US20030132603A1 - Bicycle rear suspension - Google Patents

Abstract

A rear suspension (10, 64) for mountain bikes comprises a rigid link (46, 98) pivotally mounted at opposed ends thereof to a lower rear portion of a main bicycle frame (14, 74, 96) and at a lower front portion of a bicycle swingarm (16, 92). The rigid link (46, 98) allows for relative displacements between the main bicycle frame (14, 74, 96) and the bicycle swingarm (16, 92) along two degrees of freedom and, more particularly, for displacements in an area defined by the position of the two pivots (P1, P2) with respect to a rear wheel axle (WA), by the spacing between the two pivots (P1, P2) and also by the possible deformation of a spring (48, 66) provided between the main frame (14, 74, 96) and the swingarm (16, 92). A leaf spring (48, 66) may be used within a shock absorber system which also includes a damper in order to limit relative displacements between the main frame (14, 74, 96) and the swingarm (16, 92) upon impact of the rear wheel with an obstacle.

Description

CROSS-REFERENCE
• This application is a Continuation of U.S. application Ser. No. 09/457,314 filed on Dec. 9, 1999 (pending), which is a Continuation of PCT/CA98/00574 filed Jun. 10, 1998 designating the United States and claiming priority of Canadian Patent Application serial number 2,207,802 filed Jun. 10, 1997.[0001]
BACKGROUND OF INVENTION
• 1. Field of Invention[0002]
• The present invention relates to bicycles and, more particularly, pertains to bicycle rear suspensions.[0003]
• 2. Description of Prior Art[0004]
• Generally, rear suspensions for mountain bicycles comprise shock absorber systems including various types of springs and shock absorbing devices, and a pivot system defining the path of the rear wheel upon impact thereof with an uneven ground surface.[0005]
• Simple bicycle rear suspension designs essentially comprise a main pivot located on a main frame of the bicycle for pivotally connecting thereto a swingarm or a rear frame portion. According to this type of rear suspension, the rear wheel pivotally moves in a circular path of constant radius about a single axis of rotation which is fixed relative to the main frame of the bicycle. This first category of bicycle rear suspensions may be embodied in different forms and configurations, such as the “MacPherson Strut” (see “First Dirt for Proflex 855”, Mountain Bike Action, February 1995, pp. 51-55; and “Les suspensions arriére: Des forces á domestiquer”, Yannick Boivin, Vélo Mag, Spring 1996, pp. 38-40) and its variants; the “cantilever beam” (see “Foes Fab Weasel”, Mountain Bike Action, September 1995, pp. 49-60); and the “floating drivetrain” (see “Floating Drivetrain Klein”, Mountain Bike Action, February 1995, pp. 67-70).[0006]
• Other types of bicycle rear suspensions are provided with more sophisticated linkage systems comprising upper and lower links adapted to pivotally connect the swingarm to the front frame portion of the bicycle such as to allow the rear wheel to travel in a different arc than with a single link system (see ““Floating GT's Fully Active LTS”, Mountain Bike Action, February 1995, pp. 56-63; “Dual Suspension bike of the decade?”, Vic Armijo, Guide to Suspension and high performance,[0007]volume 2, 1996, pp. 11-12; and U.S. Pat. No. 5,259,637 and No. 5,306,036 issued to Busby on Nov. 9, 1993 and on Apr. 26, 1994, respectively). More particularly, these two Busby U.S. patents disclose a bicycle rear suspension linkage system comprising two upper pivots and two lower pivots which are rigidly interconnected to constrain the motion of a swingarm with respect to a main bicycle frame. The unique rear wheel axle path upon impact of the rear wheel on an obstacle is thus determined by the relative positions of the upper and lower pivots. Busby's bicycle rear suspension linkage system further comprises a shock absorber which is adapted to limit the amplitude of the motion of the rear wheel axle without having any influence on the trajectory thereof.
• U.S. Pat. No. 5,405,159 issued to Klein et al. on Apr. 11, 1995 discloses a suspension system comprising a rotating damper link pivotally connected at a first end thereof to an upper portion of a main frame and at a second end thereof to an upper portion of a swingarm, and a composite spring disposed between lower portions of the main frame and swingarm. The composite spring is designed to act as a rigid link in a horizontal plane and thus only one variable is needed to specify the position of the rear wheel axle in the plane of the bicycle frame.[0008]
• Therefore, there is a need for a bicycle suspension system which allows the rear wheel axle to follow various paths in response to, and depending from, various obstacles encountered by the bicycle's rear wheel.[0009]
SUMMARY OF INVENTION
• It is therefore an aim of the present invention to provide a rear suspension having two degrees of freedom and which is particularly suitable for bicycles including mountain bikes.[0010]
