To adjust a rear derailleur, work in this order: straight hanger, high limit (H), cable tension, low limit (L) and B-tension screw. Nearly every everyday problem (the chain is slow to climb, skips or rubs a cog) is fixed with a quarter turn of the barrel adjuster. You only touch the limit screws if the chain comes off one end of the cassette or when you install a derailleur, and none of it works if the hanger is bent.
Before you start: what you need
- The bike in a repair stand or hung up, with the rear wheel free so you can turn the pedals.
- 2 to 5 mm hex keys and a small Phillips screwdriver (limit screws are usually Phillips or a 2 mm hex).
- A chain in good shape. If it is worn, the derailleur will never shift crisply: measure it first with the guide on when to replace your chain.
- A clean, lubed chain. Dirty cables or a dry drivetrain also mimic a derailleur that is out of adjustment; see the guide on cleaning and lubing your chain.
The parts you will adjust
| Part | What it does | When to touch it |
|---|---|---|
| H screw (high) | Outer stop: the chain can’t go past the smallest cog | When installing the derailleur or if the chain falls off the outside |
| L screw (low) | Inner stop: the chain can’t drop into the spokes | When installing or if the chain goes past the largest cog |
| Barrel adjuster | Sets cable tension and, with it, the position on each cog | Whenever shifting is off: this is the everyday adjustment |
| B-tension screw | Sets the gap between the upper jockey wheel and the cogs | After changing cassettes or if the largest cog is noisy |
| Hanger | Connects the derailleur to the frame | If it gets bent in a crash or a knock |
1. Check the hanger
Park Tool puts it bluntly: if the hanger is clearly bent, adjustments won’t work. Shimano repeats the warning in its manuals and recommends checking it with its TL-RD11 tool.
Here is how to look: shift to the smallest cog and look at the bike from behind, at hub height. Both jockey wheels should sit in a vertical plane, parallel to the cog. If the derailleur leans toward the spokes, or the big cogs shift worse than the small ones, the hanger is bent.
Straightening it properly takes a hanger alignment gauge (Park Tool DAG, Shimano TL-RD11 or similar), which measures the distance to the rim at several points. Many aluminum hangers are replaceable and cheap, and they are designed to bend before the frame does. On carbon frames, or if the hanger has already been straightened more than once, replace it instead of forcing it. If your frame uses UDH, SRAM’s Universal Derailleur Hanger, search for the replacement by that name.
2. High limit (H)
- Shift to the big chainring up front and the smallest cog in back.
- If there is a cable, take the tension off: you can loosen the cable pinch bolt or, more easily, shift to the smallest cog and thread the barrel adjuster all the way in.
- Turn the H screw until, viewed from behind, the center of the upper jockey wheel lines up with the outer face of the smallest cog. That is the reference Shimano gives for the 105 RD-R7100.
- Check by turning the pedals: the chain should run quietly on the smallest cog without rubbing the next one.
Park Tool fine-tunes it this way: tighten the limit screw until the chain rubs the neighboring cog, then back it out a quarter turn at a time until the noise stops. If two positions are equally quiet, use the tighter one.
3. Cable tension (the everyday adjustment)
With the cable clamped (Shimano specifies 6-7 N·m (53-62 in-lb) on the cable fixing bolt and leaving about 30 mm of cable, finished with an end cap), set the tension with the barrel adjuster:
- From the smallest cog, shift one at a time toward the big cogs while turning the pedals.
- If the chain won’t climb or is slow, turn the barrel adjuster out (counterclockwise viewed from behind) one turn and try again.
- If it jumps two cogs at once, turn the barrel adjuster in one turn.
- Fine-tune a quarter turn at a time until every shift is clean and the chain doesn’t rub the neighboring cog in any gear.
Shimano suggests a more precise method for the RD-R7100: shift to the big chainring and the fifth cog counting from the largest; turn the barrel adjuster out until the chain starts to rub the next larger cog, then from there turn it back in five clicks. Then run through all the gears.
A new cable stretches over the first few hundred miles. It’s normal to have to turn the barrel adjuster out half a turn after the first few rides.
4. Low limit (L)
- Shift to the small chainring and the largest cog.
- Adjust the L screw so the center of the upper jockey wheel sits under the center of the largest cog.
- Push the derailleur by hand toward the spokes (or force the shifter): it must not travel past the largest cog.
Shimano points out one detail: if the B-tension screw is backed out too far, the largest cog and the chain can touch while you adjust the L screw. Turn it in a little first.
