Mechanical Services & Maintenance
Derailleurs and Shifting:
Adjusting the Rear Derailleur
Adjusting the rear derailleur on a bicycle can seem like a tricky affair. There are screws to adjust and a barrel adjuster at the back. What do all these adjusters do?
The limit screws are the most confusing part of the rear derailleur. Most people are not sure what they do and when things are not shifting properly, they give these a turn and things get worse. The screws are there to simply limit the movement of the derailleur in each direction so it will not shift your chain over the cassette and into the spoke or jam the chain down against the frame.
You will notice most derailleurs have an L or H beside the screws. The L signifies the low limit screw. This will limit how far the derailleur travels towards the spokes of the rear wheel. The more you tighten the screw, the less movement the derailleur will have towards the spokes, thus keeping the chain from over-shifting. If the chain is jumping over the last cog and into the spokes, tighten the Low limit screw. If you are having trouble shifting into the largest cog on the cassette, you can loosen the Low limit screw.
The H signifies the high limit screw. This will limit how far the derailleur travels away from the frame, so realize that the more you tighten the screw, the less movement the derailleur will have towards from the frame. If the High limit screw is not adjusted properly, the chain could jam against the frame, then you would tighten the limit screw. If the chain is not dropping down into the smallest cog of the cassette, you can loosen the High limit screw. All limit screw adjustments should be done with no tension on the cable to eliminate any issues this could present.
Once you have the limits screws adjusted properly, the only step left is to connect the cable. When the High limit screw has been adjusted properly, the cable tension should be very close to perfect. Any adjustments on cable tension can be adjusted via the barrel adjuster on the frame or shifter.
Below is a quick guide to adjusting the rear derailleur. Armed with the knowledge of how the derailleur works, this is now a simple and straight forward process.
All adjustments should done in quarter turns.
Tools needed:
- Philips screwdriver #2
- 5mm Hex wrench
1. Shift to the big chainring and the largest cog in the rear, then loosen the cable anchor bolt.
2. Set the Low limit screw. This limits how far the derailleur can travel toward the spokes. Lightly pushing the derailleur toward the spokes by hand, be sure the upper derailleur pulley lines up directly under the largest cog. If not, turn the Low limit screw (usually the lower screw or marked with an L) in or out until the pulley is centered. You can watch it move in and out as you turn the screw while applying light pressure by hand to the derailleur. Be sure the Low limit keeps the chain from shifting into the spokes. If you tighten the limit screw it will pull the derailleur away from the spokes.
3. Set the High limit screw. This limits how close to the frame the derailleur can travel. With the cable still loosened, pedal the bicycle in the workstand. It should shift to the smallest cog. The pulleys should line up directly under the smallest cog. If not, adjust the High limit screw. If you tighten the limit screw it will pull the derailleur away from the frame.
4. With the drivetrain in the big chainring/small cog combo, turn the barrel adjuster all the way in, then back it out one full turn. Now reattach the cable, making sure to pull it taut to remove all slack. While pedaling the bicycle, click up to a lower gear. If the chain hesitates to move or moves up but clatters, turn the barrel adjuster out (counterclockwise) one quarter a turn. Shift back down and try it again.
Repeat this process until shift is smooth. Tune the shifting with the barrel adjuster. If the chain misshifts when you move to larger cogs, turn the adjuster counterclockwise. If it misshifts when you move to smaller cogs, turn the adjuster clockwise. The exception to this rule is the rapid-rise or high normal rear derailleurs, which are opposite.
Routine cleaning and lubing. Grit on the outside of the derailleur can work its way into the moving parts causing premature wear which creates slop in the derailleur’s movement and leads to lousy shifting. Use a gear brush to clean the derailleur with solvent. Let the derailleur dry for 10-15 minutes then re-lube the pivots. Don’t lube the pulleys if they are spinning freely as it attracts dirt without adding much performance.
