Sidecar frame

A motorcycle sidecar frame composed of five elongate struts secured together at their respective ends into a shape substantially conforming to that of a tetrahedron. In one embodiment, a portion of an elongate frame member found on a motorcycle comprises the sixth edge of the tetrahedron. Two of the vertices of the tetrahedral frame are respectively located at two spaced points of the frame member. The remaining two vertices of the tetrahedron are respectively secured to a sidecar suspension system. One of the vertices is secured to the top of a shock absorber, which extends downwardly to the axle of the sidecar wheel, and the other vertex is pivotally secured to the end of an arm, the other end of which is secured to the sidecar wheel axle. In an alternative embodiment of the basic tetrahedral frame, the function of the five elongate struts of the first embodiment and the sixth strut is provided by the edges or corners of a tetrahedron formed by suitable sheets of metal. Other embodiments include frame members additional to the tetrahedral struts to strengthen the basic frame, to more securely locate the frame relative to the motorcycle and to facilitate the mounting of a sidecar body. The tetrahedral frame is releasably attached to the motorcycle by clevis and pin-type connectors which are suitable for connection to motorcycle frames of different dimensions, and include, or cooperate with, means for adjusting sidecar wheel toe-in.

BACKGROUND OF THE INVENTION 
With the recent advent of increased popularity of motorcycles, both as 
sports vehicles and vehicles for basic transportation, an interest in 
motorcycle sidecars has been renewed. The substantial increase in 
passenger and loadcarrying capacity provided by connecting a sidecar to a 
motorcycle enhances the utility of the motorcycle and adds an element of 
stability, the lack of which might otherwise discourage would-be users or 
purchasers of motorcycles. Further, if a sidecar is readily detachable and 
attachable to the motorcycle, the aforementioned advantages of a sidecar 
can be enjoyed while still permitting use of the motorcycle separate from 
the sidecar with the attendant improvement in maneuverability and handling 
on occasions when the advantages provided by a sidecar are not needed. 
The fundamental elements of a typical sidecar comprise a frame, means for 
securing the frame to a motorcycle, a body supported by the sidecar frame 
and a sidecar wheel and associated axle attached to the frame on the side 
opposite the motorcycle. A suspension system for absorbing road shock may 
also be considered a fundamental element. 
Preferably, a sidecar frame should be lightweight and readily connectible 
with the motorcycle, while having the necessary strength and rigidity 
characteristics needed to withstand the various loads and stresses which 
may be applied to it during normal usage. It is further desirable that the 
frame be adaptable for mounting to different makes of motorcycles and that 
it facilitates use of an easy and simple means to absorb road shock. 
Needless to say, the fewer the number of frame elements and the lesser the 
amount of material needed for each frame element, the less expensive will 
be the manufacturing costs of the frame. 
Known sidecar frames have substantially failed to achieve many, if not all, 
of the objectives noted above. Specifically, such sidecar frames have 
included a large number of frame elements and used elements of large size 
and strength. This has added to the weight of such frames, detracted from 
the ease of interconnection of the frame and motorcycle and otherwise 
presented ancillary disadvantages. 
SUMMARY OF THE INVENTION 
The foregoing disadvantages of known sidecar frames are substantially 
overcome in a unique manner in the sidecar frame of the present invention 
by constructing that frame in a form that substantially conforms to the 
shape of a tetrahedron. A tetrahedron is the term applied to the species 
of a polyhedron which has only four faces. The four faces, each of 
triangular shape, are defined by six straight lines extending between four 
three-dimensionally spaced points or vertices. In the preferred 
embodiments of the sidecar frame of the present invention, two of the 
vertices are connected to a suspension system located at the side of the 
frame adjacent the sidecar wheel opposite the motorcycle, and two of the 
vertices are located at two connection points on the motorcycle and 
extending therebetween are at least five elongate struts defining five of 
the six edges of the tetrahedron. The sixth edge of the tetrahedron, when 
not provided by the sidecar frame, may be provided by a motorcycle frame 
member found on most, if not all, motorcycles, when the sidecar frame is 
mounted to the motorcycle. 
