Setting up the rear derailleur: indexing the cable system
Indexing setup aligns the position of the rear derailleur with each cassette sprocket. Here we're looking at a minor adjustment of a working cable system of the conventional type. If the bike has fallen, the cable is damaged, or the chain comes off the cassette, diagnostics are needed first, not turning the regulator.
When does this instruction apply
On a conventional cable-operated rear derailleur, a spring returns the mechanism to the small sprocket, and cable tension moves it to the larger ones. The reverse mechanisms have a different order. Electronic systems, planetary hubs, and SRAM Full Mount are configured according to their manuals.
Before setting up, read poor shifting diagnostics. Make sure the wheel is properly installed, the cable and housings are intact, the components are compatible, and the dropout has no obvious damage. Its alignment is checked with a tool, not by sight.
Initial installation of the shifter, cable replacement and adjustment after changing the cassette require a complete guide for a specific system. Do not use unfamiliar screws as a way to eliminate any noise.
Cable regulator and H, L, B screws
- Cable tension regulator
- The threaded regulator changes the effective length of the housing and the position of indexed gears. It can be located on the shifter, housing, or derailleur.
- H and L
- They limit the extreme positions. Their job is to prevent the chain from going past the small sprocket or towards the spokes. They do not replace the cassette center adjustment.
- B or gap regulator
- Sets the position of the upper pulley relative to the cassette. The required gap, gear for checking and tool depend on the model.
Park Tool disassembles these adjustments separately. For new installations, follow the manufacturer's complete procedure. The number of screw turns and the gap of one system cannot be transferred to another.
Preparing for a small adjustment
Secure the bicycle firmly in the repair stand and disconnect the electric drive. Slowly rotate the pedals by hand, keeping away from the chain, rollers and spokes. Without a suitable stand, do not try to hold the bicycle and adjust the mechanism at the same time.
Record the initial position of the regulator and the direction of change. Check one shifter command at a time. Start in the working section of the cassette where the chain stays on the sprocket, and follow the front gear position specified in the system instructions.
If the regulator is almost fully turned, do not continue to turn it. Check the cable and housing installation. Tightening the cable mount is a separate operation with the torque specified in the instructions.
How to adjust chain alignment with the sprocket
For a conventional mechanism, increasing tension shifts the indexed positions to the larger rear sprockets. When a properly functioning chain is late in shifting to the adjacent larger sprocket, a slight increase in tension can help; if it is late when returning to the smaller ones, a decrease is needed.
Turn the knob in small steps, for example, by a quarter of a turn, and after each step, check one transition in both directions. Do not rotate it several turns without checking. If the thread comes out or there is no predictable effect, return to diagnostics.
Look at the direction of unscrewing relative to the threaded end of the regulator: when viewed from the other side, 'clockwise' will be perceived the opposite way. It's more useful to make sure that the regulator actually lengthens or shortens the shirt support.
Directions for conventional systems and reasons for slow shifting are checked with Park Tool: Advanced Troubleshooting. For models with a different mechanism, use their manual.
Why you should not fix extreme gears at random
If the chain does not go to the outermost sprocket, the reason may be in the limiter, gap, cable, or compatibility. First, find H/L/B in the instructions for your model. Setting the limiters requires checking the protective extreme positions, not just silence.
Stop if the chain tries to go to the spokes, the derailleur touches the wheel, or the chain comes off to the outside. Do not continue the check by forcing the shifter. Order transmission setup and tell us which adjustments you have already made.
If the middle works in one regulator position and another section only in another, this is a reason to check the cable, the pulley, and compatibility. Endless adjustments do not fix the underlying cause.
How to check the result
- Check consecutive transitions across the entire range in both directions, one click at a time.
- Make sure the chain stays on the provided sprockets and the shifter does not get dangerously close to the spokes.
- If everything is in order, take a short test ride with smooth shifting, without forceful pressure during gear changes.
- If there is still slippage under load, use separate analysis: good performance in the stand does not exclude wear.
The sources were verified on October 9, 2026. Adjustment of the physical bicycle and checking the article by the mechanic as part of the preparation were not carried out; a limited adjustment is described here, not a complete installation of any transmission.