How to Adjust a Rear Derailleur – Limit Screws & Indexing

The most common question we get is, how do I fix my shifting? Maybe it's not reaching all the gears, or maybe it's making all sorts of noises. Whatever the issue, and regardless of the make or model, this video on mechanical rear derailleur adjustments will help you dial in your shifting for optimal performance. Calvin Jones here, Park Tool Company. We hope this video will give you a whole new outlook on your bike's shifting. And before we begin, here's a quick overview of the components and procedures. The rear derailleur is the mechanism that shifts the chain at the rear cogs. The derailleur is connected to the shifter by a cable that passes through housing. Bikes commonly use an index shifter that moves the cable in small, predetermined increments with each click. Inside the derailleur body is a spring that constantly pulls the derailleur outward, and our cable is constantly holding against that spring in various shift positions. Derailleurs are fitted with limit screws that stop the derailleur from moving too far inward and too far outward. Here we can actually see the limit screw stopping the linkage at each end. The function of limit screws is to prevent the chain from going into the spokes or into the frame. Our first procedure will be to set the H limit screw, and after that, we'll move on to indexing. Indexing is the process of lining up our guide pulley with the cogs so that each shift lines up with each cog. The barrel adjuster, located here while we're up at the shifter, allows us to move the shift increments as shown. After indexing, we'll dial in our other limit screw. Then we'll check our B screw adjustment, and we'll explain more on that later. For now, just grab your tools, which are a screwdriver or a hex wrench for the limit screws, and a repair stand for some way to hold your bike up so we can pedal and check those adjustments. Let's get started. Now we'll walk through the H limit screw adjustment. Our goal will be to dial it in as close as possible to that inward cog. Sometimes the limit screws are unmarked, and we'll show you how to identify which is which a little later. We begin with the visual check of the derailleur hanger, and if it's clearly bent, things are not going to work well, and you should watch this other video on hanger alignment. If the bike has multiple front chainrings, shift the front derailleur to the largest. Shift the rear derailleur to the smallest cog. Even if you're already on the smallest cog, keep clicking until there are no more clicks. This makes certain our shifter is fully actuated outward. If the chain does not shift to the smallest cog, it's likely being stopped either by the limit screw or the shift position. First, turn the H limit screw counterclockwise a few turns. Pedal and see if it makes the shift outward. If it's not shifting outward, turn the barrel adjuster clockwise a few rotations. Pedal to see if it shifts. So now everyone is on the smallest cog, and we have no more clicks at our shifter. Now even if you just did this, turn the barrel adjuster clockwise a couple of turns. If there's a barrel adjuster located at the shifter, it performs the exact same function. Turning either one clockwise a couple of turns adds slack to the cable, and this keeps us from confusing our shift position with our limit screw settings. People often get those two things confused, so here's a quick explanation. We're currently on the outermost shift position, and even if things look lined up, the limit screw might be set to stop the derailleur here, here, or it might be correct. We won't know until we take our shifting position out of the equation. There are many ways to do this, but easiest is to turn the barrel adjuster clockwise. We remember this moves the shifting positions collectively outward. Now we'll be able to set our limit screw setting without getting it confused with our shift position. We're now ready to dial in the H screw. If you can't tell which limit screw is the H screw, pick one and turn it in and out while watching the derailleur. If the derailleur does not move, try the other one. The H limit screw will cause some motion. We're going to find the correct setting by purposely making it too tight, then we'll back it out slightly until it's just right. So grab your screwdriver and tighten the H screw a half turn. Now instead of only seeing if it's too tight, we're also going to listen for excessive noise while pedaling. And if the front derailleur is making noise, do your best to ignore it for now, or find the fix in this other video. Back on the rear cogs, we hear normal noise for this bike, which tells us a limit screw is not yet too tight. We tighten the screw again a half a turn. Now we hear excessive noise, and we'll double check that it's coming from the chain rubbing against the next inboard cog. If so, the limit screw is too tight, which is what we want for now. By the way, this doesn't damage your drivetrain at all. In some cases, an overly tight limit screw can cause a shift to the next cog. Back out this limit screw until it shifts back and creates excessive noise. Once we hear the excessive noise, we begin to loosen a quarter turn at a time until the noise is gone. If there are two settings that seem equally quiet, go with the tighter of the two settings. The H limit is now set. Now we'll turn the barrel adjuster counterclockwise a couple of turns. We're getting it back approximately to where it was, and don't worry, it doesn't need to be precise just yet. As for the other limit screw, the L limit, we will wait to adjust it until after the indexing is set. Earlier we explained that the process of indexing is to line up the guide pulley with the cogs, so each incremental shift lines up with each cog. Again, the barrel adjuster allows us to make these adjustments. A quick note is that there is a range