Composite bicycle frame and production method

A one-piece, ultralight, generally hollow bicycle frame having no internal structural components, and a method of manufacturing such a frame, are disclosed.

TECHNICAL FIELD 
The present invention relates to bicycle frames. In particular, the present 
invention relates to high performance, ultralight bicycle frames made from 
composite materials, and to methods for producing bicycle frames. 
BACKGROUND ART 
Conventional bicycle frames are assemblies built from individual tubes 
which are secured together by welding, brazing or by using other means for 
joining the tubes. The individual frame tubes were, early on, designated 
by their location in relation to the other major components or assemblies 
used to make up the functioning bicycle. Thus it was that the short frame 
tube which supported the handlebar assembly and the front forks was 
referred to as the "head" tube, the tube which supported the seat and 
connected to the pedal axle support (the bottom bracket) was referred to 
as the "seat" tube, the tube which joined the seat tube and the head tube 
was referred to as the "top" tube, the tube which descended from the head 
tube to the bottom bracket was referred to as the "down" tube, the pair of 
tubes which descended from the seat tube to the ends of the rear wheel 
axle, with one tube on either side of the rear wheel, were referred to as 
the "seat stays," and the pair of tubes which connected the bottom bracket 
to the ends of the seat stays at the rear wheel axle, with one tube on 
either side of the rear wheel, were referred to as the "chain stays." 
The multiplicity of connections required to secure these individual 
structural parts together, combined with the different forces encountered 
by the bicycle as it is ridden, cause a variety of problems. It is not 
unusual, for example, for one or more of the joints or connections on a 
conventional bicycle frame to fail, making the entire frame unsuitable for 
use until the connection is repaired. For many frames, the cost of 
straightening the frame and repairing the connection is prohibitive. 
Further, the individual tubes are relatively heavy since they are generally 
made by the extrusion of or by the rolling and seaming of a metal alloy. 
The manufacture and assembly of these multiple structural parts is also 
time consuming and costly. 
Finally, most conventional bicycle frame tubes have generally circular 
cross sections, since they are made from standard, commercial tubing. 
Thus, due both to the shape of the tubes and to the multiplicity of 
connection joints, conventional frames are not particularly adaptable to 
improved aerodynamics. 
Some of the above problems have been addressed by prior inventors. For 
example, U.S. Pat. No. 4,513,986 to Trimble provides a monocoque type 
frame having a stressed, unitary outer skin over internal stiffening ribs 
and other structural elements. U.S. Pat. No. 3,833,242 to Thompson, Jr. 
provides a hard exterior skin covering a structural foam interior. These 
frames may provide aerodynamic advantages over conventional bicycle 
frames, due to the aerodynamic shape and unitary nature of the outer skin. 
However, these frames generally require the interconnection of a large 
number of interior structural support elements such as shear webs, 
reinforcing angles, reinforcing blocks and strips, and joining blocks, 
and/or the presence of structural foam in the interior to support the 
frame, thus sharing certain deficiencies of conventional frames. In 
addition, while possibly improving aerodynamic performance in forward 
motion, a stressed skin will increase the frame's sensitivity to cross 
winds. 
Thus, the need exists for a unitary, strong, lightweight bicycle frame 
which is aerodynamic, easy to construct and adaptable to mass production 
techniques. The present invention solves these problems by providing a 
one-piece, generally hollow, aerodynamic bicycle frame requiring no 
internal structural components, and constructed from inexpensive, 
lightweight and strong composite materials. 
SUMMARY OF THE INVENTION 
The present invention provides a unitary, ultralight, generally hollow 
bicycle frame having no internal structural components, and a method of 
manufacturing such a frame. 
In one embodiment, the present invention provides a generally hollow, 
tubular one-piece bicycle frame having a steering support means, a seat 
support means, a pedal support means, a rear wheel support means, a top 
tube portion, a down tube portion, a seat tube portion, a chain stay 
portion and a seat stay portion, constructed using layers of structural 
fibers usable to make composite materials, and resin. 
