MTB

Mountain Bike suspension – The differences – Technical guide MTB


The widespread use of suspensions on MTB leads us to discuss some theoretical aspects not known by everyone that can improve the efficiency of your suspension fork, but they will not be treated here, Although the delivery is similar, the rear suspension features.

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The suspension fork absorbs impact, transferring the impact of the obstacle on the bike to a spring element which after deformation tends to definition to move in starting conditions. An elastic element is characterized by the spring constant (strength / Length variation) that usually define the hardness of the element, and for the compression curve, which may be linear, progressive, or mixed. The spring constant of the element tells us, at constant force applied to deform the element, the size of the deformation. The only way to change it in our fork is to replace some or all of the elastic element. The most widely used elastic elements used in the forks are MTB-air, elastomers and metal springs. Another feature, but the forks and not elastic elements inside, is the load of detachment that is the minimum force to operate the fork. This feature depends on the amount of friction generated inside the fork from the bushes, from the seals and gaskets miscellaneous. In practice, the higher the load out and less efficient will be the ’ efficiency of the spade to absorb small bumps. Let the pros and cons of each element.

sospensioni mtb

AIR: like all gases, is easily compressible, “slight”, and presents a typical progressive compression curve, that helps prevent bottom out especially with tours limited. It would seem an ideal element, but it has two drawbacks: is very sensitive to outside temperature, that varies then the hardness of the fork, and seals used to maintain it at high pressures in the fork create a high “stiction”, also known as “load break”, that is a great initial friction that penalizes 1 ' absorption of small bumps. In the forks of last generation that load large detachment is compensated with negative springs, or springs that tend to compress the fork, thus improving the sensitivity.

ELASTOMER: first introduced by Doug Bradbury, Designer of Manitou, he dominated for a long time as spring element until 1996. Lightweight, moderately progressive, less sensitive to changes in temperature of air ’. Presents two gripes: frequent lack of homogeneity in the production, for elastomers a same House declared equal spring constant, actually have many different hardnesses, and degradation which leads him quickly to lose their elastic properties (Although I myself own a fork springs and elastomers, and after a whole season running every Sunday and a total of about two thousand kilometers I have not encountered any damage to my elatomeri).

SPRINGS: neglected in the past because heavy, were present only in low-end forks, or available as kits products from some houses specialists who then sold at outrageous prices (We talk about 150.000 livres for a couple of springs !). Today you can't do without, the environment “teems” colorful springs and expensive! A turnaround, that led to favour the absorption rather than lightness, along with a general lengthening of the excursion, introduced in most forks, Sometimes alone (Marzocchi, Peace, White Brothers, Amp, Girvin…) , with elastomers (Rock Shox, Manitou, Marzocchi…) or with air (Nitro Marzocchi and RockShox SID). Are heavier elements, but are virtually insensitive to temperature changes in the terms of use of the bike, have a compression curve linear (If you have a continuous thread), are virtually indestructible and maintenance free.

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In addition to the paper ’ flexible element, some more sophisticated forks have a device which restrains the dell riestendersi ’ elastic element, that is, the return of the fork, forcing a fluid (air or oil) to filter forced passages. The oil cartridge is the most widespread system, but there are also devices ’ bath oil (Marzocchi) and gas springs (RST, Race Factory). The presence of a hydraulic cartridge involves two other effects: increased stiction, that is, the load out, derived from the friction generated by the cartridge seals ’, and a change in velocity-dependent fork compression. The strength of ’ oil to pass through the cartridge varies with the speed of compression that the higher impact resistance and a hardening of the fork: This helps in forks with compression curve slightly progressive to hinder easy access travel fund.

We now come to the point in order to justify all this talk: the knowledge of what lies within our fork, or rather you might find, It is essential to calibrate the best depending on your weight and riding style. To change the setting of a fork most forks offers two systems: partial or total replacement of elastic element ’, dell ’ preload element, and some, in case of shock absorbers for the return, even variation of density of ’ oil or return via a speed adjustment knob that varies the size of the holes for the passage of oil ’.

Dell ’ replacement elements we talked, We come now to preload, as it is widespread use as an alternative to a ’ first judge system. Preload a ’ flexible element means pre-deforming it, in our case pre-compress it to a certain length with spade at rest, so when the fork compresses, We will have a dividend higher load and will use a portion of the compression curve. In this pre-charge linear systems involves only 1 ' strain of detachment, that affects the absorption of small bumps but diminishes the effect “Pogo”, the pitching of the fork during pedaling, While in this pre-charge progressive systems involves a hardening of any race, because we're going to take advantage of the most advanced, more sloping upwards, then harder, the compression curve. A final nod on calibration: regardless of your fork damping system, is a widespread prejudice that pitch fork leg while pedaling will lead to a disturbance of the thrust of the legs: nothing further from the truth !

As scientifically proven by research of Rock Shox (see Mountain Bike by January 1997, p. 74), even during the raising saddle and’ a maximum dispersion of’ 1%. But if the fork is working properly, This percentage is abundantly retrieved and thrown to the winds because downhill and technical sections allows higher speeds, makes it more smoothly and fast advancement of the medium, reduces the rider's arms and guarantees a better control of the vehicle.

In short, It is normal that during our off-road trips the fork reaches in the most ground in smooth motion, or getting off of the “steps”, the It will go. If there are affixed to the bottom and elastomers excursions are now on 6-7 ' ' Cross Country fork, because you make only a portion of the absorption capacity of our fork ? If then abhor the pogo effect, In addition to preload the fork (Remember that the load off you only change in this way because it depends only on the friction generated by bushings and seals, not by nature of the elastic element) you might learn to set a more roundabout, that, In addition to minimizing the side effects, It is also more profitable than a reciprocating pedaling, and/or resorting to forks lockable (have an open lever that allows you to turn them into rigid forks even while you're pedaling, See Rock Shox, Manitou, Cannondale Headshok).