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Roller wear effect on chain to chainring engagement

Updated: 09/09/2020.

In a previous post “Bicycle chain wear (elongation)” it was explained how chain wear happens and affects chain’s performance. There it was mentioned that roller wear doesn’t affect chain’s performance. The only thing that affects performance is chain’s elongation (change of pitch) – i.e. inner plates to pin contact area wear. The goal of this post is to demonstrate that in a clear(er) way.

To demonstrate that, a chain and a chainring with very little wear were taken (far from needing replacement). Also, for comparison, a worn chain was used – to show the difference that worn pin to inner plate area makes, even with rollers still in tact.


1. Test aparature

Rollers are taken out of a part of a “new” chain, while on the other parts of the same chain the rollers were left as they were. If roller wear affects chainring engagement, this will demonstrate 100% worn rollers effect.  🙂

Part of the chain with the rollers removed was marked – for easier orientation.

Test setup was simple – a vice and a heavy plank of wood.

Chain is loaded by a heavy plank of wood - to simulate pedaling load. Picture 3
Chain is loaded by a heavy plank of wood – to simulate pedaling load.
Picture 3

It is not clear in the picture, but the wood doesn’t touch the ground during the test. Even in this setup it hangs a few cm above it.


2. Test (demonstration)

In pictures 4 and 5 it is shown how a chain without the rollers (left) and with the rollers (right) engages with the chainring. There is a marked line along the chain engagement contours drawn on the chainring – for reference (not very visible unfortunately).

Zoomed in:

As can be seen from the pictures, engagement “quality” is the same for both the chain with and without the rollers. Chain without the rollers is moved slightly more to the right, but it doesn’t climb off the chainring teeth. For comparison, picture 6 shows how a worn chain (with a longer pitch) “climbs” on the chainring teeth, almost disengaging:

A chain that isn’t loaded (under tension) will sit deeper between the chainring teeth if it’s rollers are worn, but when a chain is in use, under tension, it will tend to climb as high as possible over the chainring teeth. The amount of climbing is limited by chain’s pitch and the chainring teeth profile. As was explained in the post about chain wear, roller wear doesn’t affect pitch (and definitely doesn’t alter chainring teeth profile), so it doesn’t affect the performance (and engagement) of a loaded chain in use.


3. Conclusion

Roller wear does not affect chain engagement. Plain and simple.  🙂

It should be noted that for this demonstration an extreme situation was simulated – a chain without any rollers. So roller wear that happens on a chain – in fractions of a mm is definitely not relevant for chain’s performance.

A separate post explains how to measure chain wear and when to replace the chain.

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