How a Front Derailleur Works
The bike transmission consists of the following components: Cassette. This is a part of the transmission located on the wheel and attached to it with the help of a hub. It consists of one gear or two or three gears of different sizes. They are also called “stars”.
Another part of the transmission is the “system” (also called chain drive). In addition to cassettes (these are stars or gears), it includes carriages on which moving parts rotate. connecting rods and chains. The latter link all the elements into one system. The chains are designed in such a way that they transmit the force for wheel spin with an efficiency of up to 98%.
Bicycle chains can be of different widths and have a greater or lesser distance between the nodes (backs), that is, between those places around which the sections of the chain turn during its movement and which fasten the links.
The switch of speeds (gears) is rear. It performs not only the function of shifting gears, but also regulates the chain tension (maintains it during shifting). Gear change is carried out by transferring the chain from one sprocket to another.
Front derailleur. Another speed switch (but no tension control function). The front derailleur is only available on bicycles with two or more sprockets in front. The device changes several parameters: cadence, angular speed, and also the torque of the bicycle wheel.
Shifters (shifters). These are special levers with the help of which (cables are also involved) the cyclist regulates the gear shifting. They are usually mounted on the handlebars, to the right and left of it. The cables are in a kind of protective devices. in shirts. rigid tubes that are attached directly to the frame of a large.
Gears are needed by the cyclist to regulate the forces applied to pedal on different parts of the terrain: plain, uphill, downhill. If a bicycle (for example, an older model with a small and large wheel, called a penny-farthing) has a fixed gear (one and only), then one pedaling will rotate the wheel also one revolution.
Those bicycles that have a derailleur have the ability to achieve optimal cadence with an adequate amount of effort. For mountain climbing, large chainrings (gears) at the rear are used in combination with a small chainring. For flat terrain without wind, you can switch to a smaller rear gear.
Planetary hubs with automatic controls. Manufacturers overview
An example of a hub with an automatic derailleur would be a new one from SRAM. Sram Automatix is a new two-speed hub with integrated gear selector. It changes the speeds in the hub by analyzing the cadence of movement and other mechanical and physiological factors. The bike drivetrain is designed in such a way that it provides high power at low rpm, this makes it very easy to climb the bike.
Cycling enthusiasts will note changes in speed management such as:
- no shifter;
- there is no rear derailleur;
- no cable.
The system itself controls the shifts, depending on the speed of the cyclist and on the cadence (the intensity of the pedaling). The Sram Automatix bushing does not require any maintenance. It is mounted in such a way that the person driving the bike could forget about the needles and all kinds of settings.
The transmission chain is shifted at a speed of 12, 14 or 18 km / h. This condition is discussed in advance with the bike manufacturer. It also includes a foot brake system. Sram Automatix bushing is compatible with sprockets with 15 to 21 teeth and 36 or 28 mesh contours.
The creators recommend this device for city driving, focusing on convenience, simplicity and reliability. Sram automatics will be ideal for people who do not want to take additional actions and distract from driving.
Types of bike transmissions
A bike drivetrain can be:
- Straight, when the drive wheel and pedals are attached directly, without the use of a chain system. This transmission is found on penny-farthing, monocycles (with one wheel), tricycles for children.
- Cogwheel, which uses gears with teeth.
- Shaft, which uses shafts to transmit torque.
- Belt. Belts are used here, which, unlike chains, do not require lubrication.
- Hydraulic. A hydraulic system is used, not a mechanical one.
- In the form of a planetary hub, consisting of a large number of parts and resembling a car gearbox.
- Combined, which is a hybrid of two types of transmissions for a bicycle at once: external and internal (planetary).
The planetary hub (internal gearshift mechanism) is mainly used on conventional bicycles that are not designed for special or unusual loads. It consists of the following details:
Bicycle planetary hub device
- A sun gear located in the center and attached to the axle of the bicycle wheel.
- Planetary gears or satellites revolving around the first (the parts are named so because their position resembles the planets and the sun).
- An element called a carrier. It locks the previous elements together.
- Epicycle or epicyclic gear. It surrounds all the satellites and the central sun gear. It is she who rotates from the torsion of the pedals by the cyclist.
- Spline drive, holding together and transmitting torque from the wheel sprocket to the planetary hub mechanism.
Construction and work
The principle of gear shifting is, in fact, very simple. Both devices are frames that, controlled by a shifter (shift knob) through a drive cable, shift their position relative to the stars on the system or rear hub, moving the bicycle chain with them.
