Patent Description:
Conventional bicycles typically only allow for minor adjustments of the bicycle's geometry. For example, the height and position (in a fore and aft direction) of the bicycle's seat may be adjusted to suit the user. It may also be possible to alter the reach by changing the length of the bicycle's stem.

As a result of the limited adjustment of conventional bicycles, it is essential that the frame of the bicycle is sized appropriately for the user. This is problematic for children's bicycles where the child can outgrow the frame after only a short time. Consequently, there is a tendency for children to ride bicycles which are either too large (purchased with the expectation that the child will grow into it) or too small (having already outgrown the bicycle) for them. Both scenarios can be uncomfortable and also dangerous for the child.

Efforts have been made to overcome this issue by devising bicycle frames which have more adjustability. <CIT> discloses all of the features of the preamble of claim <NUM>. For example, <CIT> describes a bicycle which has a chassis comprised of a front strut and a seat strut. The front strut has a telescoping post which carries the front wheel while the seat strut has a telescoping seat post which carries the seat. These struts are adjustable with respect to each other, and the rear wheel is mounted to said chassis to aid in support of the chassis. <CIT> describes a bicycle frame which has a telescopic structure that allows the frame to increase in size as the child grows. However, this arrangement only allows the frame to be lengthened so as to increase wheelbase (the distance from the centre of the front wheel to the centre of the rear wheel). Consequently, the geometry of the frame is not ideal in all configurations.

It is therefore desirable to provide an adjustable bicycle frame which overcomes the shortcomings of prior art frames.

In accordance with an aspect of the invention, there is provided a bicycle frame having the features of claim <NUM> below.

For a better understanding of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:-.

In the following description, the terms "front", "rear", "upper", "lower" and the like are used to describe the relative position of elements. These terms are used in the context of the conventional operation of a bicycle.

<FIG> show a bicycle frame <NUM> according to an embodiment of the invention. The frame <NUM> generally comprises a front portion <NUM>, a rear portion <NUM> and a connecting member <NUM>.

The front portion <NUM> comprises a head tube <NUM> configured to receive a front wheel assembly. The front wheel assembly is formed by a front fork and the front wheel itself, as well as any intermediate components, such as a headset. The front portion <NUM> further comprises a top tube <NUM> which extends perpendicularly from the head tube <NUM>. The front portion <NUM> comprises a plurality (three are shown - designated "front", "middle" and "rear") of mounting holes 14a, 14b, 14c spaced along the length of the top tube <NUM> between the head tube <NUM> and a distal end of the top tube <NUM>. The mounting holes 14a, 14b, 14c pass through the thickness of the top tube <NUM>.

As shown particularly in <FIG>, the distal end of the top tube <NUM> is bifurcated to form an open slot <NUM>. Specifically, the distal end of the top tube <NUM> is formed by a pair of plates 18a, 18b which are parallel to one another but spaced laterally either side of the frame <NUM>. The plates 18a, 18b are each provided with a pair of pivot holes 20a, 20b. The pivot holes 20a, 20b of each plate 18a, 18b are aligned with one another across the slot <NUM>.

The rear portion <NUM> comprises a pair of rear stays 22a, 22b which are connected to one another at a mounting bracket <NUM> and which are splayed away from one another to form a rear fork which is configured to receive a rear wheel assembly. A distal end of each rear stay 22a, 22b is provided with a fork-end <NUM> which is configured to receive a wheel axle. As shown, the fork-ends <NUM> may comprise an open slot which faces backwards. Alternatively, the fork-ends <NUM> may have a "dropout" configuration whereby the slot faces downwards or forwards to allow the wheel to be removed without first derailing a belt or chain. As a further alternative, the fork-ends <NUM> may each have a hole which receives a thru-axle.

The mounting bracket <NUM> comprises a base plate <NUM> which connects the rear stays 22a, 22b to one another and a pair of side plates 30a, 30b which extend substantially perpendicularly from either side of the base plate <NUM>. The side plates 30a, 30b are parallel to one another but spaced laterally either side of the frame <NUM> by a distance which is larger than the thickness of the top tube <NUM> in the region of the mounting holes 14a, 14b, 14c. The plates 30a, 30b are each provided with a mounting hole 31a, 31b which are aligned with one another.

