Foldable bicycle

Abstract

A folding bicycle comprising a rear wheel 4 comprising a rear wheel axle 41, and an axle guide 9 attached to a seat stay and / or chain stay of the bicycle. The axle 41 is movable along the axle guide 9

Description

FOLDABLE BICYCLE Technical Field The present disclosure relates to bicycles, and particularly, but not exclusively, foldable bicycles. Background Foldable bicycles are a popular method of transport, especially for commuters. Foldable bicycles have an unfolded configuration in which the bicycle can be ridden by the user and a folded configuration in which at least one dimension, usually the height and length, of the bicycle is reduced to allow easier storage and / or carrying of the bicycle. Foldable bicycles usually incorporate hinges and / or other mechanisms to enable the user to fold and unfold the bicycle. The reduced dimension(s) of the folded configuration allows a user to carry a foldable bicycle in places where a standard bicycle would be impractical, for example, on public transport, into the home or office, or in a private vehicle. So, a foldable bicycle can be used for many journeys for which a standard bicycle would not be suitable. Journeys made by bicycle reduce the use of other forms of transport such as cars, buses and other vehicles which may emit pollutants. Thus, foldable bicycles are a practical and environmentally friendly mode of transport. Summary There is provided a foldable bicycle comprising: a foldable bicycle frame comprising a seat tube, a head tube and a top tube connecting the seat tube and the head tube, and a brace member having a first end and a second end, the first end of the brace member being connected to the bicycle frame and the second end of the brace member being releasably attachable to the bicycle frame. The brace member provides the advantage of adding strength and rigidity to the foldable bicycle frame when it is attached to the bicycle frame at the second end. The brace member may be elongate. The ends of the brace member may comprise regions of the brace member proximate the ends and may not be restricted to end surfaces of the brace member. Each end may comprise a region of the brace member proximal to a respective end surface of the brace member. For example, the first end may comprise a first end surface and the adjacent 5, 10 or 20% of the brace member. The second end may comprise a second end surface and the adjacent 5, 10 or 20% of the brace member. The brace member may be movably connected to the bicycle frame at the first end, meaning that the brace member is connected to the bicycle frame and can move relative to the bicycle frame. For example, the brace member may be pivotally connected to the bicycle frame at the first end, such that the brace member can pivot about a point on the bicycle frame. The foldable bicycle frame may be foldable between an unfolded configuration and a folded configuration. The second end of the brace member may be releasably attachable to the bicycle frame in the unfolded configuration. The attachment of the second end of the brace member to the bicycle frame may retain the bicycle frame in its unfolded configuration. The second end may be releasably attachable to the bicycle frame via a locking means which holds the second end against the bicycle frame. The locking means may comprise a hand Screw. The brace member may comprise two twin rods. The two twin rods may have substantially the same dimensions as each other. The twin rods may be connected to the bicycle frame and to each other at the first end of the brace member. The twin rods may be parallel to one another. The twin rods may be connected to opposite sides of the bicycle frame. It will be appreciated that the term “rod” is to be interpreted broadly to include bars, poles, or other elongate members whether hollow or solid, and irrespective of cross-sectional shape. The brace member may further comprise a cross pin, the cross pin being connected to each of the twin rods at the second end of the brace member. The locking means may comprise a clamping mechanism operable to clamp the bicycle frame between the twin rods at the second end of the brace member. The hand screw may comprise the cross pin of the brace member. The locking means may comprise a slot in the bicycle frame, the slot being sized to receive the cross pin. The slot may be in a top surface of the top tube. The locking means may further comprise interlocking shapes on the second end of the brace member and bicycle frame. The interlocking nature of the shapes ensure correct location of the brace member when the brace member is attached to the bicycle frame at the second end. The second end of the brace member may comprise a V-shape and the bicycle frame may comprise a shape with a V hollow matching the V-shape of the brace member. In this way, the V-shape of the brace member may be inserted into the V hollow to secure the brace member in the correct position in relation to the bicycle frame. In a similar way to a clamshell, these shapes interlock to ensure the brace member and top tube sections of the bicycle frame are properly located and firmly closed together, thus reducing vibrations or wobbles of the parts. The brace member may be a steel brace member. The twin rods may be formed of steel. The bicycle frame may be a steel bicycle frame. The first end of the brace member may be connected to the bicycle frame at a position below the top tube. The first end of the brace member may be connected to the seat tube. The first end of the brace member may be connected to the bottom of the seat tube, for example directly or by another component of the bicycle frame, such as a bottom bracket shell. The first end of the brace member may be connected to the bicycle frame in a position in front of a bottom bracket of the bicycle. The second end of the brace member may be releasably attachable to the bicycle frame on top of the top tube. The brace member may be pivotable from a position in which the second end is attachable to the top tube to a position in which the brace member extends alongside the seat tube. The bicycle frame may comprise a top tube hinge. The hinge may be between a first section of the top tube of the bicycle frame and a second section of a top tube of the bicycle. The top tube hinge may be mounted with its pivot axis horizontal and such that the second section of the top tube of the bicycle may be folded on top of the first section of the top tube. The first section of the top tube may be attached to the seat tube. The top tube hinge may have an angular range of 180 degrees. The top tube hinge may be referred to as the first top tube hinge. The second end of the brace member may be releasably attachable to the second section of the top tube. In this way, the top tube hinge is located on the bicycle frame in a place that is between the connection of the first end of the brace member to the seat tube of the bicycle frame and the releasable attachment of the second end of the brace member. The bicycle frame may comprise a second top tube hinge. The second top tube hinge may be between the second section of the top tube and a third section of the top tube. The third section of the top tube may be attached to the head tube. The second top tube hinge may have an angular range of 180 degrees. The second top tube hinge may be mounted with its pivot axis horizontal and such that the second section of the top tube of the bicycle may be folded beneath the third section of the top tube. In this way, the top tube may be folded in a Z shape, with the third section folding on top of the second section and the second section folding on top of the first section. Having two top tube hinges advantageously decreases the length of the top tube in the folded configuration. The first section may be a seat section of the top tube and may be attached to the seat tube. The second section may be a middle section of the top tube. The third section may be a head section of the top tube and may be attached to the head tube. In an alternative arrangement, the first end of the brace member may be connected to the head tube of the bicycle frame, rather than the seat tube and the first section of the top tube may be attached to the head tube of the