How to Adjust a Rear Derailleur – Limit Screws & Indexing, by Park Tool on YouTube. 16 min 7 s.
- Video length
- 16 min 7 s
- Time to do it
- 30 minutes
- Difficulty
- Medium
- Steps
- 8
What you need
Steps
Shift the chain onto the smallest rear cog and the largest front chainring. Check that the derailleur hanger is straight and the cable moves freely before you touch any screws.
Find the two limit screws on the back of the derailleur body. The high limit screw is usually marked H and the low limit screw is marked L.
Turn the H screw so the upper pulley sits directly under the smallest cog. Sight from behind the bike and adjust until the chain runs straight and quiet.
Shift up one gear and check indexing. If the chain hesitates or rubs, turn the barrel adjuster at the shifter or derailleur a quarter turn at a time while pedaling.
Work through every gear one at a time, pedaling and adjusting the barrel adjuster until each shift is crisp and quiet in both directions.
Shift onto the largest rear cog. Turn the L screw until the pulley aligns under that cog and the chain cannot be pushed past it toward the spokes.
Check the B-screw gap between the upper pulley and the largest cog. Turn the B-screw to set the gap the manufacturer recommends, often about 5 to 6 mm.
Shift through the full range again and fine tune the barrel adjuster. Wipe the chain and derailleur clean and test ride the bike.
Tips and common mistakes
Turn the pedals by hand while adjusting so you can hear and see each shift.
Make small quarter turns on the barrel adjuster and recheck before turning more.
If a gear is still unreachable after limit and index adjustment, check the derailleur hanger alignment.
Keep fingers clear of the spinning chain and cassette when pedaling.
Questions
Which screw is which on a rear derailleur?
The H screw sets the high limit at the smallest cog and the L screw sets the low limit at the largest cog. They are usually marked on the derailleur body.
Do I need to disconnect the cable first?
No. Start with the limit screws and indexing as they are. Only reset cable tension if the derailleur cannot reach the outer gears.
How do I know the B-screw is set right?
Check the gap between the upper pulley and the largest cog. It should match your derailleur maker's spec, commonly around 5 to 6 mm.
This guide was drafted from the video's details and general task knowledge. It has not been checked against the full video. Check the video and relevant product instructions before following a procedure. Report a correction.
