Imagine your bike’s front wheel hitting a speed hump at a fast enough speed without being connected to any suspension system. The front will go flying, which will upset the balance of your bike in a big way and at the same time, a huge shockwave will be transferred to your forearms through a violent movement of the handlebar. Sounds scary, right?
Even in everyday situation, if you take the telescopic forks away, even the tiniest of imperfection on the surface will be transferred back to the handlebar and onto your arms, making the ride really uncomfortable. Gradually, the ride & handling characteristics of your bike would become so poor that it will almost become impossible to ride. Now that you understand its importance, let’s take a look at how a telescopic suspension system works.
Like an actual telescope with its overlapping barrels, where the bigger tube overlaps the smaller to allow the latter to move freely within a certain range, a telescopic suspension system works on similar principles too. The only difference here is that the movement of tubes allows the front wheel, which is connected to the larger tube, to move vertically. When the wheel travels upwards, a spring inside the telescopic suspension system compresses to absorb the energy and its rebound action puts it back in its original place, thus allowing a constant cycle of compression and rebound.
The topmost part of a telescopic suspension system is connected to the frame or the motorcycle’s chassis with the help of a clamp. This clamp, which is connected to the handlebar above, allows the forks to be turned in order to steer the motorcycle. The lower part of a telescopic suspension, the two tubes which are connected to the wheel are known as “Sliders”. For they slide up and down the exposed metallic forks you normally see, which are also known as “Fork Tubes” and are connected to the clamp.
The insides of the Sliders are filled with a slider guide bush, a thrust washer and an oil seal at the very top which is held in its place by a retaining ring. Above the ring sits a dust cap, which is the black ring you see where the fork tubes and the sliders meet. The fork tubes contain a damping cylinder which is fitted with a centring bush at the bottom. The arrangement is such that the bush sits at the very bottom, inside the sliders. The spring is positioned inside the fork tubes and is always bathed in a specific quantity and viscosity of the oil. Everything is then capped off by a top cap which fits at the very top of the fork tubes.
If a telescopic suspension system only consisted of springs, every time it absorbed a bump and compressed, the spring would want to rebound as quickly as possible and do so in a violent manner, sending itself in a pogo-like movement for quite some time. To make the coil settle down before it is ready to compress again, the oil inside a telescopic suspension system provides the damping force or the required resistance.
In a basic telescopic suspension setup, when the sliders are driven upwards by changes in the road surface, the spring compresses to absorb the resultant energy. But when the coil has to unwind and release the energy back, its rebound action meets resistance in the form of oil. The spring’s tendency to retract back into its original state pushes the centring bush to the bottom, which in turn pushes against the oil below it. Since the oil must now find some place to release and allow the spring to come back to its original state in a controlled manner, an orifice in the damping cylinder allows it to escape upwards towards the spring in a measured quantity, allowing for a resistant damping force acting on the spring at all times.
A more complex system ditches the damping cylinder or fork for a cartridge fork which uses bending-shim-type construction instead of fixed orifices. Such a system offers more control over the rate of damping and allows for variable behaviour during low and high-speed compression and rebound. On the other hand, Upside down forks aren’t just fancy to look at, but for being positioned the other way round, they account for a massive reduction in unsprung weight, which in turn enhances the handling and flickability of a motorcycle.
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Now that you have an overview of how a basic telescopic suspension system works, since it functions on basic principles and has fewer components, it doesn’t really require frequent care. However, ensure that the area near the fork seals is grime and dust free at all times. Also, if you notice any oil leaking through that space or anywhere else, visit your mechanic and get the leak fixed. Get the forks checked for oil levels and top up only if necessary with the right kind and exact amount of fluid. If you notice that the front suspension quality is not how it used to be, if things feel too firm or too soft, get those forks checked immediately.