Make It Go: Transmission
The wheels carry you across the ground; the brakes stop you; the controls keeps you in command and the frameset holds the whole process together (while providing a nice place to sit). But what about the power, where does the thrust and the force that gives you movement come from? The simple answer is: the rider, through the transmission.
Other components of the bike can seem obvious, as they are often large in size and obvious in appearance, but the parts that make up the transmission of a bike are much less well known. This is mainly due to the fact that there are many of them, and they are often very small, or even hidden, which can give the illusion of a vastly complicated mechanism, but in reality, when each part is broken down and its job identified, understanding the transmission can be quite straight forward.
To summarise, the collective job of the parts of the transmission is to most efficiently transfer the rider’s effort (rotating the legs and pushing the pedals) to the rotation of a wheel, which in turn creates movement of the whole ‘cycle.
As with many components of the bike, the transmission can be the limiting factor when the bike is to be used for a specific purpose. You can pair up the lightest bike, with the fittest rider, but if the transmission is not correctly chosen or set up this combination will be no quicker than an off-the-rack machine used for cycling to the allotment with a basket full of plants and string.
Transmission types can vary hugely depending on the type of riding for which the bike is intended. Many parts are relatively universal, but it is often the case that the more specialist any specific part becomes for one discipline of riding, the less versatile it will be for others. For example, the transmission from a BMX wouldn’t get you up a mountain with any ease, in the same way a road racing bike transmission would last about five seconds before being smashed to pieces on a BMX bike: each type of bike requires a different set of components, for slightly different jobs.
In the sections below, the key components that make up the transmission of a bicycle are identified and described. One key consideration when reading through the parts list is that not only do different style bikes use different parts, many bikes actually may not have a lot of the components.
Somewhere To Sit: The Frame
Rolling: The Wheels
Control Your Speed: The Brakes
Make It Go: Transmission
Tools & Accessories
The pedals are an obvious part of the transmission, and all bikes have them. Anyone who has ridden or even laid eyes upon a bike will easily be able to identify the pedals. In simple terms, the pedals are at the end of each (left and right) crank arm. Each pedal provides a contact point for the rider’s foot, and this provides the platform for pressure to be applied to rotate the cranks.
The design of the pedal can vary hugely depending on the desired characteristics. For example, a trial bike pedal will need to be very grippy, with a large surface area to maximise the responsiveness and feedback while increasing control through the rider’s feet. In contrast, a road racing pedal may simply act as a fixing link between the rider’s shoe and the bike itself.
The key design characteristics of a pedal depend on a number of factors, such as:
Strength – As with any part of a bike, different types of riding and different types of riders put different forces through the pedal. A town bike, or road bike will theoretically only have to deal with the force of the rider’s mass, and the force generated from the legs – this means that the pedal can be fairly minimal in size and basic in structure as the forces are not only fairly small, but also linear and gradual.
In contrast, when the bike is used for jumping down flights of stairs or dropping off the edge of canyons, the forces on the pedals are clearly very different. It is the difference between bouncing up and down on the spot on one foot, and jumping from the top of a house onto the same foot – not only is the force much greater, but it is also much more abrupt and non-linear.
This results in pedal designs for more extreme riding generally being much larger, with bigger box sections and a more solid construction.
Weight – For some riders, weight is a key consideration when choosing any part, and pedals are no different. Different materials are used to keep weight low while maintaining strength, such as titanium, magnesium, aluminium and carbon fibre. However ,these specialist materials can be expensive, and often there is no hiding the fact that real strength and versatility comes with a weight penalty.
Aerodynamics – Generally only a concern with racing, where with some designs the frontal surface area of the pedal is reduced as much as possible to allow less air resistance.
Compatibility – Many pedals are only designed for regular footwear; many are designed only for clip-in shoes. These are not universal systems, but pedals are available with each system on either side so the rider can use the same pedals for popping to the shops in shoes as going on a road ride with clip-ins.
Surface area – The surface area of the pedal varies with the type of rider. With a city bike, the rider spends most of the time sat on the saddle while pedaling, so the surface area is not as important as to a BMX rider, where very little time is spent not being stood up on the pedals.
All of these factors are relevant to all pedal designs, however the main determinant in pedal design is whether the pedal is intended for clip-in shoes or not.