• It is also an aim of the present invention to provide a rear suspension which allows a rear wheel to define different trajectories according to the type of obstacles encountered by the rear wheel of the bicycle.[0011]
• Therefore, in accordance with the present invention, there is provided a rear suspension system for a bicycle having a main frame and a swingarm supporting a rear wheel axle about which a rear wheel may rotate, comprising link means pivotally mounted at two spaced-apart locations to said main frame and to said swingarm, and biasing means for normally urging said swingarm and said main frame in a relative equilibrium position, while allowing said rear wheel axle to move along various paths relative to said main frame in response to different shock forces exerted on the rear wheel.[0012]
• Also in accordance with the present invention, there is provided a rear suspension system for a bicycle having a main frame and a swingarm, comprising a substantially rigid link means having a first end portion thereof pivotally connected to the main frame and a second opposed end portion thereof pivotally connected to the swingarm, and shock absorber means adapted to cooperate with said link means for substantially constricting relative motions of the main frame and the swingarm to two independent directions.[0013]
• Further in accordance with the present invention, there is provided a rear suspension system for a bicycle having a main frame and a swingarm, comprising a substantially rigid link means pivotally mounted at two spaced-apart locations to the main frame and to the swingarm, and resilient connecting means mounted between the main frame and the swingarm for normally urging the main frame and the swingarm in a relative equilibrium position, while enabling said rear suspension system to have two degrees of freedom.[0014]
• Still further in accordance with the present invention, there is provided a bicycle frame, comprising a main frame, a swingarm supporting a rear wheel axle about which a rear wheel may be mounted, a rear suspension system comprising link means pivotally mounted at two spaced-apart locations to said main frame and to said swingarm, and biasing means for normally urging said swingarm and said main frame in a relative equilibrium position, while allowing said rear wheel axle to move along various paths relative to said main frame in response to different shock forces exerted on the rear wheel.[0015]
• More specifically, the bicycle frame includes a pedal crankset assembly mounted to a lower portion of said swingarm, said link means being pivotally mounted at a first end portion thereof to a lower rear portion of said main frame for rotation about a first pivot axis, said link means being pivotally mounted at a second end portion thereof to a lower front portion of said swingarm for rotation about a second pivot axis, said second pivot axis being located above or below a principal axis of the bicycle when said main frame and said swingarm are in said relative equilibrium position, said principal axis extending through said first pivot axis and parallelly to a bicycle axis extending through the front and rear wheel axles of the bicycle.[0016]
• Also, the second pivot axis may be located in front of the pedal crankset assembly.[0017]
• Alternatively, the bicycle frame may include a pedal crankset assembly mounted to a lower portion of said main frame, said link means being pivotally mounted at a first end portion thereof to a lower rear portion of said main frame for rotation about a first pivot axis, said link means being pivotally mounted at a second end portion thereof to a lower front portion of said swingarm for rotation about a second pivot axis, said first pivot axis being located below the pedal crankset assembly.[0018]
• Furthermore, the biasing means may have two degrees of freedom.[0019]
• Moreover, the biasing means include spring means and damper means extending between said main frame and said swingarm, said spring means being adapted for deflection in two at least partially independent directions in a plane containing said main frame and said swingarm.[0020]
• Specifically, the spring means comprise a leaf spring located above said link means. The spring may include an upwardly arcuate portion, said leaf spring being adapted to be rigidly attached at a first end portion thereof to an upwardly extending rear member of the main frame and at a second opposed end portion thereof to an upper member of the swingarm.[0021]
• Alternatively, the leaf spring may have a substantially inverted U-shaped configuration, said leaf spring being adapted to be rigidly attached at a first end portion thereof to an upwardly extending member of the main frame and at a second opposed end portion thereof to an upwardly extending front member of the swingarm.[0022]
• Typically, the damper means are pivotally connected at opposed end portions thereof to the main frame and to the swingarm.[0023]
BRIEF DESCRIPTION OF THE DRAWINGS
• Having thus generally described the nature of the present invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which:[0024]