In another embodiment, the present invention provides a generally hollow 
unitary bicycle frame having a steering support means, a seat support 
means, a pedal support means, a rear wheel support means, a top tube 
portion, a down tube portion, a seat tube portion, a chain stay portion, 
and a seat stay portion, constructed using layers of heat curable resin 
impregnated fiberglass fibers, carbon fibers and KEVLAR.RTM. fibers. 
In various embodiments, the cross sectional shape of selected portions of a 
frame of the present invention may be altered, depending upon the position 
of the portion, to improve the aerodynamic behavior of the frame, without 
attendant increased cross wind sensitivity. 
In yet another embodiment, the present invention provides a method for 
manufacturing unitary, generally hollow ultralight bicycle frames using 
structural fibers and resins, in which the fibers and resins are initially 
shaped around mandrels having the approximate size and shape of the hollow 
interior of the various finished portions of the frame. After this initial 
layup, these hollow portions are removed from the mandrels and are united 
by using hollow corner patches comprising multiple layers of fiber strips 
and resin. Inflatable bladders are preferably placed in the larger hollows 
found in the top tube portion, down tube portion, and seat tube portion, 
and a solid piece of foam made from a heat expandable resin composition is 
provided in the smaller hollows of the seat stay and chain stay portions. 
Alternatively, a foamable liquid resin may be used in place of all or part 
of the bladders, solid foam or both. The frame is then placed in a mold, 
the bladders are inflated to compress the layers of fiber and resin 
against the walls of the mold and the curing process is initiated by 
applying heat to the mold. Further compression of the layers of fiber and 
resin occurs as the pressure within the bladder and the pressure caused by 
expansion of the foam in the seat stay and chain stay portions increases 
as the temperature rises. When curing is complete, the frame is removed 
from the mold, any inflatable bladders are removed, and any foam in any of 
the portions may be removed by dissolution in an appropriate solvent. 
In yet another embodiment, the present invention provides a method for 
manufacturing a generally unitary ultralight bicycle frame in which a 
unitary, generally hollow main component of the frame comprising at least 
two hollow tube portions integrally united by a hollow junction may be 
formed and precured in a main mold. One or more of the other hollow 
portions of the frame may be formed and precured independently and then 
connected to the main component using adhesive connections. Alternatively, 
precured hollow tube or stay portions may be attached to an uncured main 
unitary frame component comprising at least two hollow tube portions 
integrally united by a hollow junction so that the precured portions are 
adhesively bonded into the frame as the main unitary component is cured.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention provides an ultralight, generally hollow, unitary 
bicycle frame having no internal structural components, and a method of 
manufacturing such a frame. 
In one embodiment, the present invention provides a generally hollow, 
unitary tubular bicycle frame having a steering support means, a seat 
support means, a pedal support means, a rear wheel support means, a top 
tube portion, a down tube portion, a seat tube portion, a chain stay 
portion and a seat stay portion, constructed using layers of resin 
impregnated structural fibers usable to make composite materials. 
In another embodiment, the present invention provides a generally hollow, 
unitary bicycle frame having a steering support means, a seat support 
means, a pedal support means, a rear wheel support means, a top tube 
portion, a down tube portion, a seat tube portion, a chain stay portion, 
and a seat stay portion, constructed using layers of resin impregnated 
fiberglass fibers, carbon fibers and KEVLAR.RTM. fibers. 
In various embodiments of the present invention, the cross-sectional shape 
of selected portions of the frame may be altered to improve the 
aerodynamic behavior of the frame, without attendant increased cross wind 
sensitivity. 
