Abstract:
A modular suspension strut apparatus provides a bicycle with a relocatable center of gravity to adjust the bicycle to the rider and to terrain conditions. The combined center of gravity of a bicycle and rider is adjustable by moving and clamping a strut within a strut tube. A crank axle housing at the bottom of the strut and a seat post at the top are shifted vertically, while maintaining a fixed seat axle distance. The strut is resiliently mounted within the strut tube by an internal or external spring or springs to absorb shocks. Spring force is adjusted by adjusting an air pressure with an external air pump or on board pumps. Spring forces may be adjusted while seated or in motion by turning knobs or handwheel rings and/or by other means. Strut movement within the strut tube is limited to axial reciprocation in a preset range. Elastomeric rings prevent shock at limits of the strut movements. The strut tube is made of three joined parts, a center tube and top and base guides. The guides connect to frame tubes and stays and provide bearings for the strut.

Description:
This is a continuation-in-part of Application 09/800,958 filed Mar. 8, 2001 now abandoned which was based on Provisional Application 60/187,878 filed Mar. 8, 2000. 

   BACKGROUND OF THE INVENTION 
   Bicycles have been and continue to be used by many for transportation, recreation and competition. Conditions on the road and off-road place demands on a rider&#39;s body, which may result in fatigue, discomfort and soreness. It is essential, then, that a rider be able to configure his bike to best accommodate his body and the frame. Needs exist for a means to easily and quickly adjust the static frame geometry. 
   In recent years, mountain bike suspension devices have expanded in variation and complexity, generating widespread interest and acceptance. Competitors in the sport need bicycle frames that reduce forces on the bike and shock to the rider. Off-road conditions increase the physical demands on a rider&#39;s body, thereby speeding fatigue and increasing discomfort. Needs exist for energy-absorbing apparatus for bicycles that reduce rider discomfort and fatigue and lessen frame loads. 
   Existing suspension devices have proven problematic. State-of-the-art suspension units fail to maintain the basic bicycle geometry. Critical spatial relationships, such as the distance between the seat and the pedals and frame angles relative to the wheelbase, are sacrificed in efforts to enhance comfort and reduce frame loads and rider fatigue. Current bicycle frames use rear wheel suspensions for absorbing energy. Rear wheels are trailing linked and sprung such that the wheels change relative to the static geometry of frame and wheel assemblies when energy is absorbed, compromising pedaling and braking efficiency. Seats may be sprung relative to the frames, but that results in undesirable seat/pedal distance variations. Other suspension designs, such as flex-stem handlebars, strut-type energy absorbing forks, and flex frames, are hindered by similar critical relationship flaws. 
   Needs exist for bicycle frames that do not compromise critical geometry when suspension devices are incorporated. Since weights of riders are typically six times that of bicycles, frequent and abrupt suspension movements and subsequent changes in bicycle geometry can decrease rider control, as well. Suspension systems that eliminate or substantially limit changes in the critical relationships of bicycle components are needed to enhance efficiency and control. 
   Suspensions need to be simple, sturdy and not susceptible to failure. Since off-road conditions are not constant, needs exist for suspension devices that are adjustable and easily customized by riders. Energy-absorbing mechanisms need to be compatible with conventional frame configurations and adaptable to newly designed lightweight frames. 
   SUMMARY OF THE INVENTION 
   This invention provides apparatus and methods to adjust the static frame geometry of the bicycle. One of the most effective ways to customize static frame geometry is to raise or lower the position of the bottom bracket, which houses the pedal crank spindle, relative to the frame. 
   Raising the bottom bracket provides more ground clearance, everything else being the same, but the key is, even slight adjustment here results in discernable and desirable changes in how the bike frame rides and feels to a given individual rider. 
   A self-contained, modular suspension strut assembly which provides for such adjustment and permits any competent custom frame builder or bike manufacturer to weld such assembly into various frame configurations is an object of the present invention. Such adjustability does not interfere with the function of the suspension strut. 
