Choppers
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Wikipedia-Article "Choppers"
Chopper refers to a particular type of motorcycle that was radically customized to meet the owner's needs and desires, archetypical examples of which being the Harley-Davidsons as seen in the 1969 movie Easy Rider.
In California and Florida of the 1950s and 1960s, some motorcycle enthusiasts removed (or chopped) all parts which were deemed too big, too heavy, too ugly and/or not absolutely essential to the basic functionality of the machine. Typical elements fitting these criteria would be fenders, turn indicators, and even front brakes. As well, almost certainly the large, spring-suspended saddle was removed in order to sit as low as possible on the motorcycle's frame, which in most cases was a rigid "hard tail", as Harley-Davidson introduced rear suspension in 1958.
Forward-mounted foot pegs replaced the standard large 'floorboard' foot rests. Also, the standard larger front wheel, headlight and fuel tank were replaced with much smaller ones. Many choppers were painted either in all [preferably flat] black or in shiny metallic colors. Common, too, were many chromed parts (either bolt-on replacements or manually chromed stock parts). According to the taste and purse of the owner, high handle bars, stretched and raked front forks, aftermarket exhaust pipes were added. Laws required (and in many locales still do) a retention fixture for the passenger, so vertical backrests called sissy bars were a popular installation, often sticking up higher than the rider's head.
While the decreased weight and lower seat position improved handling and performance, the main reason to build a tough-looking chopper was more likely to show off and provoke others by riding a machine that was stripped and almost nude compared to the softer-styled stock Harley-Davidsons, let alone the oversized automobiles of that time.
Choppers enjoyed a large resurgence in popularity in the late 1990s with companies like Jesse James' West Coast Choppers producing extremely expensive chopper-style bikes and a wide range of chopper-themed name-brand merchandise such as clothing, automobile accessories and stickers.
A distinction should be noted between true chopper (or chopper-style) motorcycles, and custom motorcycles, or 'custom cruisers'. Despite the name, a large percentage of the motorcycles produced by popular companies such as Orange County Choppers are better described as 'custom'.
On this same subject a distinction should be made between choppers and bobbers. While both tried to improve performance by removing any part that didn't make the motorcycle perform better, they differed in an important way. Bobbers kept the original factory frame, while choppers have a modified from the factory frame.
When the guys were stripping their stock bikes and bobbing their fenders, the term "bobber" was born. When the guys started cutting (or chopping) and welding their frames thereby repositioning/restyling them, the term "chopper" was born. Chopping was the next phase in the evolution that followed bobbing. While people assume that the chopper style motorcycles were built purely for aesthetics, there is a real performance advantage to the raked front end on these choppers. These motorcycles have a much more stable feel at high speeds than motorcycles with original factory front suspensions. However, like any other modification, there's a downside: the raked front end feels heavier and less responsive at slow speeds or in curves & turns. This is due to the longer trail measurement associated with more rake.
Rake and trail are the measurements that make up frame geometry. Without going into all the geometric terminology, rake and trail can be explained in a simple manner. Rake (also known as Castor Angle) is the angle of the steering head (and consequently the forks as well as on most bikes they are parallel) in relation to a perpendicular line going from the ground through the steering head. A steeper angle yields a shorter wheelbase, a larger angle yields the chopper-esque longer wheelbase.
Trail is a somewhat confusing concept, hopefully this will make it easier to comprehend. The measurement itself is taken by drawing an imaginary line through the steering axis to the ground. Next drop a perpendicular line from the front axle to the ground, which in any production motorcycle should fall some distance behind the point where the steering axis line touches down. The distance between these two points is your trail dimension (and hence the name, the drop point "trails" the steering axis point).
Trail ultimately defines the handling characteristics of a motorcycle, how stable it will be at higher speeds, how easy it will flick through S-turns, and how easy it will be to control at sub-idle parking lot manoeuvres. Bikes with a short trail will be real easy to handle at slow speeds and quite responsive when the road gets occupied with S-turns, but at higher speeds these bikes will respond more to the road conditions and feel a bit twitchy. On the other side of the coin, bikes with longer trail dimensions may handle like a wheel barrow in the parking lot, require a bit more encouragement to tackle an S curve, but track straight and true like an arrow at freeway speeds, offering little response to the road until the handlebars are activated by the rider. The trick for the motorcycle designer is to find some happy medium for the intended design.
Typically bikes with greater rakes have longer trail dimensions. However, the design of the triple trees is what eventually defines the final trail dimension. Offset is measured by drawing an imaginary line from the center of one fork tube to the other, then dropping a perpendicular line from the center of that line to the center of the steering stem. The distance of this perpendicular line is the triple tree offset. What this does is position the front axle to a point where the trail can be made to a suitable position. This means that the closer the forks are to the steering stem (shorter offset) the longer the trail can be modified, as the axle is being positioned further back from the steering axis to ground contact point. Conversely, the farther apart the forks are from the steering stem (longer offset) the shorter the trail, as the axle is positioned closer to the steering axis line.
Which brings up one more option a chopper builder has: raked trees. Raked trees are designed so the lower tree sticks out further than the upper tree, thus increasing the rake of the forks in relation to the steering head rake. What this does, for those still following along all the imaginary lines, is position the axle closer to the frame rake measurement line, or shortening the trail. Thus, when adding raked trees to a raked frame (which sports a longer trail), the trail is shortened to a more manageable level. However, be warned that adding raked trees to a frame with short rake and trail can be hazardous, as shortening an already short trail measurement can lead to an unstable situation as speed increases. Misuse of raked trees can be quite dangerous, so a bit of research is in store before turning the first wrench on any chopper project. Just remember that because it looks good in a magazine doesn't automatically mean it will work on your bike.