FIGS. 1, 3 and 4 show a frame of the present invention, which comprises a 
generally hollow, tubular top tube portion 17 extending between steering 
support means 26 and seat support means 27; a generally hollow, tubular 
down tube portion 18 extending between the steering support means 26 and 
the pedal support means 25; a generally hollow, tubular seat tube portion 
20 extending between the seat support means 27 and a pedal support means 
25; a first and a second generally hollow, tubular chain stay portions 19, 
19', the first such portion 19 extending from the left side of pedal 
support means 25 to the left side of rear wheel support means 24 and the 
second such portion 19' extending from the right side of pedal support 
means 25 to the right side of rear wheel support means 24'; and a first 
and a second generally hollow, tubular seat stay portions 21, 21', the 
first such portion 21 extending from the left side of seat support means 
27 to the left side of rear wheel support means 24, and the second such 
portion 21' extending from the right side of seat support means 27 to the 
right side of rear wheel support means 24'. 
In this configuration, the top tube portion 17, down tube portion 18, and 
seat tube portion 20 form an open front triangle, and the seat tube 
portion 20, chain stay portions 19, 19' and seat stay portions 21, 21' 
form a pair of open rear triangles. A right rear triangle is composed of 
right chain stay portion 19', right seat stay portion 21', and seat tube 
portion 20, and a left rear triangle is composed of left chain stay 
portion 19, left seat stay portion 21, and seat tube portion 20. 
Steering support means 26 includes a hollow junction and associated 
elements for rotatably supporting at the bottom end a front fork assembly 
22 and front wheel assembly and, at the top end, a handle bar assembly. 
Seat support means 27 includes a hollow junction and associated elements 
for adjustably receiving the post of a seat assembly. Pedal support means 
25 includes a hollow junction and associated elements for supporting a 
pedal crank and chain wheel assembly. Each rear wheel support means 24, 
24' include a hollow junction which includes a slotted rear wheel dropout 
having a head 30, 30', a first leg 31, 31' and a second leg 32, 32' to 
support the axle of a rear wheel assembly. The hollow junction of each 
rear wheel support means 24, 24' is preferably provided with a recess 34, 
34' for receiving the head 30, 30' of the rear wheel dropout. The recess 
34, 34' may be either cut out of a previously molded junction or, 
preferably, molded as part of the junction when the frame is constructed, 
with the dropout being placed in position after the frame material has 
been laid up but before the uncured frame is placed in the mold. The 
molded recess 34, 34' will preferably conform closely to the shape of 
dropout received such that the dropout will not move out of position, even 
in the absence of additional adhesion between the dropout and the molded 
recess 34, 34', thus providing a means for permanently and securely 
attaching a rear dropout to the frame at each rear wheel support means 24, 
24'. 
Additional support and stability is provided by first leg 31, 31', which is 
embedded within, and preferably attached by adhesive to the bottom portion 
of the generally hollow, tubular seat stay portion 21, 21', and by second 
leg 32, 32', which is embedded within, and preferably attached by adhesive 
to the back portion of the generally hollow, tubular chain stay portion 
21, 21'. 
Likewise, a steering support sleeve 26' may be embedded within the steering 
support means 26, a seat support sleeve 27' may be embedded within seat 
support means 27, and a bottom bracket 25' for receiving the pedal crank 
axle (not shown) may be embedded within the pedal support means 25. 
FIGS. 3 and 5 through 12 show the preferred cross-sectional shape of 
various portions of a unitary frame of the present invention. Although the 
cross-sectional shape of the various hollow, tubular portions may have a 
round aerodynamic shape, non-circular, airfoil type cross-sectional shapes 
are preferred. This aerodynamic cross-sectional shape preferably extends 
along a majority of the length of the elongated tubular portions, more 
preferably over substantially the entire length thereof. The preferred 
aerodynamic shapes are substantially symmetrical relative to an imaginary 
plane in which both the front and rear wheels rotate, preferably the plane 
passing through substantially the center of the geometric cross-sectional 
shape of the tire carried by the wheel assembly. 
FIG. 7 generally illustrates the most preferred cross sectional shape for a 
tubular seat tube portion which includes a pair of trailing edges 37 and a 
concave rear wall 38 having a uniform cross-sectional curvature which 
substantially follows the cross-sectional curvature or outline of the tire 
of the wheel assembly. Rear wall 38 preferably also has a uniform 
longitudinal curve which follows the curve of the circumference of the 
wheel of the wheel assembly, as shown by the dashed, curved line in FIG. 