The unique provision of a tetrahedron-shaped frame for a motorcycle sidecar 
results in numerous advantages over prior sidecar frame structures. The 
tetrahedral frame is unique relative to known sidecar frames in that it 
may be characterized as a perfect space frame, i.e., a structure built up 
of a number of small, straight struts which is equally strong when its 
joints are connected by pins as when rigidly connected by weld joints or 
the like. Thus, the frame is well suited for detachable connection to a 
motorcycle by means of a clevis and pin connections or the like, and this 
type of connection can be utilized without detracting from the strength or 
rigidity of the frame. Further, if all the joints are pinned together and 
provided with struts adjustable in length, the frame can be varied to fit 
virtually any motorcycle regardless of its dimensions. Still a further 
feature of the tetrahedral frame of the present invention is that, because 
of its inherent strength and rigidity, the number of struts and the size, 
strength, and weight of each strut is less than that of known frames of 
comparable frame strength. 
In accordance with the present invention, an additional strut may be 
provided extending between one of the vertices adjacent the sidecar wheel 
and a third point on the motorcycle frame which is not a vertex of the 
tetrahedral frame. However, the basic tetrahedral frame carries all of the 
sidecar forces, and this additional strut is provided merely to firmly 
locate the position of the tetrahedron relative to the motorcycle and to 
facilitate securement of and support of the sidecar coach or body. 
Depending upon the shape and size of the sidecar coach, whether it be 
designed for carrying passengers or other loads, still further sidecar 
frame members may be added to facilitate the mounting and support of the 
coach body. 
A further feature of the present invention is presented in an alternate 
embodiment of the sidecar frame, in which the edges of an enclosed 
tetrahedron formed from conventional sheet plastic, sheet metal, or other 
suitable sheet material, serve the function of the elongate struts of the 
described above embodiment. All six edges of the tetrahedron, rather than 
just five, are of course provided by the frame in this alternate 
embodiment of the tetrahedral frame. A particular advantage of the 
alternate embodiment is that the frame may additionally serve as an 
auxiliary gas tank or other storage space. In the first embodiment, the 
area within the tetrahedron defined by the struts is usable to locate a 
separate auxiliary gas tank which is nonintegral with the frame. 
A simple suspension system for the tetrahedral sidecar frame is provided 
comprising a swing arm and shock absorber. The swing arm is pivotally 
connected at one end to a vertex of the tetrahedral frame and secured at 
its other end to a sidecar wheel axle bearing. One end of the shock 
absorber is also secured to the wheel axle bearing and the other end is 
secured to another vertex of the tetrahedral frame located above the first 
vertex to which the swing arm is connected.

DESCRIPTION OF PREFERRED EMBODIMENT 
The sidecar frame of the present invention may be usefully employed in 
conjunction with almost any type of vehicle to which it is desired to 
attach at its side a car to be carried by the vehicle. However, such 
sidecars are most frequently used in conjunction with motorized bicycles 
or motorcycles, and the sidecar frame of the present invention, while not 
limited to use with a motorcycle, is primarily intended for such use. With 
this understanding, the sidecar frame will be referred to as a motorcycle 
sidecar frame, and its particular use in conjunction with a motorcycle 
will be described. 
Thus, a preferred embodiment of the basic sidecar frame of the present 
invention, generally designated by reference numeral 30, is shown in the 
drawings attached to a motorcycle of common configuration, generally 
designated by reference numeral 32. The sidecar, in addition to frame 30, 
includes suitable means for attaching the sidecar frame 30 to the 
motorcycle 32 which will be referred to as mounting bracket assemblies 
generally designated by reference numeral 34, a suspension system, 
generally designated by reference numeral 36, a wheel assembly generally 
designated by reference numeral 38, and a sidecar body or coach, generally 
designated by reference numeral 40. The particular coach 40 depicted in 
the drawing is particularly adapted for carrying passengers, but coaches 
of other designs for other loadcarrying purposes could of course be 
utilized in conjunction with the frame. Likewise, other types of 
suspension systems and mounting bracket assemblies could of course be used 
with the basic sidecar frame 30. 
Referring to the drawings, particularly FIGS. 1-4, the motorcycle 32 has a 
frame 42 to which is secured a steering column bearing assembly 44. 
