The fork of a bicycle is a crucial element. With out it, the bicycle would not be able to move. The fork allows the forward movement by the wheel and also allows the bicycle to turn. It connects the frame of the bicyle to the wheel. The main parts of the fork are the steerer, fork blades, and the drop out. The steerer connects the fork to the frame, while the dropout connects the fork to the wheel. Sometimes, bicycle companies will attach the front brakes to the fork. Fork designs are based on the type of bicycle. A mountain bike will have a more tough fork, with the possibility of having a suspension system attached, while a touring bike will have a sleeker, lighter design. The materials generally used to create a fork are either aluminum, steel, titanium, or a carbon fiber. Some companies use a type of magnesium or create a combination of these materials.
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How it works
The assembly of the fork is rather basic. The fork connects to the frame by the steerer (top of the fork) going through the head tube and connecting to the handle bars. Inside the head tube consists a headset. Some advanced bicycles have a bearing system inside of the headset, but most standard bicycles only have a simply system that contacts the inside surface of the head tube. The fork connects to the wheel by the drop out. The blades move down the fork on each side of the wheel until it reaches the the drop out, which connects to the front wheel axle. Many newer bikes use a quick release mechanism to connect the wheel to the drop out, but majority of bicycles use a simple bolt on each blade. The crown of the fork keeps the head tube from moving further down the fork. It also is where the fork splits from one tube into two blades. Most bike companies connect their brakes just below the crown of the fork. This allows the brakes to easily work on the wheel.
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Evolution of the Fork
After much research, the creation date of the bicycle fork could not be determined. It is assumed then that the idea to use a fork on a bicycle was around the same time the bicycle was created, which was in 1817 when Baron von Drais invented the running machine. Since then, the fork has gone through some changes, but it has the same purpose then that it does now.
When the first bicycle created, the fork was stationary, which meant that the rider could only move in one direction. Only a year later designers improved on the design and allowed turning to be possible. This was done by drilling a hole in the frame, then placing the fork through the hole and attaching a bar across the top of the fork (the steerer) to prohibit the frame and the fork from separating. After that, as the bicycle made changes, so did the fork. As wheel size changed, so did the fork length and thickness, but the basic design of a steerer and two blades remained the same.
As time progressed so did the evolution of the bicycle. The bicycle went from have no resistance from road shock to the suspension systems we have today. Today riders feel very little discomfort from road shock. One of the first patents for front shocks on the bicycle was invented in the 1890’s. In 1891 W. W. Kenfield patented a front suspension design for a bicycle (his concept is shown below-left). The design used a spring located in the head tube to absorb the shock from the road. A hinge bracket was attached to the front forks tubes. The top edge of the hinge bracket had an external pin that engaged into the head tube. Contained within the head tube was a spring or series of springs depending on whether the rider wanted additional shock resistance within the handle bars. The first spring absorbed the shock from the road from the down tube and body of the bicycle. The second spring was used to absorb additional shock through the handle bars. This design then evolved into the first telescoping forks.
It wasn't until the early 1900's that the front suspension systems on bicycles started being incorporated into the front forks. In 1922 George W. Sage Jr. introduced telescoping forks in his patent (his concept is shown above-right). The front fork tubes of the bicycle contain a spring. The forks extend up into head tube and are constructed in two sections per side. The lower fork acts as a shaft. The upper fork is a tube. The shaft extends up through the tube section where it meets a spring. The upper section of the fork arm is then attached to the head tube. The lower section contains a slot and the upper section contains a pin. The slot attaches the lower fork arm to the upper fork arm via the pin. This prevents the two sections from separating during operation. All the shock from the riding surface is absorbed before the head tube connection. This allows the rider to be exposed to a much smoother ride than previously experienced.
The next significant evolution in bicycle front fork technology came as a result of a trend which was sweeping the extreme sports culture in California: Mountain Biking. In the mid to late 70s the sport of Bicycle Moto-Cross or BMX racing had become very popular among teenagers around the country. The sport was similar to motorcycle racing in that the racers sped around a closed loop track jumping over obstacles while trying to keep in the lead. The most significant difference was that racers did not have full sized motorcycles; instead they had small bikes with 20 inch wheels. As the racers got older they outgrew their small bikes and were forced out of the sport. Not content to give up the thrill of dangerous, high speed bike riding the former BMXers turned to adult bikes with 26 inch wheels. The larger bikes were too big for the small BMX tracks so the bikers began to race them down the mountains in California. The bikes were not strong enough to withstand some of the abuse they took, so the bikers began to customize them to make them stronger and more adept to the rocky mountain slopes. Innovations to make the frames and forks stronger and more capable finally culminated in the invention and introduction of the shock absorbing front fork in the early 90s.
Early forks, such as the one pictured below-left, were relatively simple in design. The shock absorbing feature was made possible by having a two piece fork with concentric pieces. One leg of the shock absorber would house a steel spring while and the other leg would contain an oil damper. The spring was used to absorb the impact of the wheel and the damper was used to keep the fork from bouncing and to smooth out the motion of the front wheel. Early shock absorbers were very simple with little or no adjustment available for the rider.
In recent years mountain biking has become increasingly popular which has led to many innovations for the front suspension. Groups of mountain biking enthusiasts have pushed the sport to new extremes creating a market for new super high performance parts. Whereas bicycle forks available in the early 1990’s only had a few inches of travel and cost a few hundred dollars bicycle forks can now be purchased with over 10 inches of travel and cost thousands of dollars. Mountain bike technology has evolved concurrently with motorcycle technology which has resulted in mountain bike forks with inverted forks and triple clamp headsets. An example of one of the premiere bicycle forks available is shown above-right. As you can see, fork technology has progressed by leaps and bounds in only a few years. The traditional steel springs used to absorb shock are being replaced by compressed air springs on which the spring rate can be changed to suit a rider’s exact needs. Dampers are adjustable in many different ways and sometimes even have external oil reservoirs for increased capacity.
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|Part #||Part Name||# Req'd||CAD File||Image|
|2||Fork & Frame Assembly||1||Fork & Frame Assembly|
|3||Brake Sub Assembly||1||Brake Sub Assembly|
|4||Brake Lever||2||Brake Lever|
|5||Brake Base||2||Brake Base|
|6||Brake Lever Pin||2||Brake Lever Pin|
|8||Handlebar Stem||1||Handlebar Stem|
|9||Handlebars Assembly||1||Handlebars Assembly|
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