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How To Properly Adjust The Front Derailleur On Your Bicycle

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Step 3: Front Derailleur Limit Screw Settings

The limit screws stop the inward or outward travel of the front derailleur. The limit screws should be marked “L” and “H”. The L-screw will stop the derailleur cage from moving past the inner chainring. The H-screw will stop the derailleur cage from moving past the outer chainring.

If the screws are not marked, you will have to test them to figure out which is which. Shift to the inner front chainring. Select one of the screws and turn it clockwise then counter-clockwise. If the derailleur moves then this is the “L” screw. If it does not; test the other screw. The screw that does not move the derailleur is the “H” screw. Make note of which is which.
 
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JonathanC1222 days ago

So L is to keep it from raising gears to the middle and highest end chain ring, and H to keep it from lowering to middle and lowest smallest chain ring. Got it! I'm making some adjustments on my Huffy Superia 27 inch 15 speeds bike.