What Chain Stretch Really Means

"Stretched" is the word riders use. It's also the wrong picture. The plates of the chain aren't pulled longer like a rubber band. Something quieter is happening inside each joint.

What people picture, and what happens

Cyclists often talk about chain "stretch" as if the side plates were pulled out of shape by the stress of pedaling. That is not actually how chains elongate.¹ Another reference agrees: the tension created by pedaling is insufficient to cause that kind of stretch.²

The real cause is wear. Metal wears away where the link pin turns inside the bushing, each time the chain goes onto and off a sprocket.¹

A bushing is a short tube that sits around the pin. The link pins run through the middle of the bushings, and the rollers turn around the outside of the bushings. So both the inside and the outside surfaces of the bushings are subject to wear.³

What you'd see in a worn chain

If you take apart an old, worn-out chain, you can see little notches worn into the sides of the link pins.¹ Those notches are metal that's gone.

The same article shows an unusually bad example where the roller has flopped out of position, because the bushing part of the chain has eroded away.¹ That's an extreme case.

Why a tiny change matters

A new chain has a fixed spacing. From the center of each roller to the center of the next is precisely 1/2 inch (12.7 mm).¹ The teeth on the sprockets are cut to match that spacing.

Each worn joint adds a sliver of extra length. Add that up over the whole chain, and the spacing from link to link is longer than the specification. A reference says those links will not precisely fit the spaces between the teeth on the sprockets. That can mean more wear on the sprockets, and possibly "chain skip," where pedaling tension makes the chain slide up over the tops of the teeth.²

Links don't all wear alike

One more detail. The distance between pins with inner side plates increases due to wear, while links with outer side plates, the ones that hold the pins, don't lengthen in the same way.¹ So a worn chain has links of unequal length.

What speeds the wearing up

Dirt. Grit that gets into the links makes the wearing much worse.² That's one reason cleaning and lube come up so often in this site's other pages.

What to do with this

The practical point is that "stretch" is something you measure, not something you see. The next step is to measure the chain, and to read about how chain, cassette and chainring wear together.