Abstract:
A front bicycle derailleur which utilizes a substantially annular chain guide for engagement and disengagement of the bicycle chain with multiple chain rings of a crankset. The annular chain guide provides an opening for the bicycle chain to pass through. The opening is sized only slightly larger than the cross section of the bicycle chain and is smooth and rounded along the inner surfaces that come in contact with the bicycle chain. The relatively small opening allows for precise and efficient positioning of the bicycle chain. The annular chain guide also serves to maintain the position of the bicycle chain to prevent derailment or unwanted shifting of the bicycle chain during pedaling.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to bicycle derailleurs. More specifically, this invention relates to a front bicycle derailleur which incorporates a chain guide which maintains the lateral position of the bicycle chain, reduces chain wear and drag, and keeps the bicycle chain from derailing off of a plurality of chain rings on a crankset. 
     2. Background of Related Art 
     Most bicycles have multiple gears with front and rear derailleurs to change gears. A front derailleur is used to shift a bicycle chain between two or more chain rings of a crankset. Chain rings vary in diameter, each having a different number of teeth for engagement with the bicycle chain. The force required to turn the crank is determined, in part, by the particular chain ring the bicycle chain is engaged with. The size of the chain ring can also determine the number of revolutions that will be required of the crank in order to travel a certain distance. By changing the chain engagement from a chain ring of one size to another, the bicyclist can strategically choose how much force will be required to be applied to the cranks, as well has how many revolutions the cranks will make in order to travel a relative distance. 
     A front derailleur is typically mounted on the seat tube of a bicycle frame and near the chain rings. The front chain rings are typically arranged so as to be concentric with, and parallel to each other. The smallest chain ring is typically closest to the bicycle frame with the chain rings progressively growing in diameter as they get further from the bike frame. The purpose of a front derailleur is to urge the bicycle chain laterally away from the currently engaged chain ring and towards a chain ring selected by the rider through means of a properly connected shifting device. Front derailleurs of various designs have been utilized to perform this function and most have similar features. 
     Construction and operation of a basic front derailleur is described in U.S. Pat. No. 4,734,083 to Nagano. The Nagano front derailleur includes a member for fixing the front derailleur to the bicycle, a four pin linkage mechanism to effect a pantographic type movement of two guide members, the guide members typically being designated as the inner guide member and the outer guide member. When the assembly is activated to move away from the bicycle frame and toward a larger chain ring, the inner guide pushes the bicycle chain laterally away from the bike frame until the bicycle chain leaves the currently engaged chain ring and engages the next chain ring. The action of urging the bicycle chain onto a larger chain ring often involves the step of pressing the bicycle chain against the side of the larger chain ring. By pressing the bicycle chain against the chain ring, friction combines with the circular motion of the chain ring to “pull” the bicycle chain up and on to the chain ring. When the assembly is activated to move toward the bicycle frame and toward a smaller chain ring, the outer guide urges the bicycle chain in a similar manner, with the outer guide pressing the bicycle chain off of the larger chain ring, and then allowing the bicycle chain to fall onto the smaller chain ring. 
     The inner and outer guides are spaced at a width which is wider than that of the bicycle chain, often one and a half to two times as wide as the bicycle chain. This allows the bicycle chain to run between the guides without contacting the guides while also allowing for some lateral movement of the bicycle chain which occurs when the bicycle chain is changed from one gear to another by a rear derailleur on a rear sprocket set. The inner and outer guides each typically comprise a substantially flat elongated surface. The guides are placed substantially parallel to one another and are connected together with a front and rear link. An elongated spatial channel, often referred to as a cage, is thus defined by the inner and outer guides and the front and rear links. The bicycle chain then passes through the cage without touching the inner and outer guides or the front and rear links during normal operation. There are typically multiple links of chain within the spatial area defined by the cage at any given time. 
     A typical front derailleur requires periodic adjustment to prevent the bicycle chain from engaging an undesired sprocket, or disengaging all sprockets (also known as derailing). A derailed bicycle chain causes complete loss of power transmission to the driving wheel. Bicycle chain engagement with an undesired chain ring causes the bicyclist to either apply more or less force to the cranks, or perform fewer or greater crank revolutions than would be desired. Such problems are particularly annoying to the bicyclist when ascending a slope. Because the cage of a derailleur is significantly wider than the width of the bicycle chain, a slight misadjustment of the front derailleur can allow for either of the above situations to arise during normal bicycling activities. 
