You need to know what all the parts of your transmission are called before you can start fixing them; it makes going into bike shops and asking for replacement components a whole lot easier. The appearance of each mechanism may vary from bike to bike, but don’t worry too much about the detail for different components: all do the same jobs regardless of what they look like. All the parts here are dealt with in more detail later in this chapter.
“A new set of cables and casing is the cheapest and most effective way to make your shifting much crisper”
- Shifters: It’s all very well having a million gears to choose from, but you need to be able to decide which one to be in, without taking your hands off the bars. Shifters put the controls where you need them – directly under your hands. The shifter unit might be integrated with the brake-levers, making a slightly lighter combination than two separates. However, there are a couple of advantages to having separate brake-levers and gear shifters as you can adjust them independently and also replace them independently if they wear out or break.
- Cables and casing: This is often neglected, but is much easier to replace than you’d imagine. A new set of cables and casing is the cheapest and most effective way to make your shifting much crisper. It makes you feel much faster, but also helps to make your transmission last as long as possible. Fresh cables means that your chain will run neatly over your sprockets and chainrings, rather than rubbing constantly and wearing itself out. The inner cable is the metal wire that runs all the way from the shifter to the derailleur. The outer casing is the plastic-covered tubing (usually black) that the cable runs through in short sections. The casing protects the cable and guides it around bends and curves.
- Chainset: Your chainset is the block of gear wheels on the right-hand side of your bike, along with the pedal arm that it connects to. The individual gear wheels are called chainrings and your bike will have one, two or three of them. Road bikes normally have two: hybrids and mountain bikes three. Hub gear bikes will have a single chainring at the front. Like the rest of your transmission, chainrings will wear over time and aren’t cheap to replace, but can be made to last much longer if kept clean.
- Cassette: This is the cluster of sprockets in the middle of your back wheel. Derailleur geared bikes may have five, six, seven, eight, nine or ten sprockets packed into the space between the frame and the back wheel. If the sprockets are all similar sizes, getting slightly larger as they get nearer the back wheel, your gear ratios will be very close together so that each is only slightly harder or easier than the next. Hybrids and mountain bikes tend to be fitted with cassettes that cover a wider range with larger steps between each gear.
- Rear derailleur: This cunning piece of kit shifts the chain gently across your sprockets when prompted by the right-hand shifter on your handlebars, via your gear cables. These cable movements are quite small and precise, so the quality of your shifting is dependent on the condition of your cables and the fine adjustment of the cable tension. The rear derailleur also performs a handy second function – the lower of the two jockey wheels keeps the chain tensioned, so that you can use a chain long enough to go around the big sprockets, without it dragging on the ground when you shift into small sprockets.
- Front derailleur: Front derailleurs are much simpler than rear derailleurs since they just perform a single function: as you operate the left-hand gear shifter, the derailleur pushes the chain from side to side across your chainset. Its simplicity as a mechanism means that it rarely needs attention and is usually quite straightforward to service, or replace. The trickiest part is usually ordering the correct replacement – there are a handful of different sizes, depending on your frame size and cable routing.
Source : BIKE MAINTENANCE TIPS, TRICKS & TECHNIQUES