The advantages of using a clip-in set up are vast in terms of cycling efficiency, however, it is not always a practical choice depending on what the bike will be used for. Once clipped in, the rider is able to transmit force with both legs throughout the whole 360-degree rotation of the crank arm as the foot is essentially fixed to the bike, so you can pull up on the legs as well as push down. For road riding, and times when the rider is spending a long time on the saddle, this system is advisable as it can make use of a large range of muscle groups, which aids the blood flow around the body, as well as of course increasing the potential amount of force during each rotation.
There are two main types of clip-in mechanism; MTB and Road. The fundamentals remain the same, while MTB is more commonly used for everything bar road racing.
The downside to the system is that it can be tricky to master clipping in and out, and mistakes can often result in injury. Also, often the shoes cannot be used for walking around, which can mean having to carry another pair of shoes, which isn’t ideal. Finally, in most instances, it means that the bike can only be ridden with clip in shoes, so lending it to a mate or riding into town can become impractical.
Chainset is generally a term used to collectively refer to the chainring(s) and the crank arms, and in some cases the crank axle too. Layout and design vary hugely, but the most obvious difference is the chain ring configuration.
Chainsets commonly have one, two or three chainrings depending on the type of bike. All singlespeed bikes, most older town bikes, trials bikes, dirt jumping bikes, downhill bikes, BMXs and track bikes all have only one front chainring. Two chainrings are found on most modern or vintage road bikes. Three rings are mostly found on mountain bikes, hybrid bikes, touring bikes and mid-period road bikes.
The size of the chainring dictates the gear ratio. The larger the front ring, the harder the pedal is to push, or, at a constant speed, the cranks will be rotating at a slower rate than that of a smaller front chainring. Having a selection of front chainrings to choose from widens the possible gear ratios available, which is particularly handy when cycling up-hill. Generally speaking, if the cycling terrain is flat, a single ring is enough of a range for the rider.
The three common configurations for road racing bikes are:
Compact – This makes use of two chainrings (usually with 50-34 teeth), and has been designed to be used in conjunction with a smaller rear cassette (see section: ‘Cassettes and Freewheel’). With slightly smaller chainrings than a double, this tends to be more suitable for recreational and amateur road riders, or when riding a very hilly road stage
Double – This also makes use of two chainrings but these are generally larger than the compact (for example, 53-39 teeth). This configuration is fine on flat roads or for time trials, but due to the vast demands and climbing of road racing, they are only generally used by the elite rider (due to their greater average speed).
Triple – Once the most popular set up, triples are these days rarely found on road racing bikes. This is due to the fact that the bikes have become much lighter, and the rear cassettes have evolved into providing a larger potential range, so a big range on the front is not always needed. Triples use chainring sizes such as 52-40-32.
On many types of bikes, there will only be one chainring attached to the crank arms, this is fine for riding around town or on flat ground as a large range in ratio is not necessary. Setting up the bike to shift between front chainrings can be tedious, and can often go wrong, and with a variety of rings comes a greater number of moving parts. It is these parts that many riders choose to throw in the bin, in pursuit of a cleaner, more simple and robust system, which, ultimately is much less prone to damage, or failure.
The chainring(s) on a bike does not only vary in size, but also in design and material. The mounting pattern on the chainring also varies a lot depending on the manufacture and the application, but out of the huge variety in bolt pattern, only cranks with the same bolt pattern as the chainring are compatible (the same principle applies in the way that not all wheels bolt onto the hubs of all cars – the stud pattern varies). This chainring bolt pattern is known as the BCD – so be sure to match these measurements on the cranks and chainring(s). Chainrings are also available in a number of materials, depending on the use. Generally the most popular is an aluminium type, but titanium, steel and carbon chainrings are also available depending on whether you are after strength, value or lightness.
The other element of a chainset is the crank arms or ‘cranks’ for short (often called crankset, pedal arms, or chain arms). This provides the main structure of the whole chainset, and is the part to which the pedals, chainring(s) and axle all attach. Cranks again vary widely depending on the application. The BCD varies depending on the production brand or style of riding. Some chainrings attach with five bolts, and some attach with one (and others with any number in between).
The length of the cranks is also an important factor to consider when building a bike. A longer crank arm means that the pedal travels a longer distance around the bottom bracket, but because it is a longer arm this means there is more leverage to turn the chainring. In general terms, shorter riders with shorter legs should theoretically use shorter length crank arms, whereas taller riders with longer legs should use longer cranks – but bear in mind this difference is trivial compared with that of a frame, or a wheel size; we are only talking about 15mm.
