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Derailer Adjustment
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Sheldon Brown photo
by Sheldon "Click" Brown
revised by John "Trim" Allen
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How Derailers Work



The front derailer simply consists of a cage made of sheet metal that can move back and forth from side to side. As it does so, it pushes the chain sideways until it can't run on the chainwheel it has been riding on, then the chain falls off and lands on the chainwheel closest to its new location.




Newer sprockets usually have specially shaped teeth, and ramps on their sides to make this operation run more smoothly. This is the major reason that modern derailer gear systems work better than older ones. It has very little to do with the quality of the derailer.

Rear Derailer Adjustment









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The Four Rear Derailer Adjustments, In Order of Importance


The limit-stop screws






  1. Low-gear limit stop.

  2. High-gear limit stop



  3. Indexing adjustment

    The indexing adjustment is the most frequently needed derailer adjustment. The detents (click-stops) that provide indexing are in the shifters, and the index adjustment sets the length of the cable so that the derailer is in the correct place to correspond with each click stop.







    • Shifting to larger sprockets is accomplished by tightening the cable;
      turn the barrel counterclockwise to tighten it.

    • Shifting to smaller sprockets is accomplished by loosening the cable;
      turn the barrel clockwise to loosen it.

  4. Angle adjustment ("B-tension")







    Campagnolo Rear Derailers


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Chain Length




You may need to add links on recumbent bicycle, or a touring bicycle with a large cluster. Always use new chains of the same brand and model. You could ask the bike shop for surplus links from another chain. These probably would only have been discarded anyway.


Inner and Outer half-links must alternate:

Won't Fit-Too Long
Full-link overlap, correct
with chain on the large chain-
wheel and sprocket but not yet
run through the rear derailer.
Won't Fit-Too Long
Overlaps by a half link.
Already too short
unless it could overlap
by a full link as at left.
Will Fit
Will connect, but
too short except on
a bicycle with a
non-derailer drivetrain.




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Alex Ramon has a video that shows:

How To Calculate Chain Length

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Chain Condition




Stiff links



A link that has been bent in a chain-jamming incident can cause similar symptoms. A bent link can sometimes be straightened by clamping the chain in a chain tool at one side of the bent link, and an adjustable wrench or another chain tool at the other side, and bending the link straight. The chain may run perfectly following this repair, but it should be replaced at the earliest opportunity. Another emergency repair is to shorten the chain and ride the bicycle with a reduced gear range. Adjust the derailer(s) to prevent shifting to combinations which would pull the chain completely tight and cause damage.The chain could be shortened even further to make a bicycle with horizontal dropouts into a one-speed.


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Front Derailer Adjustment





Front Derailer Adjustments

  1. Chain slope and derailer selection


  2. Clamp Position


    • Angle



    • Height


  3. Derailer/Chainwheel Mismatch





  4. Low-gear limit stop.





    Anti-derailment devices



  5. High-gear limit stop




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Front Derailer Trimming




[The SunTour Symmetric shifter -- from around 1982, non-indexed -- was designed to trim the front derailer when the rear derailer was shifted. Notice how the front shift lever moves forward and backward as the rear shift lever is rotated on the video clip below. Remarkably, this feature has not become standard on hewer systems, though it could be implemented with a simple lever device somewher along the cables. It is offered on the very expensive Shimano electornic shifting system. I thank N. Keith Duncan for this video clip. -- John Allen]


See also my Front Derailer Selection Article





This site has a separate major article on Chainline

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The most common area for this problem is the short loop of cable housing that leads from the rear stay to the derailer. The front end of this housing is exposed to road spray from the front tire, and the resulting rust can seriously degrade shifting. This cable loop should be fairly long, so that it makes a very gradual curve. Many bikes have too short a housing loop here.

Another problem area is the cable guide where the cables run under the bottom bracket. In addition to sluggish upshifting, friction in this area can cause spontaneous upshifting under load.

Cable housing for indexed shift applications uses multiple straight wires sandwiched between plastic, instead of the spiral-wound wire used in brake cable housing. This requires a fairly special tool to cut properly. When you buy such housing, you would do well to have exact length information so that the shop that sells it to you can cut it for you, if you don't have a suitable cable cutter.

When you cut housing, the plastic liner gets squished a bit. It is helpful to clean and round out the opening with an awl or scriber.

The final loop at the rear derailer is short and has a nearly 180 degree bend. "Compressionless" housing is normally used for this. I've taken to bending the piece of housing to the approximate shape it will be used in before cutting it.

If you cut the housing straight, all of the longitudinal wires come out the same length, so when you bend it, the end of the housing acquires a slanted face, since the wires on the inside of the bend have a longer way to go around the curve. It is my belief that cutting the housing while it is bent makes a smoother, more reliable connection at the end of the housing. You must have a ferrule at each end of each piece of housing. This helps keep the hole in the housing aligned with the cable stop, and also keeps the housing from falling apart.





Cable Replacement

To replace a derailer cable, you want to start out with both the derailer and the shifter in whichever position has the cable slack. This will usually be the position corresponding to the smallest chainring/rear sprocket.

