Method of joining and reinforcing molded plastic bicycle frames

A method of forming a tubular frame, e.g., a bicycle frame, from two substantially symmetrical frame-halves utilizes a plurality of interconnected half-tubular elements. Each half-tubular element has an exterior surface, an interior surface, and longitudinal edges that extend between the exterior and interior surfaces in the direction of the longitudinal axis of the half-tubular element. The surfaces of the longitudinal edges of the half-tubular elements are shaped such that corresponding edges of corresponding half-tubular elements in the left and right half-frames may easily be interengaged, and adjusted along the respective longitudinal axes of the half-tubular elements that are being joined. Preferably, the longitudinal free edges are stepped in the radial direction such that each level is substantially planar and smooth along the respective longitudinal axis of the half-tubular element. The longitudinal edge of one of the half-tubular elements may include parallel steps extending in opposite directions to thereby form a groove into which a step of the corresponding longitudinal edge of the corresponding half-tubular element in the other half-frame may be inserted. The latter joint type provides additional reinforcement of the connection of the half-frames. Further reinforcement in the stay area of the bicycle frame may be provided, either in the form of a reinforcement arch positioned within the tubular legs of the stays, or in the form of a one-piece, unitary inner stay element positioned between the outer stay elements that are part of the frame-halves.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of joining and reinforcing molded 
frames. More particularly, the present invention relates to a method of 
joining molded halves of a bicycle frame without requiring alignment 
elements on the frame halves, yet providing a sturdy connection between 
the frame halves. The present invention further relates to a method of 
reinforcing high stress areas in a bicycle frame formed from molded frame 
halves. 
Bicycle frames generally are formed from substantially hollow tubular frame 
elements connected together in a manner depending on the material and 
manner of formation of the tubular elements. When the tubular elements are 
formed from a lightweight metal, such as aluminum, the metal is generally 
cast into a single-piece tubular element. Several such tubular elements 
are connected together, such as by welding or gluing, to form the frame of 
the bicycle. When the tubular elements are formed from a fiber-reinforced 
plastic or composite material, the elements typically are adhesively 
bonded into lugs. Alternatively, composite lugs may be formed over the 
pre-fabricated composite tubular elements. Because all of the tubular 
elements must be joined together to form the finished bicycle, formation 
of a bicycle frame from tubular elements is rather labor intensive. 
Additionally, the lugs or joints with which the tubular elements are 
joined must be relatively thick and heavy in order to provide a secure 
connection between the elements. 
A method that eliminates the use of multiple parts that must be joined to 
form a finished bicycle frame involves the formation of an 
inflation-cured, one-piece hollow shell. This method uses composite 
materials typically composed of structural fibers (such as carbon fiber 
and fiberglass) and thermoset resins (such as epoxy) which are placed 
around an inflatable bladder (formed from materials such as a nylon film) 
or an expandable material (such as a heat-expandable foam). The assembly 
is placed in a cavity mold and either the bladder is inflated or the heat 
applied to cure the thermoset resin causes the expandable material to 
expand. The fiber and resin are thus pressed by the expanding base 
structure (the bladder or expandable material) against the cavity mold 
walls and thereby conformed to the shape of the mold during the curing of 
the resin. Once curing is complete, the mold is opened and the frame is 
removed, with the bladder or expandable material permanently remaining on 
the interior walls of the frame. Because the fibers are only strong in the 
fiber direction (either one or two directions, depending on the fiber tape 
or cloth available), several fiber layers, each having a different 
directional orientation, must be used in order to result in the desired 
frame structural strength. The resulting wall thickness is relatively 
thick, particularly in bent or angled areas (generally at the areas where 
joints are used in a frame formed from several tubular elements), and the 
frame is thus heavy, even though relatively heavy lugs or joints are not 
used. Because the frame remains in the mold for several hours (making the 
mold unavailable for use in forming another frame), and several layers 
must be applied, production costs typically are more expensive than for 
joined-tubing frames. Moreover, the frames are typically brittle and 
subject to cracking from use and may shatter on impact. 