   The self-contained, modular strut assembly of the present invention comprises a top strut guide, a strut tube and a bottom strut guide. A bracket may be attached to the strut tube in certain embodiments for connecting the strut tube to a commercially available adjustable air spring or other energy-absorbing mechanism. The top strut guide, strut tube and bottom strut guide are unitized, for example by welding at the joints between tube and guides; this assembly is in turn welded into a bike frame in a manner similar to present fabrication practice. 
   In one form of the invention the bottom bracket of a bicycle, which houses the pedal crank spindle, relative to the frame, is secured in the desired position relative to the frame. In this embodiment, the bottom bracket position may be secured by adjustable clamp means. That allows a strut to be moved vertically relative to said clamp and frame, lifting or lowering the strut, seat and bottom bracket as a unit. The desired static position relative to the frame is secured by tightening said clamp. This embodiment does not provide for suspending the strut. 
   In a preferred embodiment of the invention, the strut is suspended in a way so that the strut, bottom bracket seat post and seat can move as a unit relative to the frame. Such movements are described in U.S. Pat. No. 5,553,880, which is incorporated herein by reference. In this invention, new strut assemblies and suspensions are described. This invention further provides adjustments of the suspension for positioning and controlling the range and limits of movement and increasing and decreasing mechanical and air spring forces and stiffness. 
   The components of the self-contained, modular strut assembly of the present invention are a top strut guide, a strut tube and a bottom strut guide. These components are unitized, for example by welding at the seams between the strut tube and the strut guides. A bracket may be attached to the strut tube for connecting the strut tube to a commercially available energy absorbing mechanism, for example an air spring. The strut is fitted through the guide/tube assembly extending vertically through the unitized top strut guide, strut tube and bottom strut guide. 
   In a preferred embodiment, the opening in the bottom strut guide is rectangular in shape. However, the opening may have a variety of shapes. The upper strut guide is circular, but may have other shapes as well. 
   A bottom bracket is attached to the bottom of the strut for attaching a pedal crank spindle and pedals. The assembled strut with the bottom bracket is slid upward through the bottom or base strut guide, the strut tube and the top strut guide. A strut/spring clamp fits over the upward extending portion of the strut. An additional clamp fits over the top extended portion of the strut for securing a seat post in the top of the strut. The bottom bracket may be adjusted vertically by loosening the upper strut/spring clamp, allowing the strut to be slidably moved relative to said clamp. Once the desired vertical position of the bottom bracket is achieved, this position is secured by tightening the strut/spring clamp around the strut. 
   A preferred embodiment of the modular strut assembly in the suspended strut form of the present invention comprises a bracket on the strut/spring clamp for connecting the strut to an externally mounted energy absorbing mechanism, such as, but not limited to, an adjustable air cylinder. A dust boot may extend from the bottom of the strut/spring clamp to the top of the top strut guide, for keeping out dirt and debris and sealing in lubrication. The dust boot may be expandable to adapt to different strut heights, and to flex with strut movement. A similar dust boot may be used at the bottom of the strut. 
   One embodiment of the suspended modular strut assembly of the present invention incorporates an energy absorbing mechanism such as, but not limited to, an air cylinder, housed along with the strut within the unitized top strut guide and strut tube. In a preferred embodiment, the strut tube has an outside diameter of 2.84 inches, however, the strut tube may have any outside diameter sufficient to accommodate components. The air spring fits within a chamber which extends through the top strut guide and the strut tube. In a preferred embodiment, the upper chamber is circular in shape; however the chamber may be rectangular, trapezoidal, square, triangular or oval in shape. The air spring is connected at the top to the strut/spring clamp and at the -a bottom to a bracket attached to the inside circumference of the strut tube. Alternatively, the bottom portion of the air spring may be connected to the lower strut guide. 
   A dust boot may be attached to the strut/spring clamp and the air spring and extend to cover the top portion of the top strut assembly. The dust boot functions to keep the strut and air spring free of dirt, debris and water. The dust boot is capable of expanding and contracting to accommodate various strut heights. 
   An additional clamp may be fitted around the strut above the strut/spring clamp for securing a seat post and adjusting the height of a seat. 
   In one embodiment of the present invention, energy absorbing mechanisms such as, but not limited to, two air cartridges, attached at lower ends to the strut tube, are attached at upper ends to the strut/spring clamp. The energy absorbing mechanisms may be attached to the strut/spring clamp by a bolt, pin or by other means. 