bicycle frame, rather than the seat tube. In this way, the top tube hinge(s) and brace member are mounted the opposite way around, but operate in the same manner. Optionally, the first end of the brace member may be attached to the head tube via a bracket on the head tube. The brace member may be pivotally attached to the bracket on the head tube, such that the brace member pivots about its attachment to the bracket. The brace member may be pivotable from a position in which the second end is attachable to the top tube to a position in which the brace member extends alongside the head tube of the bicycle frame. The first section of the top tube may be a head section of the top tube and may be attached to the head tube. The second section of the top tube may be a middle section of the top tube. The third section of the top tube may be a seat section of the tube and may be attached to the seat tube. The head tube and / or top tube and / or seat tube may have a square sectional shape. This reduces difficulty of manufacture and brings down both material and manufacturing costs. The tube sections can be more easily cut by laser and workholding is much easier than with round tubing, facilitating a more simplistic and cost-effective tooling and fixture setup. The top tube and / or head tube and / or seat tube may be straight thus enabling a tighter, more compact Z-shaped fold. This also means that main tube sections do not have to be bent to shape. Further, this means that hinges do not have to be made from machined castings or to be joined to the frame using an autobraze machine. This allows production time savings and removes capacity bottlenecks from the process. The top tube may comprise a head section, a middle section and a seat section, the seat section being attached to the seat tube, the middle section being pivotally attached via a first top tube hinge to the seat section and pivotally attached via a second top tube hinge to the head section, and the head section being attached to the head tube. Thus the first section as discussed above may be the head section, the second section may be the middle section and the third section may be the head section. There is further provided a foldable bicycle comprising: a seat tube, a head tube and a top tube connecting the seat tube and the head tube, wherein the top tube comprises a head section, a middle section and a seat section, the seat section being attached to the seat tube, the middle section being pivotally attached via a first top tube hinge to the seat section and pivotally attached via a second top tube hinge to the head section, and the head section being attached to the head tube. The first top tube hinge and the second top tube hinge may be mounted with parallel pivot axes. In this way, the top tube may be folded in one plane which is an efficient folding shape. The first top tube hinge and the second top tube hinge may have opposite pivot directions. In this way, the top tube may be folded into a Z shape. This is an efficient use of space in the folded configuration of the bicycle. The first and / or second top tube hinges may be mounted with their pivot axes horizontal, such that folding takes place in a vertical plane. The first top tube hinge may have an angular range of 180 degrees. The second top tube hinge may have an angular range of 180 degrees. The first top tube hinge may be mounted with its pivot axis horizontal and such that the middle section of the top tube may be folded on top of the seat section of the top tube. The second top tube hinge may be mounted with its pivot axis horizontal and such that the middle section of the top tube of the bicycle may be folded beneath the head section of the top tube. In this way, the top tube may be folded in a Z shape, with the head section folding on top of the middle section and the middle section folding on top of the seat section. The bicycle may further comprise a locking means to lock one or more of the hinges in their unfolded positions. For example, a hinge lock which may comprise a hand screw may be provided. The top tube may comprise a lateral hinge with an upright pivot axis. The lateral hinge may have an angular range of 180 degrees. The lateral hinge enables the top tube to be folded laterally so that the rear and front wheels are alongside one another. In embodiments utilising a brace member and a lateral hinge, the brace member may ensure that the lateral hinge remains closed while the bicycle is in the unfolded configuration, thereby providing extra safety for the user, especially while riding the bicycle. The lateral hinge may be in the seat section of the top tube. The lateral hinge may have a pivot direction that causes the front of the bicycle to pivot towards the side of the bicycle frame on which a chain ring is mounted. For example, if the chain ring is mounted on the right of the bicycle frame, the front of the bicycle may pivot towards the right of the bicycle when the lateral hinge is opened. In this way, when the lateral hinge is opened and the front of the bicycle is folded towards the back, the front wheel of the bicycle may protect the chain ring and / or other chain components from being knocked during storage or carrying. Beneficially, the dirty chain is kept away from a user's clothing. The head tube may comprise a head tube hinge between the attachment of the head tube to the top tube and the handlebars. The head tube hinge may have an angular range of 180 degrees. The hinge may be mounted on the head tube to allow folding of the handlebars in a backwards direction and to one side of the bicycle. The pivot direction may be diagonal with respect to the head section of the top tube. This enables the handlebars to be folded down outside of the rest of the folded bicycle. The hinge may be mounted with a diagonal pivot axis. The pivot axis of the hinge may be offset from a lateral orientation in a direction opposite the pivot direction of the lateral hinge. The offset may be 45 degrees. The pivot axis may also be offset from the horizontal plane. The seat tube may comprise a seat post release mechanism. This allows the user to slide the seat post down into the seat tube, so the saddle moves towards the seat tube. There is further provided a foldable bicycle comprising: a rear wheel comprising an axle, an axle guide attached to a seat stay and / or chain stay of the bicycle, wherein the axle is movable along the axle guide from an unfolded position towards a seat tube of the bicycle. In this way, the axle is movable along the axle guide between a folded position and an unfolded position, the folded position being closer to a seat tube of the bicycle than the unfolded position. In this way, the rear wheel may be moved towards the seat tube to shorten the length of the bicycle in its folded position. This means that a compact folded position can be achieved while also providing a large wheelbase while riding. The axle guide may comprise a rail or slot, along which the axle may move, for example by sliding. The axle may be on the rail or through the slot, either directly or via an engagement member. The engagement member may be part of the axle or part of the chain tensioner, for example, part of the guide pulley arm. The axle guide may comprise a left-side guide comprising a rail or slot which is attached to the left seat and / or chain stay and a right-side guide comprising a rail or slot which is attached to the right seat and / or chain stay. This provides better and more even support for the axle during folding and unfolding. One of the side guides may be sized to accommodate only the axle and the other side of the axle guide may be sized to accommodate a guide engagement member. The axle may be movable along the axle guide from an unfolded position towards a seat tube of the bicycle and downwards relative to the chain and / or seat stays. The axle guide may be L shaped such that the axle is moveable relative to the chain and / or seat stays in a downwards direction from its unfolded position and then in a direction toward the front of the bicycle. The downwards movement of the rear wheel drops it clear of the brake blocks, and also has the advantage that the bicycle may be rolled along on the rear wheel whilst folded. The vertical