A bicycle frame that avoids many of the above-described disadvantages of 
prior art frames is formed from two molded partial shells that are joined 
to form a hollow finished frame. Such molded elements are typically formed 
from a material, such as plastic or carbon fiber, that is molded into 
open-sided halves because of the molding process. Each half has a 
plurality of interconnected half-tubes, each half-tube having a pair of 
substantially parallel longitudinal free edges extending along the 
longitudinal axis of the respective half-tube. The two half-frames are 
connected together, such as by gluing, along the free edges to form the 
completed, formed frame of the bicycle. 
The longitudinal free edges of bicycle half-frames are typically provided 
with alignment elements that facilitate alignment of the half-frames so 
that the exterior of the formed frame is substantially smooth. Such 
alignment elements may include pins in one half and corresponding 
receiving holes in the other half, such as shown in U.S. Pat. No. 
5,464,240 to Robinson et al. These alignment elements are rather small 
because of the thinness of the walls of the tubular elements, and thus are 
relatively difficult to manufacture without defects. Occasionally there 
are manufacturing defects that result in too many pins or not enough 
holes. In that case, the additional pins must be cut off, thus requiring 
yet another assembly step. Moreover, alignment of the frame halves 
requires the additional step of aligning the relatively small pins with 
their corresponding holes. Such alignment is time consuming and therefore 
labor intensive. Another disadvantage of using small pins is that they may 
break before or during alignment. 
Typically, half-frames of a bicycle are glued together at their adjoining 
longitudinal free edges to form a glued butt joint. When the halves are 
joined and pressed together, the glue spreads along the edges, as usual. 
The glue often extends past the abutting edges to the exterior of the 
tubes (the rounded exterior of the frame visible to the consumer/user). In 
order to create a neater appearance, the exterior of the now joined frame 
halves must be cleaned or smoothed to improve the appearance of the frame. 
The frame can then be painted in the usual manner. 
Bicycles frames that are formed from molded half-frames also typically 
include internal reinforcements, such as the protrusions or webs and 
corresponding slots shown in the above-mentioned Robinson Patent. As with 
the pins and holes, the internal reinforcements also make manufacture of 
the halves, and their connection to each other, more complicated. 
Moreover, although such reinforcement elements add to the strength of the 
frame, they also add to the weight of the frame, thereby making the 
bicycle heavier and thus more difficult to ride. 
Another reinforcement element that may be provided is a reinforcement 
"box." Reinforcement boxes may be formed as substantially tubular elements 
that extend from the interior surface of a frame half for connection with 
a corresponding box in a corresponding frame half. Preferably, the box has 
a longitudinal axis that is substantially perpendicular to the 
longitudinal axis of the half-tubular element of the frame half from which 
the box extends, and thus the connected corresponding boxes form a 
reinforcing element that is substantially perpendicular to the plane of 
the completed frame. A reinforcement box may be provided at any desired 
location. Typically, a box is at least provided in the chain stay area and 
in the seat stay area adjacent the adjoining tubes (i.e., the bottom 
bracket shell and seat tube, respectively). Provision of such a box 
strengthens the tubular frame. However, the chain stay and seat stay areas 
are generally subjected to substantial stresses, and thus are prone to 
having cracking problems despite the provision of boxes. Reinforcements in 
addition to the boxes are thus recommended. However, the additional 
reinforcements used in known bicycle frames add to manufacturing costs and 
the weight of the frame. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a structure 
for joining molded half-frames of a tubular frame in a manner that is 
relatively simple and not labor intensive, such that assembly of the frame 
is simple and cost effective. 
It is a related object of the present invention to provide a method of 
joining molded half-frames of a tubular frame that permits use of 
half-frames that are easy and relatively inexpensive to manufacture. 
It is a further related object of the present invention to provide a method 
of joining molded half-frames of a bicycle frame that does not require 
labor intensive finishing steps once the half-frames are joined. 
