The mountain bike (often abbreviated “MTB” - or “terrain bicycle”, in Italian also referred to as “mountain climber” - derived from the first Cinelli model produced and launched in Italy) is a bicycle with a special structure that enables to move on unpaved environments, either uphill or downhill.
The mountain bike was born in California in the United States around the end of the sixties. At the beginning, the mountain bikes were nothing more than robust bikes which were modified to support the off-road impact and were probably used by hippy groups in search for uncontaminated areas. The first serious MTB development was done by Gary Fisher, Tom Ritchey and Joe Breeze who modified the geometry of the frame and made it lighter, they also introduced a specific gear shift. The phenomenon ‘mountain bike’ spread throughout the whole United States and later on, in the eighties, also in Europe. In Italy, when many people looked down on MTBs, the company Cinelli with good intuition launched the “terrain bikes” on the market. And from that year (1985) until the end of the century, the MTB sales increased to such a point that it exceeded two thirds of the market share. When developing the culture of the mountain bike together with its enthusiasts, values such as the love for nature and uncontaminated environments, but also strong emotions, played a fundamental role. Today, the mountain bikes are produced in numerous different versions and are also very popular in the city. They have little in common with the first models and have also suspended forks (or with whole structure suspension) as well as disk brakes.
CHARACTERISTICS OF A MOUNTAIN BIKE
FRAME: Frames for mountain bikes are characterized by a different geometry compared to standard bicycles, with a tendency to be more “compact” but with equal dimensions to lend better handling and higher resistance. In the course of the last years, the so called “sloping” geometry has become widespread; this means that the horizontal tube has a strong downward inclination and the seat tube is thus very short. The materials mainly used until a couple of years ago were steel chrome-molybdenum (less expensive but heavier), whereas today most of the frames are made out of aluminium. Steel is still employed for small productions or for customized models of high quality, where the special alloys and accurate manufacturing allow similar weights to aluminium frames, but are provided with an elasticity and robustness characterized by models made out of steel (for instance the new special steel Nivacrom models were able to reduce the weight from about 2700 to 1500 grams). For more cost intensive models, designed for cross-country competition, the frame is often made out of carbon fibres which have a slight weight advantage compared to the ones out of aluminium, and more rarely out of titanic. The use of the last material represents the best compromise between lightness, resistance to mechanical fatigue and to corrosion as well as structural elasticity; however, its use is limited due to the extremely high cost of the raw material.
GEAR SHIFT: The typical transmission of a mountain bike is composed by three front gear sprockets, (with a variable number of teeth usually comprising 22 to 28 for the first gear sprocket, 32 to 38 for the second and 42 to 48 for the third) and six-or-nine rear pinion gears (usually with a variable number of teeth with minimum 11 for the smallest chain ring, and a maximum of 34 for the biggest), with the possibility to develop an 18 to 27 transmission ratio to the wheel. The effective ratios count actually two less, as the so called “chain-crossing gears” (biggest gear sprocket with biggest pinion and the smallest gear sprocket with the smallest pinion) may lead to premature fatigue of the chain and gearing if used over long periods of time. The front derailleur of the mountain bike is usually characterized by the presence of a particular long lever in comparison to the one of racing bicycles, in order to allow particularly high amplitudes of the chain (including the chain-crossing which – as much as unadvisable – should be possible to perform when the gearing is well adjusted). The principle of the gear functioning is identical to the one of road bikes. The performance of transmission ratios expressed in metres can reach particularly low values with the MTB, up to around 1,3 metres for each axis turn of the central movement (with each “push thrust” with the pedal), when using a gear sprocket with 22 teeth, pinion 34 and a standard 26” wheel with a 26x 2.00 tyre (today the most common one). On the other hand, the longest ratios permit a slightly lower performance in comparison to a racing bicycle. Unlike racing bicycles, the main producers do not offer until today specific transmission units for mountain bikes which can support more than 9 pinions. The levers are situated on the handlebar (respectively on the right and left) and can be operated without taking hands off the handlebar, which turns out very useful when the terrain is bumpy. They come as lever (not often used), as push-buttons (the exerted pressure on a button makes the chain shift to the adjacent gear of the one currently in use) or as a little rotating handle, used similar to a motorbike accelerator. It should be mentioned that by now the control of the mountain bike gearing has become standard with almost all road bicycles, with the exception of racing bicycles.