   In another embodiment, the energy absorbing mechanisms, for example, air cartridges extend through the top strut guide and the strut tube. The energy absorbing mechanisms are linked to share a common fill valve, which may be filled, for example, with hydraulic fluid or compressed air. 
   In one embodiment, the strut and both energy-absorbing mechanisms are housed within the top strut guide and the strut tube. In a preferred embodiment, the outer diameter of the strut tube measures 2.84 inches, however, the outer diameter of the strut tube may be varied. The strut is flanked by energy absorbing mechanisms, for example, two air cartridges, which extend through the unitized top strut guide and strut tube. 
   A dust boot connects to a stop ring extending around the strut/spring clamp. The dust boot extends downward and connects to the top portion of the top strut guide. The dust boot may be capable of expanding and contracting to accommodate vertically moving the strut and energy absorbing means. 
   One preferred embodiment of the modular strut assembly of the present invention incorporates an energy absorbing mechanism that is concentric to, and surrounds the strut. A coil spring, or an equivalent energy absorbing mechanism, surrounds the strut. The bottom of the coil spring is attached to or rests on an annular piston in an annular cylinder. Pressure in the cylinder may be adjusted to preload the coil spring. The annular piston rests atop the annular air chamber. The air chamber may have a valved port to adjust and preload the air pressure within the chamber. The strut has an annular lip which carries an O-ring located below the air chamber to limit rebound. 
   In that embodiment, the strut/spring clamp connects to a threaded sleeve which extends downward from the clamp and fits around the outer diameter of the strut. The stop ring has a cup which holds thrust needle bearings for easy adjustment. A threaded stop ring is connected to the sleeve just below the strut/spring clamp. The stop ring extends horizontally outward from the sleeve and has flanges which extend downward toward the top strut housing. 
   Alternatively and preferably, the invention uses double acting adjustable fluid filled shock absorbers which absorb energy and dampen responses in both up and down directions. Bumps are attached to the stop ring to provide for hand adjustment traction. In its engaged position, the stop ring rests on the upper surface of the spring above the outer lip of the top strut guide. 
   A dust boot attaches to the outer surface of the stop ring. The bottom portion of the dust boot floats around the outer lip of the top strut guide, allowing the stop ring to rotate for adjustment of spring pre-compression. 
   In a preferred embodiment, the strut tube assembly has top and bottom guides and a central oval tube. The top and bottom guides have strut-receiving apertures and weight reducing holes. The strut base has a rectangular cross-section which slides within the bottom strut guide. Weight-reducing holes extend horizontally through the lower section. The crank bottom bracket is welded to the bottom of the strut base. At its upper end, the strut is tubular, fitting snugly in the thru-bore of the upper guide. 
   New energy-absorbing apparatus for bicycle frames permit seat and pedal assemblies to maintain a fixed spatial relationship with each other while moving as units relative to bicycle frames. The present invention reduces shock to the rider and forces on the bicycle while minimizing change in the basic frame geometry. The seat and the pedal crank axle housing move vertically together as a single unit, thus maintaining the dimensional relationship between the two components. That allows for suspension action without altering the critical geometrical relationships of the bicycle. Frames can be both strong and lightweight, providing enhanced efficiency and control. 
   The present invention has an outer portion that forms part of the bicycle frame. Preferably, that portion has an outer tube that houses a close-fitting inner tube to which a seat and a pedal crank axle housing are mounted. The outer tube is a fixed part of the frame. The remainder of the bicycle frame members are connected to the outer tube. The outer tube and the inner tube are coupled such that movement of the seat and pedals, and hence movement of the inner tube is suspended and damped by spring means connected to the outer tube. The seat and the pedal crank axle housing maintain the same spatial relationship and move, relative the frame, as a unit. 
   The energy-absorbing apparatus is rugged, adjustable and compatible with existing conventional bicycle frame configurations and suspension devices. The modular strut suspension also allows for lighter frame structures. Cross-sectional shapes of the inner tube and the outer tube may prevent rotation relative to each other. 
   These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is an exploded view showing components of the self-contained, modular strut assembly of the present invention. 
