At around $20, the humble chain checker tool has the potential to save every rider hundreds, if not thousands, of dollars. Let's discuss what it is and how it can save you money.

The chain checker might be the most valuable tool in your toolbox.

Ah, the humble chain checker.  As a cyclist who’s attentive to the needs of your bicycle, you’ve no doubt observed as your bike mechanic pulls out this simple tool and checks the wear on your chain.  Do you own a chain checker of your own, though?  For most riders, the answer is “no”.  This simple tool may just be the most valuable tool you can possess, and I’ll tell you why.  Let’s look at the price of a typical bike chain.  The most popular groupset I see in my shop is SRAM AXS, so we’ll use SRAM Force AXS for our example.  A new SRAM Force chain retails for $50.  Now, SRAM 12-speed requires a special variation of the chain checker.  Where a typical chain is measured from the front of the roller to the front of another roller to determine wear, SRAM AXS chains must be measured from the back of the roller to the back of another roller as they feature a larger roller diameter than a standard chain.  In short, be sure you’re using a “3-prong” chain checker for a SRAM flat top 12-speed chain.  You can use a standard “2-prong” chain checker for any other chain, but using it on an AXS chain will indicate that the chain has not worn beyond its limits despite being well past.  Common 2-prong chain checkers are the Rohloff Caliber 2, the Park Tool CC-2, and others available from such brands as Topeak, Pedro’s and more.  Popular 3-prong chain checkers include the Park Tool CC-4, the SRAM chain wear check tool, and the Pedro’s Chain Checker Plus 2 tool.  3-prong chain checkers will work on virtually any chain, so if you do have a SRAM AXS chain in your collection, a good 3-prong chain checker will do it all.  To check for chain wear, simply follow the tool instructions and insert the chain checker between the links to see how far the measuring prong drops into the chain.  The toll will generally have a gauge on it to show the measurement.  In general, single speed chains should be replaced at or before 1% wear.  5-10 speed chains should be replaced at or before 0.75% wear.  And, 11-13 speed chains should be replaced at or before 0.5% wear.  Replacing your chain at or before its wear limit prevents damage to the drivetrain, and is a relatively inexpensive service.  

So, you’ve let your chain go too long.  Well, this is where that simple chain checker would’ve saved you some serious money.  As chains wear (commonly referred to as stretch), the pins and bushings contained within the chain wear and the bushing inner diameter increases.  This allows the pins to move off-center, which effectively lengthens the chain.  Your cassette and chainrings wear along with the chain.  As the chain lengthens, the “valley” between the teeth of your drivetrain widens.  There is, of course, an acceptable amount of drivetrain wear that will accommodate a new chain.  This is reflected in the 1%, 0.75%, and 0.5% measurements mentioned earlier.  Once worn beyond these limits, the drivetrain will not accommodate a new chain and must be replaced.  As many of us have had the misfortune of experiencing, installing a new chain on a worn drivetrain will result in a very short, and very frustrating ride.  Using our SRAM Force AXS example, a new cassette retails for $195.  A SRAM Force AXS chainring set retails for about $200.  Your $50 chain replacement just became a $450 plus labor drivetrain replacement.  In short, a $20 chain checker might just be the most valuable tool in your toolbox.