WO2016081991A2

WO2016081991A2 - Lightweight composite bicycle wheels

Info

Publication number: WO2016081991A2
Application number: PCT/AU2015/050694
Authority: WO
Inventors: Jonathan PARTINGTON
Original assignee: 36T Pty Ltd
Priority date: 2014-11-27
Filing date: 2015-11-09
Publication date: 2016-06-02
Also published as: WO2016081991A3

Abstract

A rear hub, comprising: a hub tube coaxially rotatably mounted on a hub axle; a partially hollow drive body non-rotatably mounted part way along the hub tube to leave a hub tube extension portion; and a free hub body rotatably mounted on the hub tube extension portion by a sleeve bearing; wherein the free hub body is axially retained on the hub tube extension portion to partially underlie the drive body by a split ring receivable in opposing grooves in the drive body and the free hub body.

Description

LIGHTWEIGHT COMPOSITE BICYCLE WHEELS

Field

[0001 ] The present invention relates to lightweight composite bicycle wheels. Background

[0002] Bicycle wheels comprise a hub supported by spokes within a rim. The hub, spokes and rim components are increasingly made from carbon fibre composite materials to reduce weight and improve performance of bicycle wheels.

[0003] The use of composite materials for high performance bicycle wheels creates special problems because the competing attributes of lighter weight, stiffness, strength and durability need to be optimally balanced. In addition, construction techniques must be cost effective and economical because composite bicycle wheels are manufactured in lower volumes than conventional metal bicycle wheels.

[0004] In this context, there is a need for improved composite bicycle wheels that address the above problems.

Summary

[0005] According to the present invention, there is provided a rear hub, comprising: a hub tube coaxially rotatably mounted on a hub axle;

a partially hollow drive body non-rotatably mounted part way along the hub tube to leave a hub tube extension portion; and

a free hub body rotatably mounted on the hub tube extension portion by a sleeve bearing;

wherein the free hub body is axially retained on the hub tube extension portion to partially underlie the drive body by a split ring receivable in opposing grooves in the drive body and the free hub body.

[0006] The hub tube may be made of a carbon fibre composite material. [0007] The sleeve bearing may be made of a low-friction polymer material. The low- friction polymer material may comprise fluorinated ethylene propylene copolymer (FEP) or polytetrafluoroethylene (PTFE).

[0008] The split ring may be made of an abrasion-resistant polymer material. The abrasion-resistant polymer material may comprise polyetheretherketone (PEEK).

[0009] The hub tube may be coaxially rotatably mounted on the hub axle by first and second deep groove ball bearings adjacent first and second ends of the hub tube respectively.

[0010] The hub tube extension portion may terminate at the second end of the hub tube, wherein the hub tube is further rotatably supported on the hub axle by a full complement ball bearing closely adjacent to the second deep groove ball bearing.

[001 1 ] The rear hub may further comprise a one-way clutch unidirectionally rotatably connecting the free hub body to the drive body.

[0012] The one-way clutch may comprise teeth and ratchets provided on opposing surfaces of the drive body and the free hub body respectively.

[0013] The first and second ends of the hub tube may be fluidly sealed to the hub axle by first and second radial lip seals respectively.

[0014] The opposing surfaces of the drive body and the free hub body may be fluidly sealed together by a third radial lip seal.

[0015] The rear hub may further comprise oil lubrication of the one-way clutch, the sleeve bearing, the first and second deep groove ball bearings, and the full complement ball bearing.

[0016] The present invention also provides a method, comprising:

placing a plurality of elongate carbon fibres in a tube having a longitudinal axis and a circular cross section, wherein the plurality of elongate carbon fibres are aligned parallel with the longitudinal axis of the tube; introducing a matrix material into the tube to envelop the plurality of elongate carbon fibres;

compression moulding the tube to form an elongate composite member having a non-circular cross section comprising the plurality of elongate carbon fibres in the matrix material;

removing the tube from the elongate composite member.

[0017] The elongate composite member may comprise a spoke.

[0018] The non-circular cross section may be an elliptical cross section.

[0019] The present invention further provides a spoke made by the method described above.

[0020] The present invention also provides a method, comprising:

layering a plurality of unidirectional prepreg at mutually different angles to each other to form an elongate multiaxial preform;

reforming the elongate multiaxial preform into an elongate V-shaped channel; bladder moulding the elongate V-shaped channel in an annular mould to form a rim.