Assembly 44 carries a steering column attached at a forked end thereof to 
the axle of a front wheel 46 and connected at its other end to handle bar 
48. The axle of a rear wheel 50 is secured to motorcycle frame 42 by means 
of a suitable suspension system including a shock absorber 52. One end of 
shock absorber 52 is secured to the frame adjacent a point 80 thereof near 
the top of the motorcycle and its other end is secured to a swing arm 54. 
Swing arm 54, in turn, is secured at its end adjacent the connection to 
shock absorber 52 to the axle of wheel 50 and pivotally secured at its 
other end to another point 78 on the frame located downwardly and 
forwardly with respect to point 80. Additionally, the motorcycle 32 
includes a seat cushion 56 and a gas tank 58 mounted atop the frame 42. 
Although not shown in the drawings for purposes of facilitating 
illustration of the present invention, the motorcycle 32 is of course also 
provided with an engine, generally mounted to the frame beneath the gas 
tank 58, a suitable drive linkage from the engine to the rear wheel 50, a 
braking mechanism and other associated mechanisms needed to control the 
motorcycle. Finally, with regard to the motorcycle parts attached to the 
frame as illustrated in FIG. 2, foot pedals 59 are generally provided on 
opposite sides of the motorcycle, the right side one of which being shown 
in FIG. 2. 
More specifically with regard to the motorcycle frame 42, the frame 
elements are generally formed from suitable cylindrical metal stock, which 
may be tubular, that is bent, cut and then welded as needed to form the 
frame as depicted in the drawings. As best seen in FIG. 2, the frame 
includes a left-hand section 60 and a right-hand section 62 which is a 
mirror image of section 60. Sections 60 and 62 are joined together at the 
steering column bearing assembly 44 and may also be secured together by a 
suitable cross member 64 adjacent the front of the frame and another cross 
member 66 at the back of the frame. Each of the sections includes a 
substantially straight, elongate upper frame member 68 extending from the 
steering column bearing assembly 44 to the cross member 66 located above 
and slightly forward of the rear wheel axle. Upper frame members 68 are 
located immediately beneath the seat cushion 56 and gas tank 58. Each of 
the frame sections also includes a lower frame member 70, as best seen in 
FIG. 3, which has a first portion 72 extending downwardly and rearwardly 
from adjacent the steering column bearing assembly 44 to a point 74 
substantially in alignment with or slightly below a line extending between 
the motorcycle wheel axles, and a substantially horizontal portion 76 
extending from point 74 to another point 78. A third portion 79 of lower 
frame member 70 extends from point 78 upwardly and rearwardly to a point 
80 adjacent cross member 66 located above wheel 50. Preferably, all of the 
three portions of lower frame member 70 are integrally formed by bending a 
single piece of tubular stock. An additional frame member 82 extending 
from and secured to frame member 70 at point 78 to an intermediate point 
84 of upper frame member 68 substantially defines a triangle with apexes 
at points 78, 80 and 84. The members of the frame not integrally formed 
are preferably secured together by weld joints or the like. 
While the frame depicted in the drawings and described above is a type 
commonly found in motorcycles of many manufacturers, and for this reason 
the sidecar frame of the present invention will be described in connection 
with this type of frame, it should be appreciated that the sidecar frame 
of the present invention is suitable and adaptable for connection with 
motorcycle frames of other designs and, in fact, even with other types of 
vehicles. 
Regardless of the exact design of the motorcycle frame, there are found on 
virtually all motorcycles three points on the frame of substantially more 
than adequate strength necessary for attachment to a sidecar, at relative 
locations corresponding to points 78, 80 and 74 of frame 42. These points 
on the frame, because of their strength, are ideal points for connection 
with the sidecar frame, and for this reason the sidecar frame of the 
present invention is particularly adapted for connection to a motorcycle 
frame at points having these relative locations. 