The construction of the cranks determines their use. For example, top end road bike cranks are carbon fiber, due to the advantages in the weight and stiffness department (they are light and rigid). Most commonly, cranks today are made from aluminium (either machined or forged), as it is relatively stiff and lightweight. Steel cranks are also the choice of many riders, in BMX riding for example, you need a crank that can endure large forces from all angles, as well as large physical impacts on the arms themselves. Hollow steel cranks tend to cope with huge amounts of abuse, while remaining stiff when pedaled; the downside is that they are very chunky and heavy.
One common addition to a chainset is a chaingaurd. This can take many different forms in terms of size and shape, but the concept is to have a protective ring or barrier over the edge of the chainring so that if the chainring makes contact with something, it will not slip off or become damaged. This is only necessary in some isolated cases, generally in off road mountain biking, BMX or trials, where tricky large obstacles such as logs, handrails or rocks have to be negotiated.
Repair & maintenance tutorials:
Any bike that utilises gears or variable ratios will need to have a control for the rider to change between them. Similar to a gear stick on a car, a gear shifter, located on the handlebars, is essentially responsible for changing between gears when the rider feels the need.
There are many different types of shifters, depending on the type of gears used on the bike. However, one consistent feature is the use of cables. Up until very recently, nearly all gear shifters made use of a metal cable to transfer the instruction from the control (shifter) to the gears via the tensioning and de-tensioning of the cable.
In the same way that a brake cable is attached to a brake lever (see ‘Cables’ section for cable transfer explanation), both the inner and outer gear cable are attached to the shifter. However the design only allows for the inner cable to be tensioned while the outer cable remains stationary, creating a pulling motion, which is then transferred to the derailleurs and into mechanical movement.
Before the varying designs of shifters are identified, it would be best to discuss the specifics of cable tensioning and ‘indexing’.
The position of the mech/derailleur is dictated by the shifter, so it is important for the shifter to be ‘indexed’ (configured spacing), as with the cogs/chainrings. Fitting an 11-speed cassette onto a bike with an 8-speed shifter would not work, in the same way as fitting a 10-speed shifter onto a 9-speed cassette would also not work. This is because both the spacing between the cogs, the number of cogs, differs between set ups.
However, some older gear systems have shifters that are ‘un-indexed’, meaning that the motion is gradual and undefined, and it is down to the rider to locate the exact gears by feel. This can be a positive thing, as it means that a wide range of mechs and cogs/chainrings can be used due to the undefined gearing Overall, though, the advantages of using an indexed set up are huge, mainly due to the simplicity and ease of the rider being able to click effortlessly between gears, with little need to concentrate on the exact movement, which in turn allows the focus to remain on the road (or the burning legs).
Bicycle gear configurations vary so widely that there is no real default or standard. However, most road bikes today will have a double shifter on the left hand side (for two front chainrings) and a 10 or 11-speed shifter on the right (for a 10- or 11-speed rear cassette). Left hand shifters are usually 2 or 3 speed, and right hand shifters are 6-11 speeds. Of course if the bike has only a hub gear, or a rear derailleur, there will only be one shifter.
The shifters themselves have come in many different shapes, sizes and designs over the years, their fundamental job remains the same. The most common shifter types are:
Downtube shifter – This is the simplest in design and appearance. It is basically a lever, which is attached to the sloping downtube of a bike via a metal band that is tightened around the frame, or by being bolted onto a ‘lug’, which holds the shifter in place. These shifters are usually found on older bikes with gears, generally racing bikes from around the 1980’s era. Only one lever indicates a rear derailleur, while two levers means the bike also has variable front gearing (more than one front chainring). Often downtube shifters are not indexed, and so rely on adjustment through friction rather than clicking into each gear.
Thumb shifter – This style of shifter is the evolved form of the downtube shifter and features the same mechanism, but instead is located on the handlebar (through the development of outer cable housing), or, much less commonly, on the stem. Again, some rely on friction to locate the gears, while others are indexed. This was a huge advance in gear shifting, as it meant that the gears could be accessed by the rider on the handlebar without having to laboriously reach down to the downtube and move attention from the road. During races, gearing was a clear indicator of what the rider’s next move was to be, so if all the riders can obviously see their competition reaching down to shift gear, then it was likely a sprint or breakaway was imminent; having shifters on the handlebar made it much easier to be discreet with gear-shifting and tactics.
