Friday, February 18, 2011

What Causes Chains to Skip?

Many people come in the shop complaining about their chain skipping. There are several causes of this.

1. The most common cause of chain skipping is misalignment of the rear cogs and the chain. There are several things that can cause the misalignment. The most common is improper cable tension, when the tension is incorrect the chain does not sit inline with the corresponding cassette cog and it is trying to jump to the next cog. A dirty cable can also cause the same effect since the dirt is not letting the cable move like it needs to. One more common issue is the hanger for the rear derailleur can affect the alignment if it is slightly bent.

2. The next most common cause is wear on the chain, cassette and/or the chainrings.

The chain is the most likely to wear out first since it is made entirely of very small moving parts, all of which tend to wear out faster when they are dirty or ridden dry. Chains on most modern drivetrains usually last anywhere from 1500 to 2000 miles. This can change depending on riding style, and on how you maintain your bike. If you keep your drivetrain clean and you tend to spin at a slightly higher cadence then you will get more mileage out of your chain. When the chain wears, it no longer sits evenly on the cassette cogs and chainrings. As this goes on the chain will eventually start to jump since the chain wears much faster than the cassette and chainrings. If you let your chain go too long it will start to wear down the teeth of the cassette first and finally the chainrings. If the chain is replaced before it is too worn the cassette and chainrings will outlast the chain many times over. There is a tool that measures chain wear that you can either buy for home use or you can bring your bike to Jack & Adam's and we can measure it for you.

3. This next cause is fairly rare, but it does happen. Sometimes your rear hub will start to slip or it can seize up.

There are a couple of small parts in your rear hub that if they get old or very dirty then they will not allow the clutch mechanism in your wheel to function correctly. If it gets too bad it can lead to the bearings seizing and making the hub skip or stop moving all together. The only way to prevent this is to have your rear hub overhauled periodically. Most hubs only need this once every 12 to 18 months, but there are a couple of brands that typically need to be cleaned more often( Mavic and DT are the most common ).

For the most part if you wash your bike regularly and replace your chain before it is too worn you should be able to avoid having chain skippage. And when in doubt before you start turning barrel adjusters try cleaning your chain and cassette, it can sometimes be something as small as dirt causing your bike to annoy you.

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