1. 
Regardless of the cross-sectional shape of the various portions of the 
frame of the present invention, sufficient clearance is provided between 
the surfaces of the various portions of the frame and the attached 
components, such as the rear wheel assembly and front wheel assembly, to 
permit normal operation of the bicycle without abnormal interference from 
the frame, for example, free tire rotation without contact between the 
tire surface and the frame surfaces. 
A frame of the present invention may be formed from any suitable structural 
plastic, composite material or fiber reinforced plastic formed from strips 
of structural fibers, such as, for example, fiberglass and epoxy. 
Reinforcing fibers may be unidirectional or woven. Preferably a 
combination of fiberglass, carbon, and KEVLAR.RTM. fibers are used to 
improve strength. In the most preferred embodiment, the reinforcing fibers 
are unidirectional and comprise about one-third glass, about one-third 
KEVLAR.RTM. and about one-third carbon. The resin is preferably a 
moldable, heat curable epoxy resin. A long sheet packaged as a roll and 
comprising one or more layers of fabric made from the preferred 
reinforcing fibers and impregnated with the preferred resin is available 
from the Fiberite Company of Orange, Calif. 
The present invention also provides, in a preferred embodiment, a method 
for manufacturing ultralight, unitary, generally hollow bicycle frames 
using structural fibers and resins, in which sufficient fibers and resins 
are initially shaped around mandrels having the approximate size and shape 
of the hollow interior of the various finished portions of the frame to 
achieve a cured frame wall thickness of from about 35 mils to about 125 
mils. After this initial layup, the portions are removed from the mandrels 
and are united by hollow junctions made from corner patches comprising 
layers of resin impregnated fiber strips. Inflatable bladders are placed 
in the larger hollows formed in the top tube portion, down tube portion, 
and seat tube portion. A sold piece of foam made of a heat expandable 
resin composition is provided in the smaller hollows of the seat stay and 
chain stay portions. A heat expandable solid resin foam having a closed 
cellular structure and made from a polymethacrylimide is available under 
the trademark Rohacell from Cyro Industries of Orange, Conn. This resin 
foam is rigid at ambient temperatures, but softens to a plastic state and 
expands radially at the temperature for curing the frame. 
The frame is then placed in a mold, and the bladders are inflated to 
compress the layers of fiber and resin against the walls of the mold. The 
curing process is thereafter initiated by applying heat to the mold to 
heat the frame to a temperature sufficient to cure the resin. For the 
preferred reinforcing fibers and resin obtained from the Fiberite Company, 
the frame is heated to about 250.degree. F. to cure the resin. Further 
compression of the layers of fiber and resin occurs as the pressure within 
the bladder and the pressure caused by expansion of the foam in the seat 
stay and chain stay portions increases as the temperature rises. When 
curing is complete, the frame is removed from the mold, the inflatable 
bladders are removed, and any foam in the chain stay and seat stay 
portions may be removed by dissolution in an appropriate solvent. 
The preferred method of molding the one-piece frame of the present 
invention uses a two-piece female mold having a right side and a left 
side, and interior cavities corresponding to the outer shape and size of 
the finished frame. 
To manufacture a round tube frame, the top tube portion 17, the seat tube 
portion 20 and the down tube portion 18 are separately produced by 
wrapping fiber strips impregnated with the resin around a mandrel to 
provide a tubular structure. Depending upon the strength characteristics 
desired in the particular portions, some of the strips may be spirally 
wound and some may be wrapped lengthwise to provide multiple layers. 
Spiral windings of successive layers are preferably wound in opposite 
directions using long strips of resin impregnated fabric, preferably about 
2 to 4 inches in width. Preferably, windings of a strip in the same layer 
are not overlapped. The mandrel outside diameter approximately corresponds 
to the finished inside diameter of the particular portion being produced. 
Each such portion is wrapped layer by layer over the mandrel. The number 
of layers used depends upon the desired wall thickness of the particular 
portion in the finished frame. For example, about eight layers have been 
found to produce a wall thickness in the finished frame of about 60 mils. 
