Abstract:
A pedal radius adjustment device comprised of a frame mounted onto the existing crank arm of a bicycle or similar exercise machine by a screw passing through the existing crank arm pedal mounting hole and attaching to the adjustment frame, and by a bracket mounted to the adjustment frame around the crank arm. The contact side of the frame is grooved to align with the pedal crank arm. The pedal is attached to a sliding block within the adjustment frame and is adjusted by a hand operated pull T-pin at multiple, known-radius, settings prearranged on the adjustment frame. In another embodiment, the T-pin is held in place by magnetic attraction between the T-pin and the sliding block.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to circularly movable cranks, and in particular, to crank arm radius adjusting mechanisms useful for pedal powered vehicles such as bicycles and stationary exercise cycles. 
     2. Discussion of the Prior Art 
     Devices for the adjustment of a crank arm radius or stroke length for a bicycle driving crank have been known in the art for a considerable period of time. A summary of such prior art is provided in the specification of U.S. Pat. No. 4,648,287, issued Mar. 10, 1987 to J. Preskitt for &#34;Pedal Stroke Adjuster for a Bicycle or Exercise Machine&#34;. 
     One early version of such a device can be noted in U.S. Pat. No. 2,533,011, issued Dec. 5, 1950 to W. Hill for &#34;Bicycle Pedal Adapter&#34;. In this device, a special collar or bracket is configured to slidably engage over a distal end of a standard bicycle crank arm to extend substantially radially inwardly from the typical threaded pedal engaging hole found proximate to the distal end of the crank arm. Bolt means are inserted through appropriate holes in the collar or bracket and into the threaded hole of the crank arm to secure the collar or bracket to the crank arm. The collar or bracket includes a flange portion having holes therethrough disposed to be substantially adjacent a radially inwardly extending portion of the crank arm. The pedal is engaged to the flange portion through its holes. Each pedal of the pair normally employed on a bicycle or stationary exercise cycle is so mounted to respective flanges of respective collars or brackets such that they effectively act on their respective crank arms at equally reduced radii from the center of rotation of the drive crank of the bicycle. It would appear from the teaching of the Hill patent that a single radius of adjusted stroke length is available from a particular set of collars or brackets, and that other radii would require the installation of different collars or brackets. 
     The above-mentioned patent to Preskitt, U.S. Pat. No. 4,648,287, provides a device having a range of discrete adjustment radii at which the pedals of the bicycle may be disposed to act on respective crank arms. This is accomplished by providing an adjustment frame extending substantially radially inwardly from the normal pedal engagement hole of the crank arm, located proximate to its distal end. The adjustment frame is provided with appropriate spacers to accommodate attachment of the frame to a crank arm that diverges from the plane of rotation of the crank along the length of the crank arm to its distal end. With said spacers emplaced, a first end of the adjustment frame is coupled to the distal end of the crank arm by bolt means extending through the pedal mounting hole at the distal end of the crank arm. The obverse end of the adjustment frame is held to a radially inwardly extending portion of the crank arm by a bracket encircling the crank arm. A block, containing a hole through which the pedal is engaged, is slidably coupled to the adjustment frame so that it is capable of motion relative thereto substantially along the extent of the crank arm. The frame is formed to have transverse notches along one side of the slide path followed by the sliding block, which notches are engaged by detent means carried within the sliding block. The detent means are manually operable to release the detent from engagement with a particular notch on the adjustment frame so that the sliding block, with the pedal attached thereto, may be repositioned to a differing stroke radius, whereat the detent engages an appropriate notch. Additionally, the block may be locked into a particular radial position by a set screw acting through the block against the adjustment frame. 
     Preskitt also teaches several alternate embodiments. A first is similar to the preferred embodiment except that it employs a second detent mechanism engaging notches on the adjustment frame positioned to the opposing side of the sliding block from those of the preferred embodiment. Another alternate embodiment provides for substantially continuous radial adjustment by coupling the sliding block to a lead screw extending through the adjustment frame parallel with the extent of the crank arm. Rotation of the lead screw, which is journaled to rotate within the adjustment frame at either end, causes the sliding block to move either inwardly or outwardly, depending on the pitch direction of the lead screw and the direction of its rotation about its longitudinal axis. Yet another embodiment taught by Preskitt foregoes the use of a sliding block entirely by forming a plurality of spaced apart holes along the extent of the adjustment frame substantially parallel with the extent of the crank arm. Each of these holes is independently adapted to accept engagement of the pedal. In a further variation on the immediately preceding embodiment, Preskitt replaces the existing crank arm of the bicycle with a frame clamping directly to the crank shaft at its axis of rotation, this frame having a plurality of radially spaced apart holes for accepting engagement of the pedal at differing radii. 
