<< Basics of Motorcycle Suspension
Now that your motorcycle has “absorbed” a bump, the compressed spring has stored the energy of the hit and without a damper it would be released in a fury of rebound might, extending the spring beyond its original static length and repeating the cycle until the energy had dissipated. The resultant store and release sequence would cause your bike to pogo down the road. Imagine a basketball bounced hard onto the asphalt, not only does it bounce back, but it would bounce higher than your hands where it had started. Now, imagine if you bounced it under water. This is the effect that a damper has on the stored energy of a spring. In fact, a damper, like the water analogy, uses a liquid (in this case oil) and forces it through a series of small holes. The ensuing resistance controls the return of the spring energy. The kinetic energy (motion) of the spring is transferred to the oil and dissipated as heat. Oil based damping is a clever solution, yet comes with its own set of challenges. For instance, rapid damper movement reduces the space within the shock for the fluid, thus a compressible medium must come into play or the shock would likely stop moving. The obvious solution would be to leave a bit of air space for the oil to move into, but air rapidly expands when heated (remember the shock has transferred the energy of motion to heat) and the damping characteristics of the shock would be ever changing. The solution is a separate chamber of a heat tolerant gas (in this case nitrogen) that allows the oil to expand without impacting the damping.
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