It is another object of the present invention to provide a method of 
joining molded half-frames of a bicycle frame in a manner that reduces the 
number of finishing steps required between joining the frame halves and 
painting the joined bicycle frame halves. 
It is yet another object of the present invention to provide a method of 
reinforcing molded half-frames of a bicycle frame individually, and also 
reinforcing the half-frames once joined, to form a complete frame that is 
relatively easy and inexpensive both to manufacture and work with during 
assembly of the bicycle frame. 
It is another related object of the present invention to provide a bicycle 
formed from joined half-frames that are formed and joined to result in a 
lightweight frame. 
In accordance with the principles of the present invention, a method of 
joining and reinforcing molded half-frames of a tubular frame, e.g., a 
bicycle frame, is provided. This method simplifies the joining of the 
frame halves. Also, the design and shape of the frame halves are also 
simplified, such that the manufacture of the frame halves is easier and 
thus less costly. In particular, the longitudinally extending free edges 
of the halves (i.e., the edges of the half-tubular elements that abut each 
other upon connecting the frame halves together) preferably are stepped, 
each step having a substantially planar, smooth surface along the 
longitudinal axis of its respective tubular element. If desired, at least 
one of the longitudinally extending free edges of one of the halves may be 
formed as a groove, the corresponding longitudinally extending free edge 
of the other half being formed as a tongue for fitting into the groove. 
Because the free edges are substantially planar in the longitudinal 
direction, and do not have projecting pins as in the prior art, 
longitudinal alignment is simple and requires little effort. Additionally, 
the shape of the corresponding longitudinal free edges of the frame halves 
facilitates inward driving of the glue used to couple the halves together 
towards the interior of the joined halves, thereby reducing the finishing 
steps of smoothing the frame's exterior surface required before painting 
the frame. 
The above joining method provides a sturdier connection between the frame 
halves than the connection provided by the prior art methods. Additional 
reinforcement, however, is also provided by the present invention. In 
particular, a reinforcing element is preferably provided in the stay area 
of the frame, i.e., in the seat stay area and the chain stay area. The 
reinforcing element may take the form of an arch fitted between the 
elements forming the seat and chain stays. Alternatively, the reinforcing 
element may be inherent in the design of the inner seat and chain stay 
elements. Specifically, the inner seat and chain stay elements may be 
formed as a single piece, preferably with a box element extending into the 
remainder of the bicycle frame and thus between the outer elements of the 
seat and chain stays.

DETAILED DESCRIPTION OF THE INVENTION 
A bicycle frame 10, formed in accordance with the principles of the present 
invention and having a plurality of intersecting tubular elements with 
respective intersecting longitudinal axes, is shown in FIG. 1. Frame 10 is 
formed from left and right half-frames 12, 14 (FIG. 2), each of which is 
preferably formed from a molded material. Most preferably, the half-frames 
are formed from injection molded plastic. However, any other desired 
material may be used, such as fiberglass, carbon fiber, polyurethane, 
metal (e.g. aluminum or titanium) or reinforced composite materials 
having, for example, a resin or epoxy matrix. Because the frame is formed 
by molding the material, the frame must be formed in halves that are later 
connected to form an integral frame structure. Each frame half has a 
plurality of interconnected half-tubular elements having respective 
longitudinal axes, and each half-tubular element of one frame half 12 has 
a corresponding half-tubular element in the other frame half 14, such that 
the corresponding half-tubular elements of the half-frames may be coupled 
together to form a completed bicycle frame 10. Each half-tubular element 
has an interior surface 16 that is typically concave and an exterior 
surface 18 that is typically convex, such that connection of corresponding 
half-tubular elements forms a substantially tubular element. Each 
half-tubular element has longitudinally extending free edges 20 between 
interior and exterior surfaces 16, 18 and along which the half-tubular 
elements are joined. As will be understood, each frame half 12, 14 is 
preferably a monolithic, one-piece element, such that the formed frame 10 
comprises two elements joined to form an integral unit. 
