Skid on MTB
How do you skid for tens of meters? Torquato Testa, the slopestyle champion, teaches us how. Below is the transcription of the video text.
In the video entitled "10 tricks that you have to do with the bike" by Torquato Testa, the slopestyle champion throws himself at full speed down the ramp of the underground parking of his house and performs a long skidding for tens of meters. With his permission, I wanted to explain how he succeeds and raise the challenge.
The topic is the so-called "loads distribution", fundamental to define the basic position in mountain biking and some active driving actions. The load on the two wheels, that is, the way the weight is offloaded, depends on its distribution. In particular, it is useful to understand how to load more the front or the back and in which situations to do it. It all depends on the position of the rider's and the bike’s centers of gravity which I define together as the "center of gravity of the bike-rider system".
Another necessary concept is that of the wheels' ground friction. The rear wheel, when skidding, undergoes a friction force from the ground that depends exclusively on the load on the wheel and a friction coefficient defined by the materials in contact. Therefore, when a wheel is not charged it has low friction force values.
At this point, we have all we need to understand what is going on. Torquato, moving forward, advances the center of gravity of the body and therefore that of the bike-rider system. In this way he loads the front wheel more, lightening the rear one. When braking and starting to skid, the friction on the ground is very low both because there is no load on the wheel, and because the floor of underground parking lots is usually very smooth and therefore with low values of the friction coefficient. Torquato is then subjected to a braking force, that of friction, very low and can travel undisturbed meters and meters with the wheel locked.
Let’s get to the challenge. In theory, if Torquato shifted all his bodyweight backward, with an accentuated out-of-saddle, he could do the same trick by skidding on the front wheel. The load, in this case, would be completely on the rear wheel, and the friction on the front one would be minimal. But there are two unknowns: the first is that in braking the inertia forces always generate an overload of the front, which could therefore increase the friction excessively causing the wheel to lock to the ground with a risk of overturning. The second is that, by losing adherence to the front, it will be more difficult to maintain directionality and balance. Torquato, the challenge is served!
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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