Instant steering MTB
One of the most frequent falls from a mountain bike is when the shape of the terrain results in a sharp and instant steering of the handlebars, causing the jamming of the front and likely forward tipping. You do not have much chance of avoiding the fall.
The wheel is a body constrained to rotate around the steering axis. Rotation can take place in one direction or another based on the force that is exerted on it. Assuming a horizontal force facing backward, the wheel performs a straightening motion in the direction of travel or closing, depending on the point of application of the force itself. Normally it acts under the axis of rotation, at the point of contact with the ground, giving rise to a straightening motion. If due to the conformation of the ground or its roughness the wheel is stressed on a point above the axis, it tends to instant steer.
Therefore, the part of the wheel that goes from the point of contact on the ground to the intersection with the axis of rotation can be called "safe", because at any point it is solicited it always generates a straightening motion. Traditionally, the magnitude that represents this part is called "trail" which is the segment that connects the wheel's ground contact point with the point of intersection of the steering axis with the ground. It is therefore clear that as the trail increases the safe part of the wheel increases as well and therefore decreases the probability of suffering a dangerous impact, essentially leading to greater stability of the bike.
Although the trail gives stability, it cannot be enlarged out of proportion so as not to compromise the "handling" of the bike. The trail is related to both the extent of the steering moment undergone from the ground, and the sensitivity of the steering system, elements that define the ability of the bike to easily face small-range curves.
One of the principles of good mountain biking is to keep relaxed on the bike avoiding any form of stiffening. However, we must be aware that in certain situations and under certain terrain conditions, the risk of suffering a collision on the unsafe section of the wheel is greater and we must therefore be prepared to undergo a strong rotational thrust from the ground on the handlebars. This awareness can therefore help us to counteract it, promptly exerting the right strength on the handlebars to avoid instant steering.
Uno dei principi della buona guida in mountain bike è restare morbidi sulla bici evitando ogni forma di irrigidimento. Occorre però essere consapevoli che in certe situazioni e con certe condizioni di terreno, il rischio di subire un urto sul tratto non sicuro della ruota è maggiore e dobbiamo pertanto essere pronti a subire dal terreno una forte spinta rotazionale sul manubrio. Tale consapevolezza può quindi aiutarci a contrastarla, esercitando prontamente la giusta forza sul manubrio per evitarne la chiusura.
If you are interested in the topic, more details can be found by reading "The science of Mountain Bike riding: the physics behind MTB skills" which contains all the topics, addressed to all MTB enthusiasts.
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