Gears and Shifters

Destroy my bike, you may ask? Yes, if your chain falls off of the top cog on the rear cluster, and you don't have a plastic guard in place, the chain will jam between the rear cluster and the spokes. This usually results in broken spokes, broken chain, and sometimes a bent rear axle when the whole lot jams solid. So take this article as information only, as many gear systems differ in how they are adjusted.

In the last article, Gearing Down, I mentioned the term chain suck. This refers to the front chainrings and when changing down to the smallest cog, the chain comes off of the cogs. Depending on the design of your bike, the chain usually lands on the part of the frame called the bottom bracket. You then usually have to stop and put the chain back on thus getting oily fingers. On one of my bikes, I can get the chain back on by shifting up to the largest cog and pedalling slowly, which pulls the chain back on, thus keeping my fingers clean. You may find that with some bikes, the chain comes off and jams in between the bottom bracket and the chain rings. This can sometimes break the chain.

As mentioned in the Gearing Down article, I fitted a device to stop this happening, which is pictured below. It can also be reduced in a way, by adjusting the stops on the front derailleur. These stops limit the range that the front derailleur moves, so if it is moving further out than the largest cog, naturally the chain will come off. I have not written anything in this article about adjusting this, because they all vary in how they are adjusted, but you can see the screws in the extreme left of the third photograph on this page.

Typical anti chain suck preventer.

This device is fitted on the seat downtube, slightly above, but level with the smallest cog on the front chainrings. Then if the chain falls off, it hits this device and normally falls back onto the small cog. In the picture below the red arrow points to where it will mount. In the picture, you cannot see the smallest cog or the device. The reason that I haven't fitted the device, is because it was designed for a 34.9 mm diameter downtube, and my bike has a smaller diameter downtube. The downtube sizes vary, but the common ones are 34.9 mm, 32 mm and 29 mm.

View of the front chain rings. The red arrow shows where the anti chainsuck device will fit. It will fit on the seat downtube where you can see a part of a bright green sticker.

Some bikes come with a device already fitted by the manufacturer. A lot of mountain bikes have them fitted as standard. The picture below shows one fitted to a mountain bike.

Close up view showing chain rings and plate to stop the chain coming off.

As I mentioned above at the start of this article, the chain can also come off of the rear gear cogs. If it jams between the spokes and the gear cluster, the results can be devastating. Most bikes are fitted with a plastic guard, that fits between the cluster and the spokes to prevent it happening. You can see it in the next image. It is marked as A.

View showing plastic guard to stop the chain from getting jammed in the spokes.

The above photograph is a view showing the rear gear cluster and plastic guard to stop the chain from getting jammed in the spokes. In case you were wondering what some of the other things are, here is the explanation:

• A - Plastic guard to stop chain from jamming in the spokes if it falls off of the top cog;
• B - Thumbscrew adjuster for changing the tension on the gear cable. Used to adjust the indexing;
• C - Rear Derailleur limit stop adjusting screws; and
• D - Mounting point for a BOB YAK rear trailer.

In the above picture, you may notice that there is not much gap between the smallest cog and the frame. This has the natural effect of stopping the chain from coming completely off on the smaller end of the cluster. On some bikes this may not be the case and the chain has a tendancy to jam here as well.

Before we can look at what minor adjustments, can be made, we really need to look at the different types of shifters that are available. There are two designs of shifters, friction and indexed. Friction shifters are my preference, and were used for years on older bikes. Because of the difficulty some people had when riding a bike with all these gears, indexed shifters were invented. A click on the shifter and the bike changed gear. Newer shifters have a an indicator, which shows 1 to 8 for an eight speed rear cluster. When it shows one, it's usually on the largest cog. Moving the shifter to 3 for instance changes the rear cog down to the third cog.

Of the indexed shifters, there are many designs, both with and without indicators. You can see some photos and comments on both friction and indexed shifters on this page.