• FIG. 1 is a side elevational view of a floating drivetrain type bicycle frame having a rear suspension with two degrees of freedom in accordance with the present invention;[0025]
• FIG. 2 is an isometric view of the bicycle frame of FIG. 1;[0026]
• FIG. 3 is an enlarged side elevational view of a portion of the rear suspension which comprises a link pivotally mounted at a first end thereof to a main frame and at a second end thereof to a swingarm, a leaf spring and a shock absorber;[0027]
• FIG. 4 is an enlarged side elevational view of the rear suspension showing a variant of the leaf spring of FIG. 3 in accordance with a second embodiment of the present invention;[0028]
• FIG. 5 is a schematic side elevational view of the rear suspension illustrating the limits of the area in which the rear wheel can move in response to collision forces;[0029]
• FIG. 6 is a schematic side elevational view of the rear suspension showing a possible rear wheel path resulting from a collision with a given obstacle;[0030]
• FIG. 7 is a side elevational view of a bicycle frame in accordance with a third embodiment of the present invention;[0031]
• FIG. 8 is a perspective view of the bicycle frame of FIG. 7; and[0032]
• FIG. 9 is a side elevational view of a bicycle frame of the fixed crankset assembly type in accordance with a fourth embodiment of the present invention.[0033]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• Now referring to the drawings, and in particular to FIGS. 1 and 2, there is shown a rear suspension for bicycles in accordance with the present invention which has two degrees of freedom and which is generally designated by[0034]numeral10.
• More specifically, FIGS. 1 and 2 illustrate a[0035]bicycle frame12 constructed to incorporate the two degrees of freedom bicyclerear suspension10. Thebicycle frame12 basically comprises amain frame14 and aswing arm16 rearwardly thereof. Themain frame14 is formed of a cross bar ortop tube18 and adown tube20 joined at first ends thereof by ahead tube22 and at second end portions thereof by aspring tube24. A lower end of thespring tube24 is received within a substantiallycylindrical sleeve25 extending upwardly at an angle from a lower end portion of thedown tube20. Aseat tube26 is provided at the rear end of thetop tube18 for receiving a seat post (not shown) in a way well known in the art.
• The[0036]swing arm16 essentially comprises a pair ofpivot front tubes28 having upper ends from which rearwardly extend a pair ofspring stay members30. Extending from the lower ends of the pivotfront tubes28 is alower pivot mount32 which is provided at an opposed end thereof with anaxle receiving bracket34 defining abore36 extending axially therethrough for receiving a bottom bracket axle (not shown) of a pedal crankset assembly of the bicycle.
• Extending from the rear side of the[0037]axle receiving bracket34 is a pair ofchain stay members38. A rear wheelaxle dropout bracket40 connects the rear end of eachspring stay member30 with the rear end of a respectivechain stay member38. Thedropout brackets40 are adapted to receive therebetween the axle of a rear wheel (not shown). The rearaxle dropout brackets40 are disposed on opposed sides of theswingarm16 between thespring stay members30 and thechain stay members38. Extending upwardly from theaxle receiving bracket34 is afront derailleur tube42 which is adapted to support a front derailleur (not shown).
• The lower ends of the pivot[0038]front tubes28 are rigidly connected to each other by atransversal member44 with thelower pivot mount32 extending rearwardly therefrom.
• According to a preferred embodiment of the present invention, the[0039]pivot front tubes28, thespring stay members30, the rear wheelaxle dropout brackets40, the chain staymembers38, theaxle receiving bracket34, thelower pivot mount32 and thetransversal member44 each have a generally cylindrical configuration and are secured to one another by means of welded or braised connections.
• Similarly, the components of the[0040]main frame14, namely thetop tube18, thedown tube20, thehead tube22, thespring tube24 and theseat tube26 each have a generally cylindrical configuration and are rigidly connected to one another by means of welded or braised connections.
• The two degrees of freedom bicycle[0041]rear suspension10 includes a pair of parallelrigid links46 which are pivotally mounted at respective first ends thereof to a lower end portion of thedown tube20 for rotation about a first rotation axis, P1 and at respective second ends thereof to opposed ends of thetransversal member44 for rotation about a common second pivot axis P2. Theswingarm16 is also connected to themain frame14 via aleaf spring48 having a front end thereof attached to afirst bracket50 mounted on thesleeve25 and a rear end attached to asecond bracket52 mounted to the upper ends of thespring stay members30. Theleaf spring48 has an upwardly arched configuration and is constituted of a composite material or, alternatively of a metallic substance composed of two or more metals. The shape and configuration of theleaf spring48 allows the same to be deformed in two independent directions within the plane of thebicycle frame12, e.g. in the plane x-y illustrated in FIG. 1. Theleaf spring48 thus acts as a biasing means to normally urge theswingarm16 in an equilibrium position relative to themain frame14, while allowing the rear wheel axle WA to move in two independent directions.