Each rear stay 22a, 22b is provided with a guide plate 32a, 32b which extends from a lower surface of the rear stay 22a, 22b. The guide plates 32a, 32b are located approximately midway between the mounting bracket <NUM> and the fork-ends <NUM>. The guide plates 32a, 32b are parallel to one another but spaced laterally either side of the frame <NUM>. Each guide plate 32a, 32b is provided with a curved guide slot 34a, 34b, the formation and function of which will be described in detail below.

The connecting member <NUM> comprises a seat tube <NUM> which is configured to receive a seat post assembly comprising a seat post and saddle. The connecting member <NUM> further comprises a bottom bracket shell <NUM> which is configured to receive a bottom bracket to which a crankset is mounted. An upper portion of the seat tube <NUM> is provided with a boss <NUM> (see <FIG>) having a through-bore which lies in front of the seat tube <NUM> and extends laterally across the frame <NUM>. The boss of the seat tube <NUM> is received within the slot <NUM> so that the through-bore is aligned with one of the pairs of pivot holes 20a, 20b. A pin (not shown) is passed through the pivot holes 20a, 20b and the through-bore of the boss <NUM>, and is fixed in position using a suitable fastener so as to pivotably connect the connecting member <NUM> to the front portion <NUM> (at a first connecting point).

A pair of bosses are provided at either side of the seat tube <NUM> partway along its length. A threaded guide pin 42a, 42b extends from each of the bosses. The guide pins 42a, 42b are received in the guide slots 34a, 34b of the rear portion <NUM>. The arrangement of the guide slots 34a, 34b and the guide pins 42a, 42b connects the connecting member <NUM> to the rear portion <NUM>. The arrangement of the guide slots 34a, 34b and the guide pins 42a, 42b forms a pivot (a second connecting point) which allows the rear portion <NUM> and the connecting member <NUM> to rotate relative to one another, as well as translate over the length of the guide slots 34a, 34b. The position of the guide pins 42a, 42b along the guide slots 34a, 34b can be fixed using suitable nuts or the like which are threaded onto the guide pins 42a, 42b so as to clamp the guide plates 32a, 32b against the bosses.

As will be appreciated, the front portion <NUM>, the rear portion <NUM> and the connecting member <NUM> form a Z-shaped arrangement. The orientation of the connecting member <NUM> thus determines the vertical and horizontal spacing of the front portion <NUM> from the rear portion <NUM>.

The connecting member <NUM> can be fixed in a desired orientation by connecting the mounting bracket <NUM> of the rear portion <NUM> to one of the mounting holes 14a, 14b, 14c along the top tube <NUM> of the front portion <NUM> (forming a third connecting point). This may be achieved by passing a pin (not shown) through the mounting holes 31a, 31b of the mounting bracket <NUM> and a selected one of the mounting holes 14a, 14b, 14c and fixing it in position using a suitable fastener. Alternatively, each of the mounting holes 14a, 14b, 14c may be threaded (i.e. by way of a pair of threaded inserts at either side of the top tube <NUM> or a single insert extending entirely through the top tube <NUM>) and engaged by a pair of screws or the like which are inserted through either mounting hole 31a, 31b. The rear portion <NUM> is thus indirectly connected to the front portion <NUM> by the connecting member <NUM> and then also directly connected to the front portion <NUM> via the link formed by the section of the rear portion <NUM> extending between the mounting bracket <NUM> and the pivot formed by the guide slots 34a, 34b and the guide pins 42a, 42b. The connection of the rear portion <NUM> to the front portion <NUM> provides triangulation to the frame <NUM> and therefore ensures rigidity. Further, as described further below, the link restricts the relative positions of the front and rear portions <NUM>, <NUM>.

<FIG> and <FIG> show the frame <NUM> assembled into a balance bicycle <NUM>. A balance bicycle (or run bike) is a training bicycle that helps children learn balance and steering. As shown, the balance bicycle <NUM> is not provided with a drivetrain (i.e. pedals, crankset, chain, etc.) or brakes, and does not have training wheels.

