How to Adjust a Rear Derailleur: Indexing & Limit Screws Made Simple

A bike that shifts crisply feels like a different machine - every pedal stroke goes into forward motion instead of arguing with itself. The good news: dialing in a rear derailleur is mostly a matter of doing five small adjustments in the right order. Get the order wrong and you'll chase your tail for an hour. Get it right and the whole job takes about thirty minutes the first time and ten minutes after that. This guide walks through H-limit, cable tension, L-limit, indexing, and B-tension - plus the front derailleur shortcut and a troubleshooting table for ghost shifting, slow shifts, and won't-reach-the-top-cog problems.

Who This Is For

• Riders with hesitating, ghost, or slow shifting who want to fix it at home instead of paying a $40 shop tune
• Anyone who just installed a new chain or cassette and needs to re-index the rear derailleur to match
• Used-bike buyers and weekend mechanics who want a calm, repeatable workflow that doesn't involve guessing

Tools & Parts

Most of these you'll already own if you've done any home wrenching. The cable cutter is the one item to buy nice - pliers crush the housing instead of cutting it, and crushed housing is the single biggest reason indexing won't hold.

When to Re-Index

Before you touch anything, eliminate the two things that mimic bad indexing: a worn chain and a gritty cable. Drop a chain checker on the chain (see our chain replacement guide) and run a quick clean-and-lube (cleaning routine here). If the chain is past 0.5% on 11/12-speed, no derailleur tune in the world will save it - replace it first.

Derailleur Anatomy in 90 Seconds

Five adjustment points control everything the rear mech does. Learn these and the order makes sense.

• H-limit screw (marked “H”). Sets how far outward the cage can travel. Controls the smallest (highest-gear) cog. Set first.
• L-limit screw (marked “L”). Sets how far inward the cage can travel. Controls the largest (lowest-gear) cog. Set after the cable is tensioned.
• B-tension screw. Sets the gap between the upper jockey wheel and the cassette. Too close = grindy, slow shifts. Too far = hesitant, vague shifts.
• Cable pinch bolt. The 4 or 5 mm bolt that clamps the inner shift cable to the derailleur body. Always tighten with the cable taut and the barrel adjuster wound in.
• Barrel adjuster. The knurled cylinder where the housing meets the derailleur (and often the shifter too). Quarter- turn adjustments fine-tune cable tension without re-pinching.

On Shimano and SRAM mechanical derailleurs the H/L screws are labelled. Electronic systems (Di2, AXS) skip the cable entirely - you'll still set H/L limits and B-tension but indexing happens in software. More on that in the FAQ.

How to Adjust a Rear Derailleur in 6 Steps

Hang the bike in a stand if you have one. Shift the front to the middle ring (or only ring on a 1x setup) and the rear to the smallest cog before you start. Quick check: spin the cranks backwards. If the chain runs noisy or skips, your problem may not be indexing - see the troubleshooting table first.

Step 1 - Set the H-Limit (Highest Gear)

Shift all the way to the smallest cog. If your cable is already tensioned, loosen the pinch bolt so the cable goes slack - the H-limit must be set without cable interference. Look down from above. The two jockey wheels should sit in a straight vertical line directly under the centre of the smallest cog. Turn the H-limit screw clockwise to move the cage inward (toward the wheel), counter-clockwise to move it outward. When it's centred, give the H screw a final eighth-turn clockwise so the cage sits one hair inside the cog - that prevents the chain from being thrown into the dropout.

Step 2 - Tension the Cable and Pinch It

Wind the rear derailleur barrel adjuster all the way clockwise (in), then back it out two full turns. Wind any in-line or shifter barrel adjusters in the same way. Make sure the shifter is clicked all the way to high gear (smallest cog position). Pull the inner cable taut with your fingers - firm, but don't lean on it - and tighten the pinch bolt to roughly 5 Nm. The cable should be snug with no visible slack, but not stretched. Trim the tail to about 2 cm and crimp on a cable end cap.

Step 3 - Set the L-Limit (Lowest Gear)

With your hand, push the derailleur body inward by hand toward the largest cog (don't use the shifter - you want to feel the limit). The cage should travel until the upper jockey wheel sits directly under the largest cog. If it goes too far inward (the chain wants to fall into the spokes) turn the L-limit screw clockwise. If it can't reach the largest cog, turn the L screw counter-clockwise. Done correctly, you can shove the cage hard and it stops one hair short of the spokes.

Step 4 - Index the Cable from the Highest Gear

Shift to the smallest cog. Click up one cog. The chain should jump cleanly to the next cog, no hesitation, no grinding. If the chain hesitates and won't reach the next cog, turn the barrel adjuster counter-clockwise a quarter turn (this adds cable tension, which pulls the derailleur further inward). If the chain rattles or wants to overshoot, turn the barrel adjuster clockwise a quarter turn. Climb the cassette one cog at a time, fine-tuning. By the time you're at the largest cog, every shift should land cleanly. Then shift back down through every gear - same expectation.