5. B-tension screw: the gap to the largest cog
With the small chainring and the largest cog, measure the distance between the tooth tips of the upper jockey wheel and the tips of the cog. Every manufacturer gives its own figure:
| Derailleur | Cassette | Gap | How it’s measured |
|---|---|---|---|
| Shimano 105 RD-R7100 | 11-34 | 10 mm | Small chainring, largest cog |
| Shimano 105 RD-R7100 | 11-36 | 6 mm | Small chainring, largest cog |
| SRAM RED eTap AXS (36T max) | 10-33 or 10-36 | 5 mm | Largest cog |
| SRAM RED eTap AXS (36T max) | 10-30 | 10 mm | Largest cog |
| SRAM RED eTap AXS (36T max) | 10-28 | 12 mm | Largest cog |
| SRAM XPLR 12-speed | 10-36 | 11 mm | On the second largest cog |
| SRAM XPLR 12-speed | 10-44 | 7-8 mm | On the second largest cog |
| General reference (Park Tool) | — | 5-6 mm | Small chainring, largest cog |
Turning the B-screw in moves the jockey wheel away; backing it out brings it closer. If you change the gap a lot, recheck cable tension. And if you install a cassette with a different largest cog, Shimano says to repeat this adjustment. On full-suspension bikes, SRAM reminds you to measure the gap with the suspension at sag.
Electronic derailleurs and SRAM Transmission
- Shimano Di2 and SRAM AXS road: they have limit screws and a B-screw like mechanical derailleurs, but no cable. Fine-tuning (the equivalent of the barrel adjuster) is done with the buttons or the app, in small steps.
- SRAM Eagle Transmission (mountain) and 13-speed XPLR AXS (gravel): no limit screws and no B-screw. They bolt directly to the frame instead of a hanger, on the rear axle, and the gap is set with a mounting tool (the Setup Key) for your bike. They only work on UDH-compatible frames.
If it still won’t shift right
- Noise on just one or two cogs: bent hanger or worn cassette.
- Shifts fine in the stand but skips when you pedal hard: worn chain or cassette; measure the chain.
- You have to touch the barrel adjuster every week: damaged housing, or a rusty or dirty cable. Replace them.
- The chain drops between the chainrings or comes off the cogs: limit screws set wrong or the chain is the wrong length. The chain length calculator and the chain link chart give you the number.
- After a crash: check the hanger, jockey wheels and the derailleur itself before riding. A derailleur that goes into the spokes can destroy the wheel, the derailleur and the hanger all at once.
Common mistakes
- Adjusting the derailleur with a bent hanger. You’ll get half the cogs right and the rest wrong.
- Using the limit screws to fix shifting. If the problem is in the middle of the cassette, it’s the cable, not H or L.
- Turning the barrel adjuster full turns when a quarter turn is enough.
- Forgetting the B-screw when you switch to a cassette with a bigger largest cog. The jockey wheel rubs and shifting gets sluggish.
- Overtightening the derailleur mounting bolt. Shimano specifies 8-10 N·m (71-89 in-lb); the bike torque chart has the rest.
If you’re adjusting for a new cassette, read the guide on changing a cassette first. The names of every part in six languages are in the drivetrain glossary.
Frequently asked questions
Which way do I turn the barrel adjuster on a rear derailleur?
If the chain won't climb to the bigger cogs or is slow to shift, turn the barrel adjuster out (counterclockwise, viewed from behind) to add cable tension. If it overshifts or rattles against the next larger cog, turn it in. Go a quarter turn at a time.
What do the H and L screws on a derailleur do?
They are limit stops: H (high) keeps the chain from coming off the outside of the smallest cog, and L (low) keeps it from dropping between the largest cog and the spokes. They don't fix shifting between gears; cable tension does that.
How do I know if my derailleur hanger is bent?
Look at the bike from behind with the chain on the smallest cog: both jockey wheels should line up vertically with the cog. If the derailleur leans toward the wheel, or it shifts well on the small cogs and badly on the big ones, the hanger is bent. Check it with an alignment tool such as the Park Tool DAG or Shimano TL-RD11.
What should the B-tension gap be?
Whatever your derailleur calls for. On the Shimano 105 RD-R7100, 10 mm with an 11-34 cassette and 6 mm with an 11-36, in the small chainring and largest cog. On SRAM RED eTap AXS, 5 mm with 10-36 and 12 mm with 10-28. Park Tool gives 5-6 mm as a general reference.
Is an electronic derailleur adjusted the same way?
The limit screws and B-tension, yes, but there is no cable tension: fine-tuning is done from the shifters or the app (Di2 or AXS). SRAM Eagle Transmission and 13-speed XPLR derailleurs have no limit screws or B-screw at all: they mount directly to the frame.
Sources
- Park Tool, "Rear Derailleur Adjustment"
- Shimano, dealer's manual DM-RARD011-02 for the 105 RD-R7100 rear derailleur (PDF)
- SRAM, "What is the correct chain gap setting for the SRAM RED eTap AXS 36T Max rear derailleur?"
- SRAM, "What tool is used to set the chain gap for an XPLR rear derailleur?"
- SRAM, "The SRAM Eagle AXS Transmission drivetrain doesn't have high limit, low limit, or B-Adjust screws"
