How to adjust the bike derailleur

One of the things that many people new to cycling have issues with is that they have difficulty indexing their gears. Some people adjust their gears randomly, resulting in inaccurate shifts, losing the full range of their gears, causing their gears to jump, and even chain loss. The purpose of this paper is to help new cyclists learn the principles behind gear changes and how to keep their gears running smoothly.


To start with make sure you have all the tools you’ll need. You’ll obviously need your bike and a groupset fitted or needing to be fitted. You’ll also need the correct screwdriver for the high, low and B screws on your rear derailleur.

Ready, let's talk about the basic principle of gear chaning, so that you can better understand why it works and why it sometimes doesn’t work. The transmission system is mainly composed of 5 parts:

  • Your fingers

  • Dearaileur 

  • Chain

  • Shifter

Basic principle: pull the shifter, which changes the tension in the gear cable or send a signal to the rear derailleur, so that the chain changes the position of the derailleur relative to the cassette to change the gear.


According to my observation, I found that the displacement of the transmission of the same type matching transmission system is almost equal in any speed ratio. To sum up, we can simply understand that no matter how much speed the transmission and how much speed the flywheel, we only need to manage the accuracy of the highest speed gear and the lowest speed gear. For example, for 12 speed, we only need to consider the accuracy of 1 and 12 gears to meet the accurate positioning of all gears. This is the product in the design has been considered completely.


In order to make adjusting gears easier, we need to set out a few terms. The highest-speed gear of the cassette is the smallest cog (also known as 1st gear, 10t or 11T flywheel or even smaller), and the lowest gear is the largest cog. High speed and low torque. When the thumb lever is used for upshift, the slower the upshift speed is, the greater the torque is. The shorter lever (Shimano is the lever operated by the index finger) is the downshift. The faster the lower speed is, the smaller the torque is. The high speed gear is the smallest gear, also known as the first gear. The H screw of the transmission is only used for the highest gear, and the L screw is only effective for the lowest gear.

1st Step: We need to install the dial and empty the gear, i.e. the first gear (the highest speed gear), and loosen one circle after the tightening screw of the transmission line is tightened.


Step 2: loosen the three screws (limit screw, H screw and L screw) on the transmission, and pay attention to loosen them. Do not let you remove them (anticlockwise is loose, clockwise is tight). If the chain is installed, it is considered that there is no problem. There is no need to check it.


Chain length: in case of single disc system with Shimano and SRAM 11 speed, the chain length is more than 4 links around the biggest chain ring and the biggest cog on the cassette. If it's SRAM's 12 speed hard groupset, you should pay attention to the fact that the full-suspension bikes only use 2 links more and that hardtail bikes is 4 links more. The speed change characteristics of SRAM hardtail and full-suspension are shown in the figure:

Step 3: For a derailleur without a gear cable installed, the derailleur guide wheel should be in the same line with the highest speed gear. If you find that it is not in the gear, you should adjust the H screw. Tightening the H screw will make the derailleur move closer to the wheel, and loosening the H screw will make the derailleur move towards the frame. As for whether or not to install the

chain, I personally think that it should not be removed after it has been installed. If it is not installed, it is recommended to align the derailleur before installing the chain.


Step 4: When the chain is installed, we install the cable(wireless riders can omit this step). Shimano's gear cable is very easy to install, but some of the gear couplers are installed through the pulley, and there is a slot baffle underneath. Be sure to pay attention to that if you wear the wrong gear, the gear change will never be accurate. The gear cable is generally tight, not too tight. The cable should be tightened through the barrell at the shifter.

Step 5: After installing the chain and the chain line is within the above figures, we can start to set up gear changes. Remember do not test ride the bike before completing the next steps. If the bike is adjusted to a low gear, it should be able to shift a gear successfully at the first time. If it is not successful, it indicates that the cable is tight or too loose. Then change the gear, and at each downshift, pay attention to the position of the guide wheel. If you find that the guide wheel is too close to the cassette cog, then tighten the tension screw immediately to keep the guide wheel away from the cog’s teeth. What happens if the tension is not adjusted? The answer is that the teeth of the next low gear will scratch your guide wheel on the derailleur, which may cause damage to the guide plate.


Step 6: Then shift to the next lowest gear and prepare to adjust to the new gear. We must pay attention to the possibility of two unexpected situations: the first is that it is hard to change the speed and it is hard to press the finger. The reason for this is that your L limit screw is a little tight, or there is a small probability that the gear line is a little tight. The second case is that the gear change works too well. The chain will fall between the spokes and the cassette. Adjust the L screw to solve the problem. Tightening it will make the chain move more toward the highest gear cog and effectively avoid the chain dropping. But you should also pay attention to that the cog and the chain are in a straight line. If you screw it, you will lose the lowest gear.

Step 7: Don't touch the lowest gear. Observe the distance between the guide wheel and the gear plate of the lowest gear. Use SRAM's tool to measure the distance and stick it on the guide wheel to see if the pattern on it can coincide with or basically coincide with the cog’s teeth. If the deviation is big, it indicates that the tension is not quite there, and it needs to be adjusted by tightening the tension screw. What if Shimano or no measuring board? The general distance is 1.8 cm, close to the thickness of your thumb. After doing this, you can continue to downshift through the cassette.


Step 8: Complete a full upshift and full downshift a couple of times to see how smooth it is. If there is loud noise on the smallest cog of the cassette, it shows that the adjustment of H limit is not accurate enough. You can try to loosen half a turn or tighten half a turn. Pay attention to the position with the least noise. If you fine tune the H screw in this case, you must remember to use the barrell to adjust the most corresponding position in the shifter. Generally, one turn will work.

  • Oct 23, 2020
  • Category: Articles
  • Comments: 0
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