How to Measure a Bike Chain for "Stretch"

I always go over my son's bike after a long offroad rides, cleaning, looking for anything broken, etc. This time I realized I had never checked his chain for wear. So, out came my trusty ruler. I know the bike was not well taken care of before we purchased it so I was not too surprised with what we found: it was clearly "stretched." It is time for a new chain and more than likely a freewheel.

How did I know it was no longer good? Let's measure the "stretch." Using an inch ruler, put the "0" in the center of one of the chain pins and go down to the 12" mark. When the chain was new, the 12" would be exactly in the center of a chain pin.

In our case the chain pin center was more than 1/16" past the 12" line.

Stretched chain? Well, not really. What is happening is the tolerances between the parts are getting looser. More space, the longer or "stretched" the chain becomes.  With any wear item determining how much wear is too much is the difficult part. According to every biker's favorite info website (Sheldon Brown's Bicycle Tech Information Site):

• Less than 1/16" past the mark, all is well.
• If the rivet is 1/16" past the mark, replace the chain, but the freewheel/cassette sprockets are probably undamaged.
• If the rivet is 1/8" past the mark, you have left it too long, and the sprockets (at least the favorite ones) will be too badly worn. If you replace a chain at the 1/8" point, without replacing the sprockets, it may run OK and not skip, but the worn sprockets will cause the new chain to wear much faster than it should, until it catches up with the wear state of the sprockets.

Clearly we have waited too long. We plan to get a new chain. And though we might get away without changing anything else, we plan to use a "parts bin" freewheel I have.

Watch for an update soon, after I gather parts and tools, showing how to change the chain and freewheel.