The information about the origin of the front forks is not clear in terms of time, but it is known that front forks began to be widely used on motorcycles in the early 1950s. The predecessor of the current fork is the girder fork.
The front fork is a component that connects the front wheel and the motorcycle’s steering (front end) and has the function of minimizing the shocks of the front part of the motorcycle when riding on rough roads. Thanks to the front fork, the handlebars are easier to control when encountering obstacles, and the rider will feel less fatigue in the arms and shoulders when riding on long stretches of road.
The telescopic fork uses a fork tube, inside of which contains components such as a spring, a fork piston, and damping oil to maximize the absorption of shocks from the front wheel to the handlebars. This is the most common type of fork used in most commercial motorcycle models. Depending on the manufacturer, this type of fork may or may not have a rubber protective cover. This rubber cover is intended to prevent dust from scratching the fork piston (such as the forks of Honda 67 or Bonus 125).
The operation of the damping system is as follows: Assuming the bike runs over a stone on the right side of the road, the wheel exerts force on the suspension system. At this time, the damping oil flows quickly from chamber 1 to chamber 2 through a large cross-section, so the spring compresses quickly, absorbing the shock. When the wheel is on the stone, the spring rebounds due to elastic force, and at this time, the damping oil flows in reverse from chamber 2 to chamber 1, but the flow area from chamber 2 to 1 is small, so the oil flows slowly, and the spring expands slowly, preventing the bike from bouncing.
Advantages of this type of fork:
– Easy to design, assemble, and cost-effective.
– Lighter than older fork types.
– Cleaner look and easier to adjust for the user’s purpose.
– Some forks do not have rubber sleeves for protection, so they often result in scratched or damaged fork pistons.
– Hydraulic oil inside the fork can leak through the seal if the compression force is too strong.
– Prone to bending in case of strong impact.
– Less feedback compared to other types of forks when they are damaged.
In general, this type of fork is designed with the upper part attached to the triple tree, tightened to the steering stem, and the fork tube (sliding component) fixed to the fork leg. In some modern sports and off-road motorcycles, this system is reversed (meaning the fork tube is fixed to the fork leg and the upper part is fixed to the triple tree) and is called an inverted fork or upside-down fork (USD).
Advantages of this inverted design:
– Reduces the weight of the fork (as the inverted design allows for the use of lighter materials for internal components)
– Increases the comfort and responsiveness of the fork when there is an impact (when the fork is inverted, the impact force from the front wheel on the fork is reduced, and the force from the fork leg to the fork is increased, resulting in a longer travel of the fork and a smoother ride)
– However, this type of fork is prone to leaks from the hydraulic oil inside the fork tube or the seal.
According to records, the first motorcycle to be equipped with this hydraulic telescopic fork system was the BMW R12 and R17, which were produced in 1935. Although the telescopic fork system without hydraulic oil was applied to motorcycles in 1908 by a British company and in 1934 by a Danish company, both are not officially recognized because the system was not complete at that time.