portion of the L-shaped axle guide also ensures precision in terms of the axle positioning (locked at the top of the guide) when the bicycle is unfolded. This avoids the natural tendency of rear axles to move upwards and forwards during use of a bicycle if they are not well-contained. The corner of the L shape of the axle guide may be curved. The axle may be movable downwards relative to the chain and / or seat stays by at least the radial distance between a braking surface of the rear wheel and the outside edge of a tyre of the rear wheel. The braking surface is a part of the wheel which is contacted by the brakes when the brakes are actuated. The braking surface may be the rim of the wheel. In this way, the wheel may be moved down by a distance that allows the rear wheel to move out of contact with the rear brake calipers. The axle may have a release mechanism which may be a quick release lever. The release mechanism may have a closed position in which the axle is clamped against the axle guide and an open position in which the axle is movable along the axle guide. In this way, the user may quickly open the mechanism, move the axle to the folded position and may then close the mechanism to secure the axle in its folded position to ensure that the folded position is retained while the user carries or stores the bicycle. The bicycle may comprise seat stays and chain stays, each of which extend backwards from the seat tube and meet at the rear end of the axle guide. The seat stays may extend in an upwards and forwards direction from the rear end of the axle guide by a distance greater than the radius of the wheel and then forwards to the seat tube. Brake calipers may be located on the seat stays in a position forwards and / or downwards of the seat stays. In this way, they may be protected from being knocked when the bicycle is in its folded configuration. The rear brake caliper may be front-facing so that, when folded, the brake blocks are not exposed rearwardly beyond the seat stays, and therefore are not susceptible to being knocked out of alignment. The axle may be moveable forwards by a distance substantially the same as or greater than the radius of the wheel. In this way, the wheel may be protected by the seat stays when the bicycle is in its folded configuration. The bicycle may comprise a rear brake caliper release mechanism. This allows the brake calipers to be separated to allow the rear tyre to move through the calipers when moving to the folded position without knocking or bending the calipers. The rear brake caliper release mechanism may have a quick release opening function. The rear brake caliper release mechanism may be a handlebar-mounted cable release. There is further provided a foldable bicycle comprising: a rear wheel comprising a rear wheel axle, a chain ring, a drive chain and, a chain tensioner, wherein the chain tensioner comprises: a tensioner pulley arm pivotally attached to the rear wheel axle, the tensioner pulley arm being biased away from the chain ring of the bicycle under spring torsion, and a guide pulley arm attached to the rear axle, extending forwardly and / or downwardly from the axle, and being fixedly attached to a square profile engagement member which slides in an axle slot of the bicycle frame. Both guide pulley and tensioner pulley can rotate freely. A quick-release wheel nut, a chain tensioner, and an anti-rotating sliding axle guide may be provided by a single component. There is provided a foldable bicycle comprising: a rear wheel comprising an axle, an axle guide attached to a seat stay and / or chain stay of the bicycle, wherein the axle is movable along the axle guide between a folded position and an unfolded position, the folded position being closer to a seat tube of the bicycle than the unfolded position, a chain ring, a drive chain, a guide engagement member coupled to the axle and positioned in the axle guide, and, a chain tensioner, wherein the chain tensioner comprises: a tensioner pulley arm pivotally attached to the guide engagement member, the tensioner pulley arm being biased away from the chain ring of the bicycle, and a guide pulley arm attached to the guide engagement member. In this way, when the rear wheel is moved forwards for folding the bicycle, the tensioner pulley arm pivots rearwards to retain tension on the drive chain and retain the drive chain on the tensioner pulleys / jockey wheels, sprocket / s and chainring. The guide pulley arm cannot rotate and so maintains tension between the guide pulley and the tensioner pulley. The chain tensioner may comprise a spring configured to bias the tension pulley arm away from the chain ring. The tensioner pulley arm is free to rotate under spring torsion to keep the drive chain on the tensioner pulleys / jockey wheels, sprocket / s and chainring when the rear wheel is moved forwards, closer to the chainring. The chain tensioner may comprise the guide engagement member. The chain tensioner may have a square profile to slide in an axle guide of the bicycle. The axle guide may comprise a long slot in the frame. The square profile may be a guide engagement member configured to slide in the axle guide. The guide pully arm may be fixedly attached to the guide engagement member, such that rotation of the guide engagement member causes rotation of the guide pulley arm. The axle may be positioned through a hole in the engagement member. The guide engagement member may have a square shaped profile configured to slide along the axle guide. As discussed above, the guide engagement member may be part of the axle or part of the chain tensioner, for example, part of the guide pulley arm. The engagement member and axle guide may be sized to restrict rotation of the engagement member within the axle guide such that the engagement member rotates through a quarter turn as the axle moves through the curved corner of the axle guide. For example, the width from side to side of a square profile engagement member may be smaller than a width of an axle guide slot in which the engagement member slides and the diagonal width of the square profile between opposite corners may be greater than the slot width. In this way, the square profile cannot spin within the slot. The chain tensioner is attached to the axle and so moves with the wheel when the axle is moved along the axle guide. The pivoting of the tensioner pulley arm has the additional advantage of keeping the tensioner higher off the ground, avoiding impacts with kerbs and dirt ingress. The above-described bicycles have an extremely compact folded configuration and can still have a full-length wheelbase once unfolded, thus providing a very practical bicycle. The guide pulley arm may be positioned inside of the axle guide. The tension pulley arm may be coupled to the axle outside of the axle guide. There is further provided a method of folding a bicycle as described above, the method comprising: moving the rear wheel forwards, and / or folding the top tube, and / or opening the lateral hinge to fold the front of the bicycle to the back, and / or folding the handlebars down wards towards the front wheel, and / or lowering the seat post. Moving the rear wheel forwards may comprise one or more of: opening the rear wheel release lever, opening the rear brake calipers with a rear brake caliper release mechanism, moving the rear wheel axle along the axle guide downwards to allow the rear tyre to clear the brake calipers and forwards to shorten the bicycle. Folding the top tube may comprise one or more of: loosening a hand screw on the second end of the brace member, pivoting the brace member so that the second end of the brace member moves from the top tube to a position where the brace member extends alongside the seat tube, folding the middle section of the top tube with respect to the seat section and the head section by pivoting the first top tube hinge and the second top tube hinge, this may be achieved by moving the head tube, handlebars and front wheel assembly upwards and closer to the seat tube. Opening the lateral hinge to fold the front of the bicycle to the back may comprise one or more of: opening a hinge clip or locking catch on the lateral hinge, folding the bicycle by moving the front and rear ends of the bicycle towards each