How do you confirm your bicycle chain is worn and when to replace it?

       Chain wear is often referred to as "chain stretch" because the pitch of the chain increases as it wears. This is the most critical type of chain wear and the increase in pitch comes from wear of the bushings at the chain pins. Over time, the inner diameter of these bushings increases, slotting the pins, and the chain is worn once it grows 1% from the initial 0.5-inch (12.7 mm) pitch.
     The rate at which a chain wears depends on many factors, including how often you ride, the terrain you ride on, the chain fit, proper shifting, and most importantly, how you maintain the chain.
    Chain wear is best measured with a specific chain inspection tool, but if you don't have one, you can use an accurate ruler or tape measure.
Using a ruler, the length from the center of the chain pin to the center of the other pin, across 12 links, should be 12 inches. The most common elongation between links for a worn chain is 1%.
      Therefore, anything over 1/16 of an inch in 12 is time to replace the chain, and anything over 1/8 of an inch in 12 is likely to indicate that the cassette is also damaged and will most likely need to be replaced.
     A typical chain checker is the easiest way to check chain wear. When the tool is inserted into the chain, if it can be fully inserted, it means the chain is stretched, and if the tool cannot be inserted, the chain is not worn. More expensive chain checkers can give more accurate readings, but it is important to clean the chain before using it, so that the reading will be more accurate. Regardless of the method you choose to measure the chain, if it is equipped with Velcro, remember to avoid it when measuring, as it will wear more slowly than traditional links. In addition, not all chain checkers are compatible with the flat-top chains used in SRAM's eTap AXS 12-speed drivetrain.
     It is important to get into the habit of cleaning your bicycle chain regularly. After cleaning the chain, you need to wipe it dry and then apply chain lubricant. The chain can also be waxed, which can further protect it from the harmful effects of wear and contaminants.