Front Suspension: How the Telescopic Fork Works

In this article, we'll cover the technical and operational details of telescopic fork suspension systems. This type of suspension is the most common and currently used on most motorcycles for the front end, including custom models, sportbikes, and off-road bikes.
Its success is based mainly on its simplicity and effectiveness, ease of maintenance, rigidity and reasonable cost.

Suspension: shock absorbers and springs
The suspension system is part of the motorcycle's chassis, specifically its elastic section. Its main purpose is to absorb road irregularities, allowing the wheel to move vertically to maintain contact with the ground at all times, while also ensuring controlled driving and comfort for both rider and passenger.

To better understand how the system works, let's explain the damping sequence:
-Initially, the unevenness of the ground is absorbed by the deformation of the tire, which is why, on a technical level, the tire is also considered part of the cushioning.
-Once the tire is compressed, the force exerted continues to push, in turn compressing the suspension spring. The spring can be linear or progressive; the latter has a gradually reduced "pitch" between turns so that it starts softly and hardens progressively.

The spring tightens as it compresses, absorbing the impact energy and allowing the bike's chassis to remain as horizontal as possible with respect to the ground.
In the resting position, we can adjust the spring's stiffness, either by replacing it with a stiffer or longer one or by compressing it more; this is called compression adjustment.
-When we pass the obstacle, the force exerted decreases and the spring tends to return to its original length, releasing the energy and pushing the wheel down again, so as not to lose contact with the ground.
In this very basic way, what would happen after hitting a pothole is that the motorcycle would start to bounce uncontrollably, so some energy absorption system must be added to control the movement of the spring: the shock absorber, which converts this energy into friction and heat.
In this case, the shock absorber consists of a piston with holes through which a special oil passes. By modifying or adjusting both the number and size of the holes and the density of the oil, we can regulate the speed with which the spring will rise or fall, that is, the compression and extension.

This is why the telescopic fork is a hydraulic suspension system.
There are many types of hydraulic valves or pistons, fully mechanical, fixed or adjustable, and also electronically adjustable.
Fork oils are classified according to their viscosity; the thicker the oil, the “harder” the damping.

Types of telescopic forks
When classifying this type of suspension, we can talk about conventional forks and inverted forks.
-In the conventional fork the moving part is the lower bottle, which slides along the bar attached to the seat post.
-The inverted fork is basically a conventional fork mounted "upside down," where the lower leg is at the top, attached to the seat post, and the leg slides inside it. Although more expensive to produce, it offers better results because it reduces the "unsprung mass" of the front end—that is, the weight of the components that move up and down relative to the frame—eliminating inertia and improving handling.

At the internal operating level, telescopic forks can be classified as:
-Conventional: In this type of suspension we have the spring and the piston with their holes (fixed or adjustable), as we have explained previously.
-Cartridge: This is an evolution of the previous system, and is like having "a shock absorber within a shock absorber." The main advantage of the cartridge is its high-speed circuit. When, for example, we hit a fast bump that the damping system can't absorb because the oil can't pass through the piston holes quickly enough, the cartridge springs into action, opening a passage that allows the pressure to be released, maintaining control at all times.
In these systems, used for example in Harley-Davidson Touring, Buell and some Dyna sport models, the suspension can respond efficiently to a multitude of driving situations where a conventional system would reach its limits.

Improvements and modifications
Although we'll discuss the proper maintenance and adjustment of hydraulic forks another time, here are a couple of "inventions" that significantly improve conventional systems, especially on Custom models. The user profile of these bikes doesn't require high performance, so manufacturers tend to cut costs for this important component.
-"Gold Valves" or emulators: These are extra pistons added to the system, simulating the behavior of a cartridge system. They are relatively inexpensive and adjustable.

-Bolt-On Cartridge Systems: This system allows you to quickly and easily convert your conventional telescopic fork into a cartridge suspension. Simply remove the original components and drop in this new system to achieve high-performance suspension.

Frank Burguera

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