At first glance, the trivial task is complicated by many factors:
- heavy load on the transmission. modern front and rear derailleurs place high demands on materials;
- positioning accuracy. small errors in the position of the frame (and, accordingly, the chain) can lead to rapid damage to the chain and stars by incorrect switching;
- the subtlety of the mechanism. in a modern device there are more than two dozen elements, each of which must be almost ideally positioned and work under load.
Modern models are delicate mechanisms that require serious development and no less serious maintenance.
Let’s consider these devices in more detail. It should not be forgotten that both the rear and the front derailleur have their own restrictions on the types of attachment and the size of the allowed stars in the transmission. Rear frames are also limited in overall length.
The capacitance of the switch is the value calculated as the sum of the ranges of the star sets, i.e. formula for calculation = (Teeth on the large sprocket at the front. Teeth on the small sprocket at the front) (Teeth on the large sprocket at the back. Teeth on the small sprocket at the back). After some simple calculations, a value appears in the range from 10 to 50, which can already be used when searching for the desired model.
Physically, this difference is in the length of the frame located between the two rollers of the rear derailleur, and the possibility of its deviation becomes decisive in the delta of the sizes of the stars. From below, this indicator is strictly limited to a tolerance of 10 units.
Shimano and SRAM drives
In the world of switches, there are two de facto monopolists. At least in the area of standards. There are, of course, unique items from Specialized and other VIP brands, but most bikes are equipped with accessories according to the standards of these two manufacturers.
How a Rear Derailleur Works
Shimano is promoting its own types of mounts. First of all, it is practically recognized for the universal standard E-Type with mounting on a carriage assembly. SRAM, in turn, offers several types of frame mounts.
The main difference and the main reason for incompatibility when replacing devices from Shimano and SRAM is the “gear ratio” of the cable from the shifter mounted on the handlebar. In the case of SRAM, a one-position shift means a 2.5mm cable movement, while on Shimano models this shift is 5mm of cable movement. Thus, these kinds of devices cannot be interchangeable.
By the way, there is still no consensus on which standard is more effective. Some point out that Shimano‘s travel is sharper, while others say that SRAM is more reliable and easier to use. Which opinions are more “truthful”, only practice decides.
Service and customization
Derailleurs are some of the most subtle elements of a bike to adjust. Minimal tolerances and the fatal effect of misalignment on the chain and sprockets. all of this dramatically increases the importance of correct tuning.
With the ride now standardized, cyclists have a little less set-up to worry about. Previously, it was also necessary to work with the tension of the cable. Now the main thing is to set the correct position of the extreme points of the switch.
This is done using bolts H (High, high position) and L (Low, low position). The chain is moved first to the largest chainring at the front and the smallest at the rear, and with constant observation, using the screw H, the bicycle derailleur is set so that the planes of the chainring, chain and derailleur frame become parallel. Then a similar adjustment is made for the other extreme stars using the bolt L.
There are many obstacles that can interfere with the simple setting of the switches, and which will require more serious intervention, which is already problematic to do it yourself:
- damage to any frame;
- discrepancy between the set of stars and the capacitance of the switch;
- damage to the frame or cock;
- cable drive mismatch.
It is best to avoid these issues before starting the setup.
Where did the switches come from? The idea to form a transmission that is easy to control was realized at the beginning of the twentieth century, but the system was not very convenient. there was an asterisk on each side of the rear wheel, and in order to “shift” the speed, it was necessary to literally transfer the chain from one sprocket to another.
Such a mechanism would have remained a standard (in practice, moreover, unused, since it was replaced by planetary models), if not for sports disciplines. In the 1950s, Italian Tullio Compagnolo invented and pioneered the modern rear derailleur.
What are the best gear shifters to use on a bike?
Most modern riders have two derailleurs per bike. Of course, they may not be there, and some walking models have only one, and it looks non-standard, since it is located inside the planetary hub. Nevertheless, everyone is familiar with switches in one way or another.
Bicycle front derailleur
The transition to the setting of this mechanism is possible only when the rear derailleur is set. This feature is important to take into account before starting work. The figure shows the switch (round, black).
Leave the chain on the middle sprocket of the front block and place it on the large sprocket in the rear block. If chain friction is observed, re-engage adjuster L. To adjust stop H, the chain moves to the largest sprocket at the front and smallest at the back. The adjuster will help to position the chain in the optimal position without friction and excessive tension on the chain. At the end of the work, be sure to check the quality of its implementation.
Why did the switch start to work poorly?
There can be many versions on this matter. One of the most common is the banal stretching of the cable and the sagging of the shirt. Occurs on new bicycles of any category after 200-300 km of run. Other options may be considered, or even variations of them:
- The cable is fluffed up or there are bumps on its surfaces in places of bends.