[0021 ] The method may further comprise depositing short fibres on individual ones of the plurality of unidirectional prepreg before layering.

[0022] The method may further comprise heating the individual ones of the plurality of unidirectional prepreg after depositing to recover tack thereof.

[0023] The short fibres may comprise short aramid fibres.

[0024] The method may further comprise assembling a plurality of the spokes described above with the rim, and curing the rim and the plurality of spokes together.

[0025] The present invention further provides a rim made by the method described above. [0026] The present invention also provides a bicycle wheel, comprising a plurality of the spokes described above bonded to the rim described above.

[0027] The bicycle wheel may further comprise the rear hub described above connected to the rim described above by the plurality of the spokes described above.

[0028] The present invention further provides a bicycle wheel comprising a symmetrical number of left and right spokes connecting a rim to a hub, wherein the symmetrical number of left and right spokes extend between the rim and the hub at asymmetrical left and right angles, and wherein the symmetrical number of left and right spokes comprise mouldings of composite material having asymmetrical surface area and cross sectional area, and asymmetrical strength and stiffness.

[0029] The left and right spokes may comprise a plurality of the spokes described above.

[0032] The present invention further provides a rim comprising composite material and two opposed sidewalls defining an internal annular cavity, wherein a water reservoir is annularly disposed within the internal annular cavity so that in use the two opposed sidewalls provide water cooled braking surfaces on and around the rim.

[0033] The rim may comprise the rim described above.

Brief Description of Drawings

[0034] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 is a partial section front view of a rear hub according to an embodiment of the invention;

Figure 2 is an exploded perspective view of the rear hub;

Figure 3 is an exploded perspective view of the hub tube and sleeve bearing of the rear hub;

Figure 4 is an assembled perspective view of the hub tube and sleeve bearing of the rear hub;

Figure 5 is a perspective view of a split ring of the rear hub; Figure 6 is a section front view of a front hub according to an embodiment of the invention;

Figures 7 to 12 schematically illustrate a method of making a spoke according to an embodiment of the invention;

Figure 13 is a front view of the spoke;

Figures 14 and 15 are detailed perspective views of the spoke;

Figures 16 to 18 schematically illustrate a method of making a rim according to an embodiment of the invention;

Figure 19 is a perspective view of a rear bicycle wheel assembled from the rear hub, spokes and rim of embodiments of the invention;

Figure 20 is a detailed perspective view of the rear hub and spokes; and

Figure 21 is a top plan view of an asymmetric rear bicycle wheel according to an embodiment of the invention.

Detailed Description

[0035] Figures 1 to 5 illustrate a rear hub 10 according to an embodiment of the invention. The rear hub 10 may comprise a hub tube 12 coaxially rotatably mounted on a hub axle 14. A partially hollow drive body 16 may be non-rotatably mounted part way along the hub tube 12 to leave a hub tube extension portion 18. A free hub body 20 may be rotatably mounted on the hub tube extension portion 18 by a sleeve bearing 22. The free hub body 20 may be axially retained on the hub tube extension portion 18 to partially underlie the drive body 16 by a split ring 24 that is receivable in opposing grooves in the drive body 16 and the free hub body 20.

[0036] The hub tube 12 may be made of a carbon fibre composite material. The hub tube 12 may comprise two superposed tubes - ie, inner and outer tubes - bonded together. The drive body 16 and free hub body 20 may be made of a lightweight metal, for example, aluminium. The sleeve bearing 22 may be made of a low-friction polymer material, for example, FEP or PTFE. The split ring 24 may be made of an abrasion- resistant polymer material, for example, PEEK. PEEK may be a preferred material because it has good mechanical properties, such as relatively high modulus, good abrasion resistance, coupled with good processability. Other equivalent materials may also be used for the components of the rear hub 10. [0037] Referring to Figure 5, the split ring 24 may have inherent tension or pre-bias tending to rest at a predetermined diameter, which may be equal to, or slightly less than, the root diameter of the corresponding groove in the free hub body 20. The split ring 24 may be contracted in diameter permissible by the split, and inserted into the corresponding groove in the drive body 16. Once installed, the split ring 24 may return to its natural diameter due to its inherent tension. A tapered feature on the leading side of the free hub body 20 acts as a lead to open the split ring 24 to a sufficiently large diameter so that upon assembly the split ring 24 expands to transition over the lead in of the free hub body 20, until it drops into the corresponding groove on the drive body 16. Disassembly may be possible through sacrifice of the split ring 24. A disassembly force may be applied exactly opposite in direction to assembly, but of much larger magnitude. The force may exceed the shear strength of the PEEK or other selected material at the median diameter of the split ring 24 so that it fails. The result may enable the free disassembly of the components, and opportunity to extract the split ring 24, which may then be in the form of two rings of half radial section of the original. The split ring 24 may represent a simple but effective method for retaining the free hub body 20 to the drive body 16.

