TL;DR: Keeping an unworn chain on your bike is important. I can't speak much to bike chain quality, but 15 years with one chain seems kinda exceptional. I am a

TL;DR: Keeping an unworn chain on your bike is important. I can't speak much to bike chain quality, but 15 years with one chain seems kinda exceptional. I am also relative child still, so I may just not have been alive to experience chains that last that long. Chains are tested by measuring the distance between links with a tool[0], or by checking to see how much wiggle room your chain has between links when it's on the largest cog[1]. If the distance is too great, that means the chain has "stretched" (which is a bad word for it - the pins that hold the links of your chain together wear, and the distance between each link grows, so nothing has actually stretched). Worn chains usually also start to cause wear to your cassette and cog, so getting them replaced can be important. Make sure to maintain your chain by keeping it clean, adding lubricant once in a while, etc. [0]:http://pardo.net/bike/pic/fail-004/18164_061544.jpg http://pardo.net/bike/pic/fail-004/18164_061544.jpg [1]:https://cyclingtips.com/2016/09/how-to-check-for-chain-wear-2/ https://cyclingtips.com/2016/09/how-to-check-for-chain-wear-...