In accordance with the principles of the present invention, longitudinal 
free edges 20 of corresponding half-tubular elements of frame halves 12, 
14 are shaped to smoothly interengage with each other and thereby 
facilitate smooth, easy alignment and joining of the frames halves 12, 14. 
Specifically, adjoining free edges 20 preferably have multilevel 
interengaging surfaces, each surface being substantially smooth and planar 
along longitudinal axis 32 of the respective half-tubular element along 
which the free edges 20 extend. Thus, free edges 20 do not have projecting 
elements such as pins that must be carefully aligned with corresponding 
receiving elements in the edge of the corresponding frame half. Exemplary 
edge joints are shown in detail in FIGS. 2 and 3. 
A lap splice joint 22 formed in accordance with the principles of the 
present invention is provided in the lower portion of tubular element 24 
(in this case, the down tube of frame 10) shown in FIG. 2. As may be seen 
in FIG. 3, which shows lap splice joint 22 in greater detail, lap splice 
joint 22 is formed by shaping the longitudinal free edges 20 to have 
corresponding stepped surfaces that interengage with each other. 
"Stepping", as defined herein, is a shape that extends in a direction from 
a lower step to an upper step, wherein the steps have step surfaces 
(equivalent to the tread of a step) substantially tangent to the exterior 
and interior surfaces of the tubular elements. The stepping of the edges 
is formed in the radial direction such that longitudinal free edges 20 are 
not planar in the direction extending from the interior surface 16 to the 
exterior surface 18, yet each stepped surface is substantially smooth and 
planar in the longitudinal direction. 
Lap splice joint 22 has at least one stepped surface 26 (a "tread") 
substantially tangent to exterior surface 18 and thus, typically also 
interior surface 16, an inner substantially radially extending surface 28 
(a "riser") between tread 26 and interior surface 16, and an outer 
substantially radially extending surface 30 (another "riser") between 
tread 26 and exterior surface 18. The substantially radially extending 
surface 28 that is closer to interior surface 16 is hereinafter referred 
to as an "inner riser". The tread 26 may be generally flat in 
cross-section or curved, e.g., with the same radius as the interior 
surface 16 and/or the exterior surface 18. Likewise, the substantially 
radially extending surface 30 that is closer to exterior surface 18 is 
hereinafter referred to as an "outer riser". Although only one tread 26, 
positioned between a pair of risers 28, 30, is shown in the figures, it 
will be understood that additional treads, with the requisite additional 
risers, may be provided. The treads and risers of stepped longitudinal 
free edges 20 extend substantially smoothly along longitudinal axis 32. 
Thus, longitudinal free edges 20 of lap splice joint 22 have at least 
three substantially planar, transverse surfaces, each surface preferably 
being substantially perpendicular to its adjoining surface. The surface of 
the lap joint on respective frame halves may be brought together and slid 
with respect to each other in the direction of axis 32 for alignment 
purposes and to relieve stress in the joint. 
As may be seen more clearly in FIG. 3, the stepping of longitudinal free 
edges 20a, 20b of corresponding half-tubular element of frame halves 12, 
14 extends in opposite directions such that corresponding longitudinal 
free edges 20a, 20b may interengage, as described in further detail below, 
to form completed tubular elements of frame 10. Thus, as shown in FIGS. 2 
and 3, the stepping of one longitudinal free edge 20 (in this case, the 
longitudinal free edge 20a of left half-frame 12) extends from exterior 
surface 18 to interior surface 16 to form an exterior step 26a having a 
tread 26 facing interior surface 16, whereas the stepping of the 
corresponding longitudinal free edge 20 (i.e., longitudinal free edge 20b 
of the right half-frame 14) extends from interior surface 16 to exterior 
surface 18 to form an interior step 26b having a tread 26 facing exterior 
surface 18. In other words, stepped surface 20a faces interior surface 16 
and stepped surface 20b faces exterior surface 18. Thus, outer riser 30 
precedes interior facing tread 26a, whereas inner riser 28 precedes 
exterior facing tread 26b. Likewise, interior facing tread 26a is followed 
by inner riser 28, whereas exterior facing tread 26b is followed by outer 
riser 30. Because the stepped longitudinal free edge 20a of at least one 
of the half-tubular elements of one half-frame extends inwardly and the 
stepped longitudinal free edge 20b of the corresponding half-tubular 
element in the other half-frame extends outwardly, longitudinal free edges 
20a and 20b have corresponding, interengaging shapes. 
