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Rear Derailleur Adjustment Below
When you shift from the small ring to the big ring in front, the shift isn't crisp. It takes one or two pedal revolutions to get the chain to move up. When you shift down, it takes one or two pedal revolutions to move the chain to the small ring. Sometimes, when shifting from big to small in the front, the chain goes too far inward and falls completely off the rings. Sometimes the chain goes too far the other way, and ends up wrapping itself around your crank arms. You need a derailleur adjustment.

Modern front derailleurs have two forces acting on them: the force of the return spring and the force of the cable. The return spring wants to move the derailleur (and hence the chain) as far to the left or inside as possible. When I say left, I mean as if you're straddling the bike and looking down at the front derailleur. From here on out, I'll try to say "in/out" rather than "left/right" with regards to derailleur movement. Moving the front shifter (usually on the left handlebar of the bike) either increases or decreases cable tension. An increase in cable tension moves the derailleur outward, and increases pressure on the spring. A decrease in cable tension allows the spring in the derailleur to move the derailleur inward.

How far in/out can the derailleur move? Well, that's kept in check by limit screws. If your derailleur is dumping off the inner ring in the front, or if the chain is rubbing the inside of the derailleur cage while the chain is on the biggest cog in the back, then you need to adjust your low limit screw on your front derailleur. It's usually a small screw on the derailleur with an "L" stamped beside it. Before we get started, read to the bottom and learn how to check derailleur alignment.

1) Using the right/rear shifter, move the chain to the largest cog in the back (the one farthest inward, or farthest to the left).
2) Using the left/front shifter, move the chain to the smallest gear in the front.
3) Using the appropriate tool (usually a 5mm hex wrench, but sometimes an 8mm socket), release the cable from the pinch bolt. The pinch bolt is the bolt that secures the cable to the front derailleur. We want absolutely no cable tension on the derailleur right now, and the best way to achieve that is to just take the cable out of the equation.
4) Pedal the bike. Oh, I should say at this point that it's a whole lot easier if you have your bike in a work stand. You can get a friend to lift up the rear tire so you can pedal, or you can rig up your own thing with a piece of rope around the seat and hang it from a rafter or something. Whatever you want to do, but a proper work stand is optimal.
5) Do you hear the chain rubbing against the cage of the front derailleur? See the low limit screw? While pedaling, (some derailleur/crank configurations don't allow you to pedal while adjusting the screw, because the crank arm smacks the screwdriver, so just do your best) take the appropriate screw driver and rotate that clockwise. This will move the derailleur outward. The rubbing sound should get worse. Keep pedaling, and now turn the screw counter-clockwise. The rubbing sound should decrease and then eventually go away. Neat huh?
6) With no rubbing sound happening while you pedal, you're going to turn that screw in 1/4 turn increments until you just barely hear a rubbing sound, and then you're going to back the screw out 1/8 of a turn until it goes away. This is easier to do with nicer (more expensive) derailleurs, and harder to get right with derailleurs that aren't so nice. It's the ability to make and hold little adjustments like these that increase the cost of components. Nicer components will operate like a Swiss watch. Crappy ones, well, they get the job done but it takes a lot more fiddling.
7) If you did this right, you should now be able to pedal and not hear the chain rub. Turning the low limit screw clockwise a quarter turn should produce some rubbing sound, and moving the screw back one quarter turn should make that sound go away. The low limit screw is now set.

A note about limit screws: they're easy to deform. You want to make sure whatever screwdriver you're using has good contact. If your screwdriver is too big or too small, or the angles of the tip are not appropriate, you can easily deform these screws so that they no longer work. There are several standards for screwdrivers and screws. Most derailleurs use what's called JIS standard, but not all. Don't use the wrong screwdriver.

Before you reattach the cable to the pinch bolt, find the barrel adjuster for the front derailleur cable. These allow you to increase/decrease cable tension on the fly, by turning it to the left or to the right. Sometimes they're attached to the shifter. Soemtimes they're attached to where the cable housing goes into the first cable housing stop. Sometimes they're in the middle of the cable run. They usually work by turning them counterclockwise to increase tension (when looking at the adjuster from the perspective of the cable going into it), but not always, and the ones that are in the middle of the cable housing can be installed either way. We're going to want to take that barrel adjuster and turn it all the way in so that it puts the least amount of tension on the cable, and then back it out three clicks (if it has clicks) or about one full turn. Now secure the cable in the pinch bolt.

A note about securing pinch bolts: There's usually a bolt that acts on a plate, and that plate pinches the cable against the derailleur. Usually the cable doesn't touch the bolt directly. Also, in that little plate, there's usually a small groove where the cable should sit. You want to take your time and make sure that cable is seated in that little groove properly, and you don't want to smash the cable. It needs to be firmly held, no more, no less. Too loose and your cable slips. Too tight and you kill the cable, and it will have to be replaced next time you loosen that bolt (and you might strip that bolt out). If your cable is smashed to hell and you see frayed wires, replace the cable. Maybe more on cables later. Before you tighten the pinch bolt, pull firmly on the cable to get all the slack out. You don't usually have to use pliers to pull the cable, but if your cable is cut too short and it's hard to grab, be careful when using pliers to not damage the cable.

