Frame for a bicycle

Abstract

There is provided a frame for a bicycle. The frame comprises a plurality of tube structures 106,112, 114. Each tube structure is formed from a composite material. The frame also comprises a connector

Description

FIELD The present invention relates to a frame for a bicycle and a method of manufacturing a frame for a bicycle. BACKGROUND Carbon fibre bicycle frames are typically manufactured either by moulding the frame as a single unitary structure, or using a “tube-to-tube” manufacturing approach. Moulding the frame as a single unitary structure reduces flexibility in the geometry of the frame, since a new mould is required for different frame sizes or designs. The tube-to-tube manufacturing approach requires each tube in the frame to be precisely marked and cut to the correct length for the geometry of the frame. The ends of the tubes must be notched to a specific shape to be properly mated to the adjacent tube in the frame to which the tubes join. The tubes are then connected together with an adhesive where the end of one tube meets the adjacent tube, and the joint area is wrapped with further carbon fibre material. The tube-to-tube manufacturing approach therefore requires skilled labour to accurately mark and cut each tube and add it into the frame. It also requires mechanical workshop equipment such as lathes and drills, which often requires significant workshop space. It is a process which incurs high costs in terms of skilled labour, machinery and workspace whilst being a slow, multi-stage and linear sequential process. The present invention has been devised with the forgoing in mind. SUMMARY According to a first aspect, there is provided a frame for a bicycle in accordance with independent claim 1. Some optional features are set out in dependent claims. The present invention may combine the benefits of both a composite bicycle frame (for example, a carbon fibre bicycle frame) and a traditional metal bicycle frame (for example, a steel or aluminium bicycle frame). Using connectors to form a joint between adjacent tube structures in the bicycle frame may enable an overall weight of the bicycle frame to be reduced or minimized by using a composite material for the majority of the bicycle frame, whilst enabling simple and convenient construction of the bicycle frame by providing connectors to which the tube structures can be easily connected (similar to metal tubes being welded to connectors in a metal bicycle frame), with the geometry of the joints and the overall bicycle frame determined by the connectors to which the tube structures are connected. That may also enable a composite bicycle frame having a particular geometry to be conveniently manufactured in different sizes by simply proportionally scaling the lengths of the tube structures used in the frame. That may also enable a composite bicycle frame having a different overall geometry to be easily constructed by providing different connectors (for example, connectors having different shapes or geometries) to which the tube structures can be connected to form the bicycle frame. The construction of the bicycle frame of the present invention may reduce the need for skilled labour in constructing a tube-to-tube type composite bicycle frame, by making it a modular process in which pre-formed tube structures and connectors can be simply connected together to form the frame structure in an accurate, repeatable manner. That may also enable the different parts of the frame (the connectors and the tube structures) to be manufactured separately but in parallel with one another, which may increase a speed of composite bicycle frame construction, reducing dwell time and increasing efficiency compared to conventional tube-to-tube composite bicycle frame manufacturing. That may enable the frame to be provided with an internal conduit structure for cable routing in a simple and convenient manner. That may enable cables such as brake cables and gear cables to be conveniently run through the frame, improving ease of removing and reinstalling cables during maintenance, whilst improving isolation of the cables from mechanical deformation due to contact with the frame and / or liquid or dirt that may collect within the bicycle frame. In addition, a dedicated internal conduit structure for cable routing within the frame may keep the cables substantially straight and still during operation, which may improve braking or derailleur performance (which is particularly beneficial for longer length cables in a tandem bicycle frame). Conventional moulding approaches for composite bicycle frames typically require internal pressure to be applied during forming and so prevent such internal conduit structures from being provided, whilst providing such internal conduit structures in a composite bicycle frame using a tube-to-tube manufacturing approach is excessively complex and time-consuming. The frame may comprise at least one layer of composite material disposed over or arranged to encapsulate at least a part of the joint. That may increase a strength and stiffness of the frame, by providing additional mechanical support to the joint between the tube structures and the connector. That may allow the frame to better resist forces experienced by the frame during riding and may improve performance of a bicycle incorporating the frame. That may also enable the use of connectors which can be rapidly formed (for example, using additive manufacturing processes) from materials having weaker mechanical properties than conventional bicycle frame materials (such as metal, metal alloy or composite materials) to increase manufacturing speed and flexibility without compromising mechanical performance. The one or more layers of composite material over the joint may strengthen and stiffen the joint to achieve mechanical properties comparable with conventional bicycle frame materials. The at least one layer of composite material may be disposed over or arranged to encapsulate at least a part of the joint at which each tube structure is connected to the connector. The at least one layer of composite material may be disposed over or arranged to encapsulate the joint such that the layer of composite material covers the connector and covers at least a part of each tube structure connected to the connector. The composite material may be or comprise a fibre reinforced composite material. The composite material may be or comprise a carbon fibre composite material. The connector may comprise a mating portion configured to engage each respective tube structure. At least one mating portion may be configured to engage the respective tube structure such that one of the tube structure and the mating portion is received or nested within the other of the tube structure and the mating portion. The mating portion may comprise a shape, for example a cross-sectional shape, that is the same or complementary to a shape, for example a cross-sectional shape, of a tube structure with which it is configured to engage. The mating portion may comprise a protrusion. The protrusion may be configured to be received within the tube structure. That may increase a strength and stiffness of the frame, by providing additional mechanical support to the joint between the tube structures and the connector. The protrusion of the connector being received within the tube structure may provide an internal structure that strengths and supports the tube structure at its end. That may also increase a contact area between the tube structure and the connector, which may increase a strength of an adhesive joint between the tube structure and the connector. That may allow the frame to better resist forces experienced by the frame during riding and may improve performance of a bicycle incorporating the frame. That may be particularly beneficial for tandem bicycle frames, which typically experience higher mechanical forces in use. The mating portion may comprise a shoulder or lip. The shoulder or lip may be configured to limit travel of the protrusion within the tube structure. That may enable a desired geometry of the frame to be easily formed simply by engaging the connectors with the tube structures. The shoulder or lip may provide an inherent locating mechanism to ensure the tube structures are correctly positioned relative to the connector before being secured to the connector. That may also enable an outer surface of the tube structure to be substantially flush with an outer surface of the connector when the tube structure is connected to the connector (using a conventional tube structure that does not comprise a stepped profile in its own outer surface). That may enable one or more layers of composite material to be more easily disposed over the joint. That may also improve mechanical support provided to the joint by the one or more layers of composite material, by removing one or more discontinuities in an outer surface of the frame that may act as a stress concentrator. The mating portions may be arranged at an angle to one another. The mating portions may be arranged at an angle to one another in accordance with a desired geometry of the frame or desired orientation of the tube structures relative to one another. The continuous passage formed by the internal conduit structure and the internal hollow passage of the connector may be isolated from an internal space of the tube structures. That may further improve protection of cables routed internally within the frame. The internal passage of the connector may be or comprise an integral tube structure formed in the connector. The integral tube structure may isolate the internal passage from an internal space within the connector (for example, if the connector comprises one or more