Following wrapping, the tubular portions are slid axially off the mandrel. 
The direction of wrapping the layers in relation to the longitudinal axis 
of each portion is important. When the preferred unidirectional fibers are 
used for the top tube portion 17, the down tube portion 18, the seat stay 
portions 21, and the chain stay portions 19, about one-fourth to about 
one-half of these fibers may be positioned at an angle between 0 and 45 
degrees, preferably about 45 degrees, relative to the longitudinal axis of 
these elongated portions, with the remaining fibers being generally 
parallel to the longitudinal axis. This orientation of fibers is believed 
to improve the strength of these members for carrying bending and 
torsional stresses. Thus, for example, in a frame employing 8 layers of 
resin impregnated fiber, two layers oriented at a 45 degree angle relative 
to the longitudinal axis will provide 25% angled fibers and 75% 
longitudinal fibers. It is also clear that layers can be wrapped so that 
one 45 degree layer is set at a 90 degree angle relative to the previous 
45 degree layer. In the seat tube portion 20, the unidirectional fibers 
are preferably substantially all parallel to the longitudinal axis. 
The chain stay portions 19, 19' and seat stay portions 21, 21' are 
preferably formed by wrapping resin impregnated fiber strips around a low 
density solid foam core having the approximate shape and size of the 
interior of the finished chain stay portions 19, 19' and seat stay 
portions 21, 21'. The solid foam core becomes sufficiently plastic upon 
being heated to expand without rupture of its internal structure which 
comprises small closed cells of resin containing a gas. 
After initial layup of the individual portions, the portions are cut to 
size, if necessary, and inflatable bladders are placed inside top tube 
portion 17, down tube portion 18, and seat tube portion 20. As illustrated 
in FIG. 15-18, patches 54 of resin impregnated fiber material are then 
used to unify the portions and form the common junctions for the rear 
wheel support means 24, 24', pedal support means 25, steering support 
means 26, and seat support means 27. Approximately one half of each patch 
54 is preferably laid up as a section in a corresponding half of the mold 
with a sufficient overlap between the upper and lower sections of the 
patch to unite the two sections upon curing. A half-inch overlap, for 
example, has been found to produce satisfactory results. The patch 
sections are laid up in the mold before the corresponding preformed tube 
portions are placed therein and the patches are cut so that they overlap 
an end of the corresponding preformed tube portion. An overlap of from 
about one inch to about four inches, for example, has been found to 
satisfactorily unify the portions. Alternatively, the patches may be 
formed around the ends of the tube portions on a table, and the frame thus 
assembled is then place in the mold. Any metal sleeves, for example, the 
seat support sleeve 27', head tube support sleeve 26', rear dropouts and 
bottom bracket 25' are embedded at this time. For example, the legs 31, 
31' and 32, 32' of the rear dropouts are inserted in the ends of seat stay 
portions 21, 21' and chain stay portions 19, 19', and embedded therein 
using the resin used to impregnate the fiber strips, before the recess 34, 
34' of the rear wheel support means 24, 24' is formed to receive head 30, 
30'. 
The entire assembly is then laid into one half of the mold and the second 
half of the mold is joined with the first half of the mold, holding the 
uncured frame in the interior cavity. A single bladder is preferably used 
for the top and down tube portions and a second bladder for the seat tube 
portion. The bladders are inflated to from about 15 psig to about 500 
psig, and preferably to about 100 psig, through an end of each bladder 
which extends through the mold to the outside from inside the large 
portions of the frame. Heat is applied to the mold to cure the resin and 
expand the foam in accordance with the resin manufacturer's 
recommendations. For example, when a preferred fiber and resin from the 
Fiberite Company is used, the mold is heated to a temperature of about 
250.degree.. The internal pressure from the bladder and from the expanding 
foam within the seat stay and chain stay portions compresses the 
fiber/resin layers together and against the surface of the mold as the 
resin cures. 
