A bike shop employee used a tool he said would check the wear on the chain, and said that it should be changed.

He said it took a measurement that meant the chain had expanded, but it is still hard for me understand why I should change the chain.

He said that the reason was that the expanded chain links will cause the chain rings to wear down.

That is one argument and I have no experience with it, to know if it is true.

But are there more reasons? How do I know when the chain should be changed?

My first thought is to use it until it breaks, but it probably is not the wisest option.

  • 2
    Using a chain til it breaks will be very costly. Chains are dirt cheap compared to chainrings and cogs.
    – user313
    Commented Feb 11, 2011 at 17:27
  • 3
    Another thing about using a chain "til it breaks" is that it can cause you to crash when it breaks. Or even when it starts slipping before it breaks. Another good reason to maintain your chain and replace when needed...you probably don't want to find yourself lying beside some desolate road in the cold and wet all because of a slipping/broken chain.
    – user313
    Commented Feb 11, 2011 at 21:38

2 Answers 2


You can measure the stretch of a chain with a chain gauge (or just a ruler) enter image description here

Alternately - the chain links are 1 inch long, so measure 12 of them with a ruler, if they are more than 1/8inch longer than this then they are worn.

You need to do this before it wears the rear cogs - it will cause the teeth to wear into sharp pointed spikes = need a new cassette.

  • what do you mean by "into points"? Are they marked on the cassette? What do they look like/
    – user652
    Commented Feb 11, 2011 at 16:58
  • 1
    Points as in wearing the rounded teeth away into sharp spikes
    – mgb
    Commented Feb 11, 2011 at 17:14
  • 2
    Sharp spikes, as in a new chain won't fit right and will wear out very quickly. If you let the chain wear out too quickly you have to replace the front and back gears entirely. It's significantly cheaper to replace the chain before it's too worn down than to replace everything else.
    – freiheit
    Commented Feb 11, 2011 at 17:18
  • any idea what is the general term for Rohloff Caliber? There must be some cheaper substitutes, seen many of this kind of tools in my LBS (apparently for different types of chains). Idea whether there is some do-it-all-tool to measure chain strech? Thinking...have to develop some mnemonic about stretching: when I compared my old chain to my new chain (same amount of pins), the old had stretched about 5cm. The Rohloff tool Caliber indicated chain renewing (according to my LBS). The ruler-pen-paper is more reusable but this caliber may be easier to use.
    – user652
    Commented Mar 11, 2011 at 16:39
  • Chain gauge? Fizler calls theirs a "chain wear gauge" and it's about $10
    – mgb
    Commented Mar 12, 2011 at 17:11

When the chain has "stretched" it will no longer sit properly on the teeth found on the sprockets and chainrings, symptoms of this point being reached include the chain jumping off the chainring when sufficient pressure is applied to the pedal. This usually happens when you're trying to pull away after stopping (eg at a junction). Not only is this a pain, but it can also be both dangerous and painful (my foot tended to come off the pedal and the calf/shin smacked into the teeth on the chainring when this happened to me).

The problem with leaving the chain until it gets to this state is that it also wears the sprockets at the back and the chainrings at the front. If you allow this to happen, then even buying a new chain won't do you much good as the worn teeth on the other parts of the drive system will prevent the new chain from sitting properly, and may cause the same kinds of problems as were being experienced with the old chain. If you're lucky enough not to have a problem with the chain skipping, the worn teeth will still cause the chain to wear out much faster than normal.

So, check you chain fairly regularly, if as mgb says, the chain stretched by more than 1/8 of an inch per foot, change it. Otherwise you might have to replace either the chainrings, the rear cassettes or both. A much more expensive proposition all round especially if you've got a decent chainset fitted.

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