Each of surfaces 26, 28, 30 is substantially smooth and planar in the 
longitudinal direction. Accordingly, adjoining edges 20a, 20b of the frame 
halves 12, 14 that are to be joined together may slide along the 
longitudinal axis 32 of the respective half-tubular element from which the 
edges extend, so that alignment of the frame halves 12, 14 requires very 
little skill or effort. Thus, in order to form frame 10, frame halves 12, 
14 may be joined relatively easily, without worrying about aligning 
elements such as pins, holes, tabs, and slots, such as in the prior art. 
The exterior surfaces 18 of frame halves 12, 14 are substantially aligned 
and coextensive at lap splice joint 22, as may be seen in FIGS. 2 and 3, 
to create a smooth frame exterior. 
Another benefit of lap splice joint 22 is that it may be formed to 
facilitate the flow of glue in the desired direction during connection of 
the frame halves 12, 14. As may be seen in FIG. 3, the innermost 
substantially radially extending surfaces of longitudinal free edges 20, 
in this instance inner risers 28, are preferably spaced apart when frame 
halves 12, 14 are coupled together. Such spacing is accomplished by 
forming abutting treads 26 (i.e., treads of corresponding longitudinal 
free edges 20 that are to be joined together) with different lengths. 
Preferably, the tread closest to the exterior surface 18 is longer than 
the tread closest to the interior surface 16, as shown in FIG. 3, so that 
a gap is formed between the inner risers 28. Thus, in this case, exterior 
step 26a of frame half 12 is longer than interior step 26b of frame half 
14, to thereby form an interior facing gap 34 between the inner 
substantial radially extending surfaces 28. As may be seen, gap 34 opens 
to the interior of the tubular element 24 formed upon joining frame halves 
12, 14. Thus, glue that is placed between stepped areas 26a, 26b of 
adjoining free edges 20 more easily flows towards the interior of the 
tubular element 24, rather than towards the exterior, because of the low 
resistance to flow permitted by gap 34. 
To further facilitate such desired flow of glue, the inner tread 26 (in 
this case, the tread 26 of interior step 26b of frame half 14, which, as 
described above, is closer to the interior of tubular element 24 and thus 
shorter than tread 26 of frame half 12), is chamfered at the intersection 
between tread 26 and riser 28. Chamfer 36 functions to direct the flow of 
glue placed between abutting treads 26 towards gap 34, which, in turn, 
functions as a receptacle for excess glue as well as a conduit for 
directing glue towards the interior of the frame 10 such that excess glue 
does not affect the exterior appearance of frame 10. A minimal amount of 
glue is placed between the outermost substantially radially extending 
surfaces or risers 30 to minimize the amount of excess glue that is driven 
towards the exterior of tubular element 24 and which must be cleaned off 
and smoothed before finishing the bicycle. 
Another type of edge joint 40, hereinafter known as a "tongue and groove" 
joint 40, is particularly useful at high stress areas in frame 10, such as 
at the upper longitudinal seam (i.e., upper joint) of down tube 42. Tongue 
and groove joint 40 is provided in the upper portion of tubular element 24 
shown in FIG. 2, and is shown in further detail in FIG. 4. As may be seen 
in these figures, tongue and groove joint 40 is similar to lap splice 
joint 22 in that each of frame halves 12, 14 has at least one stepped area 
26. However, at least one of the frame halves 12, 14 has an additional 
stepped area 46 extending in a second direction so as to be substantially 
parallel to and facing the first stepped area 26 such that a groove 48 is 
formed therebetween. As with lap splice joint 22, the abutting 
longitudinal free edges 20 of frame halves 12, 14 of tongue and groove 
joint 40 have abutting inner substantially radially extending surfaces 28 
and abutting outer substantially radially extending surfaces 30. However, 
in order to form an additional stepped area 46, an additional inner 
substantially radially extending surface 50 must be provided along each 
longitudinal free edge 20. Surfaces 28 and 30 abut, or at least face each 
other, upon joining corresponding half-tubular elements together. As may 
be seen in FIGS. 2 and 4, exterior surfaces 18 of frame halves 12, 14 are 
substantially aligned and coextensive along tongue and groove joint 40. 