       FIG. 1B  is an assembled view of the strut assembly. 
       FIG. 2  shows a detail of an embodiment of the modular strut assembly of the present invention in which an energy-absorbing mechanism is mounted external to the unitized strut tube and top strut guide. 
       FIG. 3  shows a detail of an alternative embodiment of the modular strut assembly of the present invention in which an energy-absorbing mechanism is housed within the unitized strut tube and top strut guide. 
       FIG. 4  shows an alternative embodiment of the modular strut assembly of the present invention in which two energy-absorbing mechanisms are connected to the strut and are housed within the strut tube and the top strut guide. 
       FIG. 5  shows a horizontal cross-sectional view of the embodiment of FIG.  4 . 
       FIG. 6  shows an embodiment of-the modular strut assembly of the present invention in which the energy absorbing mechanism is concentric within the strut tube and surrounds the strut. 
       FIG. 7  shows the modular strut assembly of  FIG. 6  in which the energy absorbing mechanism has a minimized envelope. Strut upward travel stops are shown in  FIGS. 6 and 7 . 
       FIG. 8  illustrates a bicycle frame in which the present invention is installed. 
       FIG. 9  is a view of a top strut guide similar to the top guide shown in FIG.  1 . 
       FIG. 10  is an elevation of the strut tube top guide shown in FIG.  9 . 
       FIG. 11  is a top view of a strut tube base guide. 
       FIG. 12  is an elevation of the strut tube base guide. 
       FIG. 13  is a cross-section of the strut tube base guide. 
       FIG. 14  is a plan view of a strut base. 
       FIG. 15  is a rear elevation of the strut base. 
       FIG. 16  is a cross-sectional side elevation of the strut base. 
       FIG. 17  is a cross-sectional detail of a lower end of a strut top. 
       FIG. 18  is an elevational detail of an upper end of the strut top. 
       FIG. 19  is an elevation of a strut clamp/spring mount. 
       FIG. 20  is a horizontal cross-sectional detail of the strut clamp/spring mount. 
       FIG. 21  is a perspective detail of a modular strut/frame showing a seat post, a strut and seat post clamp, an upper strut tube, spring adjuster and upper boot, a top strut guide and an upper portion of the strut tube and portions of a top tube and a seat stay. 
       FIGS. 22 and 23  are a top view and a side cross sectional view of a strut tube, top guide and internal spring housing and a strut clamp cylinder mount shown in FIG.  21 . 
       FIG. 24  is a side cross sectional view of the assembly of  FIGS. 22 and 23  with the spring. 
       FIG. 25  is a side elevation view showing a top cylinder mount with a support. 
       FIG. 26  shows the separate components of an alternate strut. 
       FIG. 27  shows an embodiment of the present invention shown  FIG. 26  having the inner tube and the outer tube coupled by an air cylinder. 
       FIG. 28  shows an embodiment of the present invention in its full up position having an air cylinder at the top of the telescoping unit underneath the seat and at the bottom of the telescoping unit above the pedal crank axle housing. 
       FIG. 29  shows an embodiment of the present invention in its full down position having an air cylinder at the top of the telescoping unit underneath the seat and at the bottom of the telescoping unit above the pedal crank axle housing. 
       FIG. 30  shows an embodiment of the present invention and the effects of downward force on the strut when riding on a flat surface. 
       FIG. 31  shows an embodiment of the present invention and the effects of downward force on the strut when riding on a downhill surface. 
       FIG. 32  shows an embodiment of the present invention and the effects of downward force on the strut when riding on an uphill surface. 
       FIG. 33  shows an embodiment of the present invention with the isolator located inside the strut assembly. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1A and 1B  show the components of the self-contained, modular strut and strut assembly  1  of the present invention. The modular strut tube assembly  2  comprises a top strut guide  3 , a main strut tube  5  and a bottom strut guide  7 . These components are unitized, for example, by welding at the seams  4  and  6  between the strut tube  5  and the strut guides  3 ,  7 . After the strut is assembled in the tube assembly, a bracket  8  may be attached to the strut tube  5  for connecting the strut tube  5  to a commercially available energy absorbing mechanism, for example, an air spring. A tubular strut  15  has a cylindrical upper part  14 . Upper part  14  is fitted through a cylindrical chamber  23  which extends vertically through the unitized top strut guide  3 . Main strut tube  5  is hollow. Bottom strut guide  7  has an opening  26  which is rectangular in shape. However, the opening  26  and corresponding strut portion  16  may be oval, trapezoidal, square or triangular in shape. A coupling  18  connects the strut parts. 