other so that the front wheel is situated next to the rear wheel. Folding the handlebars down wards towards the front wheel may comprise one or more of: opening a hinge clip or locking catch on the head tube hinge, folding the handlebars downward until they are next to the front wheel. Lowering the seat post may comprise one or more of. opening the seat post release mechanism, lowering the saddle and seat post into the seat tube, closing the seat post release mechanism. Unfolding the bicycle may require performing the opposite of the above actions, taking care to close the rear brake release lever before riding. There is provided a method of unfolding a bicycle as described above, the method comprising: raising the seat post, and / or folding the handlebars upwards into an upright position and / or closing the lateral hinge to unfold the front of the bicycle, and / or unfolding the top tube, and / or moving the rear wheel backwards. Moving the rear wheel backwards may comprise one or more of: opening the rear wheel release lever, moving the rear wheel axle along the axle guide rearwards to lengthen the bicycle and upwards to allow the brake calipers to align with the braking surface of the wheel, closing the rear wheel release lever, closing the rear brake calipers with the rear brake caliper release mechanism. Unfolding the top tube may comprise one or more of: unfolding the middle section of the top tube with respect to the seat section and the head section by pivoting about the first top tube hinge and the second top tube hinge to straighten the top tube. This may be achieved by moving the head tube, handlebars, and front wheel assembly upwards and away from the seat tube, pivoting the brace member so that the second end of the brace member moves onto the locking means of the top tube, tightening the hand screw on the second end of the brace member. Closing the lateral hinge to unfold the front of the bicycle may comprise one or more of: unfolding the bicycle by moving the front end of the bicycle away from the rear end of the bicycle, closing a hinge clip or locking catch on the lateral hinge. Folding the handlebars upwards into an upright position may comprise one or more of: folding the handlebars upward to close the head tube hinge, and closing a hinge clip or locking catch on the head tube hinge. Raising the seat post may comprise one or more of: opening the seat post release mechanism, raising the saddle and seat post, and closing the seat post release mechanism. In this application, directional terms such as forward, rearward, front, rear, above, below, left, right and others may be referred to. These terms are to be given their normal meaning and understood as relative to the bicycle and its components in its unfolded, upright riding position. For example, when discussing the top tube of the bicycle, the head tube is forward of the top tube and the seat tube is rearward of the top tube. Further, the left handlebar is that which would be held by a cyclist with their left hand while riding the bicycle. The optional features described above are equally applicable to all of the described bicycles and methods and are not limited to the particular bicycle / method with which they are described here. Further, the bicycles and methods described above may be combined in any possible combination. In particular, an essential feature of any aspect is understood to be an optional feature of any other aspect. For example, a bicycle according to this disclosure may comprise: (1) a foldable bicycle frame comprising a seat tube, a head tube and a top tube connecting the seat tube and the head tube, and a brace member having a first end and a second end, the first end of the brace member being connected to the bicycle frame and the second end of the brace member being releasably attachable to the bicycle frame, and / or the bicycle may comprise: (2) a seat tube, a head tube and a top tube connecting the seat tube and the head tube, wherein the top tube comprises a head section, a middle section and a seat section, the seat section being attached to the seat tube, the middle section being pivotally attached via a first top tube hinge to the seat section and pivotally attached via a second top tube hinge to the head section, and the head section being attached to the head tube, and / or the bicycle may comprise: (3) a rear wheel comprising an axle, an axle guide attached to a seat stay and / or chain stay of the bicycle, wherein the axle is movable along the axle guide from an unfolded position towards a seat tube of the bicycle, and / or the bicycle may comprise: (4) a rear wheel comprising a rear wheel axle, a chain ring a drive chain and, a chain tensioner, wherein the chain tensioner comprises: a tensioner pulley arm pivotally attached to the rear wheel axle, the tensioner pulley arm being biased away from the chain ring of the bicycle under spring torsion, and a guide pulley arm attached to the rear axle, extending downwardly and / or forwardly from the axle. The guide pulley arm may be fixedly attached to the rear axle, or (5) the bicycle may comprise: a chain ring, a drive chain and, a chain tensioner, wherein the chain tensioner comprises: a guide engagement member coupled to the axle and positioned in the axle guide, a tensioner pulley arm pivotally attached to the guide engagement member, the tensioner pulley arm being biased away from the chain ring of the bicycle, and a guide pulley arm attached to the guide engagement member. Further, the bicycles of this disclosure have been described by referring to a chain driven bicycle, but the invention described is equally applicable to a belt-driven bicycle. As such, throughout the application, where the term “chain” is used, it should be interpreted to include a belt-type chain. The term “chain” may be interpreted as “chain or belt”. In such embodiments, the chain stay may be a belt stay in a belt-driven bicycle, the chain ring may be a belt ring, the drive chain may be a belt, the chain tensioner may be a belt tensioner. Further features and advantages of the aspects of the present disclosure will become apparent from the claims and the following description. Brief Description of Drawings Embodiments of the present disclosure will now be described by way of example only, with reference to the following diagrams, in which:- Fig. 1 is a side view of a foldable bicycle in its unfolded configuration; Figs. 2A to 2E are side views of the foldable bicycle of Fig. 1 in the unfolded configuration (2A), a fully folded configuration (2E) and partially folded configurations (2B to 2D); Fig. 3 is a perspective left side view of a brace member and top tube of the bicycle of Fig. 1; Fig. 4 is a perspective right side view of the brace member and top tube of Fig, 3; Fig. 5 is a perspective top view of the brace member in its folded position; Fig. 6 is a side view of the bicycle of Fig. 1 in the partially folded configuration shown in Fig. 2B; Fig. 7 is a side view of the bicycle of Fig. 1 in the partially folded configuration shown in Fig. 2C; Fig. 8 is a perspective view of the bicycle of Fig. 1 in the partially folded configuration shown in Fig. 2C; Fig. 9 is a perspective view of the bicycle of Fig. 1 in the partially folded configuration shown in Fig. 2D; Fig. 10 is a perspective view of the bicycle of Fig. 1 in the fully folded configuration shown in Fig. 2E; Fig. 11 is a perspective view of part of a foldable bicycle frame; Fig. 12 is an exploded view of an axle and chain tensioner of a foldable bicycle; and Fig. 13 is a rear view of the axle and chain tensioner of Fig. 12 installed on the frame of Fig. 11. Detailed Description A number of different embodiments of the disclosure are described subsequently. Fig. 1 shows a foldable bicycle 1 having a foldable steel bicycle frame 2, front wheel 3, rear wheel 4, handlebars 5, seat post 6 and saddle 7. The bicycle frame 2 has a seat tube 21, a head tube 22 and a top tube 23 connecting the seat tube and the head tube. The bicycle frame also has seat stays 24 and chain stays 25. The bicycle 1 also has a brace member 8 having a first end 8a and a second end 8b, the first end of the brace member being connected to the bicycle frame and the second end of the brace member being releasably attachable