With the cable secure and the low limit screw set, pedal and shift from the small ring to the next bigger ring. Hopefully the chain moves crisply. Oh, you want to be pedaling at about 60rpm when doing this. If the chain doesn't move, or it moves very reluctantly, that's probably because there's inadequate cable tension. You can increase tension with the barrel adjuster (usually by turning it counter-clockwise). Turn it one click or 1/4 of a turn, then try to make the shift again. Repeat this turning of the adjuster and shifting attempt routine until you've got it dialed in, so that the chain shifts to bigger and smaller rings crisply. It's best to shift back to the small ring in front each time you go to turn the adjuster. You want to try this with the chain on the biggest cog in the back, the smallest cog in the back, and somewhere around the middle as well. Front derailleur cable tension/indexing has now been set.

Now it's time to adjust high limit screw. This is the one that's (hopefully) marked with an "H".

1) Shift the chain to the smallest cog in the back.
2) Shift the chain to the biggest ring in the front.
3) While pedaling, turn the high limit screw clockwise until you produce chain rub, like you did with the low limit screw.
4) Turn the screw out, going in very small increments, until the chain rub sound just disappears.
5) Shift to a smaller ring in the front and then back up to the biggest ring. You shouldn't hear the chain rub. If it does, keep making tiny adjustments with the high limit screw until it goes away.
6) Sometimes at this point you may notice that the chain rubs a little unless you push hard on the shifter. This usually means there's inadequate cable tension, and increasing cable tension on the front derailleur makes this go away. Check your limit screws again after you adjust cable tension.

If this doesn't resolve your front shifting issues, there are a few things to look at, all of which can ruin shifting on their own, or they can all work together to make shifting suck. It could be just your chain, or it could be your chain combined with worn chain rings, or worn chain rings combined with gummed up cables and housing. So.......

1) Check the chain. There are ways to measure the links with a ruler but I'm going to tell you to buy a proper chain gauge tool. If it's worn past 75%, consider replacing it. When's the last time you cleaned and lubricated your chain?
2) Check your chain rings. Stand over the bike while pedaling and observe the rings. Are they warped? Do they wobble side to side while you pedal? Are any teeth chipped? Are they so far worn they like they're curving backwards?
3) Check your cranks for tightness. Grab a crank arm and wiggle in in/out with the crank at 12/3/9'o clock position. Press the crank arms in and out with your palm while pulling against the down tube, seat tube, or chain stay (hard to explain, but you want to try to isolate the crank movement against the frame). It should feel rock solid. There should be absolutely no lateral movement and no "clicking" or "thunking" sound. Reach over bike, move the cranks so they're parallel with the ground, and grab them and try to wiggle them up and down together. They shouldn't move. If you feel any clicking, thunking, squeaking, or anything other than lovely buttery smoothness, try tightening your crank arms (best to use a torque wrench). If that doesn't make it go away, it's probably the bottom bracket. That's a topic for another day.
4) Check the cables and housing. Do your cables look frayed anywhere? Do they look dull and grey, or are they shiny and silver? Shift to the small ring, and while pedaling grab the exposed cable somewhere and pull firmly (but not crazy hard or anything) on it. You should see the front derailleur move, but try to imagine what the cable feels like inside the cable housing. Is it moving smoothly through the housing, or is there too much friction? Your cable and housing might need to be replaced.
5) Try to imagine how the insides of the shifter feel. Does it feel like a Swiss watch, or does it feel like a jar of marbles? Does it sometimes "grab" the cable like it should and sometimes not? You might need your shifter loved or replaced.
6) Look at the front derailleur. You want the cage of the derailleur (that's the "box" that surrounds the chain and touches the chain to make it move in and out) to just barely clear the teeth of the large chain ring. The official spec is usually 1-3mm of clearance, but ideally you want to barely see any daylight here. Having the derailleur touch the teeth in the slightest amount is absolutely unacceptable. A lot of problems can be caused by the derailleur being too high. Also, a lot of problems can be caused by the derailleur not being at the right angle. It can be either angled in or out (and some can be angled up and down). To tell if it's angled in/out, look at the derailleur from the top of the bike. It should point straight backwards, and it should be parallel to the chain rings in front. The cage of the derailleur should mostly match the curve of the chain rings. If you're going to unclamp your derailleur and adjust it's position on your frame, release the cable tension first by backing out that pinch bolt with the chain on the smallest in front. After you move the derailleur on the frame you're going to want to repeat this whole procedure, so it's best to check derailleur alignment first.

That's it for the front derailleur.


In this section I'll be referring to things like barrell adjusters and pinch bolts, the function of which are explained above. I recommend reading the above section on front derailleur (FD) adjustment first, just to get an idea of the process we'll follow for rear derailleur (RD) adjustment.

As with the front derailleur, the rear derailleur (RD) has many factors affecting shifting performance. These factors can independently degrade shifting performance, or they may all work together to hamper quick, clean shifting.

