Especially in more modern groupsets, the whole rear shifting mechanism-which encompasses the derailleur, cassette/freewheel, and chain-relies on incredible precision to function smoothly. The number of cogs on your cassette or freewheel is unquestionably the most important variable when choosing a bike chain. What to Consider When Buying a Bike Chain Speeds My knowledge stands on the shoulders of all the mechanics at my shop who raised me like my second family, starting when I was only 15. The Expert: In almost seven years as a bike mechanic at The Bicycle Shop in State College, Pennsylvania, I’ve replaced more chains than I could keep track of, and I’ve worked with every big brand a myriad of times. If you’re looking to make your bike run like new with every turn of the cranks while staying budget-savvy, I’ve got you covered. There are plenty of pitfalls when it comes to overinvesting in marginal gains, though, and it’s sometimes tricky determining when a little extra smoothness or weight reduction will truly be worth the markup. Even better, the process of finding the right one is relatively straightforward if you know what components you have. Thankfully, bike chains are inexpensive to replace, especially if you do the work yourself. Failing to replace your chain can have a deleterious effect on your shifting, perhaps even leaving you stranded on a ride if it breaks. This is commonly called 'chain stretch', even though the metal does not stretch in a measurable way. This paradoxical nature comes at a price, though: Over time, the pins and inner links of your chain will wear, and this causes the pitch of each link to grow. They manage to seamlessly glide among cogs while hardly interrupting our cadence, and they simultaneously take on the entire force of our most powerful sprints. The chains on our bikes deserve a lot more credit than we often give them.