to the bicycle frame. In Fig. 1, the second end 8b of the brace member is attached to the top tube 23 of the bicycle frame by locking means. The bicycle frame has a first top tube hinge 231. The hinge 231 is between a seat section 23a of the top tube and a middle section 23b of the top tube. The top tube hinge is mounted with its pivot axis horizontal and such that the middle section 23b of the top tube may be folded on top of the seat section 23a of the top tube. The seat section is attached to the seat tube 21. The bicycle frame also has a second top tube hinge 232. The second top tube hinge 232 is between the middle section 23b of the top tube and a head section 23c of the top tube. The head section of the top tube may be attached to the head tube 22. The second top tube hinge may be mounted with its pivot axis horizontal and such that the middle section of the top tube may be folded beneath the head section of the top tube. In this way, the top tube may be folded in a Z shape (see Figs. 2B and 6), with the head section 23c folding on top of the middle section 23b and the middle section 23b folding on top of the seat section 23a. The seat section 23a of the top tube has a lateral hinge 233 with an upright pivot axis. The head tube 22 may comprise a head tube hinge 221 between the attachment of the head tube to the top tube 23 and the handlebars 5. The seat tube 21 has a seat post release mechanism 211 to allow the seat post 6 to be moved into and out of the seat tube 21. The bicycle has an axle guide 9 attached to the seat stays 24 and chain stays 25 of the bicycle. The axle 41 of the rear wheel is movable along the axle guide 9 from the unfolded position shown in Fig. 1 towards the seat tube 21 of the bicycle 1. The bicycle 1 also has a chain ring 10, a drive chain 11 and a chain tensioner 12. The foldable bicycle of Fig. 1 is foldable as shown in Fig. 2. The unfolded configuration is suitable for cycling and is shown in Fig, 1 and Fig, 2A. The fully folded configuration is shown in Fig. 2E. Figs 2B, 2C and 2D show intermediate folding steps. Figs. 2A to 2E show an overview of the folding process and so the features of the bicycle are not labelled for simplicity. The features of the bicycle in the stages of folding shown in Figs. 2A to 2E are discussed in more detail with reference to Figs. 1 and 6 to 10 in which the features are labelled. In the unfolded configuration, the top tube 23 is linear and top tube hinges 231 and 232 are closed. Brace member 8 is attached at its second end 8b to locking means on the top tube to provide support and strength to the top tube and retain it in the unfolded, ridable configuration. Rear wheel axle 41 is in its unfolded position, which is the most rearwardly and upwardly position relative to the chain and seat stays that is allowed by the axle guide 9. Lateral hinge 233 is closed so that seat section 23a of the top tube is linear. The seat post 6 is clamped in its riding position by seat post mechanism 211. The riding position is dependent on the height and preference of the user. The handlebars 5 are upright and head tube hinge 221 is closed. An example of a method of folding the bicycle will now be described. It is understood that the steps explained may be performed in an alternative order if desired without departing from the scope of the disclosure. The rear axle 41 is moved downwards and then forwards in the axle guide 9 to the position shown in Fig. 2B. The second end 8b of brace member 8 is pivoted away from the top tube to an upright position alongside the seat tube 21. The top tube hinges 231 and 232 are opened and the top tube 23 is folded in a reverse Z shape as can be seen in Fig. 2B. Fig. 2C shows the folded configuration of the top tube where top tube hinges 231 and 232 are fully open. Head section 23c lies on middle section 23b, which in turn lies on seat section 23a. Lateral hinge 233 is opened and the front of the bicycle is folded around to meet the back as shown by the arrow A in Fig, 2D. Seat post release mechanism 211 is opened and the seat post 6 is lowered into the seat tube 21 as shown by arrow B in Fig. 2E. The handlebars 5 are folded down towards the front wheel 3 by opening head tube hinge 221 as shown by arrow C in Fig. 2E. In its folded position as shown in Fig. 2E, the length and height of the bicycle is greatly reduced with respect to the unfolded configuration in Fig. 2A. The folded configuration allows easy transportation of the bicycle in a vehicle or carried by the user and efficient storage, for example in a home or office. The unfolded configuration allows a large wheelbase and an efficient cycling position which is similar to that of a standard bicycle. To unfold the bicycle, starting from the fully folded configuration shown in Fig. 2E, the seat post 6 is raised to the preferred riding position in the opposite direction to the arrow B. The head tube hinge 221 is closed by moving the handlebars 5 to an upright position in the direction opposite to arrow C. The lateral hinge 233 is closed by moving the front of the bicycle away from the back in the opposite direction to arrow A in fig. 2D. The top tube 23 is unfolded by closing top tube hinges 231 and 232 and moving from the configuration of the top tube shown in Fig, 2C to that shown in Fig. 2B and then to the fully unfolded top tube configuration shown in Fig. 2A. This moves the front wheel 3, head tube 22 and handlebars 5 away from the seat tube 21, seat post 6, saddle 7 and rear wheel 4. The rear wheel 4 is moved backwards from the folded position shown in Fig. 2B, with the axle 41 moving along the axle guide 9. Then the rear wheel 4 is moved upwards relative to the axle guide 9 to its unfolded position shown in Fig, 2A. Fig. 3 and Fig 4 show close-up views of the brace member 8 and locking means for releasably attaching the second end 8b of the brace member to the top tube 23. The brace member 8 is elongate and comprises two steel twin rods 81 and 82 and a cross pin 83. The two twin rods have substantially the same dimensions and are parallel to one another, each being connected to an opposite side of the bicycle frame. Rod 81 is located on the right side of the bicycle frame and rod 82 is connected on the left side of the bicycle frame. The twin rods 81, 82 each extend from the first end 8a of the brace member where they attach at a pivot to the bicycle frame, to the second end 8b of the brace member where they are releasably attachable to the top tube 23. The twin rods 81, 82 are connected to the bicycle frame and to each other at the first end 8a of the brace member 8. The cross pin connects the twin rods 81, 82 at the second end 8b of the brace member. When the top tube 23 is in its unfolded configuration and hinges 231, 232 and 233 are closed, the brace member 8 may be pivoted about its first end 8a, so that its second end 8b meets the top tube 23. When secured against the top tube 23, the brace member 8 adds support to the top tube and helps to retain the top tube 23 in its unfolded configuration. Particularly, the brace member 8 ensures that first top tube hinge 231 cannot open as the brace member prevents upwards movement of middle section 23b relative to the seat section 23a of the top tube. This increases safety when the user is riding the bicycle in its unfolded position. The stability provided by the brace member 8 also acts to retain the second top tube hinge 232 in a closed position as the middle section 23b is prevented from moving upwards to open the hinge. Further, the brace member retains lateral hinge 233 in a closed position, as the brace member 8 does not allow lateral movement of the top tube relative to the seat tube. The second end 8b of the brace member is releasably attachable to the bicycle frame via locking means which can hold the second end 8b against the bicycle frame. The locking means ensures proper location of the brace member and can provide a retaining force to hold the brace member in its unfolded position. The locking means includes a slot 234 in the top of top tube 23, the slot being sized to receive the cross pin 83. The locking means further includes interlocking shapes 85, 235 on the second end 8b of the brace member and on the top tube 23. At the second end of the brace member, each of the twin