apertures or hollows to engage other components, such as a bottom bracket). The internal conduit structure may be structurally separate from the tube structure within which the internal conduit structure is disposed. That may enable the internal conduit structures to be easily formed and installed or connected to the connector separately or independently from the tube structures forming the frame, which may improve an ease of constructing the frame with internal cable routing capability. The connector may comprise a secondary mating portion configured to engage the internal conduit structure. The secondary mating portion may comprise a recess configured to receive a part of the internal conduit structure. That may provide additional mechanical support to the internal conduit structure, and may also increase a contact area between the internal conduit structure and the connector, which may increase a strength of an adhesive joint between the internal conduit structure and the connector. The recess may comprise a shoulder or lip. The should or lip may be configured to limit travel of the internal conduit structure within the recess. That may provide an inherent locating mechanism to ensure internal conduit structures are correctly positioned relative to the connector before being secured to the connector. In turn that may ensure that any internal cables routed within the frame are properly housed within the internal conduit structure. The secondary mating portion may be configured or located on the connector to engage the internal conduit structure such that the internal conduit structure is spaced apart from an internal surface of the tube structure. According to a second aspect, there is provided a method of manufacturing a frame for a bicycle. The method may comprise connecting a plurality of tube structures to a connector to form a joint between adjacent tubes in the frame. Each tube structure may be formed from a composite material. The tube structures may be pre-formed tube structures (for example, formed into a tube structure prior to being connected to the connector). The method may comprise connecting the tube structures to the connector using an adhesive material. The method may comprise disposing at least one layer of composite material over at least a part of the joint. The method may comprise disposing the at least one layer of composite material over at least a part of the joint at which each tube structure is connected to the connector. The method may comprise disposing the at least one layer of composite material over the joint such that the layer of composite material covers the connector and covers at least a part of each tube structure connected to the connector. The method may comprise engaging each tube structure with a mating portion of the connector. The method may comprise engaging the tube structure with the mating portion such that a protrusion of the mating portion is received within the tube structure. The method may comprise inserting a protrusion of the mating portion into the tube structure until the tube structure contacts a shoulder or lip of the mating portion. The method may comprise forming the connectors by an additive manufacturing process. That may enable a wide variety of different connectors to be easily and quickly produced. In turn, that may enable a wide variety of different composite bicycle frame geometries to be easily produced using the same pre-formed tube structures (optionally cut to a desired length in accordance with a desired frame geometry), by providing different connectors such that the tube structures are arranged at a desired orientation or angle relative to one another when connected to the connector. The method may comprise forming the connectors by a moulding process. The method may comprise connecting an internal conduit structure to the connector such that the internal conduit structure is disposed within one of the tube structures in use. The method may comprise connecting an internal conduit structure to the connector such that the internal conduit structure and an internal passage of the connector form a continuous passage located internally within the frame. The method may comprise connecting the internal conduit structure to the connector such that the continuous passage formed by the internal conduit structure and the internal passage of the connector is isolated from an internal space of the tube structures. The internal conduit structure may be structurally separate from the tube structure within which the internal conduit structure is disposed. The method may comprise engaging the internal conduit structure with a secondary mating portion of the connector. The method may comprise engaging the internal conduit structure with the secondary mating portion such that a part of the internal conduit structure is received within a recess of the secondary mating portion. The method may comprise inserting the internal conduit structure into the recess of the secondary mating portion until the internal conduit structure contacts a shoulder or lip of the secondary mating portion. The method of the second aspect may comprise one or more features of, or features corresponding to features of, the frame of the first aspect, and vice versa. The method of the second aspect may be carried out to form the frame of the first aspect. According to a third aspect, there is provided a kit of parts for forming a bicycle frame in accordance with independent claim 16. The kit of parts of the third aspect may comprise one or more features of, or features corresponding to features of, the frame of the first aspect and / or the method of the second aspect, and vice versa. According to a fourth aspect, there is provided a frame for a bicycle. The frame may comprise a plurality of tube structures. The frame may also comprise a connector to which the plurality of tube structures are connected to form a joint between adjacent tube structures in the frame. The connector may be configured to engage each tube structure such that at least a part of the connector is received within the tube structure. The connector may comprise a mating portion configured to engage each respective tube structure. The mating portion may be configured to be received within the tube structure. The mating portion may be or comprise a protrusion. The mating portion may comprise a shoulder or lip. The shoulder or lip may be configured to limit travel of the mating portion within the tube structure. According to a fifth aspect, there is provided a frame for a bicycle. The frame may comprise a plurality of tube structures. The frame may also comprise a connector to which the plurality of tube structures are connected to form a joint between adjacent tube structures in the frame. The frame may further comprise an internal conduit structure disposed within at least at least one of the tube structures. The connector may comprise an internal hollow passage extending through the connector. The internal conduit structure may be connected to the connector such that the internal conduit structure and the internal passage of the connector form a continuous passage located internally within the frame. The continuous passage formed by the internal conduit structure and the internal hollow passage of the connector may be isolated from an internal space of the tube structures. The internal conduit structure may be structurally separate from the tube structure within which the internal conduit structure is disposed. Features which are described in the context of separate aspects and embodiments of the invention may be used together and / or be interchangeable wherever possible. Similarly, where features are described in the context of a single embodiment for brevity, those features may also be provided separately or in any suitable sub-combination. BRIEF DESCRIPTION OF DRAWINGS Embodiments of the invention will now be described by way of example only with reference to the following drawings in which: FIG. 1 shows a frame for a tandem bicycle according to an embodiment of the present invention; FIGs. 2A to 2F show a head tube connector and its connection and relationship with a head tube, top tube and down tube of the frame shown in FIG. 1 in more detail; FIG. 3 shows an alternative embodiment of a head tube connector for use in the frame shown in FIG. 1; FIG. 4 shows an alternative embodiment in which the frame shown in FIG. 1 comprises separate connectors to connect the head tube to the top tube and the down tube respectively; FIGs. 5A to 5C show a primary bottom bracket connector and its connection and relationship with a down tube, primary seat tube and bottom tube of the frame shown in FIG. 1 in more detail; FIGs. 6A to 6D show a secondary bottom bracket connector and its connection and relationship with a bottom tube, secondary seat tube and chain stays of the frame shown in FIG. 1 in more detail; FIGs. 7A to 7C show dropouts and their connection and relationship with chain stays and seat stays of the frame shown in FIG. 1 in more detail; FIG. 8 shows an internal cable routing arrangement located internally within the frame shown in FIG. 1 extending from the head tube connector to the dropouts via the primary and secondary bottom bracket connectors; FIG. 9 shows a secondary seat tube connector and its connection and relationship with a top tube, secondary seat tube and seat stays of the frame shown in FIG. 1 in more detail; FIG. 10 shows a primary seat tube connector and its connection and relationship with a top tube and a primary seat tube of the frame shown in FIG. 1 in more detail; FIG. 11 shows a frame for a solo bicycle according to an embodiment of the present invention; and FIG. 12 shows a method of manufacturing a frame for a