One of the most overlooked things with the RD is the alignment of the derailleur with respect to the frame. With the bicycle perfectly vertical (not leaning to the left or to the right, but straight up and down with both wheels on the ground), the RD cage (the part hanging down with the chain snaking through it) should be perfectly perpindicular to the ground. You don't want it angled toward or away from the wheel. It also shouldn't be twisted in any way. There is a nice tool made by Park (the DAG-1 and DAG-2) to check and correct hanger alignment. If you suspect your hanger is bent, it's worth the money (about $15) to take your bike to a mechanic and ask them to align your hanger for you. If you've crashed and have bent your hanger severely, and it's a removable hanger, a replacement can be ordered either directly from the manufacturer (you'll probably need to have an authorized dealer place the order for you) or you can order one yourself from www.derailleurhanger.com. They're in the neighborhood of $25.

Also check the condition of your cables and housing as mentioned above. You can lubricate the pivot points of both the RD and FD with a light bicycle lubricant. I'm a fan of using Tri-Flow on derailleurs.

With that said, begin adusting the rear derailleur by shifting to the big gear on the front and the little gear in the back (HIGH/HIGH) to move the chain as far to the right or outside as possible. Disconnect the RD cable by loosening the pinch bolt, and set the barrel adjusters to the setting which provides the least amount of cable tension. Most shifters have a barrel adjuster at the shift lever. Most rear derailleurs also have a barrel adjuster where the cable housing contacts the derailleur body. You can move the barrel adjuster at the shifter all the way in, but leave the barrel adjuster at the derailleur out 3/4 to one full turn.

Locate the limit screws. As with the FD, the RD limit screws are usually marked "H" and "L". There's another screw close by, a big one, and that's called the B screw. We'll worry about that later. Screwing a limt screw IN moves the derailleur toward the center of its range. So turning the low limit screw clockwise will move the derailleur outward, and turning the high limit screw clockwise will move the derailleur inward. I remember this by telling myself "screw it in to move it in". "In" in this case being inward from the limits of the derailleur's range of motion.

With the chaing in High/High configuration (big gear in the front, little gear in the back) and thus as far outward from the bike as possible, spin the cranks at around 60 rpm. While pedaling, screw the high limit screw in (clockwise) on the RD until the chain jumps up to the next cog. If you were to attach the cable and ride away now, you'd never be able to get to your highest gear in the back, because the high limit screw is preventing the deraillur from moving outward enough to do so. Keep pedaling, and now back the screw out (counter-clockwise), going in 1/4 turn increments, until the chain just jumps down to the high gear. At this point you'll be hearing a nasty rattling sound as the derailleur cage is rubbing against the chain, so keeping backing the high limit screw out in 1/4 turn increments until that sound goes away. Your high limit screw is now set.

To adjust indexing, attach the cable to the RD in proper fashion (read above for more info on that), and while pedaling, make a shift down to the next bigger cog in the rear. If there is hesitation, shift back to the high gear, back out the barrel adjuster at the RD 1/4 turn, and try the shift again. Repeat until it makes this first shift cleanly. Then shift to the next gear, and then the next, and then the next, pausing for a moment at each gear to make sure that everything is working smoothly and there's no excess sound. If you encounter a reluctant shift, or if there's excess sound, go back to the high gear, make another 1/4 turn out, and try again until all excess noise is eliminated and all shifts are smart and clean. Indexing is now adjusted.

To adjust the low limit screw on the RD, we're first going to screw it in to a point where it makes for poor shifting, and then back it out until things are perfect again. The hardest shift for a bicycle to make is to go into the biggest cog in the back (the low, or innermost gear) while the chain is on the big ring in the front (the outermost gear). This makes the RD work as hard as it possibly can. If we adjust for this condition, then it should work fine everywhere else. With the chain on the big ring in the front, shift to the 2nd biggest cog in the back (not the innermost cog, but the cog next to it).

From this position, screw the low limit screw in one full turn, then pedal and try to make the shift to the innermost cog in the back. If it makes the shift fine, then shift back to the other cog and move the low limit screw in one full turn. Repeat this process until you find a noticeable degredation in shifting. Don't screw the low limit screw in while the RD is in the lowest gear. Instead, shift down to the next gear and make the adjustment there, and then move the RD back to the low gear. Now that you know you've found the point where shifting is negatively impacted, back the low limit screw out (counter-clockwise) 1/4 turn and try to make the shift again. If it's perfect, great, if not, then shift back, back the screw out another 1/4 turn, and try again. Repeat until you find the point of adjustment that just finally eliminates the imperfect shifiting. Over time this screw is only going to seat in and loosen, so we're shooting for the tightest possible setting that still gives optimal shift performance. The low limit screw has now been set.

Remember that big screw called the B screw? That thing controls the amount of tension in the spring that rotates the derailleur body, and therefore controls the angle of the derailleur and distance of the pulley of the RD from the cogs. Different manufacturers call for different settings (SRAM for instance calls for about a 6mm gap from the RD pulley to the biggest cog). This is measured with the RD on the biggest cog in the back and the chain on the smallest ring in the front. For most Shimano derailleurs, increasing tension on this screw will move the RD farther away from the cogs in the back. Getting the RD close, but not touching, the cog is usually optimal.