[0038] The hub tube 12 may be coaxially rotatably mounted on the hub axle 14 by first and second deep groove ball bearings 26, 28 adjacent first and second ends 30, 32 of the hub tube 12 respectively. A spacer 33 may be provided on the first end 30 of the axle 14. The hub tube extension portion 18 may terminate at the second end 32 of the hub tube 12. The hub tube 12 may be further rotatably supported on the hub axle 14 by a full complement ball bearing 34 closely adjacent to the second deep groove ball bearing 28.

[0039] The combination of the deep groove ball bearings 26, 28 and the full complement bearing 34 may permit the hub tube 12 and free hub body 20 to rotate independently of the hub axle 14. On the first end 30 of the hub tube 12, the deep groove ball bearings 26 may react both radial and unidirectional axial loads. On the second end 32, the combination of the deep groove ball bearings 28 and the full complement bearing 34 may react radial, unidirectional axial, and transmission chain loads. This pairing of deep groove ball and full complement bearing 28, 34 may serve to increase the radial load capacity of the bearing system to maxima within the constraints of the package space. The free hub body 20 is mounted concentrically, and over a significant length of the hub tube 12, coupled by the low-profile polymer sleeve bearing 22. The free hub body 20 may be free to rotate relative to the hub tube 12, and may be constrained axially by the split ring 24 engaging into the drive body 16. The resulting larger bearing span of the hub tube 12 may increase lateral stiffness of a built bicycle wheel, reduces bearing loads product of lateral wheel loads, reduce bending moment on the hub axle 14, and reduce the number of rolling elements rotating under pedalling conditions. The polymer sleeve bearing 22 between the free hub body 20 and the hub tube 12 of the design may reduce cost and mass through elimination of additional rolling elements. The slender radial section of the polymer sleeve bearing 22 may enable both larger structural elements and larger rolling elements within the hub 10 improving stiffness, strength and durability, whilst enabling mass reduction.

[0040] The rear hub 10 may further comprise a one-way clutch 36 unidirectionally rotatably connecting the free hub body 20 to the drive body 16. The one-way clutch 36 may comprise teeth and ratchets provided on opposing surfaces of the drive body 16 and the free hub body 20 respectively.

[0041 ] The first and second ends 30, 32 of the hub tube 12 may be fluidly sealed to the hub axle 14 by first and second radial lip seals 38, 40 respectively. The opposing surfaces of the drive body 16 and the free hub body 20 may be fluidly sealed together by a third radial lip seal 42. The rear hub 10 may further comprise oil lubrication of the one-way clutch 36, the sleeve bearing 22, the first and second deep groove ball bearings, and the full complement ball bearing 34. Oil lubrication may advantageously reduce viscous drag and improve bearing life enabling downsizing of the bearings 26, 28, 34 for further mass saving, and extended bearing durability. Additionally, the oil lubrication may advantageously service the sleeve bearing 22 and the ratchet system of the one-way clutch 36 providing both tribological benefits and ratchet noise attenuation, while lubricating contacting seals 38, 40, 42 to reduce associated frictional drag.

[0042] Referring to Figures 19 and 20, the rear hub 10 may further comprise first and second spoke flanges 44, 46. The first spoke flanges 44 may be provided adjacent the first end 30 of the hub tube 12, and the second spoke flanges 46 may be provided on the drive body 16. [0043] Referring to Figure 6, a front hub 10A may have a generally similar construction and components to the rear hub 10, except that the drive body 16 and free hub body 20 on the second end 32 of the hub tube 12 may be replaced with a spacer 47, and the full complement bearing 34 may be omitted.