Step 5 - Set the B-Tension

Shift to the largest rear cog. Look at the gap between the top of the upper jockey wheel and the bottom of the cassette tooth above it. Shimano road and MTB: roughly 5-6 mm. SRAM Eagle and AXS Eagle: noticeably more, typically 13-14 mm (use the supplied B-gauge if you have it). Turn the B-tension screw clockwise to increase the gap, counter-clockwise to decrease. Too tight = grinding, slow shifts to the big cog. Too loose = vague, sloppy shifts. Re-check by shifting to the smallest cog - the gap should still look reasonable.

Step 6 - Test Under Load

A repair-stand-quiet bike often shifts differently under real load. Take the bike off the stand and either ride a flat block or pedal-and-brake on the spot. Shift up and down through every cog, twice. A final quarter-turn of the barrel adjuster either way is normal - that's why barrel adjusters exist. If shifts under load still feel mushy, your housing is probably compressing (replace it) or the chain's worn (measure with our calculator).

Front Derailleur Quick Tune

The front derailleur uses the same logic with two differences: the cage angle has to be aligned over the big chainring first, and there is no B-tension screw - instead you set the height of the cage above the big ring (1-3 mm gap, parallel to the teeth).

1. Cage height: 1-3 mm above the tallest tooth of the big chainring.
2. Cage angle: outer plate parallel to the big chainring (look from above).
3. L-limit: chain on small ring + largest rear cog, set L screw so the inner cage almost touches the chain.
4. Cable tension: shifter clicked to small ring, pull cable taut, pinch.
5. H-limit: chain on big ring + smallest rear cog, set H screw so the outer cage almost touches the chain.
6. Trim: use the trim click on road shifters to eliminate cage rub at extreme cross-chain angles.

Fronts are fussier than rears because of the chainline geometry. If yours fights you, double-check chain length first (chain length calculator) - a too-long chain has slack the front cage can't take up.

Common Mistakes

• Tightening the cable before the H-limit is set. Every other adjustment depends on the cage being centred under the smallest cog with zero cable tension. Skip this and you're tuning around an offset.
• Cranking the B-tension to fix indexing. B-tension changes shift feel, not which cog the cage lands on. If the chain misses the next cog, fix cable tension (the barrel adjuster), not B-tension.
• Reusing a frayed cable end. The end you cut off to free the cable is fluffed at the strands. Trim a fresh square end with a real cable cutter (Park CN-10, Jagwire) before re-pinching, or it slips under load and the indexing drifts.
• Forgetting to wind the barrel back out two turns. You need range to fine-tune in both directions. If the barrel is all the way in, you can only loosen tension; all the way out, only tighten.
• Tuning to a worn chain or cassette. A new chain on worn cogs skips no matter what you do. Measure the chain (our guide) and inspect the cogs before blaming the mech.
• Skipping the load test. A bike-stand-tuned drivetrain can shift perfectly with no torque on it and still ghost-shift under climbing load. Always finish with a real ride.

Troubleshooting

Notice how often the answer is “quarter turn of the barrel adjuster.” That's the design intent - the barrel exists precisely so you can fix 80% of indexing complaints in five seconds, no tools required.

When to Call a Shop

Two situations are worth handing off:

• Bent derailleur hanger. If shifts are always worse on certain cogs and the cage looks visibly cocked when viewed from behind, the hanger is bent. A shop has a Park DAG-2.2 (or similar) gauge that aligns the hanger to the wheel plane. Without it you're guessing - and bending hangers cold can snap them.
• Electronic shifting (Di2, AXS) that won't pair or micro-adjust. Diagnostic mode and firmware updates are shop work. Mechanical limit screws and B-tension you can still handle yourself - the rest needs the OEM tool.

Bent hangers are surprisingly common - even a gentle drive-side tip-over on a parked bike can do it. If a tune that should have worked didn't, the hanger is the first thing a shop will check.

Tools and Parts We Recommend

These are the cable cutters, hex sets, and replacement cables we keep buying. None are required to start, but every one of them makes the job faster and the result more durable.

Frequently Asked Questions

Conclusion

Indexing a derailleur is an order-of-operations job, not a feel-it-out job. Set the H-limit with a slack cable, tension the cable, set the L-limit, index from the high gear with the barrel adjuster, set B-tension last, then test under real load. Do that and a $20 cable kit plus a hex set will keep your drivetrain crisp for a couple of years between cable changes. Pair this with our chain replacement guide and the cassette removal guide and you can refresh an entire drivetrain from your garage.