It's one of the most inexpensive, simplest, and useful tools you'll ever find, and yet, too few avid cyclists have one. A chain wear indicator helps you save money by showing you when to replace your chain and increase the life of other components.
Aside from maybe a rag to wipe your bike down, the humble chain wear indicator is the best investment you can make. Walk into my garage, and you'll find one hanging from a string that's tied around the repair stand. If a bike goes in the rack, it gets checked. Every time. The chain wear indicator gives you two numbers that gauge the wear of your chain. .5 means it's a good time to replace your chain. This is an amount of wear that should allow you to use the same cassette for a while longer, at least, and almost certainly the same chainrings. We've had riders that can get two, three, four or more chains worn with the same cassette, just by staying ahead of wear. A chain is less expensive than a chain and a cassette, and the savings add up.
The second measurement is .75, which means you may have left it too late. It's definitely time for a chain, but due to the amount of wear on your drivetrain, that fresh new chain may bounce and skip over your old cassette. Your old chain has actually rounded and warped the old cassette, and it's just different enough that shifting may not be crisp, no matter how the bike is tuned up. If it's close on the gauge, some people will try the new chain with the old cassette, especially if they want to wait to replace the cassette ahead of specific event, or if there is rain or bad weather in the next few days. If it's well past .75, we recommend replacing the chain and cassette together the first time and avoiding the headache.
Using the wear indicator can actually be pretty interesting, and you might even find a mix of components that last long and perform better. On my trusty Kona Private Jake, I went through chains non-stop. Finally, I started actually paying attention to what I was replacing. I found that PC-1130 chains, the least expensive, tended to last only a few weeks of hard, daily riding. Likewise, the PC-1130 cassettes wore out every two chains, even if the chains were replaced on schedule. After some experimentation, I've stuck with nicer Red 22 chains and 1170 chains, and I now get a new cassette every three chains, with each chain lasting much longer due to harder materials.
Stop by the shop and we'll show you how simple this handy tool is, plus more simple things to check for to make sure your bike is in great shape heading into spring!