Conversion assembly for a motorcycle

An assembly for converting a two-wheeled motorcycle into a three-wheeled motorcycle which provides independent suspension for each of the rear wheels and which has a relatively low unsprung weight, thus not substantially impairing the performance of the motorcycle after it is converted to a three-wheeled vehicle. The assembly may be bolted to the frame of a motorcycle, without the need for welds or other permanent connections, so that the three-wheeled motorcycle can be converted back into a two-wheeled motorcycle when desired.

BACKGROUND OF THE INVENTION 
The present invention is directed to an assembly for converting a 
two-wheeled motorcycle into a three-wheeled motorcycle. 
Conventional assemblies have been used to convert two-wheeled motorcycles 
into three-wheeled motorcycles. Such assemblies may utilize the rear end 
of an automobile, for example a Ford Pinto, having a single, relatively 
heavy axle which is connected to a motorcycle frame to convert the 
motorcycle into a three-wheeled vehicle. One disadvantage of such a 
construction is that the suspension of the vehicle is adversely affected 
by its single axle, which significantly increases the unsprung weight of 
the vehicle and unduly limits its performance. 
SUMMARY OF THE INVENTION 
The invention is directed to an assembly for converting a two-wheeled 
motorcycle into a three-wheeled motorcycle which provides independent 
suspension for each of the rear wheels and which has a relatively low 
unsprung weight, thus not substantially impairing the performance of the 
motorcycle after it is converted to a three-wheeled vehicle. The assembly 
may be bolted to the frame of a motorcycle, without the need for welds or 
other permanent connections, so that the three-wheeled vehicle can be 
converted back into a two-wheeled motorcycle when desired. 
An assembly in accordance with the invention includes a mounting frame and 
a plurality of couplers attached to the mounting frame, each of the 
couplers being adapted to be connected to a respective portion of a 
motorcycle frame so as to maintain the mounting frame in a fixed position 
with respect to the motorcycle frame. A pair of pivot arms are pivotally 
connected to the mounting frame, a first pivot arm being adapted to be 
connected to a portion of a first wheel assembly and a second pivot arm 
being adapted to be connected to a portion of a second wheel assembly. A 
plurality of shock absorbers are connected to the mounting frame and the 
pivot arms so that the wheel assemblies are movable with respect to each 
other, and drive means for imparting motive power to the wheel assemblies 
are connected between the mounting frame and the wheel assemblies. 
The mounting frame may have a first frame portion and a second frame 
portion, the second frame portion having a position which is adjustable 
relative to the first frame portion. The first frame portion may have a 
pair of slotted portions and the second frame portion may have a pair of 
vertically disposed plates which are slidably adjustable within the 
slotted portions of the first frame portion. 
The conversion assembly may also be as a suspension assembly in new 
three-wheeled motorcycles.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
A preferred embodiment of an assembly 10 for converting a two-wheeled 
motorcycle into a three-wheeled motorcycle is illustrated in FIGS. 1-3. 
Referring to FIGS. 1-3, the assembly 10 includes a mounting frame having a 
left frame portion 12a, a right frame portion 12b, and a pair of front 
frame portions 14a, 14b (shown in FIGS. 2 and 3), which are adjustably 
connected to the frame portions 12a, 12b. As shown in FIG. 1, the frame 
portions 12a, 12b meet at a pair of joints 16, and may be secured together 
via a number of horizontally disposed bolts 17 which are disposed in a 
number of generally cylindrical openings 19 (see FIG. 3) and which pass 
through both frame portions 12a, 12b (some of the bolts 17 and openings 19 
are omitted from FIG. 1 for purposes of clarity). The frame portions 12a, 
12b, 14a, 14b may be composed of machined aluminum, for example. The 
particular manner in which the frame portions 12a, 12b are fastened 
together is not considered important to the invention, and other 
connection means may be used. 
A pair of shock absorber mounts 18a, 18b and a pair of pivot arm mounts 
20a, 20b are integrally formed with the frame portions 12a, 12b. Each of 
the shock mounts 18a, 18b has a pair of flanged ends 22 and a central bore 
24 formed therein to facilitate the insertion of a rod 26 (see FIG. 1) 
having two threaded ends to each of which a top attachment ring 28 of a 
shock absorber 30 can be attached via a number of bolts 32, two shock 
absorbers 30 being mounted to each shock mount 18a, 18b for a total of 
four shock absorbers 30 (the springs of the shock absorbers 30 are not 
shown). Each of the pivot arm mounts 20a, 20b has a central bore 36 (see 
FIG. 3) formed therein. Any type of shock absorption mechanism or spring 
coil could be used as shock absorbers. 
A pivot arm 40 is connected to each of the pivot arm mounts 20a, 20b. 
Referring to FIGS. 1 and 5, each pivot arm 40 has a first C-shaped end 42 
which pivotably mounts to one of the pivot arm mounts 20a, 20b via a bolt 
44 (see FIG. 1) which passes through a pair of holes 46 formed in the end 
42 and the central bore 36 (FIG. 3) formed in one of the pivot arm mounts 
20a, 20b. Each pivot arm 40 has a second C-shaped end 50 having a pair of 
holes 52 (FIG. 5) formed therein which mounts to one of a pair of wheel 
assemblies 54 (FIG. 1), to which a pair of rear wheels (not shown) may be 
attached, via a bolt 56 which passes through the holes 52 (FIG. 5) formed 
in the end 50 and a central bore (not shown) formed in one of the wheel 
assemblies 54. Each pivot arm 40, which may be composed of steel, has a 
pair of rods 60 (FIG. 5) connected thereto, the end portions of which are 
threaded. As shown in FIG. 1, a bottom ring portion 62 of each of the 
shock absorbers 30 is attached to one of the rods 60 via a bolt 64. 