     One solution for bicycle chain derailment is found in a mechanism referred to as a chain guide. The general design and function of a chain guide can be seen in U.S. Pat. No. 5,782,714 to Osgood. The Osgood device is a stationary member affixed to the bicycle seat tube to prevent the bicycle chain from disengaging laterally toward the bicycle frame from the chain ring closest to the bicycle frame. The Osgood device thus places a limit on the inward movement of the bicycle chain but does not prevent a derailment of the outermost large chain ring. Another approach to bicycle chain derailment is a second outer chain guide placed on the outside of the largest chain ring. This outer chain guide is circular, typically a slightly larger diameter than that of the largest chain ring, and is placed concentric with, and adjacent to, the largest chain ring. This outer chain guide places a limit on the outward movement of the bicycle chain. However, an outer chain guide such as this is often cumbersome and unsightly. Neither of these chain guides prevent the bicycle chain from disengaging the selected chain ring to engage with a non-selected chain ring. Thus there is a need in the art for a front derailleur with a chain guide that prevents derailments, both inward and outward, and also prevents the bicycle chain from disengaging a selected chain ring and engaging a non-selected chain ring. 
     SUMMARY OF THE INVENTION 
     The present invention provides a front derailleur for engaging and disengaging the bicycle chain among various sized chain rings on a bicycle crankset. The present invention further provides a chain guide integrated with the front derailleur to maintain proper alignment of the bicycle chain with a preselected chain ring. 
     The present invention comprises an annular chain guide attached to a positioning mechanism mounted on a bicycle frame and adjacent to the chain rings. The annular chain guide serves as both a derailleur for disengaging the bicycle chain off of one chain ring for subsequent engagement with a different chain ring and also as a chain guide to prevent inadvertent shifting of the bicycle chain from one chain ring to another, thus preventing derailment of the bicycle chain. 
     The annular chain guide greatly reduces surface to surface contact between the chain and guide, thus reducing wear on the chain and the derailleur. The novel chain guide does not press the chain against the chainring during upshifting, but rather guides the chain up and onto the chainring with an annular chain guide positioned behind the chainrings. This is in contrast to a standard front derailleur in which, during upshifting, the inner chain guide presses against the chain which then presses against the chainring onto which it is being shifted, creating drag and making it difficult to shift smoothly, especially when the bicycle is moving uphill. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, which depict presently preferred embodiments of the invention and in which like reference numerals refer to like parts in different views: 
     FIG. 1 is a view of a preferred embodiment of the present invention, as viewed from the front of a bicycle; 
     FIG. 2 is a view of the embodiment of the invention of FIG. 1, viewed from the side of the bicycle; 
     FIG. 3 is a view of the embodiment of invention of FIGS. 1 and 2, viewed from above; 
     FIG. 4 is a perspective view of an alternative embodiment of the present invention. 
     FIG. 5 is an exploded view of elements of the embodiment of FIG. 4; 
     FIGS. 6A and 6B are views of a chain guide for use in the embodiment of the invention shown in FIGS. 1 through 3. 
     FIGS. 7A and 7B are views of an alternative embodiment of the chain guide for use in the embodiment of the invention shown in FIGS. 1 through 3. 
     FIGS. 8A and 8B are views of a chain guide for use in the embodiment of the invention shown in FIGS. 4 and 5. 
     FIGS. 9A and 9B are views of an alternative embodiment of the chain guide for use in the embodiment of the invention shown in FIGS. 4 and 5. 
     FIG. 10 is a perspective view of a front derailleur including a hinged mounting mechanism in accordance with the present invention. 
     FIG. 11 is a perspective view of a front derailleur including a braze-on mounting mechanism in accordance with the present invention. 
     FIG. 12 is a perspective view of a front derailleur including a bottom bracket mounting mechanism in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 through 3, a front derailleur  10  is shown comprising a mounting member  12  fastened to a bicycle frame member, such as the seat tube  20 , and disposed adjacent to the chain rings  22 ,  24 , and  26  of a bicycle crankset. While three chain rings are shown in FIGS. 1 through 3, it would be obvious to apply the instant invention to a bicycle configured with any number of chain rings, e.g., a crankset with only two chain rings. 
     The mounting member  12  is a split clamp which allows for installation on numerous bicycle frames. The mounting member  12  is shown as being a two piece clamping mechanism wherein fasteners  18  provide the clamping action between a front mounting member  14  and a rear mounting member  16 . Fasteners  18  may be screws, cam locks, rivets, hinge members or other means for securing members  14  and  16 . It is contemplated that mounting member  12  could alternatively be a bracket for fastening to a braze-on mount on the seat tube of the bicycle frame, or a bracket for fastening to another structural member of the bicycle frame. All of the above mounting methods are known to one of skill in the art and thus, are not further described herein. 
     Attached to the mounting member  12 , are two linear guide rods  28 . The linear guide rods  28  are cylindrical in shape and are typically formed of a metal such as stainless steel with a polished finish. The linear guide rods  28  are placed next to each other in a parallel orientation. Attached at the top end of the linear guide rods  28  is a structural member  30  for maintaining the parallel relationship of the two linear guide rods  28 . A sliding arm  34  houses two linear bearings  32  which are slidably disposed on and around the linear guide rods  28 . The linear guide rods  28  constrain movement of the sliding arm  34  along the length of the linear guide rods  28 . An angle θ is defined using the seat tube  20  as a reference line and by drawing a line from the vertical tip of the largest chain ring  26  through the vertical tip of the smallest chain ring  22 . The linear guide rods  28  are preferably oriented at the angle θ placing the top of the linear guide bearings  32  laterally away from the bicycle frame towards, and adjacent to, the chain rings  22 ,  24  and  26 . It will be appreciated that the specific value of the angle θ depends on the sizes and spacing of the chain rings used, and the invention is not limited to a particular value for θ. 
     Alternative shapes and designs could be utilized for the linear guide rods  28 . For example, the linear guide rods  28  need not be cylindrical. However, whatever shape the linear guide rods  28  are chosen to be, the linear bearings  32  must be compatible with, and be slidably disposed on, the linear guide rods  28 . Likewise, a different number of linear guide rods  28  may be employed, including the use of only one linear guide rod  28 . However, if only one linear guide rod  28  is utilized, other means (such as keying the guide rod  28 , with a slot for example, and then matching linear bearing  32  to the guide rod) must be employed to constrain rotational movement of the sliding arm  34 . 
     A substantially annular chain guide  236  is attached to the sliding arm  34 , and positioned so as to receive a bicycle chain  42  therethrough. The annular chain guide  236  is preferably formed of stainless steel for strength, durability and corrosion resistance. The opening in the annular chain guide  236  may be sized only slightly larger that the cross-section of the bicycle chain  42 . The annular chain guide  236  is coupled to the sliding arm  34  by means of a stem  240 . The stem  240  is fixedly attached to the annular chain guide  236 , which may be accomplished by welding, by other bonding methods, by mating threads, or by fasteners. The stem  240  may be coupled to the sliding arm  34  by insertion into a bore (not shown) in the sliding arm  34 . The stem  240  is a pre-selected length allowing for adjustment of the stem  240  axially within the bore. The stem  240  is keyed, preferably cylindrical with a flat section cut lengthwise on one side of the cylinder. A set screw (not shown) is located in the sliding arm  34  and presses against the flat section of the stem  240  to fix the position of the stem  240 , both axially and radially, within the bore. 
     Other means may be employed for coupling the annular chain guide  236  to the sliding arm  34 . For example, the annular chain guide  236  and stem may be formed as one element either by machining or casting. Alternatively, an integrated one piece unit may be employed, wherein the stem  240  is eliminated and the annular chain guide  236  is formed as an integral component of the sliding arm  34 . Again, this may be accomplished through either machining or casting of the integrated unit. Arrangements such as these have the benefit of fewer required parts for the assembly of the derailleur  10 . 
     One embodiment of annular chain guide  236  for use with the embodiment of the invention shown in FIGS. 1-3 is depicted in FIGS. 6A and 6B. An annular insert  238  is housed within the an outer rim  237 . The annular insert  238  may be formed of a relatively hard non-metallic material such as nylon, polytetrafluoroethylene, or other teflon-type materials which have desirable wear and low friction properties. By placing an annular insert  238  in this location, the bicycle chain  42  will be in contact with a wear surface which is made of a material softer than that of the bicycle chain  42 . This will prevent undue wear on the bicycle chain, which wear occurs when any derailleur repeatedly engages a bicycle chain to urge the bicycle chain from one chain ring to another. The opening in the annular insert  238  may be sized only slightly larger than the cross-section of the bicycle chain  42 . 
