A telescopic fork is a form of motorcycle front suspension whose use is so common that it is virtually universal. The telescopic fork uses fork tubes and sliders which contain the springs and dampers.
A telescopic forktelescopic fork is a form of motorcycle front suspension whose use is so common that it is virtually universal. The telescopic fork uses fork tubes and sliders which contain the springs and dampers.
The main advantages of the telescopic fork are that it is simple in design and relatively cheap to manufacture and assemble, and that it is lighter than older designs using external components and linkage systems. Telescopic forks sometimes have gaiters to protect the fork tubes from abrasion and corrosion.
A more modern (and more expensive) version of the conventional telescopic fork is the inverted or "USD" (upside-down) fork.
BMW's patented telelever front suspension appears at first glance to be conventional telescopic fork, but the fork tubes contain neither springs nor damping. Instead, a wishbone and an inboard monoshock perform suspension duties, and the forks serve to locate the front wheel and control steering.[1]
History
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Early oil-damped telescopic fork on a 1939 BMW R12The first production motorcycles with hydraulically damped telescopic forks were the German BMW R12 and R17 in 1935.[2] However, undamped telescopic forks were used on bikes made by The Scott Motorcycle Company from the beginning of production in 1908,[3] and the Danish Nimbus used them from 1934 on.[4]
Design
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1968 BMW R60US with conventional telescopic fork Telescopic fork in upside down design, with stanchions at the bottom.Conventional telescopic forks invariably have a pair of fork tubes, or "stanchions", at the top, clamped to a triple tree (also called a triple clamp or a yoke), and the sliders are at the bottom, attached to the front wheel spindle.
Inside most tubes are springs, fork oil, and air, creating a shock absorber. Some forks allow pressurized air to be added through a valve in the top of the fork to stiffen the suspension. Quality forks have a flexible air tube between both fork tubes in order to balance the air pressure in both forks. Modern fork tubes have a method which employs a screw to compress fork spring to increase or decrease spring pre-load.
Damping
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Cartridge forks provide regressive damping. Self-contained cartridges within the forks contain spring-covered orifices regulating fork oil flow. The springs resist low forces and thus provide high damping rates. Higher forces compress the springs, allowing more oil flow and less damping. Thus the fork is stiffer when responding to small bumps but will soften as larger ones are encountered.
Most modern forks also are suspended on springs and control fork movement by damping through adjustable valving to control movement by controlling the flow of fork oil. The larger the orifice, the more free the flow and the less damped the fork. A selector atop the fork engages the desired hole size or valve and corresponding damping rate in compression, while usually the lower tube has a mechanism to control rebound (extension) damping.
Single action damping is currently being manufactured, such that compression occurs in one fork tube while its partner tube controls the rebound damping. This is because the oil controlling the damping in each tube, then, has only to control one direction of damping and is therefore less aerated by it working in both directions, and it develops less heat while working, which causes a variation to the thickness of the oil, thereby adversely affecting the damping rate.
Upside down
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On most modern motorbikes this system is inverted, with the "sliders" and the spring/damper unit at the top, clamped to the yoke, while the stanchions are at the bottom. This is done (1) to reduce unsprung weight by having the heavier components suspended, and (2) to improve the strength and rigidity of the assembly by having the strong large-diameter "sliders" clamped in the yokes.[5] The inverted system is referred to as an upside-down fork, or "USD" for short. One disadvantage of the USD design is that the entire reservoir of damping oil is above the slider seal so in case of leak the oil drains out, rendering any damping ineffective.
Triple tree
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The upper triple clamp joins the top of the fork tubes and the handlebar to the frame of a Honda 919A triple tree ("triple clamp" (US) or "yoke" (UK)) attaches the fork tubes to the frame via steering head bearings, which allow the fork assembly to pivot from side to side, and therefore steer the motorcycle. Most bikes have upper and lower triple trees, providing two solid clamping points that keep the fork tubes parallel while also connecting the forks to the frame via the steering head bearings.
With the tendency to employ fork tubes with single action damping, fork triple trees need to be reinforced more than when the forks shared both damping roles, because the rigidity of the triple trees is relied upon to distribute the forces within the forks without flex.
The BMW Telever fork has only a single triple tree, which allows its fork sliders to be longer than those on telescopic forks. This in turn allows for greater overlap of the sliders over the stanchion tubes, which improves stiffness and helps to reduce flex.
