You can also turn the bike upside down, resting it on the seat and handlebars. If you do, however, know that you will have to reverse the direction you spin things in the following instructions. You can also hang the nose of your saddle in the notch of a tree or low hanging joist.
The rear derailleur is the more complex machine, consisting of the derailleur, an arm, and 1-2 smaller gears that the chain is threaded through. A cable pulls this arm back and forth, allowing the chain to switch gears. The front derailleur is clamped onto your bike’s frame, and consists of a spring and two “derailleur plates,” or small metal walls that force the chain to stay on only one gear at a time.
While testing one derailleur, put the other one in the middle gear. For example, if I am testing the back derailleur and I have 3 gears in the front, leave the front derailleur in the middle ring the entire time. This prevents the chain from stretching.
Always work slowly, adjusting by a quarter-turn at a time at most. Think of it as of turning the adjuster the way you want the chain to move. Rotate towards the bike to make the chain move towards the bike. Don’t loosen the adjuster too far[3] X Research source or it may detach from the derailleur. If you need to make a large adjustment, thread the adjust into derailleur, shift into the smallest gear, loosen the pinch bolt, and pull the cable by hand.
Think of this as turning the adjuster the way you want the chain to move. Rotate away from the bike to make the chain move away from the bike.
You want the chain to flow smoothly from gear to gear every time you shift.
You can also turn the bike upside down, resting it on the seat and handlebars. If you do, however, know that you will have to reverse all of the following instructions.
Shift the derailleur you are not working on to a gear somewhere in the middle.
Advanced Note: You’ll notice that, if you pedal the bike, the chain will slide down to the lowest ring without your help. That is because derailleurs work by tightening the cable to hold the chain in place. Similarly, you can shift your bike manually by pulling the cable.
The screw on the left, often labeled with an “H,” which limits how high the chain can go and affects the outer gears. The screw on right, often labeled with an “L,” limits how low the chain can go and affects the inner gears.
Consult with your bike’s manual if the H and L screws aren’t clearly labeled.
Tighten the low limit screw if you the chain goes too far. This will keep the derailleur from moving too much to the left. Loosen the low limit screw if you cannot shift into every gear. This will allow the derailleur to move farther in.
Shoot for 2-3 millimeters of space on each side of the chain. [5] X Research source
Often, you can see an indent in the cable indicating where it was bolted before.
