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One of the most common drivetrain problems is ‘chain skip’. This is when your chain slips forward while pedaling under pressure. There could be a few problems that are causing this. Sometimes a stiff chainlink is to blame, other times it’s a worn freehub body. However, one of the more common causes is a worn chain.
Over time, the pins and rollers that help hold together the individual links of a chain will wear and as a result the pitch (length) of each link will grow. This is why, despite the metal itself not stretching, such chain wear is commonly called chain ‘stretch’.
The standard pitch of a new chain link sits at half an inch, pin-to-pin. An inner plus an outer (wide and narrow) link of a chain makes an even inch. Chainring and cassette cogs are designed with this pitch in mind, such that the chain rides at the base of the cog/ring when new. As the chain pitch grows, it rolls higher and higher on the tooth, accelerating cog wear until eventually it just skips over the edge.
Once the chain wears, the cassette and chainrings start to wear along with it and become ‘hooked’ from the high-riding chain. It’s commonly argued that if you replace your chain before it starts to wear too badly it will dramatically increase the life of the rest of your drivetrain (cassette and chainrings). A $50 new chain every few months could save you hundreds by preserving your drivetrain.
Even when cost isn’t a factor, the likes of the top WorldTour teams regularly replace chains approximately every 1,000km (a week in a Grand Tour). Some mechanics claim they get up to three full seasons out of cassettes and chainrings this way, but more importantly, there’s far less risk of a broken chain in the heat of the moment. Additionally, a worn chain will exhibit greater twist that leads to slower and sloppier shifting.
There’s also an old mechanic saying: There’s no such thing as a broken chain – only a incorrectly installed chain!
This argument for regular chain replacement is rather clear-cut if you’re riding on Dura-Ace or Super Record components, but the value proposition becomes a tougher debate if you ride on 105 or below where replacement chainrings and cassettes are far more affordable. Additionally, you’ll need to consider the installation cost of a new chain if you’re not confident in doing it yourself. Nevertheless, if you value crisp shifting or swap between wheelsets then regularly replacing chains before significant wear is a smart choice regardless of what your components cost.
So how about measuring that chain wear? Well, the easiest (and cheapest) way is as follows:
1. Shift gears so that your chain is in the big ring and smallest gear on the cassette (e.g. 53-11T)
2. Pull at the chain at the front of the chainring as shown to the right. If the chain starts to lift off the top and/or the bottom of where it sits on the chainring teeth, this means that the chain is starting to wear or is worn. This ‘lift’ is possible because the stretched chain no longer sits properly in the teeth anymore. The photo to the right shows a brand new chain; see the feature image above for a worn chain. Chances are if your chain lifts off more than our worn example, you’ll be needing more than a new chain.
The chain in this photo doesn’t lift from the chainring and so is not worn. Compare to the worn chain in lead photo.
Once you’ve determined that your chain is worn, it’s time to check to see how worn it is. If it starts to ‘lift’ on the chainring as described above, you’ll probably need to change it.
A more accurate way to measure your chain is to do the following: with your chain still on the bike, place a ruler’s zero inch mark directly above the center of one of your chain pins. Now count 12 complete links. A complete link equals one inner and one outer. A rivet on a new chain should line up exactly to 12 inches on the ruler.
A ruler is effective, but it can be fiddly to line up perfectly.
As a general rule, if the rivet is less than 1/16″ past the mark, your chain is ok. If it’s between 1/16″ and 1/8″ past the mark you’ll likely need a new chain, but your sprockets should be ok. If it’s more than 1/8″ past the mark, you’ll probably have to replace both the chain and cassette.
There are purpose-built chain-checkers that make this job even easier. The simple fixed length, drop-in style is all you need and will quickly give you a go or no-go gauge on your chain wear. Many argue the ruler method is more accurate as it’s not affected by roller tolerances, but it can be a fiddle to precisely line it up and so the chain wear gauges do exactly what they need to.
Using the popular Park Tool CC3.2 chain wear checker as an example, the .5 marking is there to give warning of needing a new chain, and the .75 is there to show a new chain is needed. For our own bikes running the good stuff, we’ll replace a chain at the .5 marking to near guarantee against any early wear.
This big chainring is only just starting to show signs of hooking, but it’s clear the gaps between the teeth are larger than a new chainring.
While a chain showing obvious wear is likely to need a new cassette if replaced, your front chainrings generally won’t need replacing very often. If worn they are very easy to spot, as they’ll start looking thin and like shark teeth. There are, however, no perfect tools or gauges for determining cog and chainring wear, though fitting a new chain is the surest way to reveal significant wear, since it will skip and rumble on the worn teeth.
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