PROBLEM: Your bike’s been working great. But lately you notice that rear shifts to easier gears (bigger cogs) are becoming hesitant and noisy.
SOLUTION: Snug the derailleur cable. This fix is so easy that it doesn’t even require tools.
During shifts, the cable wears in and stretches. Slack develops. The derailleur no longer moves the chain cleanly onto the next cog.
Start by putting your bike in a rack, or at least elevate the rear wheel. Shift to the largest chainring and smallest cog.
Spin the crank and try a shift to the next cog. Lots of clattering? Delayed shift or no shift at all? Click back to the smallest cog.
Look where the cable housing enters the rear of the derailleur. You’ll see a knurled “barrel” that you can turn with your fingers. Rotate this barrel half a turn counterclockwise. This removes a bit of cable slack.
Try the shift again. Better, but still not like new? Give the barrel another half turn. Shift again and, if necessary, turn again. Keep it up in half-turn increments till the shift is silky.
As usual, there can be too much of a good thing. If you take up too much cable, the chain might contact the next larger cog after the shift is completed. You’ll hear rattling, and if you look from behind you’ll see the chain touching. Correct this by turning the barrel clockwise.
Once that first shift is golden, try all the others from each chainring. If shifts still seem balky going to larger cogs, turn the barrel counterclockwise. If the chain hesitates when dropping to smaller cogs, turn the barrel clockwise.
After you have the knack, you can impress your riding buddies by hopping off at a stoplight to do a five-second tune up. You’ll know exactly which way to turn the barrel to sharpen the shifting.
While on the big ring small cog, first check cable for slack, if it is slack, the initial move of the shift lever will take up the slack before moving the derailleur to take the chain to the next cog Also, a check of/for a bent RD hanger may be in order at the shoppe
The cable doesn’t stretch. Things settle in, ferrules compress, casing ends squash and all this can result in a need to use the barrel adjuster. But if that becomes a regular thing, suspect that your cable is fraying and ready to break. Another possibility is that if you have down tube barrel adjusters, I have seen them “adjust themselves” by screwing in. I didn’t understand that this was possible but I marked the barrel adjuster with a sharpie and indeed saw that the thing screwed in over the length of a ride. That’s why there is a spring on many barrel adjusters – it keeps them in place after you turn the screw.