There are some minor adjustments that can be made to the derailleurs for all type of shifters. The first adjustment that can be made is the limit stops. This is controlled by the small screws on the rear derailleur shown in the above image as C. The image above of the front derailleur, shows the two screws at the left of the image. One screw controls the limit in one direction, and the other screw controls the other direction. It is marked on some derailleurs, and others it is not. The way to tell is to move the derailler to an extreme outer gear, and have a look at the end of the screws. The one screw whose end is touching is most likely the screw that adjusts the limit stop in that direction.

For friction shifters, there are no further adjustments required. Indexed shifters require further adjustment to keep the indexed shifter in line with the cogs on the rear cluster, and the chainrings on the front. Cable tension is the major adjustment required to keep everything working properly. It differs on each type of bike, and shifter style. Some shifters even have small thumb adjusters at the point where the cable exits the gear shifter. This makes it handy to adjust the tension whilst riding.

I will deal firstly with the front derailleur, as most systems are the same. Where the cable exits the gear shifter for the front derailleur, there will be an adjustment thumb screw. Winding it out puts more tension on the cable, and winding it in reduces the tension. If your chain is rubbing, you can adjust the tension whilst riding. By turning it, the rubbing noise will either get worse (wrong way) or eventually disappear. I would not recommend playing with this unless you know what you are doing.

The reason for this, is that due to the extreme angles that the chain can run at when using the extreme range in the gears it is natural for the chain to rub on the front derailleur. Manufacturers have designed another system to account for this. On some shifters, for instance the brifter style, moving the lever a half click to the next gear, nudges the front derailleur a bit which stops the rubbing noise. Likewise with some twist grip shifters, they can nudge the front derailleur. You will really need to check the manual for your bike to determine whether you have this system.

There is another adjuster on some bikes that is mounted to the downtube which allows for a small adjustment whilst riding. There is a small bump on the adjuster that sits in a groove, and by rotating the adjuster so that the bump is out of the groove, this applies extra tension to the cable. This is shown in the image below. Other styles actually have a threaded system.

View of downtube cable tension adjuster.

Most rear derailleur systems have their cable tension adjustment thumbscrew mounted to the rear derailleur where the cable enters the mechanism. This is indicated in the above rear cluster image as B. Having the adjuster here makes it hard to adjust whilst riding.

This adjuster operates like the other adjusters. By moving it one way, it adds tension, and the other way lessens the tension. One word of warning here. Most rear derailleurs operate on the smallest cog when there is no tension, which means that if the cable snaps, the derailleur moves to the smallest cog, which is also the hardest gear. I have comes across some derailleurs which move in the opposite direction.

My own trick for adjusting the rear derailleur is to put it in the relevant gear to place the chain on the second smallest cog on the rear, and the middle cog on the front. I then raise the bike so that the rear wheel is off of the ground. By turning the pedals and moving the cable tension adjuster one way the chain will eventually start to make a noise like it is going to change gear. I make a note of this and then go in the opposite direction noting the amount of turns required until the chain makes the same noise.

I then divide the number of turns by two and back the thumbscrew off by this amount which should place the rear derailleur halfway between the "noisy" points. I then go and change gears into every gear. This is where you will need experience, and you also need to know which sort of rear derailleur you have. If it's untensioned does it move to the small cog or the large one?

If the gears are noisy and/or sluggish moving up or down the rear cluster indicates some minor adjustment is still required to the tension. This is where you need to know the derailleur type, and have experience in doing this. If you are not sure then DO NOT ATTEMPT this adjustment. Take it to your bike shop and have them show you which way it needs to go if the gear changing is sluggish or noisy in a particular direction.

New cables will stretch after initial use, or sometimes the indexing is so far out, that the cable will need to be released and everything started from scratch. This can involve a lot of adjustment, which I will not go into in this article. Because of the extra adjustment required for indexed shifters, my preference is for friction shifters whilst touring, as they don't require adjustment.