     Referring to FIG. 6A, the annular chain guide  236  of the presently preferred embodiment is shown as being annular, in the sense that it is a continuous band or ring-like element, but which is substantially rectangular rather than circular. The corners, both inside and outside, are preferably rounded. The annular insert  238  is shown as having a substantially rectangular outer perimeter sized and shaped to match the inside surface of the outer rim  237 . As seen in FIG. 6B, the inside surface of the outer rim  237  and the outer perimeter of the annular insert  238  are substantially mating parts. A lip  110  is formed on the outer perimeter of the annular insert  238 , and a matching groove  112  is formed along the inside surface of outer rim  237 . The annular insert  238  is coupled to the outer rim  237  by positioning the lip  110  of the annular insert  238  into the groove  112  of the outer rim  237 . The annular insert  238  may be installed by pressing it into the opening of the outer rim  237  until the lip  110  is securely resting in the groove  112 . Alternatively, adhesive may also be used to secure the annular insert  238  within the annular chain guide  236 . A small amount of elastic deformation of the annular insert  238  is allowed to accomplish installation of the annular insert  238 . Removal of the annular insert  238  is accomplished in a similar manner by pressing the annular insert  238  out of the outer rim  237  with an appropriate amount of force. Thus, the annular insert  238  is secured to the outer rim  237  during operation of the bicycle, but may be removed for replacement or for other maintenance requirements. 
     Referring again to FIG. 6A, the annular insert  238  defines a substantially parallelogrammatic aperture  314  through which the bicycle chain  42  passes. The aperture  314  is defined by an outer wall  280 , an inner wall  284 , a top wall  282  and a bottom wall  286 . Two obtuse corner walls  216  and  218  are formed in the aperture  314 . The corner upper-outer corner wall  216  and lower-inner corner wall  218  are oriented at an angle substantially transverse or perpendicular to the line of movement of the annular chain guide  236 . The corners of the aperture  314  are radiused. By orienting the aperture  314  as described above, the upper-outer corner wall  216  acts to pull the bicycle chain  42  both inward and downward during the operation of the derailleur  10  in urging the bicycle chain  42  toward a smaller chain ring. Likewise, the lower-inner corner wall  218  acts to push the bicycle chain  42  both upward and outward when urging the bicycle chain  42  toward a larger chain ring. Top and bottom walls  282  and  286  and inner and outer walls  284  and  280  are preferably spaced far enough apart to accomodate changes in vertical and lateral position of the chain associated with different rear sprocket positions. Alternatively, aperture  314  may be circular, oval, or any other shape which is effective for urging the bicycle chain from one chain ring to another, and which does not catch or bind the chain. 
     Referring to FIG. 6B, the walls  280 ,  282 ,  284 , and  286  of the aperture  314  are smooth and rounded as they are traversed from the front side  120  to the back side  122 . The rounded and smooth configuration of the aperture  314  allows the annular insert  238  to interact with the bicycle chain  42  while having a minimum amount of surface contact between the two elements. This configuration prevents the bicycle chain  42  from catching or binding, and reduces wear on the interacting surfaces. 
     Referring back to FIG. 1, a control wire  44 , also know as a “shifter cable”, is attached to the sliding arm  34 . The control wire  44  is also attached to a shifting device (not shown) which allows the bicyclist to control the movement of the sliding arm  34 . A biasing member, shown as a spring  46 , has one end attached to the sliding arm  34  and the other end attached to either the mounting member  12 . Thus the spring  46  acts to bias the sliding arm  34  in downward manner. 
     Still referring to FIG. 1, operation of the front derailleur  10  will now be explained. A bicyclist, desiring to engage the bicycle chain  42  with a particular chain ring  26 , will activate the shifting device (not shown) accordingly. In activating the shifting device, the control wire  44  is either pulled upwards, or relaxed and allowed to move downwards, relative to the mounting member  12 . If the control wire  44  is pulled upwards, the sliding arm  34  is motivated upward, and outward, along the axis of the linear guide rods  28  as defined by angle θ. The aperture of the annular insert  238  engages the bicycle chain  42  and urges the bicycle chain  42  upward and outward from one chain ring  24  for engagement with the next larger chain ring  26 . The chain is urged to a position slightly above the chain ring and then allowed to lower slightly so that it engages with the chain ring. If the control wire  44  is relaxed, the spring  46  pulls the sliding arm  34  downward, and inward, along the axis of the linear guide rods  28 . Again, the aperture of the annular chain guide  236  engages the bicycle chain  42 , this time motivating the bicycle chain  42  downward and inward from one chain ring  24  to the next smaller chain ring  22 . Adjustable stops  48  and  50  are attached to the rear mounting member  16  and the structural member  30  respectively. The adjustable stops  48  and  50  serve to limit the downward and upward travel of the sliding arm  34 . By properly limiting the motion of the sliding arm  34 , the bicycle chain  42  will also be limited in its range of movement as defined by the distance between largest and the smallest chain rings  26  and  22  respectively. The small aperture in the annular chain guide  236 , in combination with the properly defined limits of movement of the sliding arm  34 , work to prevent improper disengagement or derailment of the bicycle chain  42 . Once the shift has been completed (the chain has been shifted from one chain ring to another), annular chain guide  236  is positioned so that bicycle chain  42  is centered within and does not rub against annular chain guide  236 . 