   A bottom bracket  17  is attached to the bottom of the strut  15  for attaching a pedal crank spindle, on which cranks and pedals are mounted. A strut/cylinder clamp  11  fits over and is clamped to the upper cylindrical portion  14  of the strut  15 . An additional clamp  9  at the top of cylindrical portion  14  of the strut  15  clamps a seat tube in the strut  15 . 
   After the strut/spring clamp  11  has been connected to the air spring cylinder or like means, the upper portion (and bottom bracket  17 ) may be adjusted vertically by loosening the upper strut/spring clamp  11  on the strut  15 . That allows the strut  15  to be slidably moved relative to the strut/spring clamp  11 . Once the desired upper vertical position of the bottom bracket  17  is achieved, the upper position is held static by tightening the strut/cylinder clamp  11  around the strut  15 . That adjusts the feel of the bicycle for a rider as well as the pedal clearance and the bottom bracket height. The range of travel of the unitary bottom bracket  17 , strut  15 , clamp  11 , clamp  9 , seat tube and seat is controlled by the air spring cylinder or like means. The strut adjustment controls the bottom bracket height. Air pressure adjusts the pre-compression of the suspension. 
   In embodiments which use strut suspension,  FIG. 2  shows a detail of one configuration of the modular strut assembly of the present invention. In this embodiment, a bracket  8  and the strut/cylinder clamp  11  connect the top of the strut  15  to an externally mounted energy absorbing mechanism, such as, but not limited to, an adjustable air spring  19 . A dust boot  13  extends from the bottom of the strut/cylinder clamp  11  to the top of the top strut guide  3 , keeping out dirt and debris. The dust boot  13  is expandable to adapt to different strut  15  heights. 
     FIG. 3  shows an alternative embodiment of the modular strut assembly of the present invention.  FIG. 3  shows an embodiment in which an energy absorbing mechanism, such as, but not limited to, an air spring  21  is housed along with the strut  15  within the unitized top strut guide  3  and strut tube  5 . In a preferred embodiment, the strut tube  5  has an outside diameter of 2.84 inches, however, the strut tube  5  may have any outside diameter. The air spring  21  fits within a chamber which extends through the top strut guide  3 . In a preferred embodiment, the chamber is circular in shape; however the chamber may be rectangular, trapezoidal, square, triangular or oval in shape to accommodate the shape of the air spring  21 . The air spring  21  is connected by pins at the top to the strut/spring clamp  11  and at the bottom of the air spring  21  to a bracket  25  attached to the inside circumference of the strut tube  5 . Alternatively, the bottom portion of the air spring  21  may be connected to the top or base strut guide  3  or  7 . 
   A dust boot  13  attached to the strut/cylinder clamp  11  and the air spring  25  extends to cover the top portion of the top strut guide  3 . The dust boot  13  functions to keep the strut  15  and air spring  21  free from dirt, debris and water. The dust in boot  13  is capable of expanding and contracting to accommodate various strut  15  heights. 
   An additional clamp  9  may be fitted around the strut  15  above the strut/cylinder clamp  11  for attaching a seat post and adjusting the height of a seat. 
   In the embodiment of the modular strut assembly of the present invention shown in  FIG. 4 , two energy absorbing mechanisms, such as, but not limited, to air cartridges  33  are attached to the strut/cylinder clamp  11 . The energy absorbing mechanisms may be attached to the strut/cylinder clamp by one or more bolts  35  or by other means. 
   The two energy absorbing mechanisms, for example, air cartridges  33  are housed within two chambers  29 ,  31  which extend through the top strut guide  3  and the strut tube  5 . The energy absorbing mechanisms are linked to share a common fill valve, for example, with hydraulic fluid or compressed air. 
