Timing your purchase is as important as the purchase itself. Waiting until a chain "skips" usually means you have already damaged your cassette and chainrings.
For 11- or 12-speed systems, you should replace the chain when it reaches 0.5% stretch . For 9-speed systems or lower, you can usually wait until 0.75% . how to buy a bike chain
The Mechanics of Selection: A Guide to the Bicycle Chain Buying a bike chain is often viewed as a simple utility purchase, but it is actually a precise exercise in mechanical compatibility. Because the chain is the primary interface between your power and the pavement, selecting the wrong one can lead to poor shifting, accelerated wear on expensive components, or even mechanical failure. 1. The Speed Constraint Timing your purchase is as important as the purchase itself
A 12-speed chain is significantly thinner than an 8-speed chain. Using a chain with the wrong width will result in it getting stuck between cogs or failing to shift entirely. For 9-speed systems or lower, you can usually wait until 0
Higher-end chains aren't necessarily "stronger" in terms of breaking strength, but they feature nickel or titanium-nitride coatings to resist corrosion and reduce friction. Premium chains also often use hollow pins to shave weight without sacrificing integrity. 3. Sizing and Installation
A new chain is a minor expense; a new cassette and crankset are not. Investing in a simple chain checker tool can save you hundreds of dollars by alerting you when it’s time to shop. Chain Compatibility | Park Tool
You will almost certainly need a chain tool to remove excess links. The most reliable sizing method is to lay your old chain next to the new one and match the link count exactly.