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Technical Guides

Derailleur Indexing

Precision shifting through systematic cable tension, limit, and B-gap adjustment.

Dialing In Your Drivetrain

Shifting quality is a function of cable tension, derailleur alignment, and hanger straightness — in that order. Most indexing problems are cable-friction issues, not derailleur defects. This guide walks through a systematic procedure from cable pre-checks through barrel-adjuster micro-tuning, covering both mechanical and electronic drivetrains. You'll eliminate ghost shifts, chain drops, and hesitation under pedaling load.

Why Precise Indexing Matters

Properly Indexed Drivetrain

  • •Instant, one-click shifts under full pedaling load
  • •Silent running in every gear — no chain rub or ghost shifting
  • •Reduced chain and cassette wear from clean engagement
  • •Confidence in race situations — shifts work when adrenaline is high

Poorly Indexed Drivetrain

  • •Hesitation or double-shifts under load — lost momentum on climbs
  • •Chain rub noise from misaligned cage position
  • •Chain drops on extreme gears due to incorrect limit screws
  • •Accelerated cassette and chainring wear from partial engagement

Pre-Indexing Checks

Rule out mechanical issues before touching the barrel adjuster

1Hanger Alignment

A bent derailleur hanger is the #1 cause of bad shifting. Check with a DAG-2 or equivalent tool — tolerance is <1 mm across the full sweep. Straighten or replace before proceeding.

2Cable & Housing Condition

Inspect for kinked, frayed, or corroded cables. Check housing for cracks or compressed ferrules. Replace anything questionable — degraded cables add unpredictable friction that no barrel adjuster can compensate for.

3Cable Routing Friction Test

Disconnect the cable at the derailleur. Pull and release — it should spring back smoothly. Any stickiness means housing contamination, tight routing bends, or a damaged cable liner. Fix the friction source first.

4Chain Wear

A chain at or past 0.5% elongation will index poorly on a new cassette. Check with a chain checker tool. Replace when at 0.5% for 11/12-speed systems, 0.75% for 10-speed and below.

Limit Screws

Mechanical hard stops — set these first, adjust once

H-Limit (High / Small Cog)

1Shift to the smallest cog. Disconnect the cable to remove tension.
2Adjust the H-screw until the upper jockey wheel aligns directly below the smallest cog
3Sight from behind — the jockey should be perfectly centered, not offset inward or outward
4Too tight: chain can't reach the smallest cog. Too loose: chain can overshoot into the dropout.

L-Limit (Low / Largest Cog)

1Manually push the derailleur body inward to the largest cog (cable disconnected)
2Adjust the L-screw until the jockey wheel aligns directly below the largest cog
3Verify the derailleur cage clears the spokes by at least 2 mm at full extension
4Too tight: can't reach the easiest gear. Too loose: derailleur enters the spokes — catastrophic failure.

B-Tension (Gap Adjustment)

B-tension sets the distance between the upper jockey wheel and the cassette. Correct gap ensures the chain wraps cleanly around each cog without hesitation.

1Shift to the largest cog
2Measure the gap between the upper jockey wheel and the largest cog teeth — target varies by system:
3Shimano 12-speed: use the gap gauge tool (included). SRAM Eagle: 6 mm gap from the jockey to the cog teeth
4Too close: chain skips or hesitates shifting off the large cog. Too far: sluggish upshifts and chain slap
5After setting, verify smooth shifting across the full cassette range — adjust ±½ turn if needed

Cable Tension & Indexing

The barrel adjuster procedure

1Reconnect the cable. Set the barrel adjuster fully clockwise (minimum tension), then back out 2 full turns as a baseline.
2While pedaling, shift from the smallest cog to the 2nd cog. If the chain hesitates or won't climb: turn the barrel adjuster counter-clockwise ¼ turn (more tension).
3If the chain overshifts to the 3rd cog or is noisy: turn clockwise ¼ turn (less tension).
4Test across the full cassette range under pedaling load — standing climbs reveal issues that spinning in a stand won't.
5Fine-tune in ⅛-turn increments until every shift is immediate and silent in both directions.
6After 2–3 rides, re-check — new cables stretch and need a ¼–½ turn tension increase.

Under Load Testing

Always verify shifting under realistic pedaling load. A perfectly indexed derailleur on the stand can still hesitate on a climb because cable friction increases when the frame flexes under power. Test on a steep fire road or use a trainer with resistance.

Electronic Drivetrains

Shimano Di2, SRAM AXS, Campagnolo EPS

Electronic systems eliminate cable stretch and friction — but still need attention:

  • •Hanger alignment is just as critical — the motor can't compensate for a bent hanger
  • •SRAM AXS: micro-adjust via the AXS app — move the derailleur inboard or outboard in 0.1 mm increments
  • •Shimano Di2: micro-adjust via the E-Tube app or the shift buttons (hold both simultaneously for adjustment mode)
  • •Firmware updates can change shift behavior — always update before fine-tuning
  • •Battery level affects shift speed — charge fully before indexing and racing

Troubleshooting

Ghost Shifting (Unintended Gear Changes)

The chain shifts without input — causes:

  • Bent derailleur hanger — check alignment first
  • Cable friction from contaminated or kinked housing
  • Loose cable clamp bolt — cable slipping under tension
  • Worn chain or cassette creating inconsistent engagement

Won't Shift to Largest Cog

Chain can't reach the easiest gear:

  • L-limit screw is too tight — back it out ¼ turn at a time
  • Insufficient cable tension — add ½ turn counter-clockwise on the barrel adjuster
  • Cable has stretched or slipped at the clamp bolt — re-pull and clamp
  • Derailleur hanger is bent inward — straighten with a DAG tool

Chain Noise in Middle Gears

Ticking or rubbing in the mid-cassette range:

  • Cable tension is ⅛ turn off — fine-tune the barrel adjuster
  • Chain is worn beyond 0.5% — check and replace
  • Cassette cogs are worn (shark-finned) — replace cassette with new chain
  • Jockey wheels are worn — replace if teeth are visibly hooked or have >1 mm play

Pro Tips

Eliminate Cable Friction First

More indexing problems are solved by replacing housing and cables than by barrel adjuster tweaks. Coated cables (Shimano Optislick, Jagwire Elite) in compressionless housing make a bigger difference than any derailleur upgrade.

Keep Spare Hangers

Carry a spare derailleur hanger on every ride. A bent hanger from a crash or branch strike can't be reliably straightened trailside. Swap it and re-index in 5 minutes.

Clutch Tension Maintenance

Shadow+ (Shimano) and Type-3 (SRAM) clutched derailleurs slow chain slap but add friction. If shifting feels heavy, check the clutch tension set screw. Most riders run it mid-range — full force is for DH only.

Index Across the Full Range

Don't just check the first 3 gears. Ride through every gear under load. Problems typically appear at the extremes — the biggest and smallest cogs — where cable tension differs most from the mid-range.

Document Your Setup

Note how many turns out your barrel adjuster is from fully clockwise. When you replace cables, you can get 90% dialed by returning to the same baseline turn count.

Replace Cables Seasonally

Even visually good cables develop internal corrosion and micro-fraying. Replace inner cables every 6 months in mixed conditions. Housing lasts 12–18 months unless kinked or contaminated.

Shifting Sorted

A properly indexed drivetrain is silent, instant, and reliable under race load. Maintain cable quality, check hanger alignment after impacts, and your shifts will stay dialed ride after ride.

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