• By having two independent pivots (namely the first pivot axis P[0042]1 and the second pivot axis P2) with one pivot being disposed on themain frame14 and the other pivot on theswing arm16, a rear suspension having two degrees of freedom is obtained.
• The above described connection between the[0043]main frame14 and theswingarm16 allows for the rear wheel (not shown) to reduce the component of the impact speed in the moving direction of the bicycle (normally axis “x” in FIG. 1), while allowing for the rear wheel to be displaced in an independent direction perpendicular to the moving direction of the bicycle (typically axis “y” in FIG. 1) when the rear wheel encounters a bump or other obstacles. As the rear wheel may be displaced in the plane x-y, therear suspension10 is not affected by the position of a principal axis H of the bicycle (i.e. an axis extending through pivot P1 and parallel to an axis extending through the front and rear wheel axles of the bicycle) relative to the direction of the force applied to the rear wheel. Therefore, in the event that the principal axis H of the bicycle is not perpendicular to the shock force exerted on the rear wheel, therear suspension10 will perform as well as when the principal axis H is perpendicular to the direction of the shock force.
• The relative position of the pivots P[0044]1 and P2 is optimal when the axis extending through the center of pivots P1 and P2 is perpendicular to the axis extending through the center of the front and rear wheels (not shown) of the bicycle. The efficiency of the bicyclerear suspension10 reduces as the axis extending through the center of pivots P1 and P2 becomes parallel to the axis extending through the center of the rear and front wheels.
• According to the preferred embodiment illustrated in FIGS.[0045]1 to3, the two degrees of freedomrear suspension10 is provided with adamper54 which in concert with theleaf spring48 provides a shock absorbing unit to absorb the various impact forces communicated to the rear wheel of the bicycle.
• The[0046]damper54 comprises acylinder56 having areciprocating piston58 extending axially therein and outwardly from an upper end thereof. Thepiston58 of thedamper54 extends through a longitudinal slot55 defined inleaf spring48. The upper end of thepiston58 is pivotally connected to a mountingbracket60 extending between the lower end portion of theseat tube26 and thespring tube24. The lower end of thecylinder56 of thedamper54 is pivotally mounted to a mountingbracket62 secured at a front end thereof to thepivot front tubes28 and at a rear end thereof to thespring stay members30. Accordingly, thedamper54 is adapted to convert the energy of the shock force applied to the rear wheel of the bicycle into stresses within itself such as to significantly reduce the oscillation of theswingarm16 and to control the amplitude of the motion of the rear wheel.
• It is understood that other shock absorber systems may be used as long as they allow for displacements along two independent or partially independent axes. Typically, a shock absorber system having two independent axes will include at least a spring unit, such as a coil spring and/or a leaf spring, and an appropriate damping unit, whereas a shock absorber system having two partially independent axes will generally include only one leaf spring having two independent axes along which the leaf spring may be deformed.[0047]
• Referring now more specifically to FIGS. 1 and 5, it can be seen that the first pivot P[0048]1 is located on themain frame14, whereas the second pivot P2 is located on theswingarm16. As seen in FIG. 5, the first and second pivots P1 and P2 allow for the rear wheel axle WA to travel along two independent directions, i.e. according to two degrees of freedom, in an area or envelope delimited between a first circle OC having for center the pivot P1 and a radius “R+l” and a second concentric circle of radius “R−l”, wherein “R” corresponds to the distance between the second pivot P2 and the axle WA of the rear wheel and “l” to the distance between the first and second pivots P1 and P2. The pivot P2 may be displaced along a circular path of radius “l” around the pivot P1, as illustrated in FIGS. 1 and 6. The rear wheel axle WA may be displaced along a circular path (e.g. PATH2 in FIG. 1) around the second pivot P2.
