Bicycle Front Assembly
The front assembly of a bicycle plays the integral part of steering. Therefore, it has been around almost as long as the bicycle itself. The bicycle began as a foot-driven coaster, but by 1839, the bicycle had evolved into a machine propelled by pedals and steered with a rotating handle bar (The Columbia Encyclopedia). It is also assumed the fork has been the common way to attach the front wheel to the frame from origins of the bicycle. As qith most consumer products, the bicycle has evolved with time. New materials technology, bicycle uses, and ornamental designs have changed the front assembly as well as the rest of the bicycle.
The Head Tube
The head tube is a tubular member attached to the frame connecting the top tube and down tube.
The head tube is the stationary part of the front assembly that allows the handle bar and fork to rotate within it. Bearings in the head tube allow the handle bar and fork to rotate with little resistance, but provide structural support. The head tube has remained relatively unchanged since the first bicycle. One change made to the head tube is the angle of the tube. The angle of the tube can be changed for specific applications like mountain biking or touring.
The fork is the Y-shaped member connecting the front wheel to the head tube. Its basic components are the steering tube (or steerer) that interfaces directly with the handlebar assembly; the crown at the base of the steerer; and two blades. On inexpensive bikes these blades are straight, while on many quality and performance bikes the blades can be bent or even curved to place the axle more forward of the center of gravity. Curved blades can also add a degree of shock absorption. At the end of the blades are dropouts that hold the front axle in place during riding and allow for easy wheel removal.
The standard fork in its simplest form has been a part of the bicycle since its earliest incarnations in the 19th century. It only makes sense to a designer to distribute the load on the front axle symmetrically in order to aid in the rider's balance and supplement the bike's overall stability. This also reduces the individual loads on each point that the fork contacts on the axle, reducing the chance of overloading and shearing at these junctions. While the design has evolved from the straight iron columns of the penny-farthing to today's sleekly curved blades, crafted from materials ranging from steel to magnesium to carbon-fiber, its basic elements remain firmly in place.
In recent yeas, the fork has evolved to meet specialized uses. Most noted is the integration of spring-damper suspensions to reduce shocks to the bodies of mountain bikers. Most forks using this new technology simply incorporated a spring-damper systems into each prong of the fork. However, more recently, a bicycle manufacturing company has invented a single arm spring-damper fork. Cannondale's Lefty fork is a new age, complete redesign of the fork. The Lefty was designed to meet the needs of mountain bikers. The off-road nature of mountain biking subjects the not only the bicycle, but also the rider to large stresses and impacts. Cannondale has sought to create a light-weight, durable, smooth traveling, responsive fork that meets or exceeds the needs of riders.
The Lefty fork is attached to the head tube by the two chrome brackets at the top of the fork. A shaft is placed through the head tube/bearings and connected to the chrome brackets. This shaft is connected to the handle bar via a stem to allow for rotation of the fork. The front wheel is attached to the fork by means of a single attachment point axle. The Lefty fork is designed to withstand the axial and torsional stresses applied to it during normal use. The Lefty fork is specially designed to meet the needs of of the intended user requiring a lot of user input during the inital design process as with many specialty parts.
The Handle Bar
The handle bar is the horizontal member that the rider grips and turns.
The handle bar is the bar on which the rider supports him/herself with his/her arms and steers the bicycle (Note: steering is a two part process-the handle bars are turned and the bike is tilted in the intended direction of travel). The handle bar is connected to the fork via a stem. The handle bar is a key user interface of the bicycle. The handle bar is not only used to steer the bike, but also supports the brake levers and gear shifters. Handle bars have evolved over time for functional and comfort reasons. Two common types of handle bars are found today - the standard, straight handle bar and the touring/racing handle bar.
The straight, or "flat," handlebar, is most often found on mountain bikes and children's bicycles. The bar is simply a straight, horizontal column with the grips at either end, clamped in the center to the steering tube. Its simplicity of design lends itself to the fact that it's been a common sight on bicycles dating back to the earliest hobbyhorses. Design evolution has led it to its modern incarnations, though its most basic elements remain.
A common derivation of the flat handlebar is the "riser" bar. This is essentially the same as the flat, save for the fact that the bar is curved upward from the central clamp to add some additional height to the grips. This is common on children's or casual riders' bikes and can also be found on mountain bikes.
A touring/racing handle bar has a distinctive undercut curve to it. The handle bar has two grip positions for two different riding positions. The top position allows for an upright riding position while the lower position allows for a crouched position. These two riding/hand positions have come from different riding situations. A crouched position makes a rider more aerodynamic in order to achieve greater speeds. The upright position creates more drag allowing the rider to decelerate more rapidly from high speeds.