bicycle according to an embodiment of the present invention. Like reference numerals in different Figures may represent like elements. DETAILED DESCRIPTION Figure 1 shows an embodiment of a frame 100 for a bicycle according to an embodiment of the present invention. The frame 100 comprises a plurality of tube structures 102-118. Each tube structure 102-118 is formed from a composite material. In the embodiment shown, each tube structure 102-118 is formed from a carbon fibre reinforced composite material, although that is not essential and any suitable composite material may alternatively be used (such as any fibre reinforced composite material, for example a fibreglass reinforced resin or polymeric material). The frame 100 also comprises a plurality of connectors 120-132. The tube structures 102-118 are connected to the connectors 120-132 such that the connectors 120-132 each form a joint between adjacent tube structures 102-118 in the frame 100. In the embodiment shown, the connectors 120-132 are configured to engage with or connect to the tube structures 102-118 such that outer surfaces of the tube structures 102-118 are substantially flush with outer surfaces of the connectors 120-132, forming a substantially continuous outer surface of the frame 100 without any significant discontinuities or stepped profiles. That may enable one or more layers of composite material (not shown) to be easily disposed over, or arranged to encapsulate or wrapped around the frame 100 or at least a part of the frame 100 (for example, over or adjacent the joints where the tube structures 102-118 and the connectors 120-132 meet) to provide additional mechanical support to the frame 100, without any discontinuities that may act as a stress concentrator to the one or more layers of composite material. The one or more layers of composite material may be or comprise carbon fibre reinforced composite material, although that is not essential. It will also be appreciated one or more layers of composite material may not be disposed over or used to encapsulate the frame 100. In the embodiment shown, the frame 100 is for a tandem bicycle (that is, a bicycle configured to have two riders simultaneously). The tube structures 102-118 including a head tube 102, a top tube 104, a primary seat tube 106, a secondary seat tube 108, a handlebar tube 110, a down tube 112, a bottom tube 114, chain stays 116 and seat stays 118. A head tube connector 120 connects the head tube 102, the top tube 104 and the down tube 112. A primary seat tube connector 122 connects the primary seat tube 106 and the top tube 104. A secondary seat tube connector 124 connects the secondary seat tube 108, the top tube 104 and the seat stays 118. A handlebar connector 126 connects the handlebar tube 110 (for the second or rear rider of the tandem bicycle) and the top tube 104. A primary bottom bracket connector 128 connects the down tube 112, the primary seat tube 106 and the bottom tube 114 (and also comprises an aperture for receiving a bottom bracket for a first rider of the bicycle). A secondary bottom bracket connector 130 connects the secondary seat tube 108, the bottom tube 114 and the chain stays 116 (and also comprises an aperture for receiving a second bottom bracket of the bicycle). Dropouts 132 connect the chain stays 116 and the seat stays 118. Figures 2A to 2E show the head tube connector 120 and its relationship with the head tube 102, the top tube 104 and the down tube 112 in more detail. Figures 2A to 2C show the connection of the head tube connector 120 with the head tube 102, the top tube 104 and the down tube 112, with the head tube 102, the top tube 104 and the down tube 112 shown translucent in Figures 2A and 2B for clarity. The head tube connector 120 comprises a first mating portion 120a configured to engage the head tube 102. In the embodiment shown, the first mating portion 120a comprises a surface of the head tube connector 120 that is shaped complementary to a shape of an outer surface of the head tube 120 to allow the surface of the mating portion 120a to be brought substantially into contact with the outer surface of the head tube 120 and secured to the head tube 120 (for example, using an adhesive such as a structural adhesive, for example a methyl methacrylate adhesive or an epoxy adhesive). The surface of the first mating portion 120a is shaped to mate a head tube 120 having a substantially cylindrical outer surface, although it will be appreciated the head tube 120 may alternatively comprise any suitable shape or cross-sectional profile (for example, a teardrop cross-section, a D-shaped cross-section, an oval cross-section, a square cross-section etc.) and the surface of the first mating portion 120a may comprise a corresponding or complementary shape to mate to the outer surface of the head tube 120. The head tube connector 120 also comprises a second mating portion 120b configured to engage the top tube 104, and a third mating portion 120c configured to engage the down tube 112. The second mating portion 120b comprises a protrusion 120b 1 that is received within the top tube 104 when the second mating portion 120b is engaged with the top tube 104. The protrusion 120b 1 is configured to be slidingly received within the top 104 to allow simple and convenient connection of the top tube 104 to the head tube connector 120. In the embodiment shown, the protrusion 120b 1 comprises a substantially cylindrical shape having a substantially circular cross-section that is similar or complementary to a cross-sectional shape of an internal space within the top tube 104. That may allow the protrusion 120b 1 to be received within the top tube 104 such that substantially all of the outer surface of the protrusion 120b 1 contacts an internal surface of the top tube 104. An adhesive is applied to secure the outer surface of the protrusion 120b 1 to the inner surface of the top tube 104, although that is not essential. However, it will be appreciated the protrusion 120b 1 may comprise any suitable shape or cross-section receivable within the hollow space within the top tube 104, preferably a shape or cross-section similar or complementary to an internal cross-section of the top tube 104. The second mating portion 120b further comprises a shoulder or lip 120b2 configured to contact an end surface of the top tube 104 to limit travel of the protrusion 120b 1 within the top tube 104, enabling the top tube 104 to be properly located on the head tube connector 120. A contact surface of the shoulder 120b2 is arranged substantially perpendicular to a longitudinal axis of the projection 120b 1 and the top tube 104. That may allow the end surface of the top tube 104 to be conveniently cut at 90° to improve ease and speed of manufacturing the top tube 104. The shoulder 120b2 has a depth or thickness substantially equal to a wall thickness of the top tube 104 such that an outer surface of the top tube 104 is substantially flush with an outer surface of the head tube connector 120 when connected, although that is not essential. The third mating portion 120c comprises a similar structure to the second mating portion 120b, comprising a protrusion 120cl configured to be received within the down tube 112 and a shoulder or lip 120c2 configured to limit travel of the protrusion 120cl within the down tube 112. In the embodiment shown, a main body of the head tube connector 120 comprises a recessed channel 120d configured to at least partially define the protrusion 120b 1 and the shoulder 120b2 of the second mating portion 120b. That may enable the head tube connector 120 to provide additional structural support to the top tube 104 in use. In the embodiment shown, due to the angular and spatial positioning of the second and third mating portion 120b, 120c the channel 120d is provided between and adjacent both the second and third mating portions 120b, 120c. However, that is not essential. It will also be appreciated the head tube connector 120 may not comprise such a recessed channel. As shown more clearly in Figures 2D and 2E, the first mating portion 120a, the second mating portion 120b and the third mating portion 120c of the head tube connector 120 are all in fluid communication with one another via apertures 134a, 134b provided in the first mating portion 120a, aperture 136 provided in the second mating portion 120b and aperture 138 provided in the third mating portion 120c. The apertures 134a, 134b allow the head tube connector 120 to be in fluid communication with an internal space within the head tube 102, the aperture 136 allows the head tube connector 120 to be in fluid communication with an internal space within the top tube 104, and the aperture 138 allows the head tube connector 120 to be in fluid communication with an internal space within the down tube 112. However, that is not essential, and the mating portions 120a-c may not be in fluid communication with one another. For example, the surface of the first mating portion 120a may not comprise apertures 134a, 134b and so the surface of the first mating portion 120a may prevent fluid communication between each of the respective mating portions 120a-c. The head tube connector 120 is also configured to connect to a plurality of internal conduit structure 140 disposed within the down tube 112. The head tube connector 120 comprises a plurality of internal hollow passages 120e extending partially through the head tube connector 120. Each passage 120e is formed by an integral tube structure formed in the head tube connector 120. In the embodiment shown, the passages 120e extend through the head tube connector 120 within the third mating portion 120c and are in fluid communication with the aperture 134b provided in the first mating portion 120a. The