Trigger shifter – Whereas other shifters simply have a lever to adjust the cable tension, trigger shifters make use of a ratchet style system whereby a lever is moved to change tension, but then, just like a ratchet it returns to its original position. Because of this, the need for two controls becomes apparent, as one control or ‘trigger’ is in charge of shifting up, a second trigger is used for shifting down. These shifters are also located on the handlebar, and usually one trigger is located below the bar (for the thumb) and the other is located above the bar (for the index finger). This makes shifting effortless and very easy to do without moving the hand at all; often trigger shifters are packaged in the same unit as a brake lever, further increasing their ergonomic design. Trigger shifters are always indexed, as it is the shifter movement between the clicks that provide the distance for the mech to move.
Integrated shifter –As with the trigger shifter, integrated shifters are packaged in the same unit as the brake lever. The most common types are the Shimano STI, the Campagnolo Ergo and the SRAM Double Tap. These are mostly used in applications for drop handlebar bikes, so are found on road bikes, cyclo-cross bikes and touring bikes. Adopting the same ratchet system as trigger shifters, integrated shifters have one control for shifting up and a separate control for shifting down.
Grip shift – As the name suggests, these types of shifters are located at the end of the handlebar grip. They work by having a rotating section of grip, to which a cable is connected (to the housing of the shifter), so as the rider twists the grip, the cable is tensioned or de-tensioned. Many grip shift systems are indexed between gears, but those that aren’t again require the rider to carefully feel how much to twist the grip to reach the desired gear.
There are many other types of much more specialist shifter set-ups, some innovative and relatively practical, and others far less efficient, but the this list certainly covers the kit options on the vast majority of production bikes today and in the past.
4. Cassettes and freewheels
As the front end of the transmission often has multiple chainrings to give a wider a range of gear ratios, the rear end of the system very often has a group (or ‘bank’) of cogs. Each cog is a slightly different size, thus representing a different gear ratio.
The number of cogs the bike has depends on what transmission gear it is running. Generally, in the past the typical number of rear cogs was between 5 and 8. But today, most geared bikes have 9, 10 or 11.
As well as the number of cogs, another important variable is the size of the cogs. Obviously with more cogs comes the potential for a wider range of sizes, and therefore a greater range of gear ratios. However, in road riding, the bank of cogs isn’t usually designed to give a huge range of ratio, but more to give a better small-range selection. The purpose of this is to give the rider more opportunity to fine-tune the gear ratio to exact the RPM (or, leg rotation speed) needed to remain most efficient.
On the rear of a road bike it is not uncommon to find 11 different cogs, but only increasing in size by one tooth at a time, to give the smallest and finest possible adjustment between gears. This would usually mean an 11-22-tooth sized cassette.
With other riding disciplines, it is more important to have a larger range of cogs. Often in a bank of ten cogs, the cog sizes may jump by two or three teeth per cog, or sometimes even more. This would usually mean an 11-33-tooth range. This increased range is needed when steep hills are being climbed (by someone without the leg power of an elite rider), or when the bike is heavier than a racing bike, such as in mountain biking.
This requirement for a larger range of gears is especially apparent in cycle touring. It is common for riders who are touring to carry over 30kg of extra kit on the bike, in the form of panniers, tents and consumables. With this weight increase, a lower gearing will naturally be needed, in the same way a fully laden car will need to drop down to first gear on a steep assent so as not to stall. The best way for riders to have this larger range of gears is to use a bank of cogs with a greater number between the largest and the smallest (as not to loose the capability to pedal at a higher speed on the downhill sections).
As you would expect, the spacing between the cogs also varies largely, depending on the number of them. A bank of ten cogs will have a minimal amount of space between the cogs, compared to that of a bank of eight, which will be more spread out. As well as the number of cogs, the spacing will vary very slightly depending on the manufacturer. For example, things can get complicated when trying to mix Campagnolo derailleurs with a SRAM bank of cogs.
These banks of cogs come in two formats: a cassette which slides onto the splines of a ‘freehub’, or a freewheel (or ‘block’), which screws onto the thread of a hubshell. For a full explanation of these, and a breakdown of the mechanics behind, them please refer to the section ‘Rolling the wheels’, and ‘The drive system’.