[0044] The rear hub 10 may be connected to a rim 58 by a plurality of spokes 60 bonded to the hub flanges 44, 46. Referring to Figures 7 to 12, the spokes 60 may be made comprise an elongate composite member 60 that is formed by placing a plurality of elongate carbon fibres 62 in a tube (or sleeve) 64 having a longitudinal axis and a circular cross section. The plurality of elongate carbon fibres 62 may be aligned parallel with the longitudinal axis of the tube 64. A matrix material, such as resin, may be introduced into the tube 64 to envelop the plurality of elongate carbon fibres 62. The tube 64 may then be compression moulded in a two-part mould 66 to form an elongate composite member 60 having a non-circular cross section, such as an elliptical cross section, comprising the plurality of elongate carbon fibres 62 in the matrix material. After curing, the tube 64 may then be removed from the elongate composite member 60 to leave the finished spokes 60. Referring to Figure 13, the elongate composite member 60 may formed in a flattened V-shape when viewed from the side to form a pair of spokes 60 inclined at an obtuse angle to each other. Referring to Figures 14 and 15 respectively, each spoke 60 may have an elliptical cross section and a tapered end 68. Although described in the context of spokes 60, the elongate composite member 60 formed by the method described above may have a wide variety of other lightweight, high performance applications, for example, as valve springs in high performance automotive engines.

[0045] The method described above may advantageously enable the production of tension spokes 60 with well controlled geometric form, and constituent material fraction attributes. The method may use a flexible, typically polymer, cylindrical sleeve tube 64 with a relatively thin wall, and low surface energy, such as to reduce chance of adhesion to the matrix material. Alternatively the sleeve 64 may be treated with a suitable release agent. Typically, in the relaxed condition, the sleeve 64 is nominally circular in shape where the ratio circumferential length o(r chord length) and cross sectional area are at their highest. Deformation from this shape to other shapes such as an ellipse will reduce the ratio, such as the chord length remains constant with reducing cross sectional area. With the sleeve 64 in the initial, nominal circular condition, aligned carbon fibres 62 (eg, fibre tows or yarns) are drawn through or inserted in the tube 64 to some useful length. The reinforcement may not necessarily be limited to aligned long fibres 62, but could be any constitution of long, short, woven, or unwoven reinforcements, including particulate fillers on a macro or micro level. The volume of the tube occupied by fibres 62 may be kept low, for example around less than 30%, to allow for resin infusion, but this may be varied depending on the proposed useful length.

[0046] A vacuum assisted resin transfer moulding (VARTM) method may be used to introduce the liquid resin matrix material into the reinforcement along the length of the tube 64. Once the matrix material has been introduced to the reinforcement, and before polymerization onset, the prepared sleeve(s) 64 should be transferred to a multiple piece matched mould 66 to define the desired shape. Deviation from the nominal circular shape of the sleeve 64 may be encouraged so that the previously quantified ratio may reduce. The reduction in the ratio may be inversely proportional to the fibre volume fraction, thus may be directly related to the fibre volume fraction of the end product 60. The ends of the sleeve 64 should be free to vent, bleed the surplus resin.

[0047] Excellent ordering and alignment of fibres may be achieved through drawing fibre 62 into the tube 64, infusing resin down the length of the tube 64, and bleeding of the resin upon tube 64 deformation. The method may enable manufacture of complex geometries, including very fine and particular detail. The process may maintain fibre 62 continuity from the first end to the second. Explicit definition of fibre volume fractions may be possible as a product of the geometric design of the compression moulding step.

[0048] The spokes 60 may be bonded to the rim 58 and the rear hub 10 via the first and second spoke flanges 44, 46 to form a rear bicycle wheel 100. Referring to Figures 16 to 18, the rim 58 may be formed by layering a plurality of unidirectional prepreg 70, 72, 74, 76, 78, 80, 81 at mutually different angles to each other to form an elongate multiaxial preform 82. For example, the plurality of unidirectional prepreg 70, 72, 74, 76, 78, 80, 81 may, be oriented at 0°, +45°, -45°, 90°, -40° to -60°, +40° to +60°. The elongate multiaxial preform 82 may be reformed by folding into an elongate V-shaped channel 82. The elongate V-shaped channel 82 may be bladder moulded in an annular mould to form the rim 58. A plurality of the spokes 60 may be assembled and cured together with the rim 58.