With continuing reference to FIGS. 1-4, a preferred embodiment of the basic 
sidecar frame 30 of the present invention is seen to comprise five 
elongate struts 96, 98, 100, 102 and 104 connected together into a shape 
substantially conforming to that of a tetrahedron. The four points at 
which the ends of the struts are joined together define the vertices of 
the tetrahedron, and each of the struts define five of the six edges of 
the tetrahedron. A first pair of vertices 78' and 80' correspond to the 
ends of the struts adapted to be attached to the motorcycle frame 42 at 
points 78 and 80, and a second pair of vertices 86 and 88 are adapted to 
be the sidecar suspension system 36. 
Suspension system 36 includes a vertically disposed shock absorber 90 of 
the dashpot type secured at one end to the juncture of three struts 
forming vertex 86 and secured at its other end to the fixed end of a swing 
arm 92 adjacent the axle 94 of wheel assembly 38. Swing arm 92 is 
pivotally mounted at its other end to a pivot axis provided adjacent 
vertex 88. This pivotal connection, of course, permits upward forces 
applied to wheel 38 by road shock to be transmitted into upward motion of 
the piston of shock absorber 90 and thereby absorbed. 
The ends of three struts are secured together to form each of the vertices 
86 and 88 and one strut from each of vertices 86 and 88 are joined 
together at their opposite ends to form the vertex 80' of the tetrahedral 
frame adapted to be attached to motorcycle frame at point 80 and another 
one of the struts from each of vertices 86 and 88 are joined together at 
their opposite ends to form the other vertex 78' of the tetrahedron 
adapted to be secured to the motorcycle frame at point 78. A strut 
extending between vertices 86 and 88 completes the three-strut juncture 
forming vertices 86 and 88. More specifically, a first strut 96 extends 
between vertices 86 and 88; a second strut 98 extends between vertices 86 
and 80; a third strut 100 extends between vertices 88 and 80; a fourth 
strut 102 extends between vertices 86 and 78'; and a fifth strut 104 
extends between vertices 88 and 78'. 
As noted above, because of the tetrahedral shape of frame 30, it is equally 
strong whether the ends of the struts were welded together or merely 
secured together by means of pins. In the preferred embodiment shown in 
FIGS. 1-4, the ends of the struts are secured together by means of weld 
joints. 
When the sidecar frame 30 is attached to the motorcycle, as shown in FIG. 
1, the elongate portion 79 of the motorcycle frame 42 extending between 
points 78 and 80 thereof, of course, functions as, and thereby forms or 
corresponds to, the sixth edge of the tetrahedron, the other five edges of 
which are provided by struts 96, 98, 100, 102 and 104. The vertices formed 
by struts 98 and 100 and struts 102 and 104 are respectively secured to 
points 80 and 78 of motorcycle frame 42 by means of pin connections of 
suitable bracket assemblies 34 to facilitate connection and disconnection 
between the motorcycle and the sidecar frame, as will be explained in more 
detail hereinafter. 
The five struts, 96, 98, 100, 102 and 104, form the basic tetrahedral frame 
for the motorcycle sidecar of the present invention and are sufficient, in 
and of themselves, to carry and withstand all the various loads and 
stresses applied to the frame. However, to facilitate securement and 
support of the motorcycle coach 40 to the frame 30, and to more rigidly 
fix the position of the basic frame relative to the motorcycle, an 
additional elongate frame member 106 extending between vertex 88 and point 
74 on the motorcycle frame 42 may be provided. Preferably, one end of 
strut 106 is secured to the end of struts 100 and 104 at vertex 88 by 
means of a weld joint, and is secured to point 74 on motorcycle frame 42 
by means of a pin connection of the mounting bracket assembly 34 thereat. 
Strut 106 extends diagonally underneath the sidecar coach 40 and a bottom 
surface 108 of the sidecar coach 40 rests upon and is supported in part by 
strut 106. It is desirable to keep the center of gravity of the sidecar 
coach 40 as low as possible to improve stability. Consequently, strut 106 
may be bent downwardly intermediate its ends to permit mounting the 
sidecar coach 40 closer to the ground than would be permitted if strut 106 
were straight, as best seen in FIG. 3. Alternately, to lower the center of 
gravity, a straight elongate strut 106', indicated in broken lines in 
FIGS. 4 and 1, may be employed, with the lowering of the center of gravity 
of the sidecar coach being provided by means of a slot 110 extending 
diagonally across the rear left-hand corner 112 of the sidecar coach 40 
adapted to receive therewithin strut 106' when the coach 40 is mounted to 
the frame. It is contemplated that both the provision of a slot and a 
downward bend in strut 106 may be employed together to lower the center of 
gravity even further if desired. In addition to strut 106 or strut 106', 
the coach 40 is secured to the sidecar frame 30 by means of mounting 
members 114 secured to the top edge of the back wall of sidecar coach 40. 
