Bike is one of the best human creations. We have created the machine just like ourselves. On a careful stare, it becomes quite obvious that a bike is no different from our body. It also has legs, eyes, hand, back, belly etc but the only different observed is the design and material that each of the above specified parts are made of. Fork does the job of hands for a bike. It holds the wheels in place. It basically is the suspension of the bike that helps to absorb most of the forces coming from the road and usually try to travel up to the rider. A rigid fork will have no relative movement which in turn would transfer all the forces to the rider and make the ride jerky and uncomfortable. This is why suspension fork is fitted on a bike.

Conventional telescopic suspension

It is has a very easy construction with one arm inside another. The shiny chrome part which actually slides is called stanchion on the other hand the bar inside which stanchion slides is called slider bar or damping unit. Some portion of the stanchion is already there inside the slider bar. Stanchion is restricted from reaching the extreme end of the slider bar by a coil spring and this whole unit is dipped inside oil for a smooth movement and better hydraulic resistance. Stanchion is also recognized by active arm while slider bar by fixed arm. Arm or fork is basically the same thing and here I am using this alternate word to make it easy for you to understand the topic “fork”. Fixed arm is basically greater in diameter with active one smaller in diameter making active arm to perfectly fit inside the fixed arm. These are hydraulically controlled and also known as hydraulic telescopic brake. It could be imagined like a piston moving inside a cylinder. The fork with bigger diameter or slider bar could be considered like a cylinder and the fork with smaller diameter could be considered as a piston. A typical piston moves inside a cylinder and so the same scenario is observed here. The coil spring is fixed and dipped inside oil as mentioned earlier. Both coil spring and oil restrict the movement of the forks against each other. This gives the suspension a type of oscillating motion also known as damping. The restriction to the free movement of the two forks absorbs the jerk transmitted by the bumpy road to the wheel and later to the handle bar. Suspension determines the quality of your ride. The ride would still feel jerky and uncomfortable even if the best road is constructed for the bike. The main difference is created by the suspensions accommodated by both front and rear suspensions. The basic arrangement is shown in the above figure where a bicycle with a front suspension system has conventional suspension system. The smaller diameter arm is fixed to the triple clamp and the bigger diameter arm is fixed to the wheel hub. This is a basic arrangement of a conventional suspension system. The whole principle depends on the compression action of the spring which is regulated by the oil present in the forks to control the velocity.

Inverted or upside down forks or suspension (USD)

It is what the name indicates which is the inverse of a conventional telescopic system. Just turn over the entire conventional fork and you get a USD forks. Here slider bar is fixed to the triple clamp and chrome part or stanchion is fixed to the wheel hub. But initially why was this setup adapted by the developers?

 First time when forks were installed as USD position was done in 1980s by some crazy race teams which wanted to know the effect of this type of setup on handling. This repositioning does made a huge impact on handling and was later adapted by high performance street legal bikes as well. The three main processes happening in a suspension are compression, rebound and damping. It was observed that these three processes worked better in a USD fork and this was the reason why nearly all high performance bikes had and still have this type of setup as a mandatory unit.

All the forces get transferred to the front fork when the brakes are applied. This increases the stress acting on the fork which calls upon a fork with stronger material and arrangement. The component of the bike that is under maximum stress is the fork. It is prone to fatigue due to its linear design. The whole working procedure of both types of forks is the same. The only difference is actually not only seen but also felt by the rider. The reason why USD fork has become such a popular type is because of the sporty and muscular design that gives similar kind of look to the bike. Guys who workout in gym would get this very easily. The first and the foremost part or area a guy focuses on when he joins the gym is the arm. Also, the crowd mostly fear the guy with big biceps. Structurally Biceps are way bigger than the wrist portion that makes a guy look muscular in a similar fashion a bike looks muscular. Just hid the rewind button and move back to 90s era when there was a famous cartoon of POPEYE THE SAILOR which was shown on the television every evening. It had two opposite characters. Positive character was played by the Popeye and the negative one by mighty Brutus.

From the photo itself anyone could tell who looks more fearsome and powerful. The main reason becomes the biceps which obviously Brutus had that gave him that muscular look and on the other hand Popeye looked less dangerous that was because of the skinny biceps even after having insane wrist portion.