internal conduit structure 140 is connected to the head tube connector 120 such that each internal conduit structure 140 and a passage 120e form a continuous passage located internally within the frame 100 that may be used, for example, to route one or more cables internally through the frame 100. The internal conduit structure 140 is a tube structure that is structurally separate from the down tube 112 within which it is disposed. That allows the provision of a continuous internal passage within the frame 100 that is isolated from an internal space of the down tube 112, providing an additional layer of protection for any cables routed internally through the frame 100. The internal conduit structure 140 comprises a composite tube structure, although the internal conduit structure 140 may be formed from any suitable material. The fluid communication between the passage 120e and the aperture 134b allow a cable to be routed internally through the head tube 102 and into the internal conduit structure 140 disposed within the down tube 112 via the head tube connector 120, as illustrated with the dashed line C in Figure 2C (which is merely for explanatory purposes and not indicative of an actual cable path). However, that is not essential. As shown in Figure 3, in an alternative embodiment one or more holes 144 may be provided in a surface of the head tube connector 120 adjacent the third mating portion 120c. That may enable a cable that is routed internally through an internal conduit structure 140 within the down tube 112 to exit the frame 100 through the head tube connector 120, with the cable then routed externally, for example along the head tube 102 towards the handlebars. That may avoid the need for apertures 134a, 134b in the surface of the first mating portion 120a, and the first, second and third mating portions 120a-c of the head tube connector 120 need not be in fluid communication with one another. In the embodiment shown there are three internal hollow passages 120e, each configured to form a continuous passage with a separate internal conduit structure 140 (shown in more detail in Figure 2F). However, it will be appreciated any suitable number of internal hollow passages 120e may be provided in the head tube connector 120, each configured to form a continuous passage with a separate internal conduit structure 140. Turning to Figure 2E, the head tube connector 120 comprises a secondary mating portion 142 configured to engage the internal conduit structure 140. The secondary mating portion 142 is provided within the third mating portion 120c to enable the internal conduit structure 140 to be disposed or located within the down tube 112. In the embodiment shown, the secondary mating portion 142 comprises a recess 142a configured to receive a part of the internal conduit structure 140. The recess 142a is configured to slidingly receive the internal conduit structure 140 to allow simple and convenient connection of the internal conduit structure 140 to the head tube connector 120. The recess 124a comprises a substantially cylindrical shape having a substantially circular cross-section that is similar or complementary to a cross-sectional shape of the internal conduit structure 140. That may allow the internal conduit structure 140 to be received within the recess 142a such that substantially all of the inner surface of the recess 142a contacts an outer surface of the internal conduit structure 140, for example to form a press-fit or friction fit connection. An adhesive is applied to secure the outer surface of the internal conduit structure 140 to the inner surface of the recess 142a, although that is not essential. However, it will be appreciated the recess 142a may comprise any suitable shape or cross-section to receive the internal conduit structure 140, preferably a shape or cross-section similar or complementary to a cross-section of the internal conduit structure 140. The secondary mating portion 142 further comprises a shoulder or lip 142b configured to contact an end surface of the internal conduit structure 140 to limit travel of the internal conduit structure 140 within the recess 142a, enabling the internal conduit structure 140 to be properly located on the head tube connector 120. A contact surface of the shoulder 142b is arranged substantially perpendicular to a longitudinal axis of the recess 142a and the internal conduit structure 140. That may allow the end surface of the internal conduit structure 140 to be conveniently cut at 90° to improve ease and speed of manufacturing the internal conduit structure 140. Figure 4 shows an alternative embodiment in which a first head tube connector 120’ and a second head tube connector 120” are provided. The first head tube connector 120’ is configured to connect the head tube 102 to the top tube 104. The first head tube connector 120’ comprises a first mating portion 120’a configured to engage the head tube 102. The second head tube connector 120” comprises a first mating portion 120”a configured to engage the head tube 102. The first mating portions 120’a, 120”a are substantially similar in nature to the first mating portion 120a described above with respect to the head tube connector 120. The first head tube connector 120’ also comprises a second mating portion 120’b configured to engage the top tube 104. The second head tube connector 120” comprises a third mating portion 120”c configured to engage the down tube 112. The second and third mating portions 120’b, 120”c are substantially similar in nature to the second and third mating portions 120b, 120c described above with respect to the head tube connector 120. Figures 5A and 5B show the connection of the primary bottom bracket connector 128 with the down tube 112, the bottom tube 114 and the primary seat tube 106, with the down tube 112, the bottom tube 114 and the primary seat tube 106 shown translucent in Figure 5A for clarity. The primary bottom bracket connector 128 comprises a first mating portion 128a configured to engage the down tube 112, a second mating portion 128b configured to engage the bottom tube 114, and a third mating portion 128c configured to engage the primary seat tube 106. Each of the first, second and third mating portions 128a-c of the primary bottom bracket connector 128 is substantially similar in construction to the second and third mating portions 120b, 120c described above with respect to the head tube connector 120. Each of the mating portions 128a-c of the primary bottom bracket connector 128 comprises a protrusion 128al-cl received within the down tube 112, bottom tube 114 or primary seat tube 106 respectively. Each of the mating portions 128a-c of the primary bottom bracket connector 128 also comprises a shoulder or lip 128a2-c2 configured to limit travel of the protrusion 128al-cl within the down tube 112, bottom tube 114 or primary seat tube 106 respectively. The shoulders 128a2-c2 each have a depth or thickness substantially equal to a wall thickness of the respective tube structure 112, 114, 106 such that an outer surface of the tube structures 112, 114, 106 is substantially flush with an outer surface of the primary bottom bracket connector 120 when connected, although that is not essential. The primary bottom bracket connector 128 is also connected to a plurality of internal conduit structures 140 respectively disposed within the down tube 112 and the bottom tube 114. The primary bottom bracket connector 128 also comprises a plurality of internal hollow passages 146 extending through the primary bottom bracket connector 128. The passages 146 of the primary bottom bracket connector 128 extend substantially fully through the primary bottom bracket connector 128 between the first and second mating portions 128a-b of the primary bottom bracket connector 128. A continuous internal passage within the frame 100 may therefore be provided from an internal conduit structure 140 disposed within the down tube 112, through a passage 146 in the primary bottom bracket connector 128 and into an internal conduit structure 140 disposed within the bottom tube 114. As shown in Figure 5B, the passages 146 are each formed by an integral tube structure formed in the primary bottom bracket connector 128. The passages 146 are isolated from a remaining internal space within the primary bottom bracket connector 128, that extends between an aperture 148 formed in the first mating portion 128a and an aperture 150 formed in the second mating portion 128b, by the wall 152 of the integral tube structure formed within the primary bottom bracket connector 128. The passages 146 are also isolated from a space within the third mating portion 128c by a wall 154 formed within the primary bottom bracket connector 128. The primary bottom bracket connector 128 also comprises an aperture extending between its opposing lateral sides to house a bottom bracket 156. In the embodiment shown, the passages 146 are arranged to extend through the primary bottom bracket connector 12 8 over a top surface of the bottom bracket 156. At least a portion of the passages 146 extends along a curved path to follow or accommodate a curved outer surface of the bottom bracket 156 within the primary bottom bracket connector 128. As shown in Figure 5C, similar to the head tube connector 120, the primary bottom bracket connector 128 comprises secondary mating portions 142 configured to engage the internal conduit structure 140. The secondary mating portions 142 are respectively provided within the first mating portion 128a and the second mating portion 128b of the primary bottom bracket connector 128, to enable the internal conduit structures 140 to be disposed or located within the down tube 112 and the bottom tube 114 respectively. The secondary