Generally speaking, cassettes tend to indicate a much higher quality wheel, with all good quality bikes adopting this system. The freewheel system tends to be found on older style road bikes, lower quality bikes or singlespeed specific bikes.
5. Rear derailleurs
As the rear derailleur is in charge of locating the chain upon different cogs, the front derailleur (or ‘mech’) is responsible for locating the chain on the range of front chainrings.
The first thing to note is that lots of bikes do not have a front mech, as having only a single front ring is popular in many riding applications.
As explained above (the rear mech section), the front mech adopts the same process of transferring cable tension into physical movement around a fixed pivot point. In the same way the rear mech is located directly before the rear cogs in the chain flow, the front mech is located directly before the front chainrings. This essentially means that as the pedals and chainset are turning, the chain is being moved into place by either of the mechanisms.
As the front mech is located above the front chainrings of the bike, the fixing point is directly onto the vertical seat tube. There are two main types of fitment for the mech:
Braze on: This is when the front mechanism attaches to a small runner, which is attached to the frame itself. The benefits are that it looks cleaner than the band type (see below), it is lighter, and it also it reduces the amount of parts needed to repair or replace the mechanism. The negatives are that if the fitment is damaged then it means the frame is damaged, and it does not allow as much adjustment as the band type (which can get tricky if chainring sizes are changed).
Band on: This is when the front mechanism is attached to a hinged band, which is then clamped onto the frame of the bike. The advantages are that this allows much more adjustment as the band can be clamped at any height on the frame, and also means the angle of the mech can be adjusted more, and it also means that if the mech is damaged or snaps off the band then the whole unit can be replaced together. The downsides include the fact that it doesn’t look as clean as a braze on, it is heavier, and the whole unit has to be replaced if any part is damaged; with all the available band/frame tube sizes (of which there are many) it can become tricky to track down the exact part.
As with the rear mechanisms, if a front mechanism is for a road bike with a double chainring then the mech tends to be smaller with a slimmer cage. With mountain bike front mechs tend to be larger with a stouter cage, so as to be able to move a wet chain quickly between three different chainrings in muddy and sandy conditions.
The chain of the bike is a vital component. The design allows a huge amount of longitudinal force to be transferred through it without breaking. When the rider’s legs turn the front chainring via the cranks, the chain provides a direct link to the rear cog, thus driving the wheel. The chain has to be very flexible vertically, so it can flow tightly between the jockey wheels in the rear mech and then back over the chainring, but it cannot withstand horizontal force due to the restrictive nature of the design.
Rather than being made up of malleable or bendy parts as it may appear, a chain is actually made up of many extremely strong and solid parts – pins, plates and bushes.
The pins provide the structure to the chain (picture the rungs of a ladder), while passing through the other components like a skewer. The bushes (or ‘rollers’) are found in the very centre of the chain and sit between the plates and over the top of the pins like a sleeve, their purpose is to assist the chain location onto the cog, as well as reducing friction by rotating upon contact. The plates sit on the very outside edges of the chain and sandwich all the other components while providing the strong link between the pins.
Over time, as gearing systems and drivetrains develop and become more advanced, so have chains. Traditionally all chains were a standard width and any chain could be used on any bike. However, today, due to the rear cogs becoming thinner and closer together to allow more gears to be packed into the same space, the chains have had to follow suit and become much narrower in their outer width. As the groupsets evolve (apart from singlespeed types), the chains are becoming thinner and thinner: below is a list of common outer chain measurements with their application.
6 speed - 7.8 mm
7 speed - 7.3 mm
8 speed - 7.1 mm
9 speed - 6.6 to 6.8 mm
10 speed - 6.2 mm
10 speed (Narrow) - 5.88 mm
11 speed - 5.5 mm
As the chains become narrower through thinner outer plates, unsurprisingly they also become much more susceptible to damage through sideways forces, such as bending, twisting or even overzealous gear shifting. Manufacturers are therefore constantly finding ways to produce the strongest, lightest and thinnest chains.
As well as the variation in outer plate thickness, the actual width of the whole link, and specifically the inner roller, changes too. Although many gauges of chain are available, the most common are 1/8” and 3/32”. 1/8” chains are generally used for all single speed applications, such as BMX bikes, bikes with hub gears, track style bikes, fixed gear bikes and, of course, singlespeed bikes. 3/32” width chains are used for derailleur-geared applications, such as those listed above.
