chain tool in action

Here the tool is measuring a chain. The .75 side fits easily in the chain when worn. If the 1.0 side fits, it’s likely the cassette is worn as well.

You could try running the same chain until it literally falls apart, replacing the chain and gears when this happens, however you will be riding a bicycle that does not shift well, has noisier gears, and is less safe. When a chain fails, you can bet it’s not going to be while you are coasting in the saddle. It will most likely fail when you are “putting the hammer down” and are out of the saddle.


Always verify that all the gears work in a repair stand before going on a bike ride.


If the chain is replaced at the proper time, you will likely go through a few before needing to replace the cassette. As a chain wears the cassette to match it’s increasing pitch, you eventually will wear a few cogs so that a new chain will skip when heavier force is applied. You could try to avoid using these cogs, but guess what. They are your favorite gears. That is why they wore out first. On a borderline case on my own bike, I was able to avoid the bad gears long enough to “stretch” the chain so it no longer skipped and lasted through one more chain. I do not recommend you avoid replacing the cassette this way. You need to be constantly prepared for a possible chain skip.

Unchained

Hyperglide Pins

The most popular chains today are made by Shimano. Shimano’s chains are attached with a special pin. The special pin is inserted into the chain along a narrower installation section and then a chain tool is used to push the functional part of the pin into the chain. The installation section of the pin is then broken off using pliers or part of the chain tool. Some chains come with a pin installed into one of the outer side plates. These pins do not have the thinner installation section. There are several important rules to follow when installing a chain using one of these pins.

  1. Only use pins specified as safe to use with the chain you are installing. The number of speeds of the chain and the pin need to match. Don’t use pins from a different manufacturer than your chain.
  2. Do not remove an installation pin to later insert another installation pin. It is only safe to use a link once like this. Find a link with a standard pin to remove instead.
  3. Pins are installed from the drive side towards the non drive side. They have raised sections and should snap in place so that they are perfectly centered if installed properly.
  4. If standing on the drive side of the bike with the broken section of chain on the bottom run, the installation pin should be to the left side of the outer link. This is important. There are two pin holes in each outer link. The one that ends up having an installation pin should be the one that enters the rear derailleur first when rotating the cranks forward.
  5. Use the proper chain tool to install the pins if the manufacturer specifies this.
  6. Read all the installation instructions that came with your chain to be sure you have all the rules down before you attempt to install. Some chains are directional and need to be installed with printed logos facing out towards the drive side.

KMC “Missing Link”

Multi-speed master link

Scared yet? Well there’s another option. KMC makes a reusable master link that will work with geared bicycles. There are several models and you need to chose the right one for the number of gears and manufacturer of chain that you are using. How reusable are they? I would not recommend using them beyond the life of a single chain. You may find that you have to replace them more often if the chain is removed several times over its life span. For a few bucks you gain the ability to remove your chain more easily for cleaning and you don’t have the list of installation “rules” to worry about. Just choose the right model for your chain.

These things are great for on the road repairs as well. A repair with a pin will require you remove a set of links. This will require you to ride extra carefully to prevent damaging the bike. Shortening the chain is usually not necessary when doing the repair with a KMC Missing Link.

Chain of Fools

When a chain fails, it separates at the pins. I have found that the majority of the time this happens, there will be at least a limited time period where a click can be heard as the damaged link passed through the rear derailleur and catches on the cogs. This will be your only warning – if you get any at all that the chain is about to fail. If you are out on a ride and are not carrying the necessary repair kit, you’re not likely to have much choice other than to attempt to ride in, but you should stay seated and try not to put too much pressure on the drivetrain. The click will be distinct from other noises in that it happens once on each chain revolution, not each crank revolution. The noise is at regular intervals but the crank is not in the same position on each click.

Never trust a chain that fails on you. Make the repair necessary to get yourself back home, but ride with the expectation that the chain could fail again. Try to stay in the saddle as much as you can. Replace the chain before going out on another ride. Chains wear evenly. If your chain was old enough to have failed once, it’s probably getting ready to fail in a number of places. If it was a defect on a new chain, well I wouldn’t feel too confident about continuing to use a chain in that case either.

(These) Chains

Chains never come at the correct length for your bike. They always come with a few extra links that need to be removed. Installing a chain with the incorrect number of links can cause damage to the bike and possibly injury to the rider. The chain length needs to be long enough to allow for the largest cog and chainring to be shifted into without binding up the rear derailleur. It need to be short enough so that the chain does not sag or rub on the rear derailleurs cage.

Rear derailleur with proper chain length.

Rear derailleur with chain length set so chain clears the cage while in the smallest cog and smallest chainring.

My preferred method of installation is to shift the bike into the smallest cog and smallest chainring and then shorten the chain to the first set of links where the bottom run of chain does not touch the rear derailleurs cage. I then verify that the largest cog and largest chainring work properly. Some choose to fit the chain based on the largest cog and big chainring, and this would be fine as long as a lower range cassette is not used. If you install your chain based on the largest cogs and then throw on your climbing cassette, you’re in for a big surprise. If you are using cassettes within the size range that the manufacturer recommends, then fitting to the smallest cog/chainring should work no matter what range you choose. Always verify that all the gears work in a repair stand before going on a bike ride.

Unchained Melody

Chain lube is not just about silencing annoying chain noises. A squeaky chain is clearly a sign that you need some chain lube, however do no wait for your chain to get noisy before applying chain lube. Do no over lubricate the chain. This can lead to an excessive collection of dirt on the entire drivetrain which will also lead to excessive wear to the chain and other drivetrain parts. Some waxed based lubes or dry lubes will actually help clean the drivetrain. You can apply these lubes more generously, but should be wiping off the excess as you do so.

Back on the Chain Gang

How long should a chain last? Most bike shops will tell you about 2000 miles, and that’s a good estimate, but chain wear is greatly affected by a number of factors. Cleanliness of the drivetrain, terrain ridden, power of the rider, and weight of the rider all play an important role in chain wear. I had a rider claim he had close to 10,000 miles on a chain that still appeared to be okay, but he kept things pretty clean and also was not able to ride hills for a long time due to an injury. This is nowhere near what a typical rider should expect. Chain checking tools are fairly inexpensive and definitely worth their purchase price. I prefer the single piece design that Park uses as it seems less likely to give a false worn out reading than the models that have moving parts. If one side of the tool fits inside the chain, it’s getting to be about time to change the chain. If the other side fits, you may need a new cassette as well. Check several locations on the chain and don’t try to make it fit inside the chain. You’re just checking to see if it will drop between the links easily.

You should now have a better understanding of how chains work and how to keep your bike safe through proper maintenance or replacement of the bicycle’s chain. ?

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This post was written by Tom

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