     Where extension of the effective radius of a bicycle crank arm is desired, a device similar to that described in U.S. Pat. No. 4,850,245, issued Jul. 25, 1989 to N. Feamster, et. al. for &#34;Bicycle Crank and Pedal Structure&#34;, may be employed. The Feamster device utilizes a sleeve configured to slidably telescope over the extent of the existing crank arm. The sleeve contains a plurality of holes therethrough, the most outwardly radially located hole being adapted to engage and support a pedal. In use, the sleeve is telescoped onto the crank arm until the desired extended pedal radius is established. Thereat, one of the plurality of radially inwardly spaced apart holes through the sleeve is aligned with the normal pedal engaging hole at the distal end of the crank arm. Bolt means are passed and engaged through this combined hole to secure the sleeve to the crank arm. 
     Without making specific reference thereto herein, the literature surrounding the present invention contains descriptions of many differing embodiments of devices useful in changing the pedal radius of a bicycle or similar apparatus. Those set forth hereinabove are believed to be the most relevant among the art which is presently known to the inventor hereof. In brief, the simplest known of such devices is the addition of blocks directly to the foot support portions of the pedals. While this approach accommodates user leg extension relative to the seat position, it does not appreciably alter the radius through which the foot moves in following the motion of the pedal. In each of such prior art devices, cited specifically herein or otherwise, closer concern should be given the examination thereof for their respective capabilities of accommodating differing ranges of motion to which a user may be limited, while also considering the ease with which changes in radius may be accomplished. Of further concern are such factors as ease of assembly, complexity of structure and design, and stability relative to off-set of the pedal from the extent of the crank arm. All such factors appear to vary greatly between the several references and other known approaches. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an improved means for modifying the length of pedal stroke of a bicycle or stationary exercise cycle without altering an existing pedal crank arm. 
     Another object of the present invention is to provide a device for selectably adjusting the pedal stroke length of a bicycle or stationary exercise cycle that is adaptable to rapid adjustment of pedal stroke length in an efficient manner. 
     An additional object of the present invention is to provide for incremental pedal stroke length adjustment capability between at least the normal full pedal stroke length and a pedal stroke length less than twenty percent of the full stroke length. 
     A further object of the present invention is to provide a device for selectably adjusting the pedal stroke length of a bicycle or stationary exercise cycle having sufficient structural strength and features of construction to enable its safe use. 
     It is another object of the present invention to provide such a device capable of being readily produced at a reasonable cost. 
     These, and further objects, advantages, and features of the present invention that may become evident or that may be suggested through the following descriptions, are provided by an apparatus that, for each of a pair of pedal crank arms of a bicycle or stationary exercise cycle, includes a frame member that can be coupled to either pedal crank arm, with a like frame member being coupled to the other crank arm, a bracket member for securing the frame member to the crank arm, a flanged block member slidably engaging with the frame member to provide for pedal length adjustment, means for retaining the block member in a desired position relative to the frame member, and means for appropriately assembling the apparatus for use. A surface of the frame member that is intended for aligned contact with the crank arm has a notched groove extending along its length to ensure alignment of the frame member along the length of the crank arm. The slidable block member includes a threaded hole attaching a corresponding pedal thereto. As is common practice in bicycle manufacture, a right pedal and a left pedal are provided with mutually opposite threads on shanks engaging distal ends of the crank arms. Thus, the sliding block members are characterized as either right or left, with appropriate thread direction in the hole in which a corresponding right or left pedal is accepted. A pull T-pin is fitted into the slidable block member through a second, unthreaded hole therethrough as a means for releasably retaining the block member in position relative to the extent of the frame member. The frame member includes a plurality of these unthreaded holes distributed along the extent of the frame member in alignment with the extent of the crank arm for pedal stroke length adjustment and for locking and securing the block member in selectable locations along the extent of the frame member. Further detail of the present invention, and alternates thereto, will become evident through the detailed description set forth below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the accompanying drawing, wherein like elements, components, and features and respectively indicated by like reference numbers and symbols throughout: 