Mounting members 114, in turn, are adapted to be fastened to the 
substantially horizontal tetrahedral frame strut 98 extending between 
vertices 80' and 86, as best seen in FIGS. 1 and 2. 
Sidecar frame members additional to strut 106 or 106', may be provided to 
further facilitate the mounting and securement of the sidecar coach 40 to 
sidecar frame 30. Referring to FIGS. 6 and 7, another embodiment of the 
sidecar frame is shown with additional frame members being shaded to 
distinguish them from the struts of the basic tetrahedral frame 30. 
Specifically, the additional frame structure, generally designated by 
reference numeral 116, is seen to comprise four frame members, 118, 120, 
122 and 124 selectively secured together at their respective ends and to 
the basic tetrahedral frame struts. 
The additional frame structure 116 has members 112 and 120 which extend 
along the sides of sidecar coach 40 and member 118 which underlies and 
supports the forward portion of the coach bottom. 
The three members 118, 120 and 122 in combination with strut 98 preferably 
form a rectangle, the plane of which slopes downwardly from strut 98 in 
the forward direction toward point 74 on the motorcycle frame 42. More 
specifically, a first one of the frame members, frame member 122, is 
secured at one end to strut 98 adjacent vertex 80' and secured at its 
other end to the end of a third one of the frame members of structure 116, 
adapted to be connected to the motorcycle frame adjacent point 74. 
Likewise, a second one of the frame members, frame member 120, is secured 
at one of its ends to strut 98 adjacent vertex 86 and secured at its other 
end to strut 118 at the end of strut 118 opposite the juncture with frame 
member 122. A third one of the frame members, frame member 118, is secured 
at its end adjacent the juncture with frame member 122 to the frame of the 
motorcycle at point 74 by means of a suitable mounting bracket assembly 
34. Strut 106' or 106, if used in conjunction with additional frame 
members 116, may be secured to the end of frame member 116 adjacent the 
mounting bracket assembly 34 or alternately may be secured to the frame of 
the motorcycle by means of a separate connection with a mounting bracket 
assembly 34 at point 74. 
A fourth frame member of the additional frame structure 116, frame member 
124, is secured at one end to the ends of the basic tetrahedral struts 
forming vertex 88 and is secured at its other end to the juncture of the 
third and second frame members 118 and 120. As best seen in FIG. 7, the 
fourth frame member 124, the second frame member 120 and strut 96 form a 
triangle lying in a plane which is preferably transverse to strut 98. 
Each of the frame members comprising frame structure 116 may be individual 
lengths of tubular stock that are welded together at their respective ends 
into the configuration of the frame structure. However, some of the frame 
members, such as frame members 116 and 120, may be integrally formed by 
simply bending a suitable length of stock into the desired configuration. 
Along these same lines, in fact, each of frame members 116, 120 and 122 
may be integrally formed by making suitable bends in a single length of 
tubing having a portion comprising a fifth frame member 126 
interconnecting members 120 and 122, as indicated in broken lines in FIGS. 
6 and 7. In addition to permitting integral formation of the other frame 
members, frame member 126 runs parallel to and reinforces strut 98. 
As shown in FIGS. 13 and 14, the sidecar frame of the present invention may 
include, in addition to the basic tetrahedral frame 30, an additional 
frame structure, generally designated by reference numeral 128. The struts 
of structure 128 are shaded to distinguish them from the struts of the 
basic tetrahedral. Frame structure 128 is primarily provided to strengthen 
and reinforce the basic frame, but it also facilitates support and 
mounting of the sidecar coach. Thus, frames of varied strength and varied 
applications may be constructed in modular form, with the primary 
load-carrying capabilities being provided by the basic tetrahedral frame 
30, and frames of greater strength being constructed by simply adding 
additional struts to the existing basic frame. The basic tetrahedral frame 
facilitates such adaptation and is versatility and utility is thereby 
enhanced. 