     A pulley  52  is attached to the structural member  30 . The pulley allows for use of a control wire  44  that pulls downward instead of upward. The control wire  44  in a bottom pull design would run through the pulley  52  and then connect to the sliding arm  34 . Thus the preferred embodiment is easily adapted to bicycles having either top pull or bottom pull designs. 
     While various elements of the disclosed derailleur  10  have been discussed as being formed from stainless steel, other materials may be utilized in the construction of the derailleur  10  depending on the overall intended use of the bicycle to which the derailleur  10  will be mounted. Some of the contemplated materials would include carbon steel, aluminum, titanium, or a composite material such as resin-impregnated carbon fiber. Each of these materials has various desirable qualities and selection of material may depend on numerous factors such as corrosion protection, wear characteristics, strength to weight ratio, and cost to manufacture and assemble. The selection of appropriate materials is within the knowledge of one skilled in the art. 
     It is noted that various modifications could be made to the present invention without departing to from the spirit or scope of the invention. For example, the control wire  44  could be arranged so that it pulled in the downward direction, with the spring  38  biasing the sliding arm  34  in the upward direction and the pulley  52  being relocated accordingly. Also, alternative mechanisms could be utilized to induce the motion of the sliding arm  34 . In another embodiment, hydraulics may be employed to control the motion of the sliding arm  34  in place of the control wire  44 . Yet another embodiment includes an annular chain guide  236  constructed of a single material, without an annular insert  238 , as shown in FIGS. 7A and 7B. The shape and functioning of the chain guide  236  is the same as the chain guide depicted in FIGS. 6A and 6B; however, because the surface of the guide contacting the chain is a harder material (e.g., metal) the wear to the chain will be increased, while the wear to the chain guide will be reduced. Yet another embodiment may include a second mounting member coupled between structural member  30  and the seat tube or other bicycle frame member to stabilize the one or more linear guide rods  28  when the bicycle chain  42  is being shifted. Furthermore, various combinations of alternative elements as discussed are within the scope and spirit of the present invention. 
     Referring now to FIG.  4  and FIG. 5, another embodiment of a front derailleur  60  according to this invention is disclosed. A mounting member  75 , is fastened to a bicycle frame member such as a seat tube (not shown). The mounting member  75  is a split clamp which allows for installation on numerous bicycle frames. The mounting member  75  is shown as being a two piece clamping mechanism wherein fasteners  78  provide the clamping action between a front mounting member  76  and a rear mounting member  77 . Front and rear mounting members  76  and  77  may also be hinged together at one end to form a mounting member  75  with a hinged clamping mechanism. Fasteners  78  may be screws, cam locks, rivets or other means for securing members  76  and  77 . It is contemplated that mounting member  75  could alternatively be a bracket for fastening to a braze-on mount on a seat tube of the bicycle frame, or a bracket for fastening to another member of the bicycle frame. All of the above mounting methods are within the knowledge of one skilled in the art and thus, are not further described herein. 
     A pivot arm  62  may be pivotally connected to the rear bracket member  77  by means of a bearing pin  63  or other suitable means. A coil spring  70  is housed between the rear mounting member  77  and the pivot arm  62  concentric with the bearing pin  63  to provide a torsional bias to pivot arm  62 . 
     An annular chain guide  90  is connected to a stem  94  which is inserted into a bore  98  in the pivot arm  62 . The stem  94  is keyed to the bore and is axially adjustable within the bore, A set screw  96  secures the position of the stem  94 . Two embodiments of the chain guide  90  are shown in detail in FIGS. 8A,  8 B,  9 A and  9 B. A bicycle chain  42  is received through the aperture of the annular insert  92 , or alternatively through the aperture of the annular chain guide  90  if an annular insert  92  is not being utilized. 