[0049] A multiaxial preform tape may be assembled using the multiple layers of unidirectional high-strength reinforcement, pre-impregnated (prepreg) with a resin matrix system 70, 72, 74, 76, 78, 80, 81 typically b-staged to present desirable 'tack' and handling properties. As illustrated in Figure 16, a multiaxial preform may be created by sequenced assembly of the unidirectional tape at angles ranging from +/- 0- 90°, and consolidated in its uncured state, using vacuum or other means, to provide a material superior in drape and handling than any of its individual and constituent components. The end preform may be described as a stitchless, non-crimp fabric. Strategic material placement may be implemented to optimise the mechanical performance of the laminate, almost entirely at the preform stage, simplifying mould lay- up.

[0050] The preform may be reformed into a V-shaped channel, and inserted along the periphery of an annular mould interior (not shown), and may be consolidated to the mould face either manually, or by following rollers. The preform may typically overlap at joints, in the preferred embodiment occurring after a full 360° deposition.

[0051 ] In a preferred embodiment, uncured, prepreg composite material 70, 72, 74, 76, 78, 80, 81 may be assembled into the mould, and the spokes 60 arranged in a periodic manner, which may be equal or unequal mutual spacing. Further layers of uncured prepreg may be placed to constitute either a finished or partly finished assembly. The assembly may then heated to cure the prepreg material, including simultaneous cohesion of the assembled spokes 60.

[0052] The use of unidirectional prepreg material 70, 72, 74, 76, 78, 80, 81 may present significant cost savings as it alleviates the expensive weaving process typical of most fabrics. Further, an increase fibre volume fraction may be possible with use of undirectional (ie, non-crimp) fabrics, and may manifest as a higher performing material. The formation of a tape preform may not be limited to short lengths, but may be a continuous process that feeds an automated tape-to-mould deposition process, largely automating manufacture. Automated manufacture may present very desirable cost saving opportunities, along with potential for increase product quality. The process of including the spokes 60 to embody a co-curing process may reduce the post processes such as trimming, drilling, cutting and bonding, whilst simultaneously optimising the joint interface between the spoke 60 and the rim 58.

[0053] Short fibres 84 may be deposited on the unidirectional prepreg 70, 72, 74, 76, 78, 80, 81 before layering to provide inter-layer reinforcement. The unidirectional prepreg 70, 72, 74, 76, 78, 80 may be heated after deposition of the short fibres 84 to recover their tack. The short fibres may, for example, comprise short aramid fibres. Other equivalent short fibres may also be used.

[0054] The assembly of the laminate patterns 70, 72, 74, 76, 78, 80, 81 described above may coincide with the deposition of short (eg, between about 1 mm and about 25 mm), randomly, but evenly placed tenacious fibres 84, such as aramid and the like. Such a process, also known as interleaving, may involve the deposition of such short fibres 84, inter-ply (or interposed between plies). The interleaving of short fibres 84 may improve the inter lamina fracture toughness, therefore impact tolerance of layered, long fibre composites comprising the rim 58. In addition, the short fibre 84 reinforcement may improve the fracture mechanics of failed laminates, by tethering fractured segments using fibrils interposed between the discreet lamina. The short fibres 84 may approach random orientation and offer some degree of inter-ply reinforcement in the orthogonal direction. The tenacity of the short fibres 84 may serve to tether fractured segments of a failed laminate, and retain some integrity, thus reducing the likelihood of exposed sharp edges. Although described in the context of the rim 58, the methods of short fibre inter-ply reinforcement and adherend bond-line preparation described above may have a wide variety of applications in other lightweight, high performance composite components.

[0055] The short aramid fibres 84 may be disposed on the surface of the adherend 70, 72, 74, 76, 78, 80, 81 to promote aramid fibrils as preparation for adhesive, as well as cohesive reinforcement. In one embodiment, deposition of aramid fibres 84 between about 1 mm and about 10 mm in length may be made on the intended bonded surface during manufacture of the component. Application of a peel ply may be retained as per usual bond surface preparation, but the use of a hot iron may be required to recover the surface tack of the material lost through the aramid fibre covering. The component may then be cured as per usual schedule, and the peel ply may be removed as preparation of the bond surface. This process may partially raise the short aramid fibre 84 forming short fibrils that are intended to penetrate some way into the adhesive layer.