of acceptable adjustment, meaning there may be more than one barrel adjuster position that results in good shifting performance. If there are two front chainrings, stay on the largest. If there are three front chainrings, shift to the middle. On the rear, we start on the smallest cog. Pedaling at a normal riding cadence, shift the rear lever only one index click, not more than one click. Note that some shifters are designed to click multiple times with one push on the lever, so push the lever slightly until you hear one click. We need this one click to shift one and only one gear. If the chain did not make it to the next gear, return the shift lever to the outermost click. Turn the barrel adjuster one full turn counterclockwise. Try the shift again. Repeat until it makes the shift. If you have unthreaded the barrel adjuster so much that it has come out or nearly out, thread the barrel back in fully and then out one or two turns. Make sure you're on the furthest outward shift position and the smallest cog. Then remove the slack from the cable at the pinch bolt. In this different scenario, one click at the lever shifts two sprockets. Shift back to the first cog and turn the barrel adjuster clockwise and try the shift again. Now that our chain is on the second sprocket from one click, the shifting can be fine-tuned. What we're going to do is purposely turn the barrel adjuster counterclockwise until we're clearly out of the acceptable range and then slowly creep back in. Similar to the limit screw, excessive noise is our indicator. If there's not already excessive noise while pedaling, turn the barrel adjuster counterclockwise until you hear it. Once we hear excessive noise, we know we are outside the acceptable adjustment range. Now double-check that the source of the excessive noise is indeed from the chain striking the next inboard cog. Next, turn the barrel adjuster clockwise a quarter turn and check again for the noise. Repeat until the noise is gone. While this is an adequate setting in this cog, we now need to check the other sprockets one at a time. Shift and listen at each position for any excessive noise. If you hear noise in any one cog, turn the barrel adjuster clockwise a quarter turn. Test the shift to that cog again. Repeat and continue to check until we find the barrel adjustment that allows good shifting in every rear cog, with the exception of the largest cog. The shift to the largest cog will be done later. Now shift outward one cog at a time, again checking for no excessive noise once the chain is on the cog. However, if the shift is slow coming outward, that can be improved by another quarter turn clockwise at the adjuster. Our indexing is now properly set and it's time to move to the L limit screw adjustment. Similar to the H screw setting, we make the L screw too tight, then we back it out slightly until it is just right. This provides the most protection from the derailleur taking the chain past the largest cog and into the spokes. Shift the chain to the next largest chainring in front. Shift to the second largest cog in the rear. Next, we need to figure out where our limit screw is set. Is it already too tight? Is it far too loose? Shift to the largest cog to find out. If the chain does not make the shift, then the L screw is already too tight, and that's what we want for now. If the chain shifts slowly to the largest cog, that's also a symptom of too tight an L screw. If there's excessive noise once on the largest cog, again the L screw is too tight, and again, that's what we want for now. However, if it makes an acceptable shift with no excessive noise, our L screw is not too tight. We turn the derailleur one click outward, tighten the L screw a half a turn, and try the shift again. Repeat until there are symptoms. Now that the too tight L screw is causing symptoms, we'll loosen it incrementally until it's correctly set. Loosen the L screw one quarter turn and shift to see if the symptoms went away. Repeat until it shifts quickly and rides on the largest cog without excessive noise. The L limit is now set. As a check, put extra pressure on the shifter. Watch at the rear derailleur. The cage should not move inward. Most derailleurs have some form of adjustment for the spacing of the G pulley to the cogs. This spacing is controlled by the B screw, B for body angle screw. This adjustment is checked when the chain is on the smallest sprocket in front and the largest cog in back. The majority of road and mountain bike derailleurs require a gap between 5 and 6 millimeters. Use a hex wrench to gauge this distance. There are some exceptions, so consult the manufacturer's specifications. But don't get too hung up on this. If the bike is shifting well, the B screw is adequately set. To increase this gap, tighten the B screw. To decrease the gap, loosen the B screw. If you made significant changes to the B screw, double check the indexing adjustment. Otherwise, you are done and your derailleur is properly adjusted. Those are the basic steps in adjusting the rear shifting. The bike should also be test ridden because the stresses of riding on the drivetrain are different than when the bike is in a repair stand. If symptoms like slow shifting or excessive noise show up, follow the same guidelines as discussed in the video. You may need to change the barrel adjuster or limit screw another quarter turn. Also, if you've gone through these steps and something didn't seem quite right, check out our video on advanced troubleshooting and rear derailleur adjustment. And finally, be sure to check out this video for an overview of all our derailleur and shifting content. That's it for shifting adjustment. If you found this helped you, give it a thumbs up and share it with your friends. It really does help us provide content for you, and it keeps me locked up here in the studio. That's it, we'll see you on our next repair help video.