The rigidity of the fork becomes better in USD position especially the point under the triple clamp which is the hotspot of stresses. The hard brakes applied on the bike actually put force on the front wheel in opposite direction of the motion of the bike. The only thing that connects the wheel to the bike is the front fork. This becomes the medium that gets all major forces transferred from the road to the wheel and later to the forks which ultimately sends them further to the rider. The only medium that can stop the forces from reaching the rider is the fork. If proper damping occurs then most of the forces would get absorbed by the compression or lever phenomena of the forks. This is a major reason why forks become an important factor to be considered in terms of comfort. A bigger diameter tube could take up more load than a tube with reduced diameter. The region under the triple clamp undergoes maximum stress as mentioned before and it should have a tube with greater diameter which is why USD becomes a perfect fork position especially in performance bikes. This setting also makes both the forks less prone to flex under hard braking or high speed turning. USD forks give better handling to the bike and make it more responsive. The settings of USD forks have more options to give a better damping effect to the bike. The setting includes adjusting damping or rebound or compression which is possible only due to the present of complex internal parts.

The screw located on the top side of the triple clamp has markings and could be adjusted according to the rider’s requirement. How the spot under the triple clamp becomes the hotspot of the various forces or where all forces get concentrated? The reason is the dual action that comes into picture when the brakes are applied. The first action is developed as soon as the brakes are applied i.e. when the forces on the wheel get concentrated at the region below the triple clamp. The next and the last action is basically not an action but a reciprocating action or reaction developed when the wheel speed is affected under braking i.e. the weight of the bike along with the rider that shifts from its original position on to the forks or precisely at the same region under the triple clamp. These make this region or area a hotspot of the stresses. USD fork is also longer than the conventional telescopic fork. Handling gets enhanced as lighter components of the suspensions are placed at the lower end of the fork. This reduces the stiffness on the handle while turning or manoeuvring. USD fork is much more stable on turns and provides more confidence to the rider on high speed cornering.

Feedbacks

Looks cannot only be the basis on how a bike is defined. You need to look at the performance figures of any change that is made in a bike. USD fork no doubt gives a bike better handling but also at the same time induces some drawbacks which are listed below.

1. The main drawback is the oil that could travel to the disc brake in case of any broken oil seal. We know that telescopic suspension is a type of hydraulic suspension system which means that there is a fluid present inside the forks. The fluid present inside is actually high density oil. However, oil restricts the free motion of stanchion inside the fork and by this oil provides that necessary damping effect to the suspension. If the oil leaks then obviously it would slide through the stanchion to disc brake and if the disc gets laminated by oil drops then this could highly affect braking in negative manner and cause loss of braking.
2. When it comes to repairing or servicing this fork then it becomes very difficult to dismantle or a big challenge to work on this type of fork. Often USD fork faces a problem of oil leak from the slider bars and oil seal has to be replaced in order to fix it. Even an easy task of changing the oil seal also becomes a big challenge in such a fork. Just imagine how challenging it would be to take whole fork apart for a technician.
3. Bikes face a huge problem of jerky sliding in USD fork as often mud and dirt easily gets splashed to the stanchion due to its low location. Many stubborn and sticky dirt particles get stuck to the tube and often make the surface of the stanchion rough and give a jolty sliding movement. There is also a risk of dust particles getting penetrated into the slider bar.
4. This point is purely according to my own experience. I feel USD forks make the whole handle heavier than the conventional one which demands more power to turn the bike.
5. Due to low position of the stanchion, USD fork is less sturdy or less strong.
6. USD fork is more stable on smooth roads and as mentioned earlier, the main reason why it is made and fitted on performance bikes which dash on closed circuits with high precision roads. But when it comes to normal public road then USD do not perform well.
7. USD fork due to the various small components present inside it is more costly and therefore it is found in high performance costly bikes.
8. It is strictly not recommended on off road terrain which includes high number of pot holes, digs or unpaved surface if a rider rides on it frequently.

Tell me in the comment section below which fork is more comfortable according to your experience. Also, do tell me what all changes are required in a bike in order to change a conventional fork to a USD one. Thankyou!!

by AutoVogue