rods 81, 82 have a V-shape, or triangle 85 which each correspond to a V-shaped hollow 235 on the top tube. In this way, when the second end 8b of the brace member is pivoted to meet the top tube 23, the V-shapes 85 of the brace member are inserted into their corresponding V hollows 235 to ensure the brace member is in the correct position in relation to the bicycle frame. The interlocking nature of the shapes 85, 235 ensure correct location of the brace member when the brace member is attached to the brace member at the second end. In other embodiments, shapes other than a V-shape or triangle may be used to give the same effect. The locking means also includes a hand screw made up of cross pin 83 and handle 84 situated on twin rod 82. Turning handle 84 changes the distance between the twin rods 81, 82 atthe second end of the brace member via a threaded connection, which may be between the handle and the cross pin or between the cross pin and a bolt in the twin rod 81, or in another suitable location. The hand screw provides a clamping mechanism which clamps the top tube 23 between the twin rods 81, 82 at the second end 8b of the brace member. In this way, the As can be seen in Fig, 8, the first end 8a of the brace member is pivotally connected to the bicycle frame at a position in front of the bottom bracket at the bottom of the seat tube 21. The first end is pivotally connected to the bottom bracket shell 13. The first end 8a is connected to the seat tube 21 via the bottom bracket shell 13. The brace member 8 is pivotable about its connection to the bottom bracket shell 13 from a position in which the second end 8b is attachable to the top tube 23 as can be seen in Fig. 1, to a position in which the brace member extends alongside the seat tube as is shown in Figs. 6,7 and 8. To fold the top tube from the unfolded position shown in Fig. 1 to the folded position shown in Fig. 7, the user loosens the hand screw using handle 84 on the second end 8b of the brace member, pivots the brace member 8 so that the second end 8b of the brace member moves from the top tube 23 to a position where the brace member 8 extends alongside the seat tube 21, folds the middle section 23b of the top tube with respect to the seat section 23a and the head section23c by pivoting the first top tube hinge 231 and the second top tube hinge 232. The folding of the sections may be achieved by moving the head tube, handlebars, and front wheel assembly upwards and closer to the seat tube as shown by arrow Gin Fig. 6. To unfold the top tube 23, from the folded position shown in Fig. 7 to the unfolded position shown in Fig. 1, the user unfolds the middle section 23b of the top tube with respect to the seat section 23a and the head section 23c by pivoting about the first top tube hinge 231 and the second top tube hinge 232 to straighten the top tube 23. This may be achieved by moving the head tube, handlebars, and front wheel assembly upwards and away from the seat tube. The user then pivots the brace member 8 so that the cross pin 83 of the brace member moves into the slot 234 on the top tube 23, and tightens the hand screw on the second end of the brace member using handle 84. In an alternative arrangement, the brace member may be pivotally connected to the head tube rather than the seat tube. In this embodiment, the brace member operates in the same manner and may be combined with the other features of the bicycle of Figs. 1 to 10. In this alternative embodiment, the first and second top tube hinges may or may not be switched so that the seat section folds over the middle section and the middle section folds over the head section of the top tube. The brace member in this alternative embodiment is pivotable from a position in which the second end is attachable to the top tube to a position in which the brace member extends alongside the head tube of the bicycle frame. The top tube has a square sectional shape and is straight when unfolded. This reduces difficulty of manufacture and brings down both material and manufacturing costs. The tube sections can be more easily cut by laser and workholding is much easier than with round tubing, facilitating a more simplistic and cost-effective tooling and fixture setup. The straight shape means that main tube sections do not have to be bent to shape and means that hinges do not have to be made from machined castings or to be joined to the frame using an autobraze machine. This allows production time savings and removes capacity bottlenecks from the process. The seat section 23a of top tube 23 has lateral hinge 233 which has an upright pivot axis. The lateral hinge has an angular range of 180 degrees and enables the top tube 23 to be folded laterally so that the rear and front wheels are alongside one another as can be seen by arrow Ain Fig. 9. The bicycle further comprises a hand screw hinge lock 14 on the lateral hinge to retain the hinge in its closed position which can be seen in Fig. 8. The pivot of the front of the bicycle to the right means that the front wheel 3 provides protection to the drive chain components, such as the chain tensioner when in the folded position. To open the lateral hinge to fold the front of the bicycle to the back as shown in Fig. 9 the user opens the hand screw hinge lock 14 on the lateral hinge 233 and folds the bicycle by moving the front and rear ends of the bicycle towards each other so that the front wheel 3 is situated next to the rear wheel 4 following arrow A. To close the lateral hinge 233 to unfold the front of the bicycle the user unfolds the bicycle by moving the front end of the bicycle away from the rear end of the bicycle and closes the hand screw hinge lock 14 on the lateral hinge. The head tube hinge 221 between the attachment of the head tube to the top tube 23 and the handlebars 5 has an angular range of 180 degrees. The hinge 221 is mounted on the head tube 22 to allow folding of the handlebars 5 towards the back of the bicycle and to one side. The pivot direction is therefore diagonal with respect to the head section 23c of the top tube. The hinge 221 has a pivot axis which is diagonal by being offset from a lateral orientation in a direction opposite the pivot direction of the lateral hinge by 45 degrees. The pivot axis is also offset from the horizontal plane. This enables the handlebars to be folded down outside of the rest of the folded bicycle. As can be seen in Fig, 9, the lateral hinge 233 in this embodiment has a pivot direction that pivots the front of the bicycle to the right. The pivot direction of the head tube hinge 221 is therefore diagonal towards the left (relative to the unfolded configuration of the bicycle) as can be seen in Fig. 8. As can be seen in Fig. 10, this enables the handlebars 5 to fold downwards to meet the front wheel 3. In an alternative embodiment, the lateral hinge may have a pivot direction to the left of the bicycle and the pivot direction of the head tube hinge would then be diagonal towards the right. The head tube hinge has a hinge clip or locking catch which retains the hinge in its closed position and can be actuated to release the hinge for folding. To fold the handlebars 5 downwards towards the front wheel 3, the user opens the hinge clip or locking catch on the head tube hinge 221, and folds the handlebars downward as shown by arrow C in Fig. 10 until they are next to the front wheel, thereby opening head tube hinge 221. To unfold the handlebars 5 to their upright, riding position as shown in, for example, Fig, 9, the user folds the handlebars 5 upward to close the head tube hinge 221 and closes the hinge clip or locking catch on the head tube hinge. The seat tube 21 has a seat post release mechanism 211 as can be seen in Fig. 1. As shown by arrow B in Fig. 10, this allows the seat post 6 to slide down into the seat tube 21, so the saddle 7 moves towards the seat tube. To lower the seat post 6 from the unfolded position shown in Fig. 9 to the folded position shown in Fig. 10, the user opens the seat post release mechanism 211, lowers the saddle 7 and seat post 6 into the seat tube 21, and closes the seat post release mechanism 211.To raise the seat post 6 from the folded position shown in Fig. 10 to the extended, riding position shown in, for example, Fig. 9, the user