Due to the relentless demand for lighter-weight parts, many manufacturers have resorted to a range of methods to keep chain weight as low as possible. For example, exotic materials, such as titanium, are often used as a lighter alternative. Another more recent method is to use hollow components, such as plates and pins. Although the weight saving is only fractional, it is enough to encourage many riders to reach for their wallets without hesitation.
Repair & maintenance tutorials:
7. The ‘Groupset’
The term groupset (or ‘gruppo’, to which it is referred by some) is a term used by manufactures to refer to a collective group of components on a bike.
The exact definition of groupset has changed slightly over the years; when the phrase was first coined it mainly referred to the transmission components, but now it often refers to the braking and bearing systems too, and often even more.
Today a typical groupset consists of:
Gear levers (Often integrated with brake levers)
Rear bank of cogs (in the form of a cassette or freewheel)
And some groupsets also include:
There is an argument that one reason groupsets were named were as a marketing ploy to encourage riders to be brand-loyal and match the same range of parts together. Buying components from the same groupset is a guaranteed way to ensure compatibility, however, in practice many parts are cross-compatible, not only between ranges but also between manufacturers.
Different manufacturers have a number of groupsets, and overall there are more than a hundred to choose from, but it is crucial not only to identify the name of the groupset (for example: Campagnolo Record, SRAM Red or Shimano Dura-Ace), but also the year of the model: very often a couple of production years between the same groupset can result in complete incompatibility.
8. Electronic shifting
Within the last couple of years, electronic shifting has been increasing in availability, and today any rider can stump up the cash for a fully digital groupset.
As with traditional gearing systems, the information is relayed from the shifter to the derailleur through a traditional metal cable. It is this mechanical force that causes the mech to respond.
However, it is now possible to have a fully electronic system, whereby the shifter is only connected to the mech via a thin piece of wire, which passes electronic signals between the two. The shifters have effectively become a remote control passing information to the mechanisms, which have tiny electronic motors. When these motors are activated, they move the mech into pre-programmed positions, according to which gear is desired.
These electronic groupsets are currently offered by Shimano (‘Di2’ range) and Campagnolo (‘EPS’ range). The kits consist of: a central computer with display (the brains), the shifters (the remotes), the mechs, the wiring looms and the battery packs.
The advantages include:
Once set up, they are maintenance-free and do not require adjustment .
Cable stretch is eliminated, as is coming out of fine-tune through wear.
They minimise the use of bulky metal cables, which has aesthetic benefits, reduced weight, and aerodynamic advantages as the electronic wires are much thinner and easily tucked into tubing.
Mud, grit and water do not have affect the cables
The brain automatically fine-tunes trim and both mech positions together, rather than them requiring separate adjustment.
Shifting is smoother
The system is programmed to avoid any situations that may cause damage (for example, trying to shift up 10 gears at once).
The disadvantages include:
The initial purchase is costly
The batteries have to be recharged often
Electronic systems are heavier than cable systems (currently, at least)
Parts and servicing are more expensive
New potential for electronic malfunction
More complicated to set up
Cannot repair without complex parts and tools
Components are not fully maintainable, so will have to be sent back to manufacturer rather than repaired
Battery packs and mechs are much bulkier than the traditional alternative
In reality this is still a relatively new system, which has not had a huge amount of time to develop a high degree of efficiency. However, as the systems advance and become more versatile, electronic systems may well be something to consider.
Currently the only application in which electronic set ups are used tends to be on full blown racing bikes, so although the advantages maybe redeemable during a stage of Le Tour De France on a bike that is meticulously maintained at every possible opportunity, it may not be a practical addition to a bike used all year round on the roads.
9. Internal gear systems
As previously explained, many bikes utilise a potential range of varying gears, however, it is not only the combination of an external derailleur and a group of cogs that can provide this. Internal gear systems come in various shapes, sizes, qualities and specifications, but the principle behind is the same: to provide a range of gears to the rider via a single enclosed mechanism. This basically means that the chain will only travel one set path; from the chainring at the crank to the cog at the rear wheel, the gearing will be adjusted internally inside a gearbox-like sealed unit.
The most common location of these mechanisms is at the rear end of the transmission, enclosed within a wheel hub. However, internal gear systems can also be found inside a ‘gearbox’, which is located at the front end of the transmission, usually inside the frame of the bike, where the crank arm is attached.