The assembly 10 includes a differential gearbox 70 mounted to the frame 
portions 12a, 12b via a pair of holes 72 formed therein. A drive sprocket 
73 is connected to drive the differential 70 from power transmitted by the 
chain of the motorcycle (not shown). Motive power is transmitted from the 
differential 70 to each of the wheel assemblies 54 via a drive shaft 74 
connected between a pair of universal joints 76, 78. A pair of drive axles 
80 mounted to the frame portions 12a, 12b via a pair of bearing assemblies 
82 interconnect each of the universal joints 76 to the differential 70. 
The assembly 10 includes a swaybar 84 connected to the frame portions 12a, 
12b via a pair of mounting brackets 86 (only one of which is shown). The 
particular design of the drive train is not considered important to the 
invention, and the drive train could be modified to accommodate 
motorcycles which are driven via direct-drive shafts instead of chains. 
Referring to FIGS. 2-4, each of the front frame portions 14a, 14b of the 
assembly 10 has a pair of cylindrical mounting tubes 90 with a pair of 
bores 92 formed therein. As shown in FIG. 4, the front frame portions 14a, 
14b mount to a number of cylindrical tubes 94 having central bores 96 via 
a swing arm rod 98, the tubes 94 being rigidly connected, such as by 
welding, to a motorcycle frame 100. 
Referring to FIGS. 1 and 3, a pair of L-shaped clamps 102 are connected to 
the top of the frame portions 12a, 12b. The horizontal portions of the 
clamps 102 are bolted to the frame portions 12a, 12b via a number of bolts 
104, and the vertical portion of each clamp 102 is bolted to another 
portion 106 of the motorcycle frame (FIG. 1) via a bolt 110. Because the 
assembly 10 is connected to the motorcycle frame at the points described 
above, the frame portions 12a, 12b, 14a, 14b are rigidly coupled to the 
motorcycle frame. 
Referring to FIG. 3, the front frame portions 14a, 14b may have a 
rectangular groove 116 formed therein to accommodate a motorcycle battery 
(not shown), and a pair of rectangular holes 118 may be formed 
therethrough to facilitate the fastening of bolts (not shown) into a pair 
of threaded holes 120 in order to bolt the front frame portions 14a, 14b 
together. 
Referring to FIG. 2, each of the front frame portions 14a, 14b comprises a 
horizontally disposed plate 130 and a vertically disposed plate 132 
integrally formed therewith. Each plate 132 is slidably adjustable within 
a generally rectangular slotted portion 134 formed in the outer surface of 
each of the frame portions 12a, 12b. A relatively narrow slot 136 is 
formed in each of the vertical plates 132 at the same height as a 
plurality of threaded holes 138 formed in the frame portions 12a, 12b. The 
vertical plates 132 are fixed to the frame portions 12a, 12b via a number 
of bolts (not shown) which pass through the slot 136 and the threaded 
holes 138. 
A pair of adjustment blocks 140 are mounted at the intersection of the 
vertical and horizontal plates 130, 132 of the front frame portions 14a, 
14b. Each adjustment block 140 is threaded to receive a respective 
threaded adjustment bolt 142, each of which has an end which may abut a 
respective front face 144 of the frame portions 12a, 12b. 
To convert a two-wheeled motorcycle to a three-wheeled vehicle using the 
assembly 10, with the motorcycle supported in an elevated position, the 
rear wheel, fender, shocks and swing arm of the motorcycle are removed. 
Then, the motorcycle drive sprocket 73 is attached to the differential 70; 
the motorcycle chain (not shown) is placed on the drive sprocket 73; and 
the frame portions 12a, 12b are bolted together at the joints 116. 
The front frame portions 14a, 14b are bolted together and attached to the 
motorcycle via the swing arm bolt 98. The position of the frame portions 
14a, 14b with respect to the frame portions 12a, 12b is adjusted by 
turning the adjustment bolts 142 until the motorcycle chain is properly 
tensioned. Then the frame portions 14a, 14b are rigidly fastened to the 
frame portions 12a, 12b via bolts (not shown) which pass through the slots 
136 in the frame portions 14a, 14b and the threaded holes 138 in the frame 
portions 12a, 12b. The L-shaped clamps 102 are then fastened to the 
motorcycle frame portions 106 via the bolts 110. 
When mounted to a motorcycle, the assembly 10 is advantageous in that it 
provides independent suspension of the rear wheels (i.e. one rear wheel 
assembly is movable relative to the other rear wheel assembly), and in 
that the unsprung weight of the vehicle is reduced in comparison with 
conventional assemblies. As used herein, the term "unsprung weight" means 
the weight of the vehicle components which are not cushioned against 
vibration by the shock absorbers 30. Thus, the frame components 12a, 12b, 
14a, 14b and the differential 70 would not contribute to the unsprung 
weight of the vehicle. Also, since it is bolted to the motorcycle frame, 
the assembly 10 can be removed after it is installed so that the vehicle 
can be converted back into a two-wheeled motorcycle. 
The design of the assembly described above may be modified so that it may 
be retrofitted to any commercially available motorcycle. Further 
modifications and alternative embodiments of the invention will be 
apparent to those skilled in the art in view of the foregoing description. 
This description is to be construed as illustrative only, and is for the 
purpose of teaching those skilled in the art the best mode of carrying out 
the invention. The details of the structure and method may be varied 
substantially without departing from the spirit of the invention, and the 
exclusive use of all modifications which come within the scope of the 
appended claims is reserved.