[0056] In another embodiment, deposition of aramid fibres 84 between about 1 mm and about 10 mm in length may be made on the intended bonded surface during manufacture of the component. The component may then be cured as per usual schedule, and the bond surface prepared using shot, vapour or similar abrasive methods. Again, this process may partially raise the short aramid fibre 84 forming short fibrils that are intended to penetrate some way into the adhesive layer.

[0057] As discussed above, when applied to bonding composite substrates, the addition of short fibres 84 may improve cohesion of adhesive to the adherends, improving bond- line fracture toughness, and therefore improving impact tolerance of composite substrates. In addition, the short fibres 84 may mitigate in bond-line crack propagation by bridging of crack using fibrils interposed in the adhesive matrix material.

[0058] Although described in the context of the rim 58, the methods of short fibre inter- ply reinforcement and adherend bond-line preparation described above may have a wide variety of applications in other lightweight, high performance composite components.

[0059] Referring to Figures 19 and 21 , the bicycle wheel 100 may comprise a symmetrical number of left and right spokes 60 connecting the rim 58 to the rear hub 10. As best seen in Figure 21 , the symmetrical number of left and right spokes 60 may extend between the rim 58 and the rear hub 10 at asymmetrical left and right angles. The symmetrical number of left and right spokes 60 may have asymmetrical surface area and cross sectional area, and asymmetrical strength and stiffness.

[0060] In general, the bicycle wheel 100 may retain a bicycle tyre in place, provide braking surfaces, and provide attachment points for spokes 60. The wheel 100 may be subject to a variety of forces, including forces that are generated during acceleration, turning, braking, impacts as the tyre passes over variations in the terrain, forces exerted on the rim by the spokes and inflated tyre, and other forces. In addition to considering these forces in designing a wheel 100, for high performance applications, such as sprinting or bicycle racing, the mass, aerodynamics, and rotational inertia may also significant design considerations.

[0061 ] Additionally, to accommodate a number of gears, rear bicycle wheels 100 may be asymmetric (or dished). In an asymmetric wheel 100, the spokes 60 that connect the bicycle rim 58 to the hub 10 may have differences in length and tension. The asymmetry of the spokes 60 and the differences in spoke forces may directly influences the wheel performance and may lead to increased maintenance and reliability challenges.

[0062] Three principles may be described as methods for supporting the hub 10 concentric, and appropriately planar, to the rim 58.

1 . So-called disc wheels, in which the hub 10 may be supported at the centre of a disc, and the rim 58 may be supported by the outer diameter of the disc, of which is free from any inter-spaced apertures, and which may be flat sided or lenticular in shape, but not necessarily limited to these geometries.

2. The compression spoke rim uses stable spokes which do not buckle under compression loading, and transfer load from the rim portion to the hub portion through predominantly compressive components, although the spokes may also be capable of bearing bending, shear and tensile loads.

3. Tension spoke wheel supports the hub portion using typically slender spokes which may buckle under compression loading. However, the tension spokes are stable under tensile loading, and therefore the hub may be braced in relation to the rim in virtually all directions by means of balanced tensile loads, in a method that usually consists of multiple elements.

[0063] In the context of a tension spoke wheel 100, force vectors may be present and hold in equilibrium once the constituents are assembled. Different bracing angles may occur in wheels to accommodate gear clusters and/or disc brake rotors. The combined horizontal (y axis) components of the vectors from both left & right sides (-y and +y) may be equal for the wheel 100 to be in equilibrium. Horizontal force components may be expressed as a function of spoke tension F_Sp0ke, and spoke 'brace' angle G._y, Q_+y by the formula: F_y = F spoke si η(θ)

Similarly, stiffness may be expressed by the formula:

k_y = kspoke

[0064] As may be seen, the horizontal components are directly proportional to F_Sp0ke I kspoke and Θ. The packaging constraints of the wheel 100 may largely define G._y and θ₊y, and will be at maxima, thus differing from side-to-side (ie, left and right). To compensate for the side with a lesser Θ, spoke strength and stiffness need to be increased such that F._y = F_+y and k._y = k_+y.

[0065] Referring to Figures 19 and 21 , the spoke count in the wheel 100 may remain constant between left and right sides. The rationale is that the ratio of surface area to cross-sectional area reduces with any increase in spoke cross-sectional area for any constant shape. Thus, having the same number of larger spokes 60, less adversely impacts the aerodynamic performance of the wheel, both linearly and rotationally, in comparison to more spokes of a smaller cross-section. The symmetrical spoke counts between front and rear wheels may aid commonality of tooling and some laminate lay- up detail. Discreet increases in strength and stiffness of spokes 60 may be provided asymmetrically leading to balanced lateral behaviours with minimal aerodynamic impact on the wheel 100.

[0066] Referring to Figures 17 and 18, the rim 58 may comprise two opposed sidewalls 86, 88 defining an internal annular cavity 90. A water reservoir (not shown) may be annularly disposed within the internal annular cavity 90 so that in use the two opposed sidewalls 86, 88 provide water cooled braking surfaces on and around the rim 58. The water reservoir may be filled and vented by a combined fill and vent valve (not shown) provided in an upper surface of the rim 58.

[0067] Composite wheels, particularly carbon fibre wheels, have long been identified as having inferior braking characteristics, especially in comparison to their aluminium counterparts. This poor performance may be due to the following factors.

1 . The inherent lubricity of the carbon fibres may present a poor coefficient of friction. 2. The poor thermal conductivity of carbon-epoxy composites may lead to the poor dissipation of heat resulting in isolated hot regions - especially in thin laminates.

3. Hot regions may melt the elastomer-based friction material on to the braking surface resulting in deposits that result in uneven braking along the rim surface.

4. Hot regions may also cause softening of the polymer matrix material, which if exceeds a critical point, may cause wheel failure.

[0068] For example, competitors in bicycle races have measured peak brake surface temperatures of 220°C, which is in excess of the typical maximum glass transition temperature (Tg max) of epoxy polymers of between about 190°C and about 200°C. As a result, some conventional composite bicycle wheels use aluminium sub-structures to dissipate the heat through its improved thermal conductivity.

[0069] In embodiments of the present invention, a small volume of water, for example about 100 cc, potentially modified with some additive, may be retained within a cavity within the rim 58 of the wheel 100. The specific heat of water at 50°C and 1 atm is 4.18 J/g-°C (ie, 4.65 x more than aluminium (Alu), 3.7 x more than carbon fibre). The energy required to heat 100 g of water from 20°C to 100°C, would heat an equivalent mass of aluminium to 393°C, or carbon fibre to 350°C (specific heat of Alu 6061 is 0.896 J/g-°C; specific heat of carbon epoxy is 1 .13 J/g-°C). Further, the enthalpy of vaporization - 2257 J/g at 100°C and 1 atm - extends the potential thermal capacity of water by 225700J (ie, turning all the water to steam).

[0070] The poor thermal conductivity of water is compensated for by the dynamic mixing of the fluid, which would especially occur under braking when the inertia of the water would cause a differential in speed relative to the wheel 100 as it decelerates. The mobility of the water inside the wheel 100 may also permit the transfer of thermal energy to a larger proportion of the surface of the wheel 100, improving the rejection of heat to the atmosphere (thermal conductivity of water is 0.643W/m-K; thermal conductivity of Alu 6061 is 180W/m-K; thermal conductivity of carbon epoxy is 78.8W/m-K; and thermal conductivity of air is 0.027W/m-K). [0071 ] The viscous coupling of the water mass to solid mass of the wheel 100 may allow for a more responsive rigid structure, as the mass of water is somewhat decoupled from the rigid mass of the wheel 100. A further benefit of the water reservoir is the opportunity to tune the thermal mass of the wheel dependent on riding conditions, such that the rider need not incur a mass penalty in conditions that would not require the higher thermal mass.

[0072] Embodiments of the present invention provide lightweight, high performance composite bicycle wheels (both front and rear) that effectively balance the competing attributes of lighter weight, stiffness, strength and durability. Embodiments of the invention also provide cost effective and economical construction techniques for lightweight, high performance composite bicycle wheels.