     A slot  64  is provided in the back side of the pivot arm  62 . The slot  64  has a shouldered surface  66  allowing the head of a fastener  68  to be seated thereon. The fastener  68  allows for attachment of a control wire  102 . A stop  72  is shown on the top side of the pivot arm. The stop  72  interacts with an adjustment screw  74 , which is threaded in the rear mounting member  77 . The stop  72  and the adjustment screw  74  work together to define a rotational limit of the pivot arm  62 . A similar stop and adjustment screw (not shown) are found on the bottom side of the derailleur  60  to limit rotational movement of the pivot arm  62  in the opposite direction. 
     The front derailleur  60  is operated by a bicyclist activating a shifting mechanism, or shifters, (not shown) which in turn causes the control wire  102  to either pull down on the back portion of the pivot arm  62 , or to relax the tension on the control wire  102 . When the control wire  102  is relaxed, the coil spring  70  acts torsionally to rotate the front portion of the pivot arm downward until the pivot arm  62  has reached its limit of rotation. Thus, the movement of the pivot arm  62  controls the position of the annular chain guide  90 . The annular chain guide  90  travels in an arcuate path urging the bicycle chain  42  upward and outward, to the next largest chain ring (not shown in FIG. 4 or FIG.  5 ), or downward and inward to the next smallest chain ring. 
     FIGS. 8A and 8B depict a preferred embodiment of the chain guide used in the embodiment of the invention shown in FIGS. 4 and 5. The chain guide differs from the chain guide used with the embodiment of the invention in FIGS. 1 through 3 in that the shape of aperture  114  has been modified so that the side of the aperture contacting the chain is oriented appropriately throughout the movement of the chain guide. In general, the chain is urged downward and inward by upper wall  80  of aperture  114  and upward and outward by lower wall  84  and lower-inner wall  83  of aperture  114 . It will be appreciated that, because the chain guide moves in an arc rather than in a linear pattern, the side of the aperture contacting the chain varies as the chain guide is moved. Thus, when the chain guide is near the bottom of its arc (near the smallest chain ring) the chain will be urged upward by lower wall  84 , and will contact lower wall  84  in the region. closer to corner  119 . As the chain guide is moved upward and outward, in the arcuate path indicated in FIG. 4, the chain will move along lower wall  84  until it reaches corner  118 , and then move onto lower-inner wall  83 , until at the top of its arc, it will contact lower-inner wall  83  closer to corner  117 . When the chain is to moved downward, at the highest part of the arc chain  42  will contact upper wall  80  closer to corner  116 . As the chain guide is moved downward and inward, the chain will move toward corner  115  along upper wall  80 . The embodiment of the chain guide  90  shown in FIGS. 8A and 8B includes an annular insert  92  which is secured to outer rim  93  by means of a lip  810  on insert  92  which fits into groove  812  formed in outer rim  93 . The chain guide shown in FIGS. 9A and 9B is identical in shape to the chain guide of FIGS. 8A and 8B, but is constructed of a single material and does not include an annular insert  92 . 
     Again, modifications to the disclosed embodiment are contemplated as being within the scope and spirit of the invention. For example, various shapes and configurations of the annular chain guide  90  and annular insert  92  may be employed in the instant embodiment. Likewise, alternative embodiments are contemplated wherein the stem  94  is coupled to the swing arm  62  in a different manner, such as by welding or another type of bonding. The stem  94  could also be eliminated altogether to create an integral unit of the annular chain guide  90  and the swing arm  62 . Furthermore, the components of the derailleur  60  as just described may be made from various materials such as stainless steel, aluminum, titanium, or composite materials depending on the desired corrosion and wear resistance, as well as the desired strength to weight ratio. 
     In yet another embodiment, a positioning member may comprise a four pin linkage mechanism as described in U.S. Pat. No. 4,743,083 to Nagano, the disclosure of which is herein incorporated by reference. In this embodiment the annular chain guide  236  (or  90 ) is coupled to, and positioned by, a four pin linkage mechanism. 
     FIG. 10 is a perspective view of a front derailleur  1000  in accordance with the present invention including a hinged mounting mechanism  1002 . FIG. 11 is a perspective view of a front derailleur  1100  in accordance with the present invention including a braze-on mounting mechanism  1102 . FIG. 12 is a perspective view of a front derailleur  1200  in accordance with the present invention including a bottom bracket mounting mechanism  1202  configured for attaching front derailleur  1200  to a bottom bracket (not shown). 
     Although this invention has been described with reference to particular illustrated embodiments, the invention is not limited to the embodiments described. Rather, it should be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention as defined by the following claims.