mating portions 142 each comprise a recess 142a and a shoulder or lip 142 substantially as described above with respect to the secondary mating portion 142 of the head tube connector 120. Figures 6A to 6D show the connection of the secondary bottom bracket connector 130 with the bottom tube 114, the chain stays 116 and the secondary seat tube 108, with the bottom tube 114, the chain stays 116 and the secondary seat tube 108 shown translucent in Figure 6A for clarity. The secondary bottom bracket connector 130 comprises a first mating portion 130a configured to engage the bottom tube 114, a second mating portion 130b configured to engage the secondary seat tube 108, and third mating portions 130c-d each configured to engage one of the chain stays 116. The first and second mating portions 130a-b of the secondary bottom bracket connector 130 are substantially similar in construction to the second and third mating portions 120b-c described above with respect to the head tube connector 120. Each of the first and second mating portions 130a-b comprises a protrusion 130al-bl received within the bottom tube 114 or the secondary seat tube 10 respectively. Each of the first and second mating portions 130a-b also comprises a shoulder or lip 130a2-b2 configured to limit travel of the protrusion 130al-bl within the bottom tube 114 or the secondary seat tube 108. The third mating portions 130c-d are similar in construction to the first and second mating portions 130a-b but comprise a protrusion 130cl-dl and a shoulder or lip 130c2-d2 having a substantially rectangular cross-section to engage the substantially rectangular chain stays 116 (rather than a substantially circular cross-section to engage a cylindrical tube). The shoulders 130a2-d2 each have a depth or thickness substantially equal to a wall thickness of the respective tube structure 114, 108, 116 such that an outer surface of the tube structures 114, 108, 116 is substantially flush with an outer surface of the secondary bottom bracket connector 120 when connected, although that is not essential. The secondary bottom bracket connector 130 is also connected to a plurality of internal conduit structures 140 respectively disposed within the bottom tube 114 and the secondary seat tube 108. The secondary bottom bracket connector 130 also comprises a plurality of internal hollow passages 158 extending through the secondary bottom bracket connector 130. The passages 158 extend substantially fully through the secondary bottom bracket connector 130. A first passage 158a extends between the first mating portion 130a and the second mating portion 130b. The first passage 158a also extends longitudinally beyond the protrusion 130b 1 of the second mating portion 130b but comprises an opening 158al of the first passage 158a oriented towards a sidewall of the secondary seat tube 108. The opening 158al is positioned or oriented to allow a cable routed through the passage 158a to exit the frame 100 through a hole (not shown) provided in a sidewall of the secondary seat tube 108. A continuous internal passage within the frame 100 may therefore be provided from an internal conduit structure 140 disposed within the bottom tube 140, through the passage 158a to a hole in the secondary seat tube 108 to exit the frame 100. That may enable, for example, a cable for a front derailleur (not shown) to be routed internally through the frame 100 and exit the frame 100 adjacent the front derailleur. A second passage 158b extends between the first mating portion 130a and the third mating portion 130c which connects to the left chain stay 116a. A third passage 158c extends between the first mating portion 130a and the third mating portion 130d which connects to the right chain stay 116b. In the embodiment shown, the second and third passages 158b, 158c are provided substantially symmetrically on opposing lateral sides of the first passage 158a (see Figure 6C) although that is not essential. Continuous internal passages within the frame 100 may therefore be provided from an internal conduit structure 140 disposed within the bottom tube 140, through the passages 158b, 158c in the secondary bottom bracket connector 130 and into an internal conduit structure 140 disposed within the left or right chain stays 116a-b respectively. Each of the passages 158a-c is formed by an integral tube structure formed in the secondary bottom bracket connector 130 which isolates the passages 158a-c from a remaining internal space within the secondary bottom bracket connector 130. The secondary bottom bracket connector 130 also comprises an aperture extending between its opposing lateral sides to house a secondary bottom bracket 160. In the embodiment shown, the passages 158a-c and arranged to extend through the secondary bottom bracket connector 13 0 over a top surface of the secondary bottom bracket 160. At least a portion of each passage 158a-c extends along a curved path to follow or accommodate a curved outer surface of the secondary bottom bracket 160 within the secondary bottom bracket connector 130. As shown in Figure 6D, similar to the head tube connector 120, the secondary bottom bracket connector 130 comprises secondary mating portions 142 configured to engage the internal conduit structures 140. The secondary mating portions 142 are respectively provided within the first mating portion 130a and the third mating portions 130c-d of the secondary bottom bracket connector 128, to enable the internal conduit structures 140 to be disposed or located within the bottom tube 114 and the chain stays 116 respectively. The secondary mating portions 142 each comprise a recess 142a and a shoulder or lip 142 substantially as described above with respect to the secondary mating portion 142 of the head tube connector 120. Figures 7A to 7C show the connection of the dropouts 132 with the chain stays 116 and the seat stays 118, with the chain stays 116 and the seat stays 118 shown translucent for clarity. Each of the left and right dropouts 132a-b comprises a first mating portion 133a configured to engage the respective left or right chain stay 116a-b, and a second mating portion 133b configured to engage the respective left or right seat stay 118a-b. The first mating portions 133a each comprise a protrusion 133al received within the respective chain stay 116a-b. The second mating portions 133b each comprise a protrusion 133bl received within the respective seat stay 118a-b. Each of the first and second mating portions 133a-b also comprises a shoulder or lip 133a2-b2 configured to limit travel of the protrusion 133al-bl within the respective tube structure 116a-b, 118a-b. In the embodiment shown, the shoulder or lip 133a2-b2 is not perpendicular to the longitudinal axis of the protrusion 133al-bl, but arranged at an oblique angle to the longitudinal axis of the projection 133al-bl. However, that is not essential, and the shoulder or lip may be arranged at any suitable angle. The right dropout 132b is also connected to an internal conduit structure 140 disposed within the right chain stay 116b. The right dropout 132b also comprises an internal hollow passage 162 extending through the right dropout 132b from the first mating portion 133a to an opening 162a in an outer surface of the right dropout 132b (in the embodiment shown, the opening 162a is positioned on a top surface of an arm of the right dropout 132b that engages the right chain stay 116b, although that is not essential and the opening 162a may be provided at any suitable location in the outer surface of the right dropout 132b). A continuous internal passage within the frame 100 may therefore be provided from an internal conduit structure 140 disposed within the right chain stay 116b, through the passage 162 to the opening 162a to exit the frame 100. That may enable, for example, a cable for a rear derailleur (not shown) to be routed internally through the frame 100 and exit the frame 100 adjacent the rear derailleur on the right dropout 132b. The right dropout 132b comprises a secondary mating portion 142 configured to engage the internal conduit structure 140. The secondary mating portion 142 is provided within the first mating portion 133a, to enable the internal conduit structure 140 to be disposed or located within the right chain stay 116b. The secondary mating portion 142 comprises a recess 142a and a shoulder or lip 142 substantially as described above with respect to the secondary mating portion 142 of the head tube connector 120. In the embodiment shown, the left dropout 132a is not directly connected to an internal conduit structure 140 disposed within the left chain stay 116a. A separate internal connector structure 164 is provided within the left chain stay 116a which connects to the internal conduit structure 140 disposed within the left chain stay 116a, as shown in Figure 7C. The internal connector structure 164 is located adjacent the first mating portion 133a of the left dropout 132a when the left chain stay 116a is connected to the left dropout 132a. A secondary mating portion 142 is provided on the internal connector structure 164 to connect to the internal conduit structure 140. The internal connector structure 164 comprises an internal hollow passage 166 extending through the internal connector structure 164. The passage 166 extends longitudinally from the secondary mating portion 142 but comprises an opening 166a in the internal connector structure 164 that is positioned or oriented to allow a cable routed through the passage 166 to exit the frame 100 through a hole (not shown) provided in a sidewall of the left chain stay 116a. A continuous internal passage within the frame 100 may therefore be provided from an internal conduit structure 140 disposed within the left chain