     FIG. 1 is a perspective exploded view of an apparatus in accordance with the present invention, indicating its assembly and the manner of attachment thereof to standard bicycle components; 
     FIG. 2 is a cross-sectional view of a frame member of the apparatus in accordance with the present invention, taken along a plane indicated as 2--2 in FIG. 1; 
     FIG. 3 is a perspective view of the apparatus of the present invention, illustrating, for one side of a crank structure, a principal orientation of assembly of a slidable block member thereof; 
     FIG. 4 is a perspective view of one side assembly of the apparatus of the present invention, illustrating an assembly of the slidable block member thereto to attain a shortest pedal stroke length; 
     FIG. 5 is a partial end view of a bicycle or stationary exercise cycle indicating a plurality of pedal stroke lengths, with slidable block members of both sides being at equal stroke radii; and 
     FIG. 6 is a partial end view, as in FIG. 5, showing slidable members of opposed sides at unequal stroke radii. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to FIG. 1, an apparatus for adjustably varying a pedal stroke length of a bicycle or stationary exercise cycle in accordance with the present invention is indicated, in exploded perspective view, generally at 10. The apparatus 10, shown in relation to a crank assembly of a standard bicycle or stationary exercise cycle having diametrically opposed crank arms respectively coupled to axially opposed sides of the crank, may be observed to comprise, for each side of the crank 19, a frame member 11, a slidable block member 12, a bracket member 13, a T-pin 14, a pair of bolts 16 for coupling the bracket member 13 to the frame member 11, and a bolt 17 for coupling the frame member 11 to a crank arm 18 on the corresponding side of the crank 19. For simplification of further description, those elements of the apparatus 10 residing on one side of the crank 19 are described in detail hereinbelow. The like elements residing on the other side of the crank 19 are to be understood as being identical to those described hereinbelow, except as may be particularly pointed out in these descriptions. 
     With reference to FIG. 2 in conjunction with FIG. 1, the frame member 11 is configured generally as a rectangular solid from which portions are removed. Such a rectangular solid is defined to have a length approximately equal to, and directed substantially along, a length of a standard bicycle crank arm 18, a width approximately three times the dimension of the crank arm 18 measurable in a plane parallel to the plane of revolution of the crank 19, and a thickness, directed normal to the plane of revolution of the crank 19, sufficient to provide for engagement of the slidable block member 12 with the frame member 11 while maintaining structural integrity and durability of the apparatus 10 as assembled onto the crank arm 18. The aforesaid dimensions of the frame member 11 are provided as examples to establish the relative size of the frame member 11, and are not to be construced as limiting the configuration of the frame member 11 beyond any mechanical constraints that may arise to accommodate operation of the crank arm 18 to drive the bicycle or stationary exercise cycle. 
     The general rectangular block configuration of the frame member 11 is modified for the stated purposes herein to include set-back, notch, groove and hole arrangements. A first surface 20 of the frame member 11, identifiable as a planar surface bounded by the length and width of the generally rectangular block of the frame member 11, hereinafter to be known as the contact surface 20 of the frame member 11, is configured to have a substantially V-shaped groove 21 extending centrally along the length of the frame member 11. This V-shaped groove 21 is further configured to include a web surface 22 substantially parallel to said contact surface 20, said web surface 22 separating dihedral surfaces 50 and 51 forming the V-shape. An illustrated lower end 23 of the frame member 11 appearing to the right of the crank 19 is configured to have a set-back planar surface 24 formed to be parallel to the plane of the contact surface 20 and extending along the length of the frame member 11 from said upper end 23 to a shoulder 26. Thus, the groove 21 extends from the shoulder 26 to an end 34 of the frame member 11 obverse to the upper end 23. The contact surface 20 is, of course, not present in the set-back surface 24 portion of the frame member 11. The importance of the several surfaces thus described will be revealed during description of the installation of the frame member 11 to the crank arm 18, to be given below. 
