This is a quick how-to tune your derailers. This will work for all derailers but if you have indexed shifters you’re going to need 1 or 2 more steps to get it to click perfectly into each gear. For this demonstration i’ve used a bike with friction shifters, its the simplest type and gets the point accross.
If you are not sure what parts of a derailer are what go here first: Derailers
Before Tuning anything you must first check that the derailers are aligned!!! if they aren't, you can tune all day and it’ll still run like crap.
For the front make sure that the derailer is mounted so that the cage is parallel with the chainring. Some people have angles that they like to use on this, but for starters leaving it parallel is easiest. While you’re messing with the mounting, make sure that the derailer cage is high enough from the big chainring to not rub it as it spins, but low enough so that when the chain is on the smaller chainring, it doesn't drag on the tail end of the derailer cage.
For the rear derailer stand in the back of the bike like so and make sure that whole pulley and chain system lines up as so. Any twisting and angle in this will cause some issues. A lot of times the derailer hanger is bent from falling or just having something leaning on it and this causes the whole derailer and pulley system to angle to a side. If its a steel bike, you can carefully bend it back. I will have a short write-up on this later as it is a common problem with old bikes. As for now, use your imagination, just don't break it!
On to tuning.
First thing: put your shifters in their starting positions as far forward as possible. At this position, there there should be least tension in the cables.
If you didn’t know already. The left shifter is for the front derailer, the right shifter is for the rear. We will tune the front first.
There are two set screws (adjustment screws) for high and low positions. For most bikes, if your shifter is all the way forward, your chain should be in the smaller chainring (low gear).
Now with the chain on the inner smaller chainring, adjust the low adjustment screw so that the derailer cage doesn't rub the chain on either side. When the set screw is further down, the derailer should move towards the bigger chainring. Get it in the middle, again neither rubbing the chain on either side of the cage. give the crank a couple of turns. it shouldnt make any rubbing sounds. If you’re too far towards the outter right, the chain will want to jump to that ring, adjust accordingly. If its too far inside, the chain will pop out of the ring, again, adjust accordingly.
Now you adjust the position of the cage using the high gear set screw. If you haven’t figured it out yet, the high gear set screw limits how far out you can pull the derailer with your shifter lever. This works the same as in the low gear position but that is pulled by the derailer’s spring when you relax the cable. So in high gear, adjust as you would in low gear. if its too far inward, make sure your shifter is pulled all the way down. If its still too far in and rubbing the derailer cage on the outside, uncrew the set screw.
If you pull your shifter all the way down while turning the crank and the derailer is set too far forward, your chain will jump out of the ring like this. In this case, screw the high gear set screw in and it will alleviate this problem. Get the adjustment so that the cage doesn't rub the chain on either side.
Once that’s done, shift it back and forth from high gear to low gear while turning the crank to make sure everything works well and it doesn't rub on either gear.
For the rear derailer, the steps are exactly the same. The high gear set screw limits how far the derailer’s internal spring can pull the chain towards the outside. The low gear set screw limits how far your shifter can pull the derailer inside, towards the bigger gears. to save time and pictures I’m going to list steps for doing this. You’ll find them similar to what’s been done above.
1. Set the right shifter (rear derailer) all the way forward so that there is least tension in the cable.
2. Turn the crank several times. make sure the chain is on the smallest gear in the rear. If the derailer is pulling too far to the outside, turning the set screw clockwise (more in) should push the derailer inwards.
3. Turn the crank, check that the chain doesn't make rubbing noises or want to jump onto the bigger gear or off of the cassette altogether. Adjust accordingly so that the whole pulley and chain system lines up when viewed from the rear.
4. When the highest gear is done, pull the shifter all the way down as you turn the crank to shift into low gear.
5. Repeat as before, if its too far in towards the center of the wheel, adjust accordingly with set screw.
6. After you’ve set the rear, the front might be off a little bit so test it our again and adjust accordingly. Sometimes when you shift from the biggest gear in the rear to the smallest, it causes the chain to rub the front derailer. This is normal, its just a geometry problem. the chain is pulled one side to the other so expect that. You can adjust your derailer a little further either side to avoid this rub.
7. If you have indexed shifters, you will have to play with the tension of the cable to get the shifts crisp. There are several tension adjusters for the rear derailer. Try ‘em out for yourself first. I’ll have a writeup for it later!
8. Make sure that your cables are tensioned well. If it has major slack when you pull the shifters all the way forward, it wont shift as quickly as you want. Sometimes it wont even get as much range as it needs if this is the case.