You may wonder why you should replace a chain in the first place. Chains, cassettes and sprockets are all part of the drivetrain. The other parts also suffer from increased wear and tear if the chain is worn out. In the system of these three parts, the chain is the weakest link, because it has the most fragile elements: the chain links. You can use a SHIMANO chain gauge to determine whether a chain is still good to go or whether it needs replacement.
Due to normal wear and tear, the chain elements eventually grow apart, so that the teeth of the chain gauge completely fall into the chain. Then, it is time to replace the chain. For SHIMANO chains, it is important to use a SHIMANO chain gauge. Many dealers use chain gauges from other brands which often leads to premature chain replacements.
Once a chain is worn out, it will need replacement to save it from breaking, which is less than ideal on the trail and can result in the loss of an entire day of fun riding. Chain wear can be positively influenced by proper chain maintenance. Read more about this below.