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I've bought a chain wear checker made by BBB, but not sure what the percentage of worn is about? enter image description here
It has 2 sides, one of them indicates that the chain is worn 75% and I should replace it in the near future. The other side shows, that the chain is 100% used and should replace it as soon as possible.

My detailed question :

What does these percentage mean? What is the equivalent of it in the metric system?

Will 75% worn state affect my cogwheels also? Can I replace the chain to a new one without changing the drivetrain's other elements?

I use a single-speed bike. Chain width is 1/8 inch. It consists 94 chain. (400km (250miles) / month)

  • That's six questions in one, touching at least three different topics (What's the 75% about? Do 1/8 and 3/32 inch chains differ? What is a good single speed chain?) I'm sure that there are already questions dealing with the second topic and for the third topic this site might be the wrong platform. Maybe you should edit your question to restrict it to the first topic of what these 75% are about. – Benedikt Bauer Jan 22 '15 at 11:47
  • There's a couple of vids on YouTube which should help enlighten you as regards this tool. Try Googlong "how to use a chain wear indicator" – PeteH Jan 22 '15 at 12:49
  • yes thank you, I have already done this, but still do not know what exactly 75% means. What are the wearing limits? Is the normal length = streched length * 0.75 ? – kisp Jan 22 '15 at 13:04
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    Thats not 75%, its 0.75%. – Batman Jan 22 '15 at 13:05
  • @Batman if you are sure I would give you the points in an answer. – kisp Jan 22 '15 at 13:08
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The .75 is not 75% worn per se. A chain checker measures chain stretch. Chain stretch is an indicator or wear-and-tear. Parts of a drive train wear at different rates. For instance the teeth of the chainset will show wear when they become "shark-finned". But this could be long after the point at which you should replace a worn chain. If you persist in using a worn chain - though you may not notice anything detrimental - but when the chain eventually gives up - and you put a new chain on - you may find it skipping under load through the gears. This requires replacement of chain-rings / cassettes. An earlier replacement sought - would have prolonged the life of chain-rings / cassettes.

As for your last question - it is difficult to say - if you ask a manufacturer - they will say no difference. Personally, I think the wider chains lasted longer and are stronger than the narrower 10/11 speed chains of today.

Don't know of any exceptional single-speed chains ... just keep it well oiled and it will last longer.

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    To clarify a bit, replacing your chain before it is completely worn is what will prevent your more expensive components like front chainrings and your cassette from needing to be replaced. – Stephen Touset Jan 23 '15 at 0:33
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That is not 75%, it is 0.75%. - as @Batman said.

According to other sources, it is already too late to change the chain. (Than what the purpose of this tool? - would be the next question)

From wikipedia : "Twenty half-links in a new chain measure 10" (254 mm), and replacement is recommended before the old chain measures 256 mm (0.7% wear)"

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On a non-single speed bike, rear cogs are pretty pricy, and when chain measure tool showing 1.0 it's probably already affected cogs. At 0.75 it's probably didn't affect the cogs yet. So it's preferable to change the chain before.
On a single speed bike it will not greatly affect cogs. Thou it sensible when riding and you should feel the ride better with new chain.
Personally, I don't use this tool, but a meter. As @kisp brought from wiki, if every 2 half-links equals 1 inch (20 half links are 10 inches), if those 2 half links become 2.56cm, it's up to change the chain. It's a bit hard to measure 2 half links, but when you take 20 it become easier. Yet, if you have a ruler with inches, it's very easy to measure 2 half links.

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