     In accordance with the objects of the present invention, the apparatus 10 is to be configured to be attachable to a crank arm 18 of a bicycle or stationary exercise cycle so as to allow adjustment of the pedal stroke length. To that end, the pedals 27 of the bicycle or stationary exercise cycle are first removed from their respective engagement with distal ends 28 of the crank arms 18. While describing only the crank arm 18, illustrated to the right of the crank 19, the following has equal application to the other crank arm 18. The frame member 11 is placed along the extent of the crank arm 18 such that the dihedral surfaces 50 and 51 forming the V-shaped groove 21 and the web surface 22 therebetween are in substantial contact with the extent of the crank arm 18. Since the typical crank arm 18 includes an enlarged portion, including an increased thickness, at its distal end 28 to accommodate normal attachment of the corresponding pedal 27 thereto, the set-back surface 24 of the frame member 11 is disposed to be positioned substantially in alignment with the distal end 28 portion of the crank arm 18. A first hole 29, formed through the thickness of the frame member 11 proximate to its upper end 23 and centrally of the width of the frame member 11, is disposed to be within the set-back surface 24 region of the frame member 11. When the hole 29 is in alignment with a pedal engaging hole 30 through the distal end 28 of the crank arm 18, the bolt 17 is passed through the pedal engaging hole 30 at the distal end 28 of the crank arm 18 so as to threadably engage matching threads formed internally in the first hole 29 of the frame member 11, thereby holding the frame member 11 in the appropriate longitudinal position relative to the extent of the crank arm 18. 
     The bracket member 13 is configured to include a V-shaped groove 31 complementing that formed on the contact surface 20 of the frame member 11. The bracket 13 has an extent to each side of the V-shaped groove 31 such that it has a total width substantially equal to the width of the frame member 11. Each such side extent of the bracket member 13 has a hole 32 formed therethrough in a direction normal to the surface containing the groove 31. A further pair of holes 33 are formed through the thickness of the frame member 11 at transversely spaced apart positions disposed substantially proximate to a second end 34 of the frame member 11 obverse to said upper end 23, the transverse spacing between centers of said holes 33 being equal to the spacing between centers of the holes 32 in the bracket member 13. With the frame member 11 being held at its upper end 23 to the distal end 28 of the crank arm 18 by the bolt 17, the bracket member 13 is placed between the crank arm 18 and the crank 19 such that the extent of the groove 31 is in contact with the extent of the crank arm 18. Translation of the bracket member 13 along the extent of the crank arm 18 will produce a position of the bracket member 13 whereat the holes 32 in the bracket member 13 are aligned with the holes 33 in the frame member 11. The bolts 16 are then passed, respectively, through the holes 33 in the frame member 11 to threadably engage with matching threads formed in the holes 32 in the bracket member 13. Upon appropriate tightening of the bolts 16 and the bolt 17, the frame member 11 will be rigidly coupled to the crank arm 18, with a fixed longitudinal position and rotational orientation established therebetween. 
     It is to be noted that the length of the bolt 17 is to be sufficient to engage the frame member 11 through the pedal egaging hole 30 of the crank arm 18, but it is to be limited in length not to project through the thickness of the frame member 11, as said thickness is further limited below. Similarly, the lengths of bolts 16 are limited to that length sufficient to pass through the holes 33 in the frame member 11 so as to engage with the holes 32 in the bracket member 13 without projecting fully through the holes 32. With regard to the lengths of the bolts 16, the holes 33 in the frame member 11 are countersunk appropriately to place the heads of bolts 16 fully within the surfaces defining the frame member 11 such that said heads do not impede the further functioning of the frame member 11, as set forth below. 
     Continuing with reference to FIG. 1 and FIG. 2, a surface 52 of the frame member 11, obverse to the contact surface 20 thereof, is configured along its entire length to include a generally T-shaped notch 36 accommodating the slidable block member 12. The desired characteristics of the notch 36 may be more readily determined from reference to the configuration of the slidable block member 12. The slidable block member 12 is configured as a generally rectangular element having a length oriented in a direction parallel to the length of the frame member 11, a width parallel to the width of the frame member 11, and a thickness oriented in a direction parallel to thickness of the frame member 11. The width and length of the slidable block member 12 are adapted to accommodate forming a threaded hole 37, centrally of the width of the slidable block member 12, through the thickness of the slidable block member 12, said hole 37 being so adapted and threaded to accept a correspondingly threaded shank 53 of the pedal 27. It is to be noted that the shanks 53 of the pedals 27 utilized on opposite sides of a bicycle or similar apparatus are provided with oppositely directed threads to prevent unscrewing of the pedals 27 during forward pedaling of the apparatus. Thus, the slidable block members 12 are to be identified as either left or right. The length of the slidable block member 12 is further adapted to accommodate the independent formation of a further hole 38 through its thickness, said hole 38 also being disposed centrally with respect to the width of the slidable block member 12. The slidable block member 12 is further formed to include an integrally formed pair of flanges 40 increasing the width of the slidable block member 12 along the length of the sides forming the thickness dimension, said flanges 40 having a thickness from a surface 41 of said slidable block member 12 adapted to slide along the notch 36 of the frame member 11 to as to slidably engage grooves 42 forming a part of the notch 36. 