- The shirts are dirty. They are enough for a maximum of two cable changes. As a preventive measure, flushing the inner surfaces of WD-40 can be considered (splash and move the cable along the guide).
- Bent cock (part that holds the “cross-link” on the frame). Sometimes the traditional Shimano bike rear derailleur setting does not work. In this case, it is worth inspecting the holder for bending. The rooster is leveled with a special machine or on a frame. Care must be taken when performing an operation on an aluminum frame structure. the material is fragile.
- Backlash in the spreader. It is revealed very simply. it is enough to stand on the side of the bike, grab the place where the cable enters and move it away from you. On Shimano Tourney, Altus equipment groups, backlash is allowed. The rest should be absent. The presence of large displacements introduces fuzziness in the switching mechanics.
- It is not recommended to lubricate the cable, especially with viscous consistencies such as grease. the effect of light switching will disappear quickly, and the lubricant will attract dirt.
- It is undesirable to deliberately lengthen or shorten the shirts. there will be increased friction in the bending points.
Briefly about the main
The idea of setting the rear derailleur from the Shimano range is to achieve an immediate busting of the cassette chain by the chain at the command of the shifter. There may be several reasons for the incorrect operation of the mechanism, and not all of them are eliminated by adjustment. There can be only two versions of the poor functioning of the rear transmission, which can be eliminated by adjustment:
- The spreader has been in operation for a long time or has been replaced: adjust the border positions of the frame.
- The dereiler has an impressive resource reserve, but it went wrong. clean / replace the cable and shirts, adjust the cable tension by rotating the drum.
How the switches work
Using the handle and shifter, the cyclist activates the required speed. In a certain position of the handle, the cable is pulled. As a result of this tension, the frame is thrown onto larger sprockets; when the cable is loosened, it is not thrown onto small sprockets. As mentioned above, you can start setting up your bike from the rear derailleur. Procedure for adjusting the rear derailleur:
- select the second star in the front block, and the smallest in the rear one and set the switch chain on them;
- The bike’s rear derailleur system has two bolts that act as stops. One is abbreviated as H, and on the other. L. These two bolts are used to adjust the high and low gears on the sprockets. If during the adjustment process any extraneous sounds arise, you can get rid of them with the help of the latch;
- check the tension of the cable and if the tension does not correspond to the required one, use the regulator located on the shifter;
- Test the switching quality. If the switching occurs smoothly, no extraneous sounds are heard, then you did everything right.
The essence of the basic setup is to set the boundary positions of the switch. In this case, it is advisable to remove the chain. it will be more convenient that way. Standing behind the bike, we perform the following operations:
- Using the adjusting screw for the limitation of the highest gear (H), achieve the location of the transfer rollers and the smallest cassette sprocket in the same plane. There is one secret. if the device is not new and has backlash, the rollers are placed not in one line with the extreme star of the cassette, but literally by a hair’s breadth from the sleeve.
- Overcoming the spring force, move the derailer by hand to the extreme left position (closer to the bushing) and, turning the screw L, ensure the alignment of the plane of the rollers with the line of the largest sprocket. Again, if there was a difficult transfer to the rear sprocket with the most teeth, the switch should be shifted a few microns closer to the spokes.
- Put on the chain.
To understand the process of self-adjusting the speed switch, you need to know the definition of some specific terms, otherwise it will be difficult to understand the instructions.
- Speed switch (crossover). This is a transmission element that is specifically responsible for gear shifting. If there is a rear crossover, then it also acts as a support for the tension of the bicycle chain. The crossover (back and front) can be described as follows: it is a parallelogram mechanism equipped with a powerful return spring, on which the frame is fixed. The rear derailleur has two rollers inside the frame. if the level of cable tension increases, then the frame shifts the chain to large stars, and if this cable tension decreases, then the chain is shifted towards small stars with the help of the frame. The mechanism of the front derailleur works in the same way.
- Shifter. It is designed to switch speeds by changing the tension level of the cable. Most often, the shifter is located on the handlebars, but in some models of bicycles it can also be located on the lower tube of the frame triangle. Note:shifters and speed switches have a common connection on the steering wheel (this is provided by a cable) and are covered with a jacket.
- Cassette. This is the name of the rear transmission unit, which consists of stars of different sizes (of different diameters and with a different number of teeth) and is installed on the rear hub drum. If the bike is old, then a ratchet is used instead of a drum in the rear hub.
- Cock. It is a metal part that helps maintain the integrity of the frame and rear derailleur in the event that the vehicle has been hit. The rooster is always attached to the frame, and a cross-over is already attached to this metal part. When a blow occurs, it is this very cock that breaks, and the frame and the speed switch (crossover) remain intact.
