3.15 drivetrain

Rear Derailleur Setup (Mechanical)

Rear Derailleur Setup (Mechanical). Step-by-step procedure for bike maintenance — tools, time, and what to watch out for.

Difficulty ★★☆ moderate
Time ~20 min
Applies to All bikes with rear derailleur (Road, Gravel, MTB; not internal hub bikes)
Rear derailleur H/L limits and B-tension setup

Tools

  • 2.5–4mm hex (cable bolt and limits)
  • Phillips or hex for limit screws and B-tension
  • cable cutter

Procedure

  1. Verify hanger is straight first

    (3.16). All other steps are wasted if it's bent.

  2. Disconnect the shift cable

    at the pinch bolt.

  3. Set the high limit (H screw)

    • Manually move the derailleur so the upper jockey wheel sits directly under the smallest cog when viewed from behind.
    • Adjust the H screw until this alignment is correct. Look down the chain line — upper pulley should be in plane with the smallest cog.

  4. Set the low limit (L screw)

    • Push the derailleur inward (toward the spokes) by hand or pull the cable.
    • Adjust the L screw so the upper jockey wheel sits directly under the largest cog, but the derailleur cage cannot move further inward and contact the spokes.

  5. Set the B-tension screw

    • Shift the chain to the largest cog (or hold the derailleur there manually).
    • Set the gap between the upper jockey wheel and the largest cog to the derailleur manufacturer's specification. Some Shimano road/older MTB setups are commonly around 5–6 mm, while many modern wide-range derailleurs require a setup gauge or a larger specified gap.
    • Turn the B-screw clockwise to increase the gap, counter-clockwise to decrease.

  6. Reconnect the cable

    • Ensure the shifter is in its highest position (smallest cog).
    • Turn the barrel adjuster on the derailleur (or shifter) all the way in, then back out 1 turn — this gives you adjustment range in both directions.
    • Pull the cable taut through the pinch bolt; tighten to spec (4–5 Nm).

  7. Index the gears

    • Shift the lever one click toward a larger cog.
    • The chain should hop cleanly to the next cog.
    • If it hesitates or fails to shift up: add tension (turn barrel adjuster counter-clockwise, 1/4 turn at a time).
    • If it overshoots or skips two cogs: reduce tension (turn barrel adjuster clockwise).
    • Work through every cog in both directions, fine-tuning until shifts are crisp throughout.