     The T-shaped notch 36 of the frame member 11 can, in an alternative, be described as a generally rectangular cavity 54 extending fully along the length of the frame member 11, said cavity 54 having a width accommodating passage of the slidable block member 12, as described above, therealong, with grooves 42 formed proximate to an innermost longitudinal surface 43 of said cavity 54, said grooves 42 increasing the width of that portion of the cavity 54 so as to accommodate sliding of the flanges 40 of the slidable block member 12 along the length of the frame member 11. 
     The frame member 11 is further formed to include a plurality of pedal stroke length positioning holes 44, each extending through the thickness of the frame member 11, said holes 44 being disposed in a calibrated spaced apart arrangement along a line located centrally of the width of said frame member 11. The holes 44 in the frame member 11 and the hole 38 in the slidable block member 12 are so configured and sized that a central leg 46 of the T-pin 14 is removably insertable therethrough when the hole 38 is appropriately aligned with a selected one of the holes 44 corresponding to a desired pedal stroke length of the apparatus 10. 
     Referring next to FIG. 3, a right half of the apparatus 10 is illustrated as partially assembled onto the crank arm 18, with the slidable block member 12 held in a selected pedal stroke length position by the T-pin 14. The pedal 27 is shown in an exploded position for clarity. With the shank 53 of the pedal 27 engaged with the hole 37 in the slidable block member 12, the pedal stroke length of the apparatus 10 may be varied by removing the T-pin 14 from the slidable block member 12 by manually translating it in the direction indicated by an arrow 47. The slidable block member 12 and the attached pedal 27 may then be repositioned along the length of the frame member 11 such that the hole 38 in the slidable block member 12 becomes aligned with another, selected, one of the holes 44 in the frame member 11, whereat the T-pin 14 is manually reinserted into the hole 38 and the selected hole 44 in a direction opposite to that indicated by the arrow 47. The positioning of the illustrated uppermost hole 44, most proximate to the upper end 23 of the frame member 11, is such that the pedal axis defined by the hole 37 in the slidable block member 12, when the slidable block member 12 is oriented relative to the frame member 11 as shown in FIG. 3, is substantially aligned with the pedal engaging hole 30 at the distal end 28 of the crank arm 18, thereby providing a pedal stroke length substantially equal to that of the bicycle or stationary exercise cycle not employing the apparatus 10 of the present invention. Relocation of the slidable block member 12 to be positioned at each of the holes 44, in sequence progressing away from the upper end 23 of the frame member 11, accordingly reduces the pedal stroke length. In a preferred embodiment of the apparatus 10 serving as the primary basis for the drawings herein, the approximate selectable pedal stroke lengths are established to be, sequentially inwardly starting from the upper end 23 of the frame member 11: 6.5 inches (approximately 165 millimeters); 5.75 inches (approximately 146 millimeters); 5.0 inches (approximately 127 millimeters); 4.25 inches (approximately 108 millimeters); 3.5 inches (approximately 89 millimeters); and 2.75 inches (approximately 70 millimeters). Alternate configurations providing a differing number of holes 44 and a differing set of pedal stroke lengths may be fabricated as an alternate frame member 11 including the desired set of holes 44. 
     The T-pin 14 is further configured to be used as a tool for the assembly and disassembly of the apparatus 10. The central leg 46 of the T-pin 14 is formed of a sufficiently rigid and durable material to have a shape engagable with the heads of bolt 17 and bolts 16 in order to rotate them about their respective axes for removal or insertion with respect to their threaded holes. In the preferred embodiment herein, the central leg 46 of the T-pin is formed to have a hexagonal cross-section appropriately matching Allen head bolts 16 and 17. The T-pin 14 includes a cross bar 48 to serve both as a handle during use of the T-pin 14 as a tool and as a stop determining the extent to which the central leg 46 of the T-pin 14 may be inserted into the combined holes 38 and 44. 