References
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edit
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Media related to Telescopic forks at Wikimedia Commons
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
#mecanicaharley
The main advantages of the telescopic fork are that it is simple in design and relatively cheap to manufacture and assemble, and that it is lighter than older designs using external components and linkage systems. Telescopic forks sometimes have gaiters to protect the fork tubes from abrasion and corrosion.
A more modern (and more expensive) version of the conventional telescopic fork is the inverted or "USD" (upside-down) fork.
BMW's patented telelever front suspension appears at first glance to be conventional telescopic fork, but the fork tubes contain neither springs nor damping. Instead, a wishbone and an inboard monoshock perform suspension duties, and the forks serve to locate the front wheel and control steering.[1]
History
[
edit
]
Early oil-damped telescopic fork on a 1939 BMW R12The first production motorcycles with hydraulically damped telescopic forks were the German BMW R12 and R17 in 1935.[2] However, undamped telescopic forks were used on bikes made by The Scott Motorcycle Company from the beginning of production in 1908,[3] and the Danish Nimbus used them from 1934 on.[4]
Design
[
edit
]
1968 BMW R60US with conventional telescopic fork Telescopic fork in upside down design, with stanchions at the bottom.Conventional telescopic forks invariably have a pair of fork tubes, or "stanchions", at the top, clamped to a triple tree (also called a triple clamp or a yoke), and the sliders are at the bottom, attached to the front wheel spindle.
Inside most tubes are springs, fork oil, and air, creating a shock absorber. Some forks allow pressurized air to be added through a valve in the top of the fork to stiffen the suspension. Quality forks have a flexible air tube between both fork tubes in order to balance the air pressure in both forks. Modern fork tubes have a method which employs a screw to compress fork spring to increase or decrease spring pre-load.
Damping
[
edit
]
Cartridge forks provide regressive damping. Self-contained cartridges within the forks contain spring-covered orifices regulating fork oil flow. The springs resist low forces and thus provide high damping rates. Higher forces compress the springs, allowing more oil flow and less damping. Thus the fork is stiffer when responding to small bumps but will soften as larger ones are encountered.
Most modern forks also are suspended on springs and control fork movement by damping through adjustable valving to control movement by controlling the flow of fork oil. The larger the orifice, the more free the flow and the less damped the fork. A selector atop the fork engages the desired hole size or valve and corresponding damping rate in compression, while usually the lower tube has a mechanism to control rebound (extension) damping.
Single action damping is currently being manufactured, such that compression occurs in one fork tube while its partner tube controls the rebound damping. This is because the oil controlling the damping in each tube, then, has only to control one direction of damping and is therefore less aerated by it working in both directions, and it develops less heat while working, which causes a variation to the thickness of the oil, thereby adversely affecting the damping rate.
Upside down
[
edit
]
On most modern motorbikes this system is inverted, with the "sliders" and the spring/damper unit at the top, clamped to the yoke, while the stanchions are at the bottom. This is done (1) to reduce unsprung weight by having the heavier components suspended, and (2) to improve the strength and rigidity of the assembly by having the strong large-diameter "sliders" clamped in the yokes.[5] The inverted system is referred to as an upside-down fork, or "USD" for short. One disadvantage of the USD design is that the entire reservoir of damping oil is above the slider seal so in case of leak the oil drains out, rendering any damping ineffective.
Triple tree
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[
edit
]
The upper triple clamp joins the top of the fork tubes and the handlebar to the frame of a Honda 919A triple tree ("triple clamp" (US) or "yoke" (UK)) attaches the fork tubes to the frame via steering head bearings, which allow the fork assembly to pivot from side to side, and therefore steer the motorcycle. Most bikes have upper and lower triple trees, providing two solid clamping points that keep the fork tubes parallel while also connecting the forks to the frame via the steering head bearings.
With the tendency to employ fork tubes with single action damping, fork triple trees need to be reinforced more than when the forks shared both damping roles, because the rigidity of the triple trees is relied upon to distribute the forces within the forks without flex.
The BMW Telever fork has only a single triple tree, which allows its fork sliders to be longer than those on telescopic forks. This in turn allows for greater overlap of the sliders over the stanchion tubes, which improves stiffness and helps to reduce flex.
References
[
edit
]
Media related to Telescopic forks at Wikimedia Commons
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
#mecanicaharley
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