stay 116a, through the passage 166 to a hole in the left chain stay 116a to exit the frame 100. That may enable, for example, a cable for a rear brake (not shown) to be routed internally through the frame 100 and exit the frame 100 adjacent the rear brake on the left dropout 132a. However, it will be appreciated the left dropout 132a may be directly connected to an internal conduit structure 140 disposed within the left chain stay 116a and comprise an internal passage having an opening formed in an outer surface of the left dropout 132a, substantially as described with respect to the right dropout 132b. Figure 8 shows the connection between the internal conduit structures 140 and the connectors 120, 128, 130, 132a, 132b to provide one or more continuous internal passages through the frame 100. The tube structures that are connected to the connectors 120 to form the frame 100 are not shown for clarity. In the embodiment shown, the frame 100 comprises three continuous internal passages. A first continuous internal passage through the frame 100 extends through the head tube connector 120 to the primary bottom bracket connector 128 via an internal conduit structure 140 connected between the head tube connector 120 and the primary bottom bracket connector 128. The first continuous internal passage then extends through the primary bottom bracket connector 128 to the secondary bottom bracket connector 130 via an internal conduit structure 140 connected between the primary and secondary bottom bracket connectors 128, 130. The first continuous internal passage then extends through the first passage 158a in the secondary bottom bracket connector 128 to exit the frame through a hole in the secondary seat tube 108 via the opening 158al in the first passage 158a, as described above. The first continuous internal passage through the frame 100 may be used to route a cable for a front derailleur of the bicycle (not shown). A second continuous internal passage through the frame 100 extends through the head tube connector 120 to the primary bottom bracket connector 128 via an internal conduit structure 140 connected between the head tube connector 120 and the primary bottom bracket connector 128. The second continuous internal passage then extends through the primary bottom bracket connector 128 to the secondary bottom bracket connector 130 via an internal conduit structure 140 connected between the primary and secondary bottom bracket connectors 128, 130. The second continuous internal passage then extends through the second passage 158b in the secondary bottom bracket connector 130 to the internal connector structure 164 disposed in the left chain stay 116b via an internal conduit structure 140 connected between the secondary bottom bracket connector 130 and the internal connector structure 164. The second continuous internal passage then extends through the passage 166 in the internal connector structure 164 to exit the frame through a hole in the left chain stay 116a via the opening 166a in the passage 166, as described above. The second continuous internal passage through the frame 100 may be used to route a cable for a rear brake of the bicycle (not shown). A third continuous internal passage through the frame 100 extends through the head tube connector 120 to the primary bottom bracket connector 128 via an internal conduit structure 140 connected between the head tube connector 120 and the primary bottom bracket connector 128. The third continuous internal passage then extends through the primary bottom bracket connector 128 to the secondary bottom bracket connector 130 via an internal conduit structure 140 connected between the primary and secondary bottom bracket connectors 128, 130. The third continuous internal passage then extends through the third passage 158c in the secondary bottom bracket connector 130 to the right dropout 132b via an internal conduit structure 140 connected between the secondary bottom bracket connector 130 and the right dropout 132. The third continuous internal passage then extends through the passage 162 in the right dropout 132b to exit the frame 100 via the opening 162a n the passage 162, as described above. The third continuous internal passage through the frame 100 may be used to route a cable for a rear derailleur of the bicycle (not shown). Figure 9 shows the connection of the secondary seat tube connector 124 with the top tube 104, the secondary seat tube 108 and the seat stays 118, with the top tube 104, the secondary seat tube 108 and the seat stays 118 shown translucent for clarity. The secondary seat tube connector 124 comprises a first mating portion 124a configured to engage the top tube 104. In the embodiment shown, the first mating portion 124a comprises a protrusion 124al received within the top tube 104, and a shoulder or lip 124a2 configured to limit travel of the protrusion 124al within the top tube 104. The shoulder 124a2 has a depth or thickness substantially equal to a wall thickness of the top tube 104, although that is not essential. In the embodiment shown, the secondary seat tube connector 124 comprises a recessed channel 124c configured to at least partially define the protrusion 124al and the shoulder 124a2 of the first mating portion 124a, substantially similar to the recessed channel 120d of the head tube connector 120 described above. However, that is not essential. The secondary seat tube connector 124 also comprises second mating portions 124b each configured to engage a respective one of the seat stays 118a-b. The second mating portions 124b each comprise a protrusion 124b 1 received within the respective seat stay 118a-b. The second mating portions 124b also comprise a shoulder or lip 124b2 configured to limit travel of the protrusion 124b 1 within the seat stay 118-b. In the embodiment shown, the shoulders 124a2-b2 of the first and second mating portions 124a-b are arranged substantially perpendicular to a longitudinal axis of the projections 124al -bl, although that is not essential. The secondary seat tube connector 124 further comprises an aperture 168 extending though a main body of the connector 124. The aperture 168 is configured to receive the secondary seat tube 108 such that the secondary seat tube 108 passes through the aperture 168 from one side of the secondary seat tube connector 124 to the other. The aperture 168 is defined by internal walls of the secondary seat tube connector 124 such that the aperture 168 is not in fluid communication with the first mating portion 124a or the second mating portions 124b. That may provide a greater internal surface area of the secondary seat tube connector 124 configured to contact and support the secondary seat tube 108, which may improve a rigidity and stability of the secondary seat tube 108 in use. However, it will be appreciated that is not essential, and one or more apertures or openings may be provided in the internal walls defining the aperture 168 such that the first and second mating portions 124a-b are in fluid communication with the aperture 168. In the embodiment shown, the secondary seat tube connector 124 does not comprise any internal hollow passages extending through the connector 124, such that the secondary seat tube connector 124 is not configured to provide a part of a continuous internal passage within the frame 100 (for example, through which a cable may be routed). However, that is not essential, and it will be appreciated the secondary seat tube connector 124 may comprise one or more internal hollow passages similar to those described above with respect to the head tube connector 120, for the primary and secondary bottom bracket connectors 128, 130. In such alternative arrangements, the secondary seat tube connector 124 may be configured to connect to one or more internal conduit structures 124 provided within the tube structures 104, 108, 118 to which the secondary seat tube connector 124 is connected. The secondary seat tube connector 124 may comprise one or more secondary mating portions 142 substantially similar to those described above. Figure 10 shows the connection of the primary seat tube connector 122 with the top tube 104 and the primary seat tube 106, with the top tube 104 and the primary seat tube 106 shown translucent for clarity. The primary seat tube connector 122 comprises a first portion 122a and a second portion 122b. The first portion 122a is configured to engage a top surface of the top tube 104, and the second portion 122b is configured to engage a bottom surface of the top tube 104. Each portion 122a-b of the primary seat tube connector 122 comprises a mating portion 123 configured to engage the top tube 104. In the embodiment shown, the mating portion 123 comprises a surface of each of the first and second portions 122a-b that is shaped complementary to a shape of an outer surface of the top tube 104 to allow the surface of the mating portion 123 to be brought substantially into contact with the outer surface of the top tube 104 and secured to the top tube 104 (for example, using an adhesive), similar to the first mating portion 120a of the head tube connector 120 described above. The surface of the mating portions 123 is shaped to mate a top tube 104 having a substantially cylindrical outer surface, although it will be appreciated the top tube 104 may alternatively comprise any suitable shape or cross-sectional profile (for example, a teardrop cross-section, a D-shaped cross-section, an oval cross-section, a square cross-section etc.) and the surface of the mating portions 123 may comprise a corresponding or complementary shape to mate to the outer surface of the top tube 104. Each of the first and second portions 122a-b also comprises an aperture 125 extending fully through the portion 