When is a chain worn out?
Check your chain with a wear gauge. On an 11 or 12 speed drivetrain, Park Tool says to replace it at or just before 0.5 percent wear. On 5 to 10 speed, at or just before 0.75 percent. Catch it there and you usually replace a chain. Miss it and you can end up replacing the cassette and chainrings too.
The chain wears faster than anything else in the drivetrain, and it does it quietly. Nothing actually breaks, but shifting gets a little worse, a little louder and a little less sure, until one day the chain slips under load and you finally notice. Here is what is going on and how to stay ahead of it.
Chains do not really stretch
Everybody calls it chain stretch, us included, but the side plates are not actually getting longer. Park Tool explains that the internal parts of the chain, the rivets and rollers, wear out, and that gives the illusion of stretching.
Each link gets a hair longer as those parts wear. Add that up over a hundred-plus links and the chain no longer sits where the teeth on your cogs and chainrings expect it to. The chain rides higher on each tooth and loads it in the wrong spot. Park Tool puts it plainly: using a chain beyond its intended wear limit will prematurely wear out your cogs and chainrings.
That is the whole reason to measure: a chain is a wear item, while the cassette and chainrings cost more and are supposed to outlast several chains.
Which number applies to you
Park Tool's guidance splits by how many cogs you have. More cogs means thinner chains and tighter tolerances, so the replace point comes sooner.
The Park Tool CC-2 is the dial-style checker, and it is the one we reach for. Park says it reads chain wear from 0 to 1 percent. The CC-3.2 and CC-4.2 are drop-in gauges: the CC-3.2 checks for 0.5 and 0.75 percent, and the CC-4.2 adds a 1.0 percent check. If you run a SRAM Flattop road chain or a SRAM T-Type 12 speed chain, Park Tool points you to the CC-4.2 instead of the CC-2 or CC-3.2.
Park Tool also says every drivetrain maker has its own specs, so check the manufacturer's recommendation for your system. SRAM makes its own Chain Wear Check Tool for SRAM chains.
If you do not have a gauge, Park Tool describes a ballpark ruler method. Count 24 rivets from a starting rivet, and the last one should sit right on the 12 inch mark. If it is off by more than 1/16 inch, Park Tool says the chain is ready to replace. It gives you one cutoff, not the 0.5 versus 0.75 split, so a proper checker is the better tool for an 11 or 12 speed bike.
What a worn chain feels like. Park Tool lists a chain that consistently slips under load, chain suck, and poor shifting. You may also hear it before you feel it.
What it costs if you wait. You end up with worn cogs and chainrings. In our experience at the lab, a fresh chain often skips on cogs that wore in alongside a chain run too long.
Measure the chain so you only have to buy a chain.
Why your chain wears faster than your friend's
There is no mileage number that works for everyone, and we would rather not make one up. In our experience at the lab, chain life comes down to a handful of things:
- How much power you put through it, and how much of your riding is climbing.
- How much you ride, because volume adds up.
- Wet weather, because gritty roads are hard on a drivetrain, and around here that covers a big part of the year.
- How well you take care of it, since a clean, lubed chain lasts longer than a dirty one. Park Tool says the same: keep shifting adjusted and the chain clean and lubed.
So measure instead of guessing. It is a quick check, so do it every so often, and more often in the wet months.
Not sure where yours is?
A chain checker is the quickest way to find out, and it costs less than the cassette it protects. If your chain is due, we stock chains for most drivetrains, and installing one at the lab is billed bench work.
Need a chain or a checker? Every chain we stock, sorted by speed, is on one page.
Shop bike chainsThen wipe it down and lube it while you are at it.