Fixing the height is a subtle adjustment, based on a difference of millimeters. You will need to be precise. Having your bike on a repair stand can make this work easier. You can use a penny to try and estimate if you have adjusted to the right height, as a penny is 1. 5 millimetres (0. 059 in) thick. [3] X Research source
This should be done while your bike is on its lowest gear so that there is not too much tension on the inner wire. [5] X Research source
It is easier to see what adjustments you have to make while you are looking down at the derailleur from above. Envision an alignment between the center of the cage and the centerline of the bike frame.
Once you have the angle set in the proper place, you can tighten the positioning clamp. [8] X Research source
You can try spinning the crank to make sure the chain is not catching. [10] X Research source The inner screw of the derailleur is usually the one closer to the frame that controls the lower limit. This screw is sometimes marked as “L. “[11] X Research source
Setting this limit will make sure that the chain does not over-shift and fall out again. [13] X Research source The outer or second screw is the one that controls how far the derailleur shifts outwardly. This screw is sometimes marked as “H. “[14] X Research source
If you can push the derailleur out, it can mean your cable tension is not right. Turn the barrel adjuster to fix this.
Shimano bicycles come with a half-click on the lever so that you can make these adjustments easily.
If you feel like you can´t fix it yourself, you can ask a bike mechanic for help.
