If the derailleur is rubbing up against a ring or is caught on something, do not ride the bike. Instead, reset your front derailleur.
If the front derailleur doesn’t move when you actuate the shifter, the cable could be corroded. If this is the case or if you notice cracks, splinters, or fraying, replace both the cable and the housing. Place the chain on the smallest gear in the front and release all tension from the shifter. Feel the cable and adjust the tension until it is barely taut. Reposition the derailleur if it appears to be crooked. Replace the derailleur or shifter if they are broken. Also, the rear derailleur needs to be correctly adjusted before continuing, so check it if it is shifting correctly.
This may move the derailleur slightly, but you’ll be adjusting it again in a minute. Right now you want to make sure that your derailleur cable is tight and has no slack so that the whole thing functions smoothly.
The L controls how far towards your bike the derailleur can go. The H controls how far out and away from your bike it can go. If your screws aren’t labeled, you can easily test them out. Shift into your smallest ring up front. Turn one screw a full turn in each direction, watching the derailleur. If it moves, this is the Lower (L) limit, if it does not, try the other one. When this one moves, mark it with an L for future reference. [3] X Research source
You should see the derailleur move as you turn the screw.
Setting your limits too far to either side can cause the chain to slip off, but you should be able to see if it is this far before you start testing.
Count the number of rotations you make on the barrel. You’ll want to return it back into approximately the same position when you’re done.
1-3 mm above the largest chainring. You should be able to snugly fit a penny between the outer plate of the derailleur and the teeth of the ring. Both plates parallel to the chain. Curve of derailleur matches the curve of the cogs. [6] X Research source
Be sure to lube your chain and keep it clean for the best shifting. Retighten your barrel adjusters too.
