Does your chain skip between gears when you pedal, phantom shift, shift twice instead of once, or refuse to shift when you need it to? Abby Hippley, mechanic, bike builder and former demo driver for Santa Cruz Bikes says, “Your chain—more accurately the cables that connect your shifters to your derailleurs to move the chain from cog to cog—need their tension adjusted—a fix you can most likely make without interrupting your ride.”
Most of the time, a skipping chain is caused by cable stretch. In the first half dozen rides on a new bike your shift cables stretch the most. They can also stretch over time as you ride.
Hippley explains, “It takes cable tension to open a derailleur, which shifts your chain between gears. To solve cable stretch, you have to add tension to your cables.”
To fix a skip in the rear derailleur, shift your chain into the smallest ring on your rear cassette (the hardest gear) and the middle or larger ring on your front derailleur. Press your shifter once. If the chain doesn’t move up a gear, you need to add tension. Twist your right barrel adjuster, which will be on your brake laterally opposite from your brake lever—the brake cable passes through it as it enters your shifter. Unscrew the adjuster by turning it away from you half a turn.
Shift down into the smallest ring in the rear cassette again, and press your shifter again to see if the bike shifts properly. If the bike still does not shift, repeat the entire process. When the first cog shifts correctly, continue to move through the gears in your cassette, fine tuning with the barrel adjuster as you go.
The same technique works for the front derailleur, which also has a barrel adjuster. However, the front derailleur barrel adjuster tensions in the opposite direction. Screw the adjuster towards you to add tension.
If barrel adjusting doesn’t resolve your shifting issues, you may need a mechanic. Cables may have been incorrectly tensioned to start, and they may need to be adjusted where they enter the derailleur. Or, if you’ve crashed, your derailleur or derailleur hanger may be bent.