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Why Are My Bike Gears Not Changing? Full Instruction on How to Adjust Bike Gears

how to adjust shimano rear derailleur

Every cyclist sooner or later encounters the problem of poor gear shifting on a bicycle and asks a question: why are my bike gears not changing correctly? There can be several reasons for this – damaged cables or dirty outer casing, stretched chain, poorly tuned front or rear derailleurs.

Many beginners entrust this procedure of adjusting bike gears to an experienced mechanic. It’s the right approach. But over time, you realize that you need to learn how to fix gears on a bike yourself. This article provides specific steps that even novice cyclists can follow to adjust the speeds on their bikes.

Rear Derailleur Adjustment

how to fix gears on bike

​​The first place to start is an external inspection of the gearset with the derailleur. Make sure that the shift cable is securely fastened, that it is intact, that the top and bottom derailleur rollers are clean and free of wear. And also do not forget to check the smoothness of the foot, which in the operation of the bike can be deformed in the fall. If all the above conditions are met, you can safely move on to the bike chain adjustment.

It is necessary to set the chain to the minimum rear sprocket, accordingly turning the bike to the maximum rear speed. To make the adjustment, both the front and rear shifters have two adjustment screws on their bodies, designated by the letters H and L (High and Low, respectively). Here comes the question of how to fit lower gears on my crankset? Since the chain was set to maximum rear gear at the beginning of the adjustment, it is the H screw, which is responsible for the high-speed adjustment, that will be needed to make the adjustment. Turn it clockwise or counterclockwise to get the derailleur foot in such a position that both its rollers are strictly in line with the smallest rear sprocket.

why are my bike gears not changing

Now you know how to install a rear derailleur on the small sprocket. After that, it is necessary to turn on the minimum reverse gear, with the chain on the largest sprocket at the back. And with another screw, which is designated by the letter L, make an identical adjustment until the rollers are aligned with the large sprocket.

Sometimes after the rear derailleur has been properly and thoroughly set up, there is a problem where the shifting is poor in high or low gears. This is due to either a tight or loose shifting cable. To solve the problem, you have to put the chain on the biggest sprocket in the rear and the biggest sprocket in the front. In this position, the rear derailleur’s foot is tensioned as much as possible.

You should achieve a distance of about 5 mm from the top roller to the sprocket teeth with the adjustment screw. This is the distance at which the smoothest and most accurate gear shifting occurs. This instruction fully answers the question of how to adjust Shimano rear derailleur, as all derailleurs have similar construction.

How to Adjust Front Derailleur on a Mountain Bike?

Before adjusting the front derailleur, first, make sure that it is correctly positioned on the bike frame. Make sure that when the biggest front sprocket is engaged, its teeth are a little away from the derailleur frame, and the same distance from it. In doing so, they should by no means touch the frame or, on the contrary, be far away from it.

bike chain adjustment

You should start the adjustment by setting the chain to the minimum front sprocket and maximum rear sprocket. Next, you must unscrew the bolt that secures the cable to the derailleur housing. After this, it will take its natural position and you can proceed directly to the adjustment.

Turning the screw-marked L (Low) in different directions, you need to set the gap between the chain and the derailleur frame in the region of 1-2 mm. This is the distance that will give you a perfect shift and also prevent the chain from rubbing against the frame while you are riding. After that, you should fasten the shift cable with a little tension, first making sure that it fits into the necessary groove in the clamping area.

Having set the chain to the maximum front chainring and the minimum rear chainring, use the adjustment screw marked H to make a similar adjustment until you find the minimum clearance between the chain on the large front chainring and the derailleur frame.

By learning as quickly as possible both types of speed adjustments on your bicycle, you will protect yourself from unpleasant surprises that may occur while riding, being able to make the necessary adjustments at any time with a minimum of time and effort.

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