   The strut top  14  of strut  15  and both energy-absorbing mechanisms  33  are housed within the top strut guide  3  and within the strut tube  5 . In a preferred embodiment, the outer diameter of the strut tube  5  measures 2.84 inches, however, the outer diameter of the strut tube  5  may be varied. A dust boot  13  connects to a stop ring  53  extending from the strut/cylinder clamp  11 . The dust boot  13  extends downward and connects to the top portion of the top strut guide  3 . The dust boot  13  is capable of expanding and contracting to accommodate vertically moving the strut top  14  and the energy absorbing means  33 . 
     FIG. 5  shows a horizontal cross-sectional view of the embodiment of FIG.  4 . The strut top  14  is flanked by two energy-absorbing mechanisms, for example, air cartridges  33  which are fitted into chambers  29 ,  31  which extend through the unitized top strut guide  3  and strut tube. Both energy-absorbing mechanisms are connected to a fill valve  37 . 
     FIG. 6  shows a preferred embodiment of the modular strut assembly of the present invention in which the energy absorbing mechanism is concentric to, and surrounds the strut top  14 . A coil spring  41  or an equivalent energy absorbing mechanism surrounds the strut top  14 . The bottom portion of the coil spring  41  is attached to an annular piston  43 , which may be adjusted to preload the coil spring  41 . The annular piston  43  rests atop an air chamber  45 . The air chamber  45  may have a valved port to adjust and preload the air pressure within the chamber  45 . An O-ring rebound stop  59  is supported on a bracket  60  located below the air chamber  45  to contact the bottom  61  of the top guide  3 . 
   The strut/cylinder clamp  11  connects to a sleeve  47  which extends downward from the clamp  11  and fits around the outer diameter of the strut top  14 . The sleeve  47  has external threads  49 . A stop ring  53  is threaded on the sleeve  47  just below the strut/cylinder clamp  11 . The stop ring  53  has a needle thrust bearing  51  engaging the top of the spring for easy adjustment. The stop ring  53  extends horizontally outward from the sleeve  47  and has flanges  55  which extend downward toward the top strut guide  3  and hold the needle bearing  51 . Bumps  63  are attached to the stop ring  53  to provide finger-gripping traction. In its fully adjusted and fully compressed position, the stop ring  53  flanges  55  contact the outer lip  57  of the top strut guide  3 , preventing the strut/cylinder clamp  11  from entering into the top guide  3  and damaging the annular piston  43  housed therein. 
   A dust boot  13  attaches to the flanges  55  extending from the stop ring  53 . The bottom portion of the dust boot  13  floats around the outer lip  57  of the top strut housing  1 , allowing the stop ring  53  to rotate. 
   An additional clamp  9  is fitted around the strut  14 , above the strut/cylinder clamp  11  for holding a seat post. 
     FIG. 7  shows one embodiment of the modular strut assembly of the present invention in which the energy absorbing mechanism is concentric to, and surrounds the strut top  14  with a minimized envelope. A coil spring  41  or an equivalent energy absorbing mechanism surrounds the strut top  14 . The bottom portion of the coil spring  41  is attached to an annular piston  43 , which may be adjusted to preload the coil spring  41 . The annular piston  43  rests atop an air chamber  45 . The air chamber  45  may have a valved port to adjust and preload the air pressure within the chamber  45 . The outside wall  64  of the top strut guide  3  is thick to allow for welding. O-ring rebound stops  59  are located below the top guide  3  and the air chamber  45 . 
   The strut/cylinder clamp  11  is connected to a sleeve  47  which extends downward from the clamp  11  and fits around the outer diameter of the strut  14 . The sleeve  47  is threaded  49 . A stop ring  53  is threaded on the sleeve  47  below the strut/cylinder clamp  11 . The stop ring  53  extends horizontally outward from the sleeve  47  a minimum distance and has flanges  55  which extend downward toward the top strut guide  3 . Bumps  63  on the stop ring  53  provide hand traction. In its full downward adjusted position, with the spring compressed, the stop ring  53  rests on a snap ring in the sleeve  47 . 