When the resin is cured, the mold is cooled and opened, and the unitary 
frame is removed. The bladders are deflated and may be removed or, because 
of their light weight, may be left within the hollow of the large members. 
The expanded foam may be removed from the seat stay and chain stay 
portions by dissolution in an appropriate solvent. 
To produce a frame with portions having a more aerodynamic cross section, 
the same basic procedure is followed with some variation. While the top 
tube portion 17 is preferably wrapped on a mandrel, and the chain stay 
portions 19, 19' and seat stay portions 21, 21' are preferably wrapped on 
a low density foam core as discussed above, the down tube portion 18 and 
the seat tube portion 20 are preferably formed from resin impregnated 
strips of a multi-layer fabric of fiber and resin materials laid directly 
in each half of the mold. The width of the strips in the first half 40 of 
the mold are about equal to half of the circumference of the finished 
portion, while the width of the strips in the second half 42 of the mold 
are cut wider to allow for an overlap on all sides for uniting the two 
halves of the portions in the mold. For example, a half-inch overlap on 
all sides has been found to provide a satisfactory overlap. The 
multi-layer fiber and resin fabric is composed of individual layers or 
plies of unidirectional fibers, and the orientation of the layers in the 
multi-layer fabric can be changed to optimize strength as discussed above. 
The number of layers to be used will depend upon the desired wall 
thickness of the particular portion of the finished frame. As discussed 
above, 8 layers will produce a finished wall thickness of about 60 mils, 
which provides satisfactory strength for most purposes. 
Patches 54 of resin impregnated fiber material are similarly laid into each 
half of the mold to form half of the hollow junctions of the rear wheel 
support means 24, 24', pedal support means 25, steering support means 26, 
and seat support means 27. Any desired metal inserts such as head tube 
26', are emplaced in these common junctions in one mold half, preferably 
in the second or lower half 42 as shown in FIGS. 16 and 18. The prewrapped 
top tube portion 17 is then laid in place in one mold half, preferably 
second half 42, and one patch 54 is wrapped around one end of tube portion 
17 and one end of seat tube portion 20 and another patch 54 is wrapped 
around the other end of tube portion 17 and one end of the down tube 
portion 18 to provide common hollow junctions uniting these portions. The 
chain stay portions 19, 19' and the seat stay portions 21, 21' are laid, 
one each in their respective positions in each half of the mold such that 
in either mold half one end of each seat stay portion 21, 21' is wrapped 
by the hollow junction patch of the seat support means 27, while the other 
end is wrapped by the hollow junction patch of the rear wheel support 
means 24, 24', and such that one end of each chain stay portion 19, 19' is 
wrapped by a hollow junction patch of the pedal support means 25 while the 
other end is wrapped by a hollow junction patch of the rear wheel support 
means 24, 24'. One or more bladders are placed in the mold half having the 
wider strips of material in the down tube portion and the seat tube 
portion and slid into the mandrel wrapped top tube portion. The overlap on 
each side is draped over the bladder before the two mold halves are 
joined. A cross-sectional view of the two joined halves is shown in FIG. 
13. The bladder 46 is then inflated through an end extending through the 
mold to from about 15 psig to about 500 psig. Thus, as shown in FIG. 14, 
the pressure exerted by bladder 46 compresses the overlap 44 of second 
frame half 50 against first frame half 48, integrally sealing the two 
sections together as the frame cures. 
As discussed above, heat is desirably applied to cure the resin, and the 
pressure exerted by bladder 46 and by the expanding foam cores of the seat 
stay and chain stay portions compresses the fiber/resin composite against 
the inside surface of the mold as the resin cures. Following cure, the 
one-piece frame is removed from the mold, and the bladder and foam cores 
are optionally removed. A frame thus formed has a wall thickness ranging 
from about 35 mils to about 125 mils, depending upon the number of layers 
of resin impregnated fiber used initially to form the various portions of 
the frame. Thus, the wall thickness of the various portions can be 
selectively increased or decreased during manufacture, depending upon the 
strength required. The result is a bicycle frame having an unusually low 
weight ("ultralight") while providing unexpectedly high levels of 
strength, rigidity and durability. The unitary, one-piece design further 
provides unusually low aerodynamic drag of a level formerly achievable 
only with a monocoque-type frame but without the cross-wind sensitivity of 
monocoque-type frames, and eliminates the problems of joint failures 
commonly experienced by conventional frame assemblies. 