A front fork <NUM> is received by the head tube <NUM> of the frame <NUM>. The front fork <NUM> passes through the head tube <NUM> and is connected to a handlebar <NUM> in a conventional manner. The front fork <NUM> comprises first and second pairs of fork-ends 46a, 46b. Each fork-end 46a, 46b may be formed as an open dropout. Alternatively, the fork-ends 46a, 46b may have a hole which receives a thru-axle. The first and second pairs of fork-ends 46a, 46b are spaced different distances from the head tube <NUM> so as to accommodate wheels of different sizes. In the balance bicycle configuration, a smaller front wheel 48a is used, preferably a standard <NUM>" (diameter) wheel. The front wheel 48a is located in the upper pair of fork ends 46a so as to lower the front of the balance bicycle <NUM>. Similarly, a standard <NUM>" wheel 48b is located in the rear fork-ends <NUM>. A seat pad <NUM> is affixed to the top tube <NUM> of the frame <NUM>. As shown, the seat pad <NUM> extends past and may cover the rear mounting hole 14c which is not needed for the balance bicycle configuration.

As shown, in the balance bicycle configuration, the connecting member <NUM> is removed from the frame <NUM> and replaced by connecting member <NUM>. The connecting member <NUM> is connected to the front and rear portions <NUM>, <NUM> in a similar manner to the connecting member <NUM>, but is provided with a pair of footpegs <NUM> at its distal, free end, instead of the bottom bracket shell <NUM>. The footpegs <NUM> extend laterally from either side of the connecting member <NUM> and can be used to support the child. The connecting member <NUM> may be provided with a detachable lower section which carries the bottom bracket shell <NUM> and may be removed and replaced with a lower section having the footpegs <NUM> to form the replacement connecting member <NUM> (utilising guide pins located in an appropriate position). Alternatively, the footpegs <NUM> may be received by the bottom bracket shell <NUM> itself.

<FIG> shows the balance bicycle <NUM> in a first, smaller mode where the rear portion <NUM> is connected to the front portion <NUM> via the front mounting hole 14a.

In this smaller configuration, the connecting member <NUM> is angled furthest away from vertical, thus reducing the vertical and horizontal distances between the front and rear portions <NUM>, <NUM>. As a result, the frame <NUM> is at its smallest size, as defined by its vertical and horizontal dimensions, and thus will be suitable for the smallest children.

Specifically, the orientation of the connecting member <NUM> draws the rear wheel 48b (i.e. rear axle) and footpegs <NUM> horizontally towards the front wheel 48a and the head tube <NUM>. This minimises the horizontal dimensions of wheelbase (the separation between the front and rear axles), reach (the horizontal separation between the footpegs <NUM> and the top of the head tube <NUM>) and axle-reach (as per reach, but measured from the rear axle rather than the footpegs <NUM>).

The orientation of the connecting member <NUM> also draws the footpegs <NUM> vertically towards the head tube <NUM>. This increases the angle of the top tube <NUM> and decreases the angle of the head tube <NUM> (from horizontal). As a result, the vertical dimensions of stack (the vertical separation between the footpegs <NUM> and the top of the head tube), axle-stack (as per stack, but measured from the rear axle rather than the footpegs <NUM>), head tube height, top tube height (both at the front and rear), standover height and seat height are all minimised.

The slack head angle also increases the trail of the front fork <NUM>, thereby providing slower steering characteristics and thus improved stability. The orientation of the connecting member <NUM> also raises the height of the footpegs <NUM> so as to reduce the vertical distance between the footpegs <NUM> and the seat pad <NUM>.

As shown in <FIG>, once the child has outgrown the smaller configuration, the balance bicycle <NUM> can be transitioned to a second, larger configuration where the rear portion <NUM> is connected to the front portion <NUM> via the middle mounting hole 14b.

In the larger configuration, the connecting member <NUM> is pivoted toward vertical about the rear pivot hole 20b. As a result, the previously described vertical and horizontal dimensions of the balance bicycle <NUM> are increased simultaneously. In addition, the angle of the top tube <NUM> decreases and the angle of the head tube <NUM> increