The transmission is a set of components and gears which transforms your pedalling into the movement of the rear wheel. It is a sort of brain of the bicycle, requiring the utmost care and attention in the selection and maintenance of all its parts: the two sprocket wheels, the chain that connects them, the gearing and the derailleurs.
In some cases, these are complicated tasks, which require an expert's intervention, but for other ordinary tasks, DIY works fine, provided that you are well advised. Here, with the help of Stefano Casiraghi, the mechanic from the Colpack Ballan team, we explain how to intervene on the transmission of your bicycle.
Choice of components
“A transmission is designed to work like clockwork, all together and completely in synch: if I change just a single component, whether this is a simple gasket or a cable in the gears, the performance of the entire transmission drops," explains Stefano, who thus recommends the use of original spare parts alone in the event of replacement as these are designed specifically for a particular transmission, and guarantee a longer life and improved performance. In any case, there is a compatibility chart on the manufacturer's website that shows which transmissions a particular part works with.
The first step is to check the alignment of the bottom bracket, the small support connecting the gearing to the frame. “You need to see that the gearing is perfectly perpendicular to the sprocket assembly". There are instruments you can use to measure this, but "this adjustment - explains Casiraghi - can also be done using the naked eye. It is vital because if the gearing operates while askew, in other words not perpendicular to the sprockets (and therefore parallel to the wheel, editor's note), it ends up wearing the components prematurely and above all it may not work at all”. So, a strange noise from the gearing could be a warning that the bottom bracket is not aligned properly.
Another standard job involving the rear derailleur is the adjustment of the two screws found on the body of the derailleur, which are referred to as the limit stops. These are simply mechanical stops, whose task is physically to stop the gearing on the last sprockets, both at the top and at the bottom, so that the gearing cannot go any further, causing the chain to fall or in the worst cases causing the gearing itself to break.
There is also another adjustment, a knob, which regulates the tension of the cable in the gears: turn it anti-clockwise to tighten the cable, clockwise to loosen it. “Bearing in mind that you need to pull the cable to raise the gears, and that you need to slacken it to lower it onto the longest ratio, if the gears have difficulty rising, you need to loosen the adjustment, so that as it lengthens it makes the cable tauter. If on the other hand the gears have difficulty lowering onto the longest ratio, simply tighten this adjustment appropriately, in order to shorten it and make the cable a little slacker”.
You need to be a true expert to check the condition of your chain. Luckily, there is a simple and cheap tool, the gauge, which determines whether the chain needs to be replaced, something which is nevertheless necessary after 4-5,000 kilometres.
The gauge usually has two indicators, which determine the wear condition, 0.75 and 1. When the chain is extended, the 0.75 pin is inserted into the link: if it does not penetrate fully, this means that the chain is not extended, and therefore is still in good condition. If on the other hand it penetrates fully, the chain needs to be replaced. If indicator 1 penetrates, this means the chain may have already damaged the sprockets.
There are also other types of instruments designed to be inserted in the links and, once a dedicated wheel has been turned, they indicate the state of wear with a numerical scale or using various colours.
Replacing the chain
To fit a new chain you must first purchase one that is specifically designed for the number of gear ratios of the bicycle, compatible with the transmission (even better if it is original). Once you have removed the old chain with the chain rivet extractor, lay it out on a flat surface next to the new one to measure the correct length of the new chain. Next, remove the excess links from the new chain (again using the chain rivet extractor, which is very easy to use) and start fitting the new chain on.
It is best to start by placing it around the smallest sprocket of the rear derailleur and then around the front chainwheel. When the chain has been placed correctly around the entire gear system, join the two ends of the chain together using the chain rivet extractor and hey presto.
These are also very popular on amateur bicycles. Each unit has its own adjustment method and also its own diagnostics system. These are not very cheap instruments: “They cost about 2-300 Euros, but once you have purchased them, you can check the wear of all the components from a computer.”
You can also update the firmware and make all the adjustments you want on the interface: “You can even associate each command with a specific function. Let's take for example a Paralympic athlete who needs to have both commands on the left, because he doesn't have a right arm: with an electronic unit diagnostics system, a setting can be made for the derailleur to be controlled by a button on the left”.