   A dust boot  13  attaches to the flanges  55  extending from the stop ring  53 . The bottom portion of the dust boot  13  floats around the outer lip  57  of the top strut guide  3 , allowing the stop ring  53  to rotate. 
   An additional clamp  9  is fitted around the strut  14 , above the strut/cylinder clamp  11  for holding a seat post. 
     FIG. 8  is a schematic representation of the modular strut assembly of the present invention in place on a bicycle frame  65 . As shown in  FIG. 8 , a bicycle frame having the present invention is generally indicated by the number  65 . The bicycle has a seat  67  and a seat post  69 , a head tube  71  and a strut tube  5 . The top tube  73  and down tube  75  are welded to the head tube  11  and to the top strut guide  3  and the bottom strut guide  7 , respectively. The rear stays  77  and the chain stays  79  are also welded to the top strut guide  3  and the bottom strut guide  7 , respectively. The bottom bracket  17  is welded on the strut base  81 , and the clamp  11  is connected near an upper end of the strut. 
   As shown in  FIG. 9 , one strut top guide  3  has a main aperture  23  for receiving the strut. Lightening holes  27 ,  29 ,  31  and smaller lightening holes  83 ,  85  are formed through the strut top guide to lighten the guide. 
   As shown in  FIG. 10 , the strut top guide  3  has a slight relief  87  at its top for receiving the dust boot. An indented portion  89  at the base of the strut top guide  3  fits within the upper end of the strut tube  5 . 
   As shown in  FIG. 11 , the strut tube base  7  has a central rectangular aperture  26  for receiving the strut base and has several lightening holes  91  which reduce its weight. 
   As shown in  FIGS. 12 and 13 , the lightening holes  91  are blind holes terminating above the inward sloping walls  93 . A recess  97  at the lower end of the extension  95  holds the top edge of the lower boot. The recessed area  99  at the top of the strut guide base  7  fits within the lower end of the strut tube  5 . 
   As shown in  FIGS. 14 ,  15  and  16 , the strut base  16  has a generally rectangular shape  101  with trapezoidal upper and lower end sections  103 ,  105 . Section  105  is radiused  107  to receive the welded bottom bracket. Through-holes  109  extend through the strut base  16  to lighten the strut base. The upper end  111  shows a central through-hole opening  113  to receive the lower end of the strut top. 
     FIGS. 17 and 18  are foreshortened views of the lower and upper ends of the strut top  14 . The strut top has an inset lower end  115  which is machined to fit snugly in the through-hole opening  113  in the strut base. A portion of increased thickness  117  near the bottom of the tubular middle  119  absorbs stress. The upper end of the top strut  14  may be necked down in  121  to receive a seat tube clamp. A slot  123  with a rounded lower end  125  is formed in the upper end of the strut to permit inward movement to grip a seat tube. 
   The cylinder clamp  11  shown in  FIGS. 19 and 20  is also referred to as the strut cylinder clamp. The strut cylinder clamp  11  has a generally cylindrical body  127  with an opening  129 , which is closed as a bolt inserted through openings  131  is tightened. The bolt through the openings  131  tightens the clamp on the strut. The upper portion of the clamp adjustably connects the upper portion of the strut to position the strut with respect to the strut tube. In non-suspension forms the clamp clamps the strut to the strut tube for fixing the position of the lower bracket and creating the proper feeling of the bicycle to the rider. When used in the external suspension system, a bolt extending through holes  133  is used as a pin to connect the upper end of one or more shock absorbers to the clamp and thus to the strut. Clamping leverage is provided through the extension  135 . 
     FIG. 21  shows the upper end of strut tube  5  and a top strut guide  3 . Upper tube  73  and seat stays  77  are connected to the top strut guide  3 . Clamp  11  squeezes the top of strut  14  and narrows the gap  123 , securing the seat post  69  in position in the strut top and securing the clamp on the strut top. Adjuster  64  adjusts the spring force on the spring which is inside of the top strut guide  3  and the strut tube  5 . 
     FIG. 22  shows the top of the top strut guide  3 . A square opening  82  receives a rounded and flattened upper portion  84  of the strut  14 . A large recess  86  in the top strut guide  3  holds a spring and damper assembly. 
