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Speed Wobble Science
More than you'll ever need to know about the dreaded Speed Wobble. Neil Carver breaks down the science behind this phenomenon. A WOBBLE THEORY This recent inquiry into waveforms and steering, along with my years as a trucksmith, has led me to extrapolate that there are two types of wobble that skaters experience. The first kind is of the “loose truck” variety. This is where there is excessive play in an undampened system that allows for a self-exciting oscillation to take over once critical speed is attained. In order to remedy this kind of wobble you want to remove loose play, like under-compressed bushings and pivot cup slop. The second type of wobble is “us.” We can be the source of oscillation excitement as we attempt to counteract a wobble that may have started with a pebble or a flinch, only to add to it with the energy of our synchronized reactions. This is a situation where it’s a good idea to control one’s over-reactive tendency and hope that you can keep from feeding into the loop vortex. In order to grok our role in the whole steering system it’s important to see us as the chassis of a human/skateboard unit, because we do function as one. Flexible chassis are shown to feed oscillating systems with the energy from their spring-back, even at lower speeds. Thus there is a need for Positive Feedback systems (also known as Feedforward systems), which utilize a controlled counter-action to the undesired frequency. Luckily, we are the ultimate feed-forward system, in that we can use our skill and confidence to counteract the sometimes wayward mechanical tendencies of our boards. WEATHER VANING AND THE STABLE TAIL As I searched for solutions to the wobble tendency, I noticed that most of the examples of stable steering systems were ones in which the front of the vehicle turned more than the rear. This configuration creates a sort of Weather Vane Effect, where a trailing wing pivots the vane into the wind – also known as Passive Steering Stabilization. A more stable back truck creates a similar effect, where the tail becomes a sort of trailing stabilizer. The front truck then provides the majority of steering without the propensity for the vehicle to oversteer from the rear. Directionality is a big part of this, so it’s not ideal for riding that involves reversing board direction at speed. If that works with your riding style, then you can easily make a version of this design by using a wedged Reverse Kingpin truck with soft bushings on the front and a de-wedged Standard Kingpin truck with firmer bushings at the rear. You can feel how stable it is when ridden forward compared with when you ride the board in reverse. USE THE FORCE Knowing the science behind wobbles has helped me understand why some commonly practiced methods work. What a looseness of body can do, for example, is separate the oscillating board from the mass of the rider so that we don’t feed the oscillation any further, and may even dampen it. Because when we add our body weight to the oscillating system, we provide a lot of mass for the oscillation loop to feed off of. So as it turns out, according to traditional steering analysis, the skateboard is just a twitchy animal that is prone to fits of instability, exacerbated at every turn by its own design. So why don’t we just fix all these problems, then? I pondered this question while pumping my board around in front of my house and the answer came to me in a flash of obviousness; it’s all that volatile energy from the system that makes it so much fun. The very essence of the pump comes from our ability to harness the instability, tap into the oversteer, accentuate the positive 4WS, even feed off the negative trail and ultimately jump on the negative caster. All of the things that make a skateboard categorically “ill-tempered” are the exact same things we love about it. It’s good to understand the geometry of our boards so we can fine-tune them to suit our styles, but ultimately it is we who need to adapt to riding this wild horse, and not tame the animal so much that it loses its buck. BY: NEIL CARVER, Concrete Wave Magazine For the complete article, please click here: http://www.freeridesurfshop.com/index.php/skate/longboarding/the-science-behind-speed-wobble
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