The preferred embodiment of the reinforcing frame structure 128 comprises 
three elongate frame members 130, 132 and 134. One end of each of these 
frame members are joined together at a juncture 136 by means of weld 
joints or by a weld joint securing the end of one of the frame members to 
a bend at juncture 136 in a single length of tubular stock forming the 
other two of the three members. The other end of a first one of the frame 
members, frame members 130, is secured to the juncture of the struts of 
the basic tetrahedral frame forming vertex 88. The other end of a second 
one of the frame members, frame member 132, is secured to the juncture of 
struts of the basic tetrahedral frame forming vertex 80' adapted to be 
connected to point 80 on the motorcycle frame 42, and the other end of the 
third frame member 134 is connected to the juncture of the struts of the 
basic tetrahedral frame forming vertex 78'. Preferably, frame members 130 
and 132 form a rectangle with struts 96 and 98, frame member 130 being 
parallel to strut 98 and frame member 132 being parallel to strut 96. 
Frame members 130 and 134 form a right triangle with strut 104. Frame 
members 130, 132 and 134 and struts 100 and 104 define five edges of a 
second tetrahedron having two edges shared with the basic tetrahedral 
frame 30. 
A preferred means of securing the sidecar frame to the motorcycle frame is 
provided by mounting bracket assembly 34, different versions of which are 
shown in FIGS. 8, 9, 10, 11 and 12. Each of the mounting bracket 
assemblies 34 includes a clevis 140 which may be in the form of a 
cylindrical member having a slot 142 at one end with aligned holes 144 
extending through the two portions of the cylindrical member separated by 
the slot and means for securing the clevis 140 to the motorcycle frame. 
Assembly 34 also includes a male connector 146 to be secured to the ends 
of the struts or frame members, as shown in FIG. 11, having an ear 148 
with a hole extending therethrough adapted to be received within slot 142 
with hole 150 in alignment with holes 144. When male connector 146 is 
matingly engaged with clevis 140, a suitable pin member 148 extending 
through each of the holes 144 and 150 pivotally secures together the 
clevis and the male connector. Pin 148 may comprise a cotter pin, a headed 
bolt or any other like device of suitable strength and appropriate 
dimension. Clevis 140 may be secured to the frame by means of a plate 151 
secured to the clevis 140 and which, in turn, may be secured to the frame 
members by means of U-bolt 152 and nuts 154, as illustrated in FIGS. 9 and 
12. The plate 151 may be integrally formed with clevis 140, or they may be 
welded together. This type of detachable connection has been found to be 
quite suitable for connection at points 78 and 80 of the motorcycle frame. 
Alternately, the clevis 140 may be more permanently secured to the frame 
by means of weld joints such as at 141 shown in FIG. 10. This alternate 
type of connection is necessary at point 74 on same motorcycle frames due 
to the shape of the frame 42. 
A male connector 146 is provided at the juncture of the struts forming the 
vertex desired to be connected to the motorcycle frame at each of points 
78 and 80. Preferably, male connector 146 is secured to the end of one of 
the struts of the juncture by being directly welded thereto and secured to 
the ends of the other struts of the vertex through the weld joints at the 
ends of the other struts to the end of the one strut to which the male 
connector 146 is directly welded. Alternately, a male connector 146 could 
be provided at the end of each of the struts of the juncture and secured 
to a single enlarged clevis adapted for receipt of all of the male 
connectors or secured to separate clevises, all located at approximately 
the same point on the frame. If this alternate is utilized, the means for 
securing the sidecar frame to the motorcycle also comprises the means of 
securing the ends of the struts together to form the vertex of the 
tetrahedron. 
Referring to FIG. 11, another manner of securing the male connector 146 to 
the end of a strut may be provided by means of a threaded member 160 
which, in turn, is itself secured to the end of the strut. Threaded member 
160 may simply comprise a threaded bolt having a head 162 secured to the 
end of the strut by a weld joint, or the threaded member 160 may be 
integrally formed with the strut or screwed into a suitably tapped hole at 
the end of the strut. In either event, the male connector 146 is adapted 
for use with threaded member 160 by providing it with an axial, internally 
threaded shaft to permit the male connector to be screwed onto the end of 
the threaded member 160. 