If you disconnect the cable (or if it broke) and pedal the bike a couple of times the derailer will automatically go to the correct position.

You may need to pull on the end of the cable while operating the shifter to get it to shift to the loosest position. If the shifter indexes, it will stay in that position. If it is a friction shifter with a return spring, you may have to tighten the friction adjustment to get the shifter to stay in the loosest position.

Once the derailer is disconnected from the derailer's anchor bolt, pull the housing (if any) away from the shifter, and then push the exposed inner cable into the shifter. The moulded end of the inner cable should then pop out of the shifter. If it's a simple lever shifter, such as a down-tube or bar-end shifter, the cable end is readily visible.

If it's a more complicated ratcheting type shifter, there will usually be an access hole where the cable end can pop out...but his access hole may only line up correctly if you remembered to shift to the loosest gear position first. In case a Shimano STI shifter does not release to this position, please see advice on another page.

Hole for cable insertion is visible after releasing the shifter to the loosest position and squeezing the brake lever. Cable insertion into STI brake-shift lever. Arrow indicates forward motion of cover plate when brake lever is squeezed.
Cable insertion hole in STI shfiter cable insertion in STI shfiter


Twist-grip shifters such as SRAM GripShift are typically the most difficult for cable changing, and these commonly require disassembly.

Generally, the derailer limit stops should not require any adjustment when you replace a cable, but you will need to adjust the indexing.

Before connecting the cable, screw the adjusting barrel all the way in, then back it out maybe a turn or a turn and a half. This will give you the opportunity to loosen the cable a little or to tighten it a little or a lot.

Front Cable Replacement

Thread the cable through the shifter and any housing. Check the condition of the housing and particularly the open ends. Replace or trim if needed. See also my Cables Article. Pull on the cable and operate the shifter until you have the slackest position. The chain will normally be on the smallest chainring.

Run the cable under the anchor bolt hardware and secure it. If it's an indexing system, and particularly with triple chainrings, you will need to fine-tune the indexing to get it to shift well and run smoothly on the middle chainring.

Rear Cable Replacement


Method A:

Use a pair of pliers to pull the cable really tight and secure the anchor bolt. Use the adjusting barrel to correct the indexing adjustment.

Method B:

(This is how I do it. Only works if you have the bike in a work stand of some sort, unless you have three hands.)

Hand pedal forward with your right hand while manually pushing the rear derailer inward until the chain engages the 3rd smallest sprocket. Stop pedaling, then let go of the derailer. The derailer spring will try to move the derailer outward toward the smallest sprocket, but the stopped chain won't let it go all the way.

Pull fairly firmly on the end of the cable to take up the slack and secure it with the anchor bolt. Then you can pedal and check the indexing adjustment. I find that this usually gets me quite close, with only a minimal amount of fine tuning needed to the indexing adjustment.

Cable Attachment (rear)

One area that commonly causes problems is the attachment of the inner cable end to the derailer's anchor bolt. If this comes in at the wrong angle, it can change the geometry of the parallelogram and make it impossible to get the derailer to index properly across its range.

There is usually a groove in the derailer body or a washer with a bent corner to determine that the cable is running correctly.

Alternate Cable Routings

Two alternate cable routings for Shimano derailers adapt them for use with nonstandard shifters or cassettes.

Shimano originally publicized an alternate cable routing which placed the cable slightly closer to the pivot, making the derailer move slightly farther for each click. This adaptation makes newer Shimano derailers work with older Dura-Ace shifters, but it is also useful when you want to use a 9-speed cassette with 10 speed shifters, or 8-speed cassette with 9-speed shifters, or a 7-speed cluster with 8-speed shifters. You may need to fine-tune the amount the cable deviates from the standard position, so the derailer sweep matches the sprocket spacing.

cable routing to increase derailer travel

The other alternate cable routing, suggested by Brian Jenks, proprietor of Hubbub Cycles, decreases the derailer travel for each click. This makes some Shimano derailers and shifters compatible with Campagnolo cassettes. It is also useful when you want to use a 10-speed cassette with 9-speed shifters, or 9-speed cassette with 8-speed shifters, or an 8-speed cassette with 7-speed shifters. You will then lose the use of one sprocket, unless you are using a shortened cassette such as an 8 of 9 on 7, or 9 of 10 on 7. Note the two tabbed washers in the drawing below -- one to change the cable routing, and the other to secure the cable. Again, you may need to fine-tune the cable position.

cable routing to increase derailer travel

Unlike the Dura-Ace modification, the Hubbub modification is nonstandard, and not all of the ratio changes are accurate. Chris Juden of the Cyclist Touring Club (U.K.) has posted a Web page listing usable combinations. Pulley-type adapters from JTek Engineering offer a more precise alternative.

Cable Attachment (front)









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Thanks to Andrew M. Torres for his kind assistance.

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See: A Blast From The Past

Spoke divider has a video that covers some of this material.

See also the Park Tool Website.

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Articles by Sheldon Brown and others
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Fixed Gear
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Tandems Touring What's
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