While not preferred from a structural standpoint, one skilled in the art 
will recognize that certain production advantages may arise by applying 
the methods disclosed above to the independent production of major 
portions of a bicycle frame. Thus, these methods can be used to produce a 
unitary main component of the bicycle frame comprising at least two hollow 
tube portions integrally united by a hollow junction. For example, a 
unified front triangle could be produced and the frame completed by adding 
a unified stay assembly comprising the two chain stay portions 19, 19', 
the two seat stay portions 21, 21', and the common junctions 34, 34'. The 
connection can be made by producing and curing the unified stay assembly 
separately, and then placing the pre-cured stay assembly in the patches 
used to form common junctions 25 and 27 and wrapping them into the front 
triangle in the same manner as disclosed above for the uncured wrapped 
stay portions. Alternatively, the connection between the cured and uncured 
portions can be made by providing the junctions between the portions to be 
joined with slip fit connections such as that illustrated in FIG. 19 which 
shows a hollow projecting stub 56 over which the end of the precured 
tubular portion may be slid. For example, the chain stay portions 19, 19' 
and seat stay portions 21, 21' with hollow common junctions 34, 34' may be 
molded and cured separately and then connected to the uncured front 
triangle by providing hollow stubs 56 projecting rearwardly from common 
junctions 27 and 25, over which the ends of the chain stay portions 19, 
19' and the ends of the seat stay portions 21, 21' may be slid. The hollow 
stubs are provided with an expansion means for pressing the stubs 56 
against the interior surface of the ends of the precured portions and 
bonding the stubs to the ends of the precured portions during final cure 
of the front triangle. When this means of connection is used, the stubs 
extend into the ends of the hollow attached portions preferably at least 
about one inch and more preferably at least about two inches, and may have 
additional resin placed on the surface of the stubs 56 at the interface 
between the stubs and the inner surface of the attached, precured hollow 
portions. The entire assembly is then cured as disclosed above. 
Following cure, the unified stay assembly will be rigidly attached to the 
front triangle by the adhesive force of the cured resin. Although joints 
will exist where the seat stays 21, 21' and the chain stays 19, 19' are 
joined to the front triangle, such joints will not be visible from the 
exterior. 
Alternatively, a pre-cured stay assembly can be rigidly attached to a front 
triangle which is produced and cured as disclosed above using a means of 
connection such as that illustrated in FIG. 19. Rigid attachment is 
assured by providing the ends of seat stays 21, 21', the ends of chain 
stays 19, 19' and the common junctions 27, and 25 with slip fit joints. 
Thus, as illustrated in FIG. 19, in a frame of the present invention it is 
possible to provide junction 25 with a rearwardly projecting stub 
connector 56 having an outer diameter only slightly smaller than the inner 
diameter of the end of chain stay 19, allowing the end of chain stay 19 to 
slip over connector 56 and abut the front triangle at the rear edge of 
common junction 25. A rigid and permanent attachment is obtained by 
applying a suitable adhesive to the interface between the outer surface of 
connector 56 and the inner surface at the end of chain stay 19. This 
adhesive may be the same resin used to impregnate the fibers from which 
the walls of the frame are preferably molded. The other portions of the 
unified rear triangle can be similarly attached to the front triangle to 
complete the bicycle frame. Thus, a frame can be obtained which has fewer 
joints than a conventional bicycle and which may provide production 
advantages over an entirely unified frame. 
One skilled in the art will recognize at once that it would be possible to 
construct the frame of the present invention from a variety of materials 
and to modify the process in a variety of ways. While the preferred 
embodiment has been described in detail, and shown in the accompanying 
drawings, it will be evident that various further modifications are 
possible without departing from the scope of the invention.