     For convenience of use, including safety of the user, appropriate surfaces of the components of the apparatus 10 may be provided with rounded edges and corners. To preclude interference between the cross bar 48 of the T-pin 14, engaged into the holes 38 and 44, and the pedal 27, engaged into the hole 37, the slidable block member 12 may be provided with a transverse notch 49 accepting the cross bar 48. The length of the central leg 46 of the T-pin 14 is thus to be foreshortened accordingly such that full insertion thereof into a selected hole 44 may be accomplished without contacting the crank arm 18 with the distal end of the central leg 46. Additionally, the frame member 11 may be provided with indexing markings 56 corresponding to the pedal stroke lengths at the several positions of the slidable block member 12, as indicatable by the position of the cross bar 48 of the T-pin 14, in the notch 49, at each such position. It is preferred that the markings 56 be etched into the surface of the frame member 11, with a high visibility paint or other similar product affixed into the etched markings 56. In the alternative, the markings 56 may be embossed, or applied in the form of decals or paint. 
     Referring next to FIG. 4, an extremely short pedal stroke length may be established for the present apparatus 10 through removal of the T-pin 14, sliding the slidable block member 12 and attached pedal 27 completely out of the notch 39 of the frame member 11, reversing, by rotating the slidable block member about the axis of the hole 37 through 180 degrees of angle, the orientation of the slidable block member 12 from that shown by FIG. 3 to that shown by FIG. 4, reengaging the thus reoriented slidable block member 12 partially with the notch 39 of the frame member 11, aligning the hole 38 in the slidable block member 12 with the lowermost hole 44 in the frame member 11, and reinserting the T-pin into the aligned holes 38 and 44. In this assembled configuration, the slidable block member 12 projects partially beyond the lowermost extent of the length of the frame member 11 such that the position of the pedal axis at hole 37 of the slidable block member 12 is more proximate to a central axis of the crank 19 than is attainable for any selected positioning of the slidable block member 12 in the orientation shown by FIG. 3. For the reversed orientation of the slidable block member 12 illustrated by FIG. 4, the preferred embodiment provides a pedal stroke length of approximately 1.25 inches (approximately 32 millimeters). 
     Referring next to FIG. 5, as viewed from an end of the bicycle or stationary exercise cycle, the crank 19 is illustrated to be at a rotational position whereat the crank arms 18 are respectively up and down. The slidable block members 12 are shown to be positioned along the corresponding frame members 11 at respectively equal radii 57 from the axis of rotation of the crank 19. Other optional pedal stroke lengths may be established, as previously described, for radii indicated generally at 58. 
     Referring lastly to FIG. 6, an end view of the crank 19 is illustrated to show the slidable block member 12 of the right side to be coupled to its corresponding frame member 11 at a first pedal stroke length radius 57, while the slidable block member 12 of the left side is coupled to its corresponding frame member 11 at a different pedal stroke radius 58. This unbalanced condition is useful when a user has limitation of leg lotion, with the right leg being more severely restricted. Of course, the situation could be reversed, and the difference between the radius and the left radius either reduced or increased, depending upon particular user circumstances and physcial limitations. 
     From the preceding descriptions, it can be readily noted that variation in the number of holes 44 incorporated in the frame member 11, variation in their mutual spacing, and variation in the separation between hole 37 and hole 38 on the slidable block member 12, can provide an apparatus 10 having one discrete set of pedal stroke lengths for orientaton of the slidable block member 12 as shown by FIG. 3 and a second, distinct, discrete set of pedal stroke lengths for orientation of the slidable block member 12 as shown by FIG. 4. 
     In each of the embodiments illustrated, described, or suggested hereinabove, the T-pin 14 is envisioned to be held in its inserted position through the hole 38 of the slidable block member 12 and into one of the holes 44 of the frame member 11 by frictional engagement arising from the tendency for the slidable block member 12 to move along the notch 39 of the frame member 11 during pedaling force applied by a user. Additional security against the inadvertent disengagement of the T-pin 14 from the selected hole 44 of the frame member 11 can be provided through the use of magnetic attraction between the cross bar 48 and the slidable block member 12. In one such embodiment, the cross bar 48 of the T-pin 14 is formed as a magnet, while the slidable block member 12 is made of a magnetic material. Another alternative for this purpose would include incorporation of a detent housed within the slidable block member 12 to engage a notch formed around the circumference of the central leg 46 of the T-pin 14 when the T-pin 14 is fully inserted in its proper position. 
     While the preceding descriptions, with reference to the accompanying drawings, have indicated a preferred embodiment with specific detail, other embodiments, configurations, and modifications thereof, or of specific elements of the apparatus 10 set forth herein, are readily apparent to those having ordinary knowledge of the art in view of the present teachings. All such alternate embodiments, mechanizations and modifications are contemplated to be within the intent of the present invention, which shall be limited only by the scope of the claims appended hereto.