122a-b, configured to receive the primary seat tube 106. The first and second portions 122a-b are configured to be located on the top tube 104 such that the respective apertures 125 of each portion 122a-b are substantially aligned with one another to allow the primary seat tube 106 to pass through the apertures 125 in both portions 122a-b of the primary seat tube connector 122. The top tube 104 also comprises an aperture through which the primary seat tube 106 can pass, such that the primary seat tube extends through the first portion 122a, through the top tube 104, through the second portion 122b and on to the primary bottom bracket connector 128 as described above. In the embodiment shown, the handlebar connector 126 connecting the handlebar tube 110 to the top tube 104 comprises a substantially similar structure and configuration to the first portion 122a of the primary seat tube connector 124. Where connectors 120-132 are configured to engage the tube structures 102-118 such that at least a portion of the connector is received within the tube structure, it will be appreciated that in alternative arrangements the connectors 120-32 may be configured to engage the tube structures 102-118 such that the tube structures are received within the connector. In the embodiment shown, each of the tube structures 102-118 comprises a composite material, and each of the connectors 120-32 comprises a polymer material, for example a thermoplastic polymer material such as a nylon, polycarbonate, acrylonitrile butadiene styrene, acrylic. However, it will be appreciated the frame 100 may be constructed in a substantially similar manner using tube structures 102-118 and connectors 120-132 formed from any suitable material, for example a metal or metal alloy material (such as steel, aluminium or an aluminium alloy, titanium or a titanium alloy), a composite material (such as a fibre reinforced composite material, for example carbon fibre reinforced composite or fibreglass reinforced composite). In some embodiments one or more layers of composite material (for example, a carbon fibre composite material) are disposed over the outer surface of the frame 100 in order to encapsulate at least a part of the frame 100, as described above. However, that is not essential. Although the embodiment shown in and described with respect to Figures 1 to 10 relates to a frame 100 for a tandem bicycle, it will be appreciated a similar frame construction may be used for any suitable bicycle frame, for example a solo bicycle, a recumbent bicycle, a hand bicycle, a tricycle etc. It will be appreciated the frame geometry required for each different bicycle frame may be provided by adjusting spatial and angular relationships between mating portions on one or more connectors 120-132 and / or by adjusting a length of one or more tube structures 102-118. For example, Figure 11 shows an embodiment of a bicycle frame 200 for a solo bicycle having a substantially similar construction to the bicycle frame 100 described above. The frame 200 comprises a head tube connector 220 connecting a head tube 202, a top tube 204 and a down tube 212. The frame 200 also comprises a seat tube connector 224 (substantially similar to the secondary seat tube connector 124 of the frame 100) connecting the top tube, a seat tube 208 and seat stays 218. The frame 200 also comprises a bottom bracket connector 228 (comprising features from one or both the primary and secondary bottom bracket connectors 128, 130 of the frame 100) connecting the down tube 212, the seat tube 208 and chain stays 216. The frame 200 comprises dropouts 232 (substantially similar to dropouts 132 of the frame 100) connecting the chain stays 216 and the seat stays 218. Figure 12 shows a method 300 of manufacturing a frame for a bicycle. The method 300 may be used to manufacture, and is described with respect to, the frames 100 shown in Figures 1 to 10. It will be appreciated the method 300 may alternatively be used to manufacture any suitable bicycle frame, for example the frame 200 shown in Figure 11. Step 302 of the method 300 comprises forming connectors 120-132 for the frame 100. In the embodiment shown, the connectors 120-132 are formed using an additive manufacturing process (for example, fused deposition modelling, stereolithography, multi-jet fusion, selective laser sintering etc.). However, it will be appreciated the connectors 120-132 may be formed using any suitable manufacturing approach, for example a moulding process, machining process etc. The connectors 120-132 may be formed from a polymeric material, although it will be appreciated the connectors may alternative be formed from any suitable material such as a metal or metal alloy, or a composite material such as a carbon fibre composite material. Step 304 optionally comprises forming the tube structures 102-118. In the embodiment shown, the tube structures 102-118 are moulded into a desired shape or profile using carbon fibre composite material. However, that is not essential, and the tube structures 102-118 may be manufactured using any suitable manufacturing approach, for example, an extrusion process. It will also be appreciated the tube structures 102-118 may alternatively be formed from any suitable material such as a metal or metal alloy, or a polymer material. In alternative embodiments, the tubes 102-118 are pre-formed. Regardless, the tube structures 102-118 are formed into their finished structure or configuration prior to being connected to the connectors 120-132. Step 306 of the method 300 optionally comprises connecting an internal conduit structure 140 to one or more of the connectors 120-132, such that the internal conduit structure 140 and an internal passage (for example, the internal passage 146 of the primary bottom bracket connector 128) form a continuous passage located internally within the frame 100 in use, substantially as described above. In the embodiment shown, step 306 comprises inserting an internal conduit structure 140 into a secondary mating portion 142 of the connectors 120-132 such that the internal conduit structure 140 is received within a recess 142a of the secondary mating portion 142 substantially as described above, although that is not essential. In the embodiment shown, step 306 comprises connecting the internal conduit structure 140 to the connector 120-132 using an adhesive, although that is not essential. In the embodiment shown, each internal conduit structure 140 comprises a composite tube structure, although the internal conduit structure 140 may be formed from or comprise any suitable material. The internal conduit structures 140 may be formed using the same or a similar manufacturing process used to form the tube structures 102-118, although that is not essential and the internal conduit structures 140 may be formed using any suitable manufacturing process. Step 308 of the method 300 comprises connecting the tube structures 102-118 to the connectors 120-132 to form joints between adjacent tube structures 102-118 in the frame 100. Once all the tube structures 102-118 are connected to the relevant connectors 120-132, the frame 100 is constructed. In the embodiment shown, step 308 comprises inserting a protrusion of a mating portion of a connector 120-132 (for example, the protrusion 120cl of the third mating portion 120c of the head tube connector 120) into an internal space within a tube structure 102-118 (for example, the down tube 112). Once the tube structure 102-118 is connected to the connector 120-132, any internal conduit structures 140 connected to the same connector 120-132 are surrounded by and disposed within the tube structure 102-118 such that the internal conduit structures 140 are entirely located within the frame 100. In the embodiment shown, step 308 comprises connecting the tube structures 102-118 to the connectors 120-132 using an adhesive, although that is not essential. Step 310 of the method 300 optionally comprises disposing one or more layers of composite material over the frame 100. In the embodiment shown, step 310 comprises encapsulating or wrapping substantially the whole structure of the frame 100 in at least one layer of composite material. However, it will be appreciated only a part of the frame 100 may be covered with one or more layers of composite material, for example at least a part of the joint formed between the tube structures 102-118 and the connectors 120-132, for such that the layer(s) of composite material covers the connector 120-132 and also extends over the area at which each tube structure 102-118 is connected to the connector 120-130 to cover at least a part of each tube structure 102-118 connected to the connector 120-132. However, that is not essential. The one or more layers of composite material over the frame 100 may be formed by applying layers of pre-preg carbon fibre composite fabric over the frame 100 following a surface profile of the frame 100, and curing the layers in place on the frame 100 to form a finished composite material disposed over the frame 100. From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of bicycle frames, in particular composite bicycle frames, and which may be used instead of, or in addition to, features already described herein. Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The applicant hereby gives notice that new claims may be formulated to such features and / or combinations of such features during the prosecution of the present application or of any further application derived therefrom. For the sake of completeness, it is also stated that the term “comprising” does not exclude other elements or steps, the term “a” or “an” does not exclude a plurality, and any reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