opens the seat post release mechanism 211, raises the saddle 7 and seat post 6, and closes the seat post release mechanism 211. As shown in Fig. 1, the rear wheel 4 has axle 41 which is engaged with axle guide 9. The axle guide 9 is attached to seat stays 24 and chain stays 25. The axle 41 is movable along the axle guide 9 from an unfolded position as shown in Fig, 1 towards the seat tube 21 of the bicycle to its folded position as shown in Fig. 6. In this way, the rear wheel may be moved towards the seat tube to shorten the length of the bicycle in its folded position. This means that the compact folded position shown in Fig. 6 can be achieved while also providing a large wheelbase while riding as shown in Fig. 1. The axle guide 9 has two slots along which the axle 41 can move by sliding. The axle is located through the slots. The axle guide 9 has a left-side guide which is attached to the left seat and chain stays and can be seen in Fig, 8 and a right-side guide which is attached to the right seat and chain stays and can be seen in Fig. 1. This provides better and more laterally even support for the axle during folding and unfolding. The side opposite the chain (the left- side in this embodiment) guide is sized to accommodate the axle and the chain-side (right- side in this embodiment) guide is sized to accommodate the engagement member. This can be seen in Fig. 8 and in Fig. 11 in relation to alternative axle guide 19. The axle guide 9 is L shaped such that the axle 41 is moveable relative to the chain and seat stays 24, 25 in a downwards direction from its unfolded position as shown by arrow E in Fig. 6 and then in a direction toward the front of the bicycle as shown by arrow F in Fig. 6. As shown in Fig. 11, an alternative axle guide 19 also has an L shape and all other features of the axle guide 9. However, the corner of the L shape of axle guide 19 is curved to enable smoother sliding of the axle through the guide and to cause rotation of a square profile guide engagement member 16 in the axle guide. The rotation is in the direction of a backwards rear wheel rotation. The axle 41 is movable downwards relative to the chain and seat stays 24, 25 by at least the radial distance between a braking surface of the rear wheel and the outside edge of the tyre of the rear wheel. In this way, the wheel is moved down by a distance that allows the rear wheel to move out of contact with the rear brake calipers 15. The axle 41 has a release lever with a closed position in which the axle 41 is clamped against the axle guide 9 and an open position in which the axle 41 is movable along the axle guide 9. In this way, the user may quickly open the lever, move the axle 41 to the folded position and may then close the lever to secure the axle 41 in its folded position to ensure that the folded position is retained while the user carries or stores the bicycle. The seat stays 24 and chain stays 25, each extend backwards from the seat tube 21 and meet at the unfolded axle position at the rear end of the axle guide. The seat stays 24 extend in an upwards and forwards direction from the rear end of the axle guide by a distance greater than the radius of the rear wheel 4 and then forwards to the seat tube 21. Rear brake calipers 15 are located on the seat stays 24 in a position forwards and downwards of the seat stays 24. In this way, they are protected from being knocked out of alignment when the bicycle is folded. The bicycle has a rear brake caliper release mechanism which allows the rear brake calipers 15 to be separated to allow the rear tyre to move through the calipers when the rear wheel is moving to the folded position, without knocking or bending the calipers 15. The rear brake caliper release mechanism may have a quick release opening function and / or may be a handlebar-mounted cable release. As can be seen in Fig. 6, Fig. 12 and Fig. 13, the chain tensioner 12 has a tensioner pulley arm 12a pivotally attached to the rear wheel axle 41, the tensioner pulley arm 12a being biased away from the chain ring 10 of the bicycle under spring torsion, and a guide pulley arm 12b which may be fixedly attached to the rear axle 41, extending forwardly from the axle. In this way, when the rear wheel is moved forwards for folding the bicycle as in Fig. 6, the tensioner pulley arm 12a pivots rearwards to retain tension on the drive chain 11 and retain the drive chain 11 on the tensioner pulleys / jockey wheels, sprocket / s and chainring. The guide pulley arm 12b cannot rotate relative to the rear wheel axle and so maintains tension on the chain 11 between the guide pulley and the tensioner pulley. The guide pully arm 12b is fixedly attached to the guide engagement member 16, so that rotation of the guide engagement member 16 causes rotation of the guide pulley arm. Figure 12 shows an exploded view of chain tensioner 12 and axle 41. Spring 17 provides the spring torsion force that biases tension pulley arm 12a away from the chain ring. The tensioner pulley arm 12a is free to rotate under spring torsion to keep the drive chain 11 on the tensioner pulleys / jockey wheels, sprocket / s and chainring when the rear wheel is moved forwards, closer to the chainring. The difference in position and orientation of the tensioner pulley arm can be seen when comparing Fig. 1 showing the rear wheel in the unfolded riding position and Fig. 6, in which the rear wheel is in the folded position. As shown in Figure 12, the chain tensioner 12 may have a square profile guide engagement member 16. In use, the guide engagement member 16 can slide in the axle guide of the bicycle to assist in guiding the axle along the path of the guide. The axle 41 is positioned through a hole in the engagement member 16. When used with the axle guide 19 shown in Figure 11, the square profile of the engagement member 16 along with the curved corner of the guide 19 causes the engagement member to rotate as the axle moves through the curved corner of the axle guide. As the guide pulley arm 12b is rotationally fixed to the guide engagement member 16, the guide pulley arm also rotates. If the guide pulley arm 12b extends downwards from the axle in an unfolded configuration, then the guide pully arm will point forwards in the folded configuration. The axle guide may be a long slot in the frame. The width from side to side of the square profile may be smaller than a width of the axle guide slot and the diagonal width of the square profile between opposite corners of the square profile may be greater than the slot width. In this way, the square profile cannot spin within the slot. The chain tensioner 12 is attached to the rear axle 41 and so moves with the rear wheel when the axle 41 is moved along the axle guide 9. The pivoting of the tensioner pulley arm 12a has the additional advantage of keeping the tensioner higher off the ground, avoiding impacts with kerbs and dirt ingress when the bicycle is folded. To move the rear wheel from the unfolded position in Fig. 1 to the folded position in Fig. 6, the user opens the rear wheel release lever, opens the rear brake calipers 15 with the rear brake caliper release mechanism, slides the rear wheel axle 41 along the axle guide 9 downwards (arrow E) to allow the rear tyre to clear the brake calipers 15 and forwards (arrow F) to shorten the bicycle. The user may then close the rear wheel release lever. To move the rear wheel from the folded position in Fig. 6 to the unfolded position in Fig. 1, the user opens the rear wheel release lever, slides the rear wheel axle 41 along the axle guide 9 rearwards to lengthen the bicycle and upwards to allow the brake calipers 15 to align with the braking surface of the wheel, closes the rear wheel release lever, and closes the rear brake calipers 15 with the rear brake caliper release mechanism. Although particular embodiments of the disclosure have been disclosed herein in detail, this has been done by way of example and for the purposes of illustration only. The aforementioned embodiments are not intended to be limiting with respect to the scope of the invention. It is contemplated by the inventors that various substitutions, alterations, and modifications may be made to the invention without departing from the scope of the invention as defined by the claims.