Additional stepped area 46, additional inner substantially radially 
extending surface 50, and interior surface 16 form a wall that provides 
additional reinforcement for joint 40. Tongue and groove joint 40 thus is 
particularly beneficial in high stress areas of the bicycle frame 10 
because the additional stepped areas provide greater shear area over which 
the glue used to connect the frame halves may act. However, as is readily 
apparent from observation, assembly of frame halves 12, 14 with a tongue 
and groove joint 40 requires more care than that required to assemble lap 
splice joint 22, even if the latter joint has a plurality of steps 
(extending in generally the same direction). Thus, it is not particularly 
desirable to provide more than one pair of stepped areas extending in 
opposite directions and thus forming more than one groove for receiving a 
corresponding tongue. Nonetheless, more than one tongue and groove may be 
provided along either or both sides of any desired half-tubular elements. 
Another particularly high stress area of the frame 10 is the stay area 60, 
which includes the seat stay 62, and the chain stay 64. In particular, the 
area of intersection of the right and left outer seat stay elements (i.e., 
the respective seat stays of frame halves 12, 14), before the right and 
left seat stay elements fork apart, is prone to cracking because loads 
tend to separate the seat stays at the point where they are glued 
together. The same is true, albeit to a slightly lesser extent, in the 
chain stay area. Thus, additional reinforcement in the stay area 60, in 
general, is desirable. In prior art frames, a box 66 is provided in each 
of seat stay 62 and chain stay 64. Typically, box 66 is formed from 
corresponding boxes 66a, 66b extending from the interior surface 16 of 
each of frame halves 12, 14. Corresponding boxes 66a, 66b are shaped so 
that one fits into the other to form an overlapping box structure 66, as 
shown in FIG. 5. Box 66 is shown in FIG. 1 as having a substantially 
square cross section, with a longitudinal axis 68 substantially 
perpendicular to the respective longitudinal axis 70, 72 of the stay 62, 
64 from which box 66 extends. However, the cross section of box 66 may 
have any other desired shape. 
In accordance with the principles of the present invention, the stay area 
60 is reinforced such that a box 66 is not necessary because additional 
reinforcement is provided as shown in FIGS. 5-8. The additional 
reinforcement of the present invention not only reinforces the high stress 
stay areas, but also reduces, if not eliminates, cracking in this area. 
In the embodiment of FIG. 5, the additional reinforcement is in the form of 
a substantially continuous reinforcement arch 80. Reinforcement arch 80 is 
preferably formed from any sturdy material such as injection molded 
plastic, a plastic composite, fiberglass, carbon fiber, polyurethane, 
metal or a composite material having a resin or epoxy matrix reinforced 
with, for example, fiberglass or carbon fiber. As shown in FIG. 5, 
reinforcement arch 80 is shown positioned within the seat stay elements 
62, as described in further detail below. Seat stay 62 is particularly 
subject to excessive forces from the rear axle of the bicycle and thus 
benefits from the use of an additional reinforcement element such as a 
reinforcement arch 80 as formed in accordance with the principles of the 
present invention. A similar reinforcement arch may be provided in chain 
stay 64 as well. 