1. A frame for a bicycle, comprising:a plurality of tube structures, each tube structure formed from a composite material;a connector to which the plurality of tube structures are connected to form a joint between adjacent tube structures in the frame; andan internal conduit structure disposed within at least one of the tube structures;wherein the connector comprises an internal passage extending through the connector; andwherein the internal conduit structure is connected to the connector such that the internal conduit structure and the internal passage of the connector form a continuous passage located internally within the frame.

2. The frame of claim 1, comprising at least one layer of composite material disposed over at least a part of the joint.

3. The frame of claim 2, wherein the at least one layer of composite material is disposed over at least a part of the joint at which each tube structure is connected to the connector.

4. The frame of claim 3, wherein the at least one layer of composite material is disposed over the joint such that the layer of composite material covers the connector and covers at least a part of each tube structure connected to the connector.

5. The frame of any preceding claim 1, wherein the composite material comprises a fibre reinforced composite material.

6. The frame of claim 5, wherein the composite material comprises a carbon fibre composite material.

7. The frame of any preceding claim, where the connector comprises a mating portion configured to engage each respective tube structure.

8. The frame of claim 7. wherein the mating portion comprises a protrusion configured to be received within the tube structure.

9. The frame of claim 8, wherein the mating portion comprises a shoulder or lip configured to limit travel of the protrusion within the tube structure.

10. The frame of any of claims 7 to 9, wherein the mating portions configured to engage different tube structures are arranged at an angle to one another.

11. The frame of any preceding claim, wherein the continuous passage formed by the internal conduit structure and the internal passage of the connector is isolated from an internal space of the tube structures.

12. The frame of any preceding claim, wherein the internal conduit structure is structurally separate from the tube structure within which the internal conduit structure is disposed.

13. The frame of any preceding claim, wherein the connector comprises a secondary mating portion configured to engage the internal conduit structure.

14. The frame of claim 13, wherein the secondary mating portion comprises a recess configured to receive a part of the internal conduit structure.

15. The frame of claim 14, wherein the recess comprises a shoulder or lip configured to limit travel of the internal conduit structure within the recess.

16. A kit of parts for forming a frame for a bicycle comprising:a plurality of pre-formed tube structures, each tube structure comprising a composite material;one or more connectors to which the tube structures are configured to be connected to form the frame; andan internal conduit structure configured to be connected to a connector such that: the internal conduit structure is disposed within a tube structure in use; and the internal conduit structure together with an internal passage of the connector form a continuous passage located internally within the frame in use .

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