When the type of connection shown in FIG. 11 is utilized, it may serve as a 
means to adjust the sidecar wheel toe-in. Toe-in refers to the slight 
inward set of the sidecar wheel in relation to the wheels of the 
motorcycle. Improper toe-in adjustment results in excessive and uneven 
tire wear and can contribute to handling difficulties. 
Briefly, the threaded connection provides a means for adjusting the 
effective length of the struts which are secured thereto. Adjusting male 
connector 146 so that it is closer to the base or head 162 of threaded 
member 160 shortens the effective length of the struts secured to the male 
connector, and adjusting male connector 146 so that it is further away 
from the base of the threaded member increases the effective length of the 
struts. In this manner, the toe-in of the sidecar wheel may be adjusted. 
Additionally, the type of threaded connection shown in FIG. 11 may be 
utilized to facilitate connection of a single frame with struts of fixed 
dimensions to motorcycles of different dimensions by permitting adjustment 
of the effective lengths of the struts. 
Another way in which the toe-in may be adjusted is illustrated in FIG. 12. 
As seen in FIG. 12, the use of a plate 151 in combination with a U-bolt 
152 for the mounting bracket assembly permits the use of a shim 164. Shims 
of selected thicknesses may be placed between the motorcycle frame and 
plate 150 to selectively adjust the effective length of the struts secured 
thereto and thereby adjust the toe-in of the sidecar wheel. 
Turning now to FIG. 15, an alternate embodiment of the basic tetrahedral 
frame of the present invention, generally designated by reference numeral 
166, is shown in which the struts comprise the corners of a tetrahedron 
having closed faces that is fabricated from a suitable sheet material, 
such as sheet plastic or metal, and thus may additionally serve as an 
auxiliary gas tank or the like. The edges or struts of the tetrahedral 
frame 166 are designated with the reference numeral given to the struts in 
the first embodiment corresponding thereto followed by a prime. These 
edges are interconnected with one another to form all of the vertices of 
the sidecar frame and they function in the same way and for the same 
purpose as the corresponding struts of the frame 30 of the first 
embodiment discussed above. Tetrahedral frame 166 is completely enclosed 
and thus an additional strut 168 formed by the edge of the tetrahedron 
extending between the vertices 78' and 80' adapted to be connected to 
points 78 and 80 is provided which, in the frame 30 of the first 
embodiment, is provided by the motorcycle frame. However, it should be 
understood that a sixth strut corresponding to strut 166 could of course 
be readily added to the first embodiment of the basic tetrahedral frame 
30. 
Frame 166 may be used in the same manner as frame 30. The mounting bracket 
assembly 34 of the same type discussed above and shown in FIGS. 8, 9, 10, 
11 and 12 can be used with tetrahedral frame 166. Further, the additional 
frame members discussed above and shown in FIGS. 13, 14 and 6 and 7, or 
other additional frame members, may likewise be used in conjunction with 
the basic tetrahedral frame 166 in the same manner as they are used in 
conjunction with the basic tetrahedral frame 30. The struts 130, 132 and 
134, shown in FIGS. 13 and 14, may themselves comprise the edges of a 
tetrahedron fabricated from sheet material in the same manner that basic 
frame 166 is fabricated. 
The alternate embodiment of the tetrahedral frame shown in FIG. 15 defines 
an enclosed space between the struts of the frame formed by the edges of 
the tetrahedron such that the frame may be adapted by a gasoline inlet 
opening 170 and a gasoline outlet 172, for instance, to serve as an 
auxiliary gas tank or other storage space. If the space between struts 
130, 132 and 134 shown in FIG. 13 were to be enclosed, it likewise could 
be utilized for storage. It is contemplated that frames of other designs, 
but which also define a three-dimensional space that can be enclosed, 
could advantageously be fabricated from sheet material to also form a 
storage area. Also, the open faces of a frame in which the struts comprise 
elongate cylindrical members or the like, as frame 30 of the first 
embodiment, could be covered with a suitable material to form a storage 
area.