[0073] For the purpose of this specification the word "comprising" means "including but not limited to", and the word "comprises" has a corresponding meaning.

[0074] The above embodiments have been described by way of example only and modifications are possible within the scope of the claims that follow.

Claims

1 . A rear hub, comprising:

a hub tube coaxially rotatably mounted on a hub axle;

2. The rear hub of claim 1 , wherein the hub tube is made of a carbon fibre composite material.

3. The rear hub of claim 1 or 2, wherein the sleeve bearing is made of a low-friction polymer material.

4. The rear hub of claim 3, wherein the low-friction polymer material comprises fluorinated ethylene propylene copolymer (FEP) or polytetrafluoroethylene (PTFE).

5. The rear hub of any preceding claim, wherein the split ring is made of an abrasion-resistant polymer material.

6. The rear hub of claim 5, wherein the abrasion-resistant polymer material comprises polyetheretherketone (PEEK).

7. The rear hub of claim 6, wherein the hub tube is coaxially rotatably mounted on the hub axle by first and second deep groove ball bearings adjacent first and second ends of the hub tube respectively.

8. The rear hub of claim 7, wherein the hub tube extension portion terminates at the second end of the hub tube, and wherein the hub tube is further rotatably supported on the hub axle by a full complement ball bearing closely adjacent to the second deep groove ball bearing.

9. The rear hub of claim 8, further comprising a one-way clutch unidirectionally rotatably connecting the free hub body to the drive body.

10. The rear hub of claim 9, wherein the one-way clutch comprises teeth and ratchets provided on opposing surfaces of the drive body and the free hub body respectively.

1 1 . The rear hub of any one of claims 7 to 10, wherein the first and second ends of the hub tube are fluidly sealed to the hub axle by first and second radial lip seals respectively.

12. The rear hub of claim 1 1 , wherein the opposing surfaces of the drive body and the free hub body are fluidly sealed together by a third radial lip seal.

13. The rear hub of any one of claims 9 to 12, further comprising oil lubrication of the one-way clutch, the sleeve bearing, and the first and second deep groove ball bearings.

14. A method, comprising:

placing a plurality of elongate carbon fibres in a tube having a longitudinal axis and a circular cross section, wherein the plurality of elongate carbon fibres are aligned parallel with the longitudinal axis of the tube;

introducing a matrix material into the tube to envelop the plurality of elongate carbon fibres;

removing the tube from the elongate composite member.

15. The method of claim 14, wherein the elongate composite member comprises a spoke.

16. The method of claim 14 or 15, wherein the non-circular cross section is an elliptical cross section.

17. A spoke made by the method of claim 15 or 16.

18. A method, comprising:

19. The method of claim 18, further comprising depositing short fibres on individual ones of the plurality of unidirectional prepreg before layering.

20. The method of claim 19, further comprising heating the individual ones of the plurality of unidirectional prepreg after depositing to recover tack thereof.

21 . The method of claim 19 or 20, wherein the short fibres comprise short aramid fibres.

22. The method of any one of claims 18 to 21 , further comprising assembling a plurality of the spokes of claim 17 with the rim, and curing the rim and the plurality of spokes together.

22. A rim made by the method of any one of claims 18 to 20.

23. A bicycle wheel, comprising a plurality of the spokes of claim 17 bonded to the rim of claim 22.

24. The bicycle wheel of claim 23, further comprising the rear hub of any one of claims 1 to 13 connected to the rim of claim 22 by the plurality of the spokes of claim 17.

25. A bicycle wheel comprising a symmetrical number of left and right spokes connecting a rim to a hub, wherein the symmetrical number of left and right spokes extend between the rim and the hub at asymmetrical left and right angles, and wherein the symmetrical number of left and right spokes comprise mouldings of composite material having asymmetrical surface area and cross sectional, and asymmetrical strength and stiffness.

26. The bicycle wheel of claim 25, wherein the left and right spokes comprise a plurality of the spokes of claim 17.

27. A rim comprising composite material and two opposed sidewalls defining an internal annular cavity, wherein a water reservoir is annularly disposed within the internal annular cavity so that in use the two opposed sidewalls provide water cooled braking surfaces on and around the rim.

28. The rim of claim 27, wherein the rim comprises the rim of claim 22.