• The linear combination of the two rotational movements permit an infinite number of rear wheel axle WA trajectories within the area delimited by the difference between the inner surfaces OC and IC. Furthermore, the area accessible by the rear wheel axle WA will be limited by the possible deformation of the[0049]leaf spring48 and by the maximal amplitude of thedamper54, as represented by the square area SQ1 in FIG. 5. The intersection of the area OC-IC with the area SQ1 determines the accessible area within which the rear wheel axle WA may move. FIG. 6 illustrates an example of a possible trajectory of the rear wheel axle WA when the rear wheel encounters a given obstacle.
• The shock absorber system may be comprised of a number of springs and of a conventional damper, but it is preferable to use a composite leaf spring having two degrees of freedom, as it enhances lateral rigidity and contributes to minimizing the weight of the bicycle.[0050]
• Although a plurality of pivot locations are possible to enable the rear wheel axle WA to be displaced in a plane in response to a shock force applied to the rear wheel, it is understood that some special configurations and locations are preferable to achieve the full benefit of the suspension and to provide increased torsional rigidity.[0051]
• Indeed, the locations of the first and second pivots P[0052]1 and P2 and of theleaf spring48 are not important for allowing the bicyclerear suspension10 to have two degrees of freedom but greatly affect the sensibility of the suspension and the lateral rigidity of the overall system. When the crankset pedal assembly (not shown) is mounted to theswingarm16 as described hereinbefore, it is preferable to place the first pivot P1 in the lower area of themain frame14, at the lower end of thedown tube20. The second pivot P2 may be located in front of theaxle receiving bracket34 but must be disposed above or below the principal axis H extending through the first pivot P1 and parallelly to an axis extending through both the front and rear wheel axles. Finally, it is preferable to place theleaf spring48 above the first and second pivots P1 and P2.
• FIG. 4 illustrates a two degrees of freedom bicycle[0053]rear suspension64 in accordance with a second embodiment of the present invention, wherein aleaf spring66 having a substantially inverted U-shaped configuration is attached at a front end thereof to afirst bracket68 mounted to thesleeve25 and at an opposed rear end thereof to asecond bracket70 secured to thepivot front tubes28. Theleaf spring66 is deformable along independent directions in the plane of thebicycle frame12 and is adapted to generate trajectories for the rear wheel axle WA which are different than those produced by theleaf spring48.
• FIGS. 7 and 8 illustrate a different[0054]bicycle frame configuration72 which may be used in combination with the above described two degrees of freedom bicyclerear suspensions10 and64 in accordance with a third embodiment of the present invention. Thebicycle frame configuration72 includes amain frame74 including a curvedtop tube76 and adown tube77 rigidly connected to each other by ahead tube78 disposed at the front end of themain frame74 and by aninclined tube80 extending upwardly and forwardly from ajunction member82 welded to a lower end portion of thedown tube77. Aseat tube84 is rigidly connected to a rear end of the curvedtop tube76 for slidably receiving a seat post (not shown). A pair of parallel spaced apart three-branched supportingbrackets86 are secured to the topcurved tube76, to theseat tube84 and to thejunction member82 for pivotally receiving therebetween the upper end of thereciprocating piston58 of thedamper54. The lower end of thedamper54 is pivotally mounted between a pair of spaced apart parallel supportingbrackets88 having three branches rigidly connected respectively to an upper end of afront derailleur tube90, to theaxle receiving bracket34 and to thelower pivot mount32 forming part of aswingarm92. The main difference between theswingarm16 and theswingarm92 is that thefront derailleur tube90 of theswingarm92 extends from theaxle receiving bracket34 to thespring stay member30, thereby eliminating the necessity of having pivotfront tubes28. Furthermore, it is noted that, according to the embodiment illustrated in FIGS. 7 and 8, the connection of thedamper54 to theswingarm92 is located in front of thefront derailleur tube90.
• FIG. 9 illustrates another bicycle frame configuration according to a fourth embodiment of the present invention, wherein the pedal crankset assembly (not shown) is mounted on the[0055]main frame96 of the bicycle and, more particularly to a lower end of the down tube thereof. This type of design is known as a fixed pedal crankset assembly because the location of the pedal crankset assembly is fixed with respect to themain frame96. According to this embodiment, it can be seen that the first pivot P1 is located below theaxle receiving bracket34, and that therigid link98 and thepivot front tubes100 are elbowed such that their apexes extend rearwardly. It is pointed out that the fixed crankset assembly configuration illustrated in FIG. 9 allows for the rear suspension to react similarly whether the user stands on the pedals (not shown) or sits on the seat (not shown).

