How to build a bike - Part 4: Derailleurs and chain

Other parts:
introduction
Headset
Bottom bracket and crankset
Derailleurs and chain
Steer and cables
Make the brakes and shifters work
Finishing up!

Yet another part that might seem intimidating initially, but will turn out to be as simple as making yourself a cup of tea... Actually it might be a good idea to make yourself one before starting. Tea can work amazingly motivating, especially when knowing that by having made one, you've already had the most difficult part.

I already had some experience with deraillieurs before starting with this project. The deraillieur of my old bike already survived multiple (dis)assemble sessions, so I was sure I was able to handle this.

Ok, first take the rear derailleur. You should attach it to the frame using a hex-key. Only thing to notice here is that the 'block' is positioned correctly. The derailleur must be able to turn counter clockwise when shifting to bigger gears. When doing so, a spring in the derailleur is keeping the chain tightened. One side of the spring should be resting against the frame. The picture should explain this a bit... Do not worry yet about the adjustment of the derailleur, we'll take care of that later.

Next, you need to install your cogset (set of sprockets at the rear wheel) to the wheel. Almost all new bikes have a cassette system. For installation you'll need a special tool. This tool actually might be worth owning yourself. I already owned one, since I needed it before on my old bike (I needed it because I quickly learned that a 21T sprocket is not quite big enough with a 42T in front when trying to get up a +20% hill). Shimano and SRAM use the same type of tool, while Campagnolo has a different type.

The cassette will fit in only one way to the freehub on the wheel. I bought a ready made wheelset including the hub. I've no experience building wheels myself. Anyway, first grease the freehub, then put on the cassette and simply tighten it with the tool. Take a look at the pictures.

Now install the front derailleur. Most frames will have a special part included to which you can attach the front derailleur. Mine had not, so I had to buy a ring which attaches to the seat tube.

The height of the front derailleur should be such that there is a few mm space between the biggest sprocket and the derailleur. Furthermore it's important to align the front derailleur exactly with the line of the sprockets as well. See the pictures again for a visual explanation.

Align with the chain:Align with the big sprocket:

Now put the rear wheel in the frame and install the chain. The length of the chain needs to be adjusted correctly. You will need a chain tool for this. Again this might be a good tool to own, since you might need it again when you run into the not so pleasant situation of breaking your chain....

The SRAM manual showed a good way of determining the right size for the chain. Put the chain on the biggest sprockets, both at the front and back, but do not put it through the rear derailleur. The correct length of the chain is equivalent to the length corresponding to this distance, plus two additional chains (link). Now cut the chain to the right length, while having it installed through the front and rear derailleur.

Now you need to set the upper and lower boundaries for your derailleurs. Probably it's best to simply check the manual for your derailleur for how to do it exactly. I'll explain shortly how it worked for my derailleur.

Adjusting the rear derailleur
First set the lower boundary, which corresponds to the smallest sprocket. Align the derailleur with this smallest sprocket by turning the adjustment bolt. Next push the derailleur by hand towards the biggest sprocket. Now turn the high limit adjustment bolt in such a way that you can't push the deraillieur further then this last sprocket. This adjustment is very important, because if it can be pushed further, you might push it in your spokes, which will lead to a lot of damage.

Next adjust the height of the deraillieur such that the highest sprocket always has a few mm's space under the cassette. In my case no adjustment was needed.

Adjusting the front derailleur
The front derailleur is similar to the rear derailleur. It might be easier to adjust this one after you've connected the shifters to the rear derailleur. This is because you need to shift the rear derailleur while adjusting the front derailleur.

First set the lower boundary by adjusting the appropriate bolt. The lower boundary corresponds to the small sprocket. Put the rear derailleur on the largest sprocket and now adjust the front derailleur such that it does not touch the chain anymore.

To adjust the high boundary, put the rear derailleur on the smallest sprocket. Now push the front derailleur by hand to the large sprocket and adjust the boundary such that is does not touch the chain anymore.

Since you already took care of the height adjustment when installing the front derailleur, there's no need to adjust that anymore.

That's it! All derailleurs are adjusted within the boundaries. The shifters will take care of shifting the deraileurs with the appropriate amount to shift one gear higher or lower. Now it's time to tell as many people as possible that you're able to properly install and adjust derailleurs. It might sound impressive at a birthday party....