The range of internal hub gears is large, also reflected in the prices. The most common types are: Sturmey Archer, Sachs, Torpedo, SRAM i, Shimano Nexus, Shimano Alfine and Rohloff.
Traditional hub gears are common on older town bikes in Europe, and usually come in the form of Sturmey Archer in the UK, and Torpedo or Sachs on the Continent. Although when properly serviced and set up these early models have the potential to perform adequately, due to the long and arduous process of adjusting and re-adjusting the cable tension, and the poorly designed shifters, they are uncommon and tend to be avoided where possible. Due to the design of the cable attaching to the rear hub, rather than an external derailleur, every time the rear wheel has to be taken out or moved, the gearing system has to be set up again, which can become a real chore.
More modern systems prove to be much more versatile and reliable, due to the improved technology and research that has gone into perfecting the designs. These modern equivalents include Shimano’s Alfine and Nexus systems, as well as Rohloff’s Speedhub. Often used by riders opting for a maintenance free system, the advantage of having all the gearing sealed away from the elements can be large, especially in day-to-day riding or touring where derailleurs can be knocked out of alignment, and grit from the road can be picked up in any of the moving parts of a conventional gear system.
Generally, the older systems tend to have between 3 and 5 gear ratios, whereas the modern systems will usually have 8 or 11, with some top-of-the-range systems housing 14 different ratios; a hub gear system can be a robust alternative to a traditional groupset. However, arguably the largest drawback to complex internal gearing systems is the weight. Hub gears are often heavy, with some systems weighing over 2kg, although it is important to bear in mind that they do eliminate the need for the derailleurs, chainrings and cogs.
Gearboxes are also available in some ultra-specialist applications. Although possibly the biggest drawback to these systems is the fact that it cannot be fitted onto any frame, but has to actually be fully integrated into the frame manufacturing process as it is built into the bottom bracket area. This means that if you want such a gearbox system, you have to buy a specialist frame from a specialist manufacturer (of which there are very few). The gearbox system boasts all the positives of a hub gear, but with the added strength and reliability of being located in a bigger space. Honda, Sunrace and Pinion are, and have been, the biggest producers of these internal gearboxes, with up to 16 gears available.
In summary, each of these systems incorporates a complicated array of cogs, splines, drivers gears and rings, enclosed within a shell, and controlled through an external shifter. There will be more detailed analyses and servicing tips popping up at a later date for those who are interested.
10. Fixed wheel transmission
All the above gear systems allow the rider to ‘freewheel’ at will. Freewheeling basically refers to the situation when the bike is rolling forward and not being pedaled, for example when rolling down a hill, or when stopping pedaling before braking. However, for some bikes freewheeling is not possible due to their fixed wheel set up.
By eliminating a freewheel, freehub or internal gearbox system, a fixed wheel transmission is extremely simple – consisting of only a chain, a front chainring, and a rear cog. It is this simplicity and minimalism that attracts so many people to a fixed wheel system.
Traditionally fixed wheel set-ups were used on the track, because the riding was about short sprints and dynamic bursts of power, during which freewheeling is certainly not on the menu.
However, in recent times, ‘fixies’ as they are known, have been increasing in popularity in the urban environment. Fifteen years ago the trend was having the most gears, ten years ago it was about riding around with the most suspension travel, and five years ago it was the rise of the disc brake; one of the big current trends is that of the fixed gear.
Besides the obvious aesthetic reasons for adopting a fixed wheel system, there are also many practical reasons. Firstly, it is believed that it increases feedback of the road to the rider, as the whole pedal stroke is relayed back through the feet. This system also enables the rider to brake by applying counter-pressure through the pedals, which can again be advantageous in strengthening legs as it significantly increases the load.
Many riders of fixed gear bikes feel the need to remove the brakes, as it is believed that a fixed rear wheel alone can provide sufficient braking power. However, any inexperienced rider with a half decent brake set-up will easily out-stop even the most experienced rider on a fixie. As well as the actual braking force that is needed, safe braking has a lot to do with how quickly and effortlessly the brakes can be applied. Especially in emergency-stop situations, brakeless fixed gear bikes can prove very dangerous.
Due to the simplified set up on a fixed gear, it is very light, which is often why it appeals to riders. By getting rid of chainrings, freewheels, derailleurs, shifters, cables, and other ratchet systems, a fixed wheel bike can be built to an exceptionally lightweight standard.