Claims (24)

1. A rear suspension system for a bicycle having a main frame and a swingarm supporting a rear wheel axle about which a rear wheel may rotate, comprising link means pivotally mounted at two spaced-apart locations to said main frame and to said swingarm, and biasing means for normally urging said swingarm and said main frame in a relative equilibrium position, while allowing said rear wheel axle to move along various paths relative to said main frame in response to different shock forces exerted on the rear wheel.

2. A rear suspension system as defined inclaim 1, wherein said link means is substantially rigid.

3. A rear suspension system as defined inclaim 1, wherein, for a bicycle having a pedal crankset assembly adapted to be mounted to a lower portion of said swingarm, said link means are pivotally mounted at a first end portion thereof to a lower rear portion of said main frame for rotation about a first pivot axis, said link means being pivotally mounted at a second end portion thereof to a lower front portion of said swingarm for rotation about a second pivot axis, said second pivot axis being located above or below a principal axis of the bicycle when said main frame and said swingarm are in said relative equilibrium position, said principal axis extending through said first pivot axis and parallelly to a bicycle axis extending through the front and rear wheel axles of the bicycle.

4. A rear suspension system as defined inclaim 3, wherein said second pivot axis is located in front of the pedal crankset assembly.

5. A rear suspension system as defined inclaim 1, wherein, for a bicycle having a pedal crankset assembly mounted to a lower portion of said main frame, said link means are pivotally mounted at a first end portion thereof to a lower rear portion of said main frame for rotation about a first pivot axis, said link means being pivotally mounted at a second end portion thereof to a lower front portion of said swingarm for rotation about a second pivot axis, said first pivot axis being located below the pedal crankset assembly.

6. A rear suspension system as defined inclaim 1, wherein said biasing means have two degrees of freedom.

7. A rear suspension system as defined inclaim 6, wherein said biasing means include spring means and damper means extending between said main frame and said swingarm, said spring means being adapted for deflection in two at least partially independent directions in a plane containing said main frame and said swingarm.

8. A rear suspension system as defined inclaim 7, wherein said spring means comprise a leaf spring located above said link means.

9. A rear suspension system as defined inclaim 8, wherein said leaf spring includes an upwardly arcuate portion, said leaf spring being adapted to be rigidly attached at a first end portion thereof to an upwardly extending rear member of the main frame and at a second opposed end portion thereof to an upper member of the swingarm.

