Mountain Bike Action Tech: Drivetrain Checkup

It doesn’t matter if you use a single speed, a traditional 3×9 drivetrain or one of the newfangled drivetrains, including 1×10, 2×10, 2×9 and 3×10 combinations; they all connect with a chain, and that series of links is what runs the show. Allow the chain to wear out or ride with a chain that is too long or too short, and you will drive that fancy drivetrain to an early grave. The “Garage Files” visited Michael Bennett at Wins Wheels in Westlake Village, California, and threw the bike in the workstand to take a look at how to measure chain wear, choose just the right number of links and install a chain without ending up with a weak link.

The fastest and cheapest way to gauge chain wear is to shift the chain to the largest chainring of the crank, pinch the chain at the 3 o’clock position and give it a firm pull forward. If you can see this much space between the chain and the chainring, your chain is ready to be replaced.

Another budget chain check tool is a tape measure. Start at the center pin of a link and measure 12 links of your chain. The 1-foot mark should be dead center in the middle of the 12th link. If it is short, your chain is shot.

The Park Tool chain wear tool is placed on top of the chain between the cassette and the chainrings. If the tool does not drop between the links (A), your chain is in good shape. If it drops into the chain (B), you need a new chain. The .75 measurement was so loose that we flipped the tool. The 1.0 measurement fell into our old chain easily. That’s worse news. This much wear probably means you will need to replace the cassette and maybe a chainring or two.

Park Tools offers a number of chain wear measurement tools. This one is made for professional use and is overkill for the garage mechanic.

If you determine that your chain needs replacement, find the master link. Almost all mountain bike chains have master links, but yours might not. If you don’t find a master link, go to step 7.

If your chain has a master link, you can see how the plates are grooved to slip over the chain pin, and then lock in place. Hold the chain on each side of the master link and push the links together to separate the link’s plates. The chain will be broken and can be removed.

If your chain does not have a master link, use a chain tool to push out the pin on a link.

A new chain is usually a few links too long, so you do not need to use the entire chain. It is not a good idea to use your old chain as a reference, because it may have stretched enough to give you a bad measurement.

Put the loose chain on the smallest chainring and smallest cog on the cassette. Pull the two ends together.

You want your rear derailleur cage to be neutral (you should not feel resistance from the spring that is attached to the cage). The chain should run close to parallel with the two derailleur pulleys when it is at its proper length. Put the loose chain on the smallest chainring and smallest cog on the cassette. Pull the two ends together.

If the chain is too long, you will need to remove the extra links with your chain breaker. If the new chain uses a master link, install it in the reverse order that you removed it. If there is no master link, use the pin supplied with the new chain to connect the chain. If your new chain skips on select cassette cogs, you waited too long to replace the chain, and the cassette will also have to be replaced.
Important Tip: Almost all full suspension bikes have some amount of “chain growth” as they move through their travel. It is critical to check that the chain is long enough when in the big chainring and biggest cog, at full compression. To check this, remove rear shock and cycle the bike through its travel. If it bottoms out on the drivetrain instead of the shock, your chain is too short and could cause severe damage.

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