Seat stay 62 is formed from left and right outer seat stay elements 82, 84 
which, respectively, are a part of left and right frame halves 12, 14, and 
left and right inner seat stay caps 86, 88. Left and right outer seat stay 
elements 82, 84 extend from seat tube 83 of frame 10 (FIG. 1) and fork 
apart to accommodate a rear wheel of the bicycle formed from frame 10. In 
assembling frame 10 with reinforcement arch 80 in accordance with the 
principles of the present invention, preferably a portion of box 66 is 
removed from the stay area to make room for reinforcement arch 80. 
Reinforcement arch 80 is then glued to interior surface 16 of outer seat 
stay elements 82, 84. Then, inner stay caps 86, 88 are glued to the other 
side of reinforcement arch 80 so that seat stay 62 with left and right 
stay legs 92, 94 is thereby assembled. However, it is not essential that 
arch 80 be glued to the interior surfaces of each half of the stay legs, 
as long as at least one half of each of the seat stay legs is glued to 
arch 80. 
Arch 80 has left and right legs 96, 98 which extend into left and right 
seat stay legs 92, 94 to pick up loads in seat stay legs 92, 94 and absorb 
excess forces therein, thereby protecting the structural integrity of seat 
stay 62. Additionally, because arch 80 is glued to the interior surfaces 
16 of each part of seat stay legs 92, 94 (i.e., left and right outer seat 
stay elements 82, 84 and left and right inner seat stay caps 86, 88), 
shear stresses are absorbed by the arch through the adhesive, and 
therefore are not passed to the seat stay parts and do not cause the parts 
to separate or crack. It is noted that the cross section of seat stay legs 
92, 94 is not uniform, and typically decreases in size in the direction of 
the rear wheel axle 97. Additionally, the cross section of seat stay legs 
92, 94 is not necessarily circular, but may be oval or square with rounded 
edges. 
A modified, Y-shaped reinforcement arch 180 is shown in FIG. 6. Y-shaped 
reinforcement arch 180 is similar to arch 80 in most respects, but further 
includes an extension 182 that extends into monostay 100 (the portion of 
seat stay 62 extending between seat stay legs 92, 94 and seat tube 83). 
When Y-shaped reinforcement arch 180 is used, extension 182 may extend 
into the area of monostay 100 in which box 66 is provided. Accordingly, 
box 66 may be eliminated. 
Another solution to reinforcing stay area 60 is shown in FIGS. 7 and 8. In 
this reinforcement embodiment, the left and right inner stay caps are 
formed as a single piece. Thus, as shown in FIG. 7, the seat stay 162 
formed in accordance with the principles of the present invention has a 
single-piece inner seat stay cap 110. Preferably, single-piece inner seat 
stay cap 110 is formed as a unitary, monolithic piece (e.g., by molding as 
a unit) such that there are no seams between the inner surfaces of left 
and right seat stay legs 192, 194. Thus, there are no seams along which 
the excess forces in the seat stay 162 could cause cracking, and no arch 
80 or 180 is necessary. Because outer seat stay elements 82, 84 preferably 
are formed substantially similar to those of seat stay 62 of FIG. 3 (i.e., 
outer seat stay elements 82, 84 preferably are formed as part of the main 
frame halves 12, 14), frame 10 has a bonding line along monostay 100 which 
should be reinforced. Accordingly, single-piece inner seat stay cap 110 
preferably further includes an extension 112 which fits within monostay 
100 and functions as a reinforcement box similar to box 66. Extension 112 
preferably has open sides 114, 116 which reduce the weight of the 
extension and also facilitate injection molding of the single-piece inner 
seat stay cap 110. Unlike box 66, extension 112 preferably is formed as a 
single, unitary piece that is glued to the interior surfaces 16 of the 
portion of frame halves 12, 14 forming the monostay 100. Extension 112 
thus absorbs forces in the seat stay area and reinforces the seat stay 
area sufficiently to eliminate box 66. Additionally, because extension 112 
is formed as part of single-piece inner seat stay cap 110, extension 112 
also reinforces single-piece inner seat stay cap 110 by absorbing forces 
transmitted thereto during riding of the bicycle formed with frame 10. 
