According to the international standard, ISO-9633, the method to evaluate the chain stretch is to measure the length between 2 pins.
However, most tools measure the stretch between two rollers which can give an entirely different reading, leading to some confusion about whether the chain is worn or not.
So what do we do?
Analogy- Using a Ruler for testing
Using a chain measure for testing
The inch is the basic unit of measure for all chains. Each link is one inch long (the same length as three chain bolts) and the distance between two chain bolts is 0.5 inches.
Testing over 6 inches of the chain means the testing point is in the middle of the pin.
If the tool shows a stretch of more than 1/16 inches then the chain should be replaced.
If the tool shows a stretch of more than 1/8 inches then the cassette should be replaced as well as the chain.
Put the chain on the biggest ring, if you have more than one, and try to pull the chain up from the cassette
If you can easily pull the chain up from the cassette it means both chain and cassette need replacing.
Please note that TAYA’s safety margin of chain stretch is between 0.4 to 0.8 percentage according to the Park Tool.
Good maintenance extends the life of the chain massively. Regular cleaning and lubrication will make your chain and cassette last longer and keep shifting sweet.