Mechanical Services & Maintenance
Derailleurs and Shifting:
Rear Derailleur Adjustment Fundamentals
Adjusting the rear derailleur on a bicycle can be a daunting task. However, armed with an understanding of what the primary adjustments control, basic derailleur adjustments are not as complicated as they seem.
- Philips screwdriver #2 or 2.5mm hex (SRAM RED)
- 5mm Hex wrench
Overview – The two primary adjustments on a rear derailleur are stop screws and cable tension. Once adjusted, unless a new wheelset is installed, you should not need to touch your stop screws again. The stop screws determine how far the derailleur can travel in and out and if they are not adjusted correctly, the chain will over-shift into the wheel (low stop), jam between the frame and cassette (high stop) or not allow the chain to go into the biggest (low stop) or smallest cogs (high stop). If this is your issue, proceed with the stop adjustments outlined in #1 and #2. Keep in mind that the stop screws have nothing to do with shift quality between gears; if your bike is hesitating or noisy shifting between gears, skip to the cable tension adjustments in #3.
We’ll assume that a chain is already installed on the bike and that the rear wheel is elevated in a workstand (or on a stationary trainer) during the following adjustments.
1) High Stop Adjustment – Many derailleurs have a “L” or “H” beside the stop screws to signify whether they control the high (smallest cog) or the low (biggest cog) gear stop. The “H” stop limits how far the derailleur can travel to the outside of the frame. Your goal is to have the “H” stop turned in as far as possible while still allowing the chain to smoothly and quietly engage the smallest cog. Adjust the high stop as follows:
a) Make sure the rear shift lever is fully released so that the derailleur can go into the highest gear (smallest cog).
b) Once in the smallest cog, back the derailleur cable tension off by turning the cable’s barrel adjuster all the way in (or unbolt the cable altogether) so that the derailleur can naturally travel until it hits the stop without interference from cable tension.
c) Shift the chain into the biggest chainring in the front and slowly turn the pedals. From behind the bike, sight the relationship of the derailleur’s upper pulley to the smallest cog. The pulley should line up directly under the smallest cog. If it does not, turn the “H” stop screw clockwise to push the derailleur towards the center of the bike or counter-clockwise to allow it to travel further towards the outside of the bike. The chain should stay in alignment with the pulley and cog and rotate smoothly without trying to skip into the next biggest cog or off towards the frame.
d) If the chain tries to jump into the second cog without shift lever input, turn the “H” stop screw counterclockwise in 1/4 turn increments until it no longer does this. If the chain tries to jump off the smallest cog (towards the frame) turn the “H” stop screw clockwise in 1/4 turn increments until it no longer does.
e) Check the adjustment by rotating the crank and manually pushing the derailleur to shift the chain into a bigger cog and then releasing. The chain should return to the smallest cog quickly and smoothly without over-shifting into the frame.
2) Low Stop Adjustment – The low stop (“L”) works the same as the “H” stop, but in the opposite direction – it limits how far the derailleur travels towards the spokes in the wheel. The goal is to adjust the “L” stop in as far as possible, so that the chain cannot travel beyond the largest cog (into the spokes), while still allowing the chain to engage the biggest (high) cog smoothly and consistently. Adjust the low stop as follows:
(a) While rotating the crank slowly with one hand, manually push the derailleur towards the inside of the bike/wheel with your other hand to shift the chain into the biggest cog.
(b) If you can push the chain beyond the biggest cog (into the wheel) turn the “L” stop screw clockwise until it no longer allows for this, but don’t turn it in so far that it restricts the chain from shifting into the largest cog smoothly. If you cannot push the chain into the biggest cog at all, turn the “L” stop counter-clockwise to allow the derailleur to move further towards the center of the bike. Once you get this adjustment “in the ballpark”, work in 1/4 turn increments.
(c) Check the adjustment. The chain should go into the biggest cog quickly and smoothly without over shifting into the wheel or skipping.
3) Cable Tension Adjustment – The vast majority of shifting issues are caused by cable tension and friction issues. The good news is that rear derailleur cable tension adjustment operates on a simple rule – turn the barrel adjuster on the back of the rear derailleur in the direction the chain is not shifting smoothly. If the derailleur is not engaging the bigger cogs well, turn it counter-clockwise. If the derailleur is having trouble dropping into the smaller cogs turn the barrel clockwise. The exception to this rule is the “rapid-rise” or “high normal” rear derailleurs found on some mountain bikes, which are opposite. More detailed instructions on cable tension are as follows:
(a) If the cable is currently affixed to the derailleur and just needs a minor adjustment, proceed to step d). If installing a new cable, turn the barrel adjuster on the back of the derailleur one turn out from its fully bottomed (clockwise) position and make sure any other rear derailleur barrel adjusters located on the front of the bike are also turned in (clockwise) most of the way.
(b) With the rear shift lever in the fully released position (chain in the highest gear/smallest cog), and paying attention to the particulars of your derailleur (cable routing varies between brands), use the 5mm Hex to affix the cable to the rear derailleur. Pull the derailleur cable fairly taut, but not rigid.
(c) If the cable or housing is new, firmly push on a section of exposed cable with your hand to stretch the cable and seat all housing and ferules in their stops. If the cable is internally routed, push on the shifter (without pedaling) to stretch and pull the cable firmly against the housing and stops. If the cable becomes slack, repeat step b) before proceeding.
(d) With the drivetrain in the big chainring/small cog combination, manually pedal the bicycle and click the shifter into the next biggest cog. If the chain hesitates to move or is sluggish, turn the barrel adjuster on the rear of the derailleur counterclockwise to add tension to the cable and allow the cable to pull the derailleur further with each click of the shift lever. If the chain tries to over-shift or skip to the third cog, turn the barrel adjuster clockwise to reduce tension on the cable and thus reduce the amount of derailleur motion with each shift.
(e) Shift back into the smallest cog and adjust the barrel adjuster in 1/4 turn increments until the shift is smooth.
(f) Test the shifting in the remaining gears and adjust tension as needed.
That’s it! If you understand how adding or subtracting cable tension affects shifting, you can fix the vast majority of shifting issues on your bike.
If your bike is still not shifting well, you either need a “B Tension” adjustment (beyond the scope of this article), your derailleur hanger is out of alignment (see a shop to replace or realign the hanger) or a drivetrain component is worn and needs replacement. Keeping your cables and drivetrain clean and well-lubricated goes a long way towards improving shift quality and minimizing wear, so be sure to stay on top of these items.