PEDALS: Taloned so that the foot does not glide off. In order to facilitate the thrust on the pedals, toe clips can be installed, also specific for mountain bikes (laces are not necessary). Very popular are pedals with a quick connection, which is used with appropriate shoes, and which in contrast to road bike pedals can be used on both sides. This gives an additional possibility to hook to the pedal in case mud or earth blocks the pedal itself. These pedals are also used for cross-country. The pitch of the thread on which the pedals are screwed on, is standard for road and racing bicycles, so it is possible to mount any type of pedal.
WHEELS: With rims which have almost always the standard size of 26 inches, but their actual diameter is 559 mm, measured from the impact point of the pneumatic on the rim, corresponding to around Anglo-Saxon 22 inches. On the market, there are also so called “29 inches” wheels for mountain bikes, but less widespread, and which have the same rim diameter as the normal road bikes (622 mm). Rim, hub and spokes are built and assembled in an analogue way such as road bicycles, with the same materials (usually rims out of aluminum, hubs and spokes out of steel), in particular the thread axis of the front wheels is interchangeable with the one of racing and mountain bikes, and the internal construction of hubs does not present substantial differences apart from the dimensions and maybe a different arrangement of the spikes (and a disk brake, if designated). The slightly higher resistance to impact of the MTB wheels compared to racing bicycles is in principle due to the smaller diameter of the rim and to its larger section. Exceptions are bikes primarily designed for descents (“downhill” or “freeride”) which can have hubs with a thread axis similar to motor bikes and rims with triple walls.
TIRES: Grooved and with a wide width, in most cases variable between 1,9 and 2,3 inches, with air chamber or tubeless. The design of the tread pattern is sometimes adapted to a particular type of terrain, and sometimes it represents a compromise. In general, for muddy terrains, it is advisable to use knobs that are arranged with a large distance from each other that limit the accumulation of mud, whereas narrowly arranged knobs should be chosen for hard terrains. In any case, it is possible to assemble any kind of tire, including road bicycle tires with smooth even profile and very narrow section as long as the diameter is the correct one. There are numerous tires of different kind on the market. The air pressure depends on the employed tire; usually, a maximum pressure of 5 atm is not exceeded for tires with a large section and with an air chamber. It is quite common to let the air partially out of the tires before facing challenging descents, to better absorb the roughness of the terrain and, in case of slippery grounds, optimal adherence. The pressure in these cases can be reduced to about 2 atm (the tire easily gives way to the pressure of one single finger), depending on the weight of the cyclist.
HANDLEBAR: Very broad and straight or only slightly inclined to guarantee a better control over the bicycle on uneven terrain (the cyclist’s arms act on a bigger lever arm). Like the frame, the handlebar can be made out of aluminium, steel, light alloy or titanium. Special bar end extensions or “horns” can be added which are useful when climbing hills, especially in a standing position.
BRAKES: The most important characteristics of MTB brakes, in comparison to racing bicycles, is that they have to leave a wide space between the brakes arms and the wheel, in order to enable the mounting of tires with a wide section while still leaving a margin to avoid mud accumulations. This is the reason why ordinary arch brakes cannot be used. Until the end of the nineties, only cantilever brakes were employed, like it is the case with cross-country bicycles. And the so called V-brakes were almost exclusively used until a few years ago, whereas today they are mounted on only the most economic bikes; these rim brakes are characterized by having very long break arms to guarantee high braking power while exerting low pressure on the handlebar lever. Today, mountain bikes are fitted almost exclusively with disk brakes similar in their construction and functioning to the ones employed for motorbikes, with the difference that the more economic models are operated by a cable and not by a pressurized fluid. Disk brakes can only be installed on specifically designed tires, with a different positioning of spokes to support the strong torque which is created between the hub and rim during the braking process. Furthermore, the frame has to be designed with the appropriate supports to fix the pincer. The modern disk brakes have a considerably higher breaking power than V-brakes, also thanks to the use of disk brakes of considerable diameter (they usually come in sizes 160, 180 e 200 mm).