10. A rear suspension system as defined inclaim 8, wherein said leaf spring has a substantially inverted U-shaped configuration, said leaf spring being adapted to be rigidly attached at a first end portion thereof to an upwardly extending member of the main frame and at a second opposed end portion thereof to an upwardly extending front member of the swingarm.

11. A rear suspension system as defined inclaim 8, wherein said damper means are pivotally connected at opposed end portions thereof to the main frame and to the swingarm.

12. A rear suspension system as defined inclaim 11, wherein said damper means extend through a longitudinal slot defined in said leaf spring.

13. A rear suspension system for a bicycle having a main frame and a swingarm, comprising a substantially rigid link means having a first end portion thereof pivotally connected to the main frame and a second opposed end portion thereof pivotally connected to the swingarm, and shock absorber means adapted to cooperate with said link means for substantially constricting relative motions of the main frame and the swingarm to two independent directions.

14. A rear suspension system for a bicycle having a main frame and a swingarm, comprising a substantially rigid link means pivotally mounted at two spaced-apart locations to the main frame and to the swingarm, and resilient connecting means mounted between the main frame and the swingarm for normally urging the main frame and the swingarm in a relative equilibrium position, while enabling said rear suspension system to have two degrees of freedom.

15. A bicycle frame, comprising a main frame, a swingarm supporting a rear wheel axle about which a rear wheel may be mounted, a rear suspension system comprising link means pivotally mounted at two spaced-apart locations to said main frame and to said swingarm, and biasing means for normally urging said swingarm and said main frame in a relative equilibrium position, while allowing said rear wheel axle to move along various paths relative to said main frame in response to different shock forces exerted on the rear wheel.

16. A bicycle frame as defined inclaim 15, wherein a pedal crankset assembly is mounted to a lower portion of said swingarm, said link means being pivotally mounted at a first end portion thereof to a lower rear portion of said main frame for rotation about a first pivot axis, said link means being pivotally mounted at a second end portion thereof to a lower front portion of said swingarm for rotation about a second pivot axis, said second pivot axis being located above or below a principal axis of the bicycle when said main frame and said swingarm are in said relative equilibrium position, said principal axis extending through said first pivot axis and parallelly to a bicycle axis extending through the front and rear wheel axles of the bicycle.

17. A bicycle frame as defined inclaim 16, wherein said second pivot axis is located in front of the pedal crankset assembly.

18. A bicycle frame as defined inclaim 15, wherein a pedal crankset assembly is mounted to a lower portion of said main frame, said link means being pivotally mounted at a first end portion thereof to a lower rear portion of said main frame for rotation about a first pivot axis, said link means being pivotally mounted at a second end portion thereof to a lower front portion of said swingarm for rotation about a second pivot axis, said first pivot axis being located below the pedal crankset assembly.

19. A bicycle frame as defined inclaim 15, wherein said biasing means have two degrees of freedom.

20. A bicycle frame as defined inclaim 19, wherein said biasing means include spring means and damper means extending between said main frame and said swingarm, said spring means being adapted for deflection in two at least partially independent directions in a plane containing said main frame and said swingarm.

21. A bicycle frame as defined inclaim 20, wherein said spring means comprise a leaf spring located above said link means.

22. A bicycle frame as defined inclaim 21, wherein said leaf spring includes an upwardly arcuate portion, said leaf spring being adapted to be rigidly attached at a first end portion thereof to an upwardly extending rear member of the main frame and at a second opposed end portion thereof to an upper member of the swingarm.

23. A bicycle frame as defined inclaim 22, wherein said leaf spring has a substantially inverted U-shaped configuration, said leaf spring being adapted to be rigidly attached at a first end portion thereof to an upwardly extending member of the main frame and at a second opposed end portion thereof to an upwardly extending front member of the swingarm.

24. A bicycle frame as defined inclaim 22, wherein said damper means are pivotally connected at opposed end portions thereof to the main frame and to the swingarm.

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