Claims

CLAIMS 1. A foldable bicycle, the foldable bicycle comprising: a rear wheel comprising a rear wheel axle, and an axle guide attached to a seat stay and / or chain stay of the bicycle, wherein the axle is movable along the axle guide between a folded position and an unfolded position, the folded position being closer to a seat tube of the bicycle than the unfolded position.

2. A foldable bicycle according to claim 1, wherein the axle guide comprises a slot, along which the axle is movable.

3. A foldable bicycle according to claim 1 or 2, wherein the axle guide is L shaped such that the axle is moveable relative to the chain and / or seat stays in a downwards direction from its unfolded position and then in a direction toward the front of the bicycle.

4. A foldable bicycle according to claim 3, wherein the corner of the L shape of the axle guide is curved.

5. A foldable bicycle according to any of claims 1 to 4, wherein the axle is movable downwards relative to the chain and / or seat stays by at least the radial distance between a braking surface of the rear wheel and the outside edge of a tyre of the rear wheel.

6. A foldable bicycle according to any of claims 1 to 5, wherein the axle comprises a quick release lever.

7. A foldable bicycle according to any of claims 1 to 6, further comprising: a chain ring, a drive chain, a chain tensioner and a guide engagement member coupled to the axle and positioned in the axle guide, wherein the chain tensioner comprises: a tensioner pulley arm pivotally attached to the guide engagement member, the tensioner pulley arm being biased away from the chain ring of the bicycle, and a guide pulley arm attached to the guide engagement member.

8. A foldable bicycle according to claim 7, wherein the guide pully arm is fixedly attached to the guide engagement member, such that rotation of the guide engagement member causes rotation of the guide pulley arm.

9. A foldable bicycle according to claim 7 or 8, wherein the axle is positioned through a hole in the engagement member.

10. A foldable bicycle according to claim 7, 8 or 9, wherein the guide engagement member has a square shaped profile configured to slide along the axle guide.

11. A foldable bicycle according to claim 10 and claim 4, wherein the engagement member and axle guide are sized to restrict rotation of the engagement member within the axle guide such that the engagement member rotates through a quarter turn as the axle moves through the curved corner of the axle guide.

12. A foldable bicycle according to any of claims 7 to 11, the chain tensioner further comprising a spring configured to bias the tension pulley arm away from the chain ring.

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