     FIG. 23  shows the top of the strut tube  5  and the top strut guide  3  which surround the rounded and flattened upper portion  84  at the upper end of the strut  14 . Upper boot  13  joins the clamp  11  and the top strut guide  3 . Recess  88  on the upper side of the clamp receives the adjuster  64  shown in FIG.  21 . 
     FIG. 24  is a view similar to that shown in FIG.  23 . Two set screws  91  are inserted in threaded openings  93  within the recess  88  and extend into openings  95  in the upper end of the strut  14 . A Viton compression ring  96  absorbs downward shock. Adjuster  64  is connected to the threaded upper end of rod  97  to adjust the force of the spring  99 . Elastomeric annular springs  98  surrounding the exposed end of rod  97  provide rebound and bump stop adjustment. 
     FIG. 25  shows an embodiment of the invention with an outwardly mounted air cylinder  19  and a welded alternative triangular lower cylinder mount  100 . 
   Unlike existing bicycle suspension devices, the present invention reduces shock to the rider and forces on the bicycle frame without causing any significant change in the basic frame geometry. 
   As shown in  FIG. 26 , an alternate assembly  201  has a main inner strut portion  202 . A non-round outer tube  211  houses a close-fitting, complementary inner tube  202 . A bicycle seat post is mounted by a clamping bracket  203  above a top end of a transition clamp tube  205  which connects the upper end of isolator  209  to the inner tube  202 . The lower end of isolator  209  is connected by bracket  210  to the outer tube  211 . A pedal crank axle housing  214  is mounted at a bottom end of the inner tube  202 . Upper bracket  207  and lower bracket  213  are welded, or clamped to the outer tube  211  and provide mounting points for the remaining frame members depicted in  FIGS. 28 and 29 . 
     FIG. 27  shows the embodiment of the present invention in its fully assembled state. The ability to drop the inner tube  202  allows for interchangeable front crank sets and gear arrangements. 
     FIGS. 28 and 29  show the remaining members, including the chain stays  221 , the rear stays  219 , the top tube  215 , and the down tube  217 , of the bicycle frame connected directly to the upper bracket  207  and lower bracket  213 . These mounting brackets  207  and  213  facilitate rapid assembly or replacement of components to suit manufacturing needs or riding conditions. 
   The outer tube  211  and the inner tube  202  are coupled such that movement of the seat and crank housing  214 , and hence movement of the inner tube  202 , are damped by isolator  209  from the rest of the frame. Thus, the seat and pedal crank axle housing  214  maintain the same spatial relationship and move as a unit, by movement of the inner tube  202  relative to the outer tube  211 . Suspension of the major mass, the rider, seat and cranks is accomplished without significant frame and wheel stresses or distortions by interconnecting the seat and pedal crank housing  214  with a telescoping inner tube  202 .  FIG. 28 and 29  schematically illustrate how all critical angles and spatial relationships, including seat-to-pedal distances, remain unchanged when the new suspension is active between the full up and the full down positions. Hand to seat distances change, but it is normal to flex and extend arms with typical upper body movements. 
     FIGS. 30 ,  31 , and  32  illustrate the effect of a downward force on the invention while positioned on level, downhill, and uphill surfaces, respectively. As the angle  225  between the invention  201  and the downward force  223  decreases, the amount of energy transferred to the invention  201  increases. This inverse relationship causes the invention  201  to be most active when riding downhill, least active when riding uphill, and moderately active when riding on a level surface, thus optimizing the utility of the invention. The preferred embodiment of the present invention demonstrates how changes in the static geometry of the bicycle frame, wheel position, seat, and pedal crank axle housing are maintained as energy is dissipated. 
     FIG. 33  depicts an embodiment of the invention where the isolator  209  is located inside the inner tube  202  and outer tube  211 . A mount  231  mounts the bottom of the isolator in the inner tube  202 . A top mount  233  connects an upper end of the isolator to the outer tube  211 . This arrangement makes the strut more compact, protects the isolator from road grit thrown up by the rear tire, lowers the center of gravity on the strut, and optimizes force directions acting on the strut. The isolator means shown is generic. A coil spring, elastomeric springs, or gas filled cylinder could be employed. 
   While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention.