Front suspension: how telescopic fork works

In this article we will deal with the technical and operating details of telescopic fork suspension systems, this type of suspension is the most common and currently used in most motorcycles for the front in custom models, sports motorcycles, offroad...
Its success is based mainly on its simplicity and effectiveness, ease of maintenance, rigidity and reasonable cost.

Suspension: buffers and docks
The suspension system is part of the motorcycle chassis, in particular the elastic part of the motorcycle, and its main mission is to absorb the irregularities of the road, allowing vertical wheel movement to maintain at all times contact with the ground while enabling driver and passenger to drive under control and comfort.

To better understand how the system works, let's explain the damping sequence:
-In the first moment the irregularity of the soil is absorbed by the deformation of the tyre, it is by this that at technical level the tyre is also considered as part of the damping.
- Once the tyre is compressed, the force exerted continues to push, compressing in turn the dock of the suspension. The pier can be linear or progressive, the latter has the space between turns or "pitch" gradually reduced to make the principle soft and gradually hardening.

The dock is strained at the same time as it is compressed, absorbing the energy of the impact and allowing the motorcycle chassis to follow as horizontally as possible from the ground.
In rest position we can regulate the hardness of the pier, either by replacing it with another more rigid or long or by compressing it more, this is called compression adjustment.
-When we pass the obstacle the force exerted decreases and the pier tends to regain its original length, releasing the energy and pushing the wheel back down, so as not to lose contact with the ground.
So basic what would happen after going through a bump is that the motorcycle would start bounced without control, so we must add some energy absorption system to control the wharf’s motion: the buffer, which turns this energy into friction and heat.
In the case we are dealing with the buffer is made up of a piston with holes through which a special oil passes, modifying or adjusting both the quantity and size of the holes and the density of the oil we can regulate the speed with which the pier will climb or fall, i.e. compression and extension.

This is why telescopic fork is a hydraulic suspension system.
There are many types of hydraulic valves or pistons, fully mechanical, fixed or adjustable, and also electronic adjustment.
Fork oils are classified according to their viscosity, to more densely “hard” the damping.

Types of telescopic fork
When classifying this type of suspension we can talk about conventional fork and reverse fork.
-In the conventional fork the moving part is the bottom bottle, which slides down the bar attached to the tija.
-The reverse fork is basically a conventional fork mounted "backwards", where the bottle is on top, attached to the tija, and the bar slides into it. Although more expensive to produce, it offers better results as it decreases the “unsuspended mass” of the front train, i.e. the weight of the components that go up and down from the chassis, eliminating inertia and improving driving.

At the internal working level, telescopic forks can be classified as:
-Conventional: In this type of suspension we have the pier and piston with its holes (fixed or regulable), as we have explained above.
-From cartridge: It is an evolution of the previous system, and it is like having "a damper inside the damper". The main advantage of the cartridge is its high-speed circuit, when for example we take a fast bump that the buffer system cannot absorb because the oil cannot pass so fast through the piston holes, the cartridge enters action by opening a step that allows the pressure to be released, while maintaining control at all times.
In these systems, used for example in the Harley-Davidson Touring, Buell and some sports Dyna models, suspension can efficiently respond to a multitude of driving situations where a conventional system would reach its limits.

Improvements and modifications
Although on another occasion we will talk about the correct maintenance and adjustment of the hydraulic forks, here is a couple of “invents” that improve conventional systems quite significantly, especially in Custom models. The user profile of these motorcycles will not require great sport performance, so manufacturers often lower costs in this important component.
- "Gold Valves" or emulators: This is an extra piston that is added to the system, simulating the behaviour of a cartridge system. They are relatively economic and adjustable.

-Bolt-On cartridge systems: In this case it is a simple and quick turn of our conventional telescopic fork into a cartridge suspension, only the original components need to be removed and this new system “drop down” to obtain a high performance suspension.

Frank Burguera

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