- System. This is the name of the front transmission unit, which consists of stars of different diameters and with a different number of teeth. These stars are fastened to each other and the connecting rods with special hollow bolts on the connecting rods, but you need to know that there are no hollow bolts in cheap bicycles. the stars and connecting rods are riveted to each other.
To set up a Shimano front derailleur, you need the following set of tools: a screwdriver, a set of hex wrenches, and a pair of pliers. The main task here is to correctly set the speed device at the beginning of the setup.
When the device is set up correctly, the bike chain can only travel 1-2 mm from the chain toggling it. The frame moves both horizontally and vertically during gearshifts.
When adjusting the front derailleur, make sure that the frame is parallel to the chainrings. When the device is set to the largest sprocket (i.e. set to the highest speed), the distance between the ends of the sprocket teeth and the bottom of the frame should be about 3 mm. Shimano derailleur height and rotation are easy to adjust. just loosen the mounting bolt using the polyhedron. Adjust the position of the device, but do not tighten the bolt. you may need to move the device during the setup process. Now you can start setting up. Set the speed to the lowest. Unscrew the cable holder and release it. Then unscrew the cable tension grandmother until it stops and return it 1-2 turns back.
Now set the speed to maximum. You need to get the position of the device at which the gap between the chain and the part of the frame farthest from the frame will be minimal. This is done with the High screw. Rotate it, making sure that the device itself does not move.
Then test the speed control. To adjust the rear derailleur of the Shimano bike up and down, you can twist the grandmother, if the chain comes off the stars. turn the bolts: High. if with a large sprocket, Low. if with a small.
Correct installation of the front derailleur
You can only start the front derailleur setting after adjusting the rear derailleur. Installation is the initial step in adjusting the speed switch. It’s very important to do it right.
- before installing the switch, it is necessary to inspect the condition of the constituent parts and, if necessary, clean them from dirt and lubricate.
- The next step is to adjust the location of the front derailleur. On the frame, it should be located along the pipe under the saddle.
- Set the steering angle parallel to the drive sprocket on the front cassette of the transmission unit.
- Next, you need to adjust the gap between the underside of the derailleur frame and the upper mowing line of the teeth of the large gear. The gap should be minimal.
- Adjust the cable tension.
- Place the chain close to the inside of the frame.
It is also worth paying attention to setting up the chain. The bicycle chain is a very important element, with the help of which the impulse is transmitted from one chain to another and the adjustment process takes place. The technical condition of the circuit is of great importance for the operation of the entire system. If, for some reason, the bicycle chain stretches or deforms, this cannot but adversely affect the operation of the entire transmission unit. To prevent this from happening, the chain must be periodically removed and cleaned, and then set the correct position. There are lock and lockless models of bicycle chains. They differ in the way they are connected. To remove the locking chain, it is enough to find the link with the lock and disconnect it with a screwdriver. The lockless bicycle chain is disconnected using a squeeze. This tool helps to push the link axle out and make the connector. If it skews for some reason, this can adversely affect the gearshift process.
One of the best manufacturers of bicycle parts, including derailleurs, is the Japanese company Shimano, which has a proven track record of producing products in which Japanese quality is combined with budget and price. Shimano derailleurs are suitable for all types of bicycles. Shimano derailleurs are installed on both regular touring bicycles and mountain and track bikes with gearboxes up to 33 speeds.
Another recognized market leader is Sram. The products of this company are used on bicycles of the city bike category, as well as on sports bicycles. Sram products are of good quality and affordable price for cycling enthusiasts.
Every bicycle owner who prefers this type of transport to others is obliged to understand how to switch its speeds. It is believed that the more speeds a bike has, the better it is. But in fact, speed only allows you to improve the quality of maneuvering and squeeze the maximum out of the bike’s capabilities, so then everything depends on the dynamic efforts of the person riding the bike. Conventional bicycles have a simpler design compared to high-speed ones. With a bike like this, there is less hassle, but it also has fewer options. In the transmission unit of such bicycles there are only two stars: one large and one small. Multi-speed bikes, which have gained popularity in recent years, have two sets of sprockets in their transmission units: front and rear. Each cassette consists of stars of different sizes. To switch gears correctly, you need to remember a few basic rules:
- If your bike is not equipped with a planetary hub, you only need to switch gears on it while driving, otherwise there is a danger of damage to the bike.
- During gear shifting, it is not necessary to apply significant dynamic forces, in order to eliminate the danger of a burst of flowers, it is advisable to change gears sequentially, without making sharp jerks.