A single-piece inner stay may also be used in modified chain stay 164, as 
shown in FIG. 8, which extends from bottom bracket shell 165 (FIG. 1). As 
in seat stay 162, chain stay 164 has left and right stay legs 120, 122, 
each formed from an inner and an outer stay element. Specifically, left 
chain stay leg 120 is formed from a left outer chain stay element 124, 
formed as a part of left frame half 12, and a left inner chain stay cap 
126. Likewise, right chain stay leg 122 is formed from a right outer chain 
stay element 128, formed as a part of right frame half 14, and a right 
inner chain stay cap 130. Like single-piece inner seat stay cap 110, left 
and right inner chain stay caps 126, 130 are preferably formed as a 
monolithic, unitary piece so that modified chain stay 164 has a 
single-piece inner chain stay cap 132. Accordingly, there is no seam 
between left and right inner chain stay caps 126, 130, and thus stresses 
in the area of chain stay 164 cannot cause cracking between left and right 
inner chain stay caps 126, 130. Also as in single-piece inner seat stay 
cap 110, single-piece inner chain stay cap 132 preferably includes an 
extension 134. Extension 134 is preferably formed with open sides 136, 
138, which reduce the weight of the extension, and also facilitate 
injection molding of the single-piece inner chain stay cap 132. Extension 
134 reinforces the bonding line of the left and right frame halves 12, 14 
in the area of the chain stay 164 such that a separate box 66 is no longer 
required. Preferably, extension 134 does not have any seam lines (i.e., is 
monolithic with single-piece inner chain stay cap 132) and thus reinforces 
the legs of chain stay cap 132, as described above with respect to 
single-piece inner seat stay cap 110. 
The above-described stay area reinforcements provide a stronger connection 
of the stay legs than possible in the prior art. It is preferable to use, 
nonetheless, either a lap splice joint 22 or a tongue and groove joint 40 
along the free edges of the stay elements to secure the connection between 
these elements, i.e., the connection between the outer stay elements and 
the inner stay caps. Optionally, reinforcement 74 may also be included, or 
substituted for, the joint 22 or 40 to further strengthen the connection 
of the frame halves in the stay area, such as shown in FIGS. 1 and 9. 
Reinforcement 74, shown in cross-section in FIG. 9, has pins or posts 74a 
which interlock with corresponding receptacles 74b. Preferably at least 
two posts 74a and corresponding receptacles 74b are provided on each stay 
leg, preferably approximately 1 in. (2.54 cm) from the end of the stay 
leg. Thus, each of the inner and outer stay elements has at least two 
posts or receptacles. It will be understood that each stay element may 
have a post and a receptacle, or two of the same reinforcement element 
(i.e., two posts or two receptacles), or more than two of either 
reinforcement element, the corresponding stay element having corresponding 
reinforcement elements. It will further be understood that reinforcement 
74 may take on any other desired configuration that provides the desired 
reinforcement of the stay areas. However, reinforcement 74 may be 
eliminated and the same effect achieved with an external fastener or clamp 
located in the same general area. 
While the foregoing description and drawings represent the preferred 
embodiments of the present invention, it will be understood that various 
additions, modifications and substitutions may be made without departing 
from the spirit and scope of the present invention as defined in the 
accompanying claims. In particular, it will be clear that the present 
invention may be embodied in other specific forms, structures, 
arrangements, proportions, and with other elements, materials, and 
components, without departing from the spirit or essential characteristics 
thereof. One skilled in the art will appreciate that the invention may be 
used with many modifications of structure, arrangement, proportions, 
materials, and components and otherwise, used in the practice of the 
invention, which are particularly adapted to specific environments and 
operative requirements without departing from the principles of the 
present invention. In particular, while a bicycle frame is described, the 
invention extends to other tubular frames, e.g., to a chair, a wheelchair, 
a storage rack, etc. The presently disclosed embodiments are therefore to 
be considered in all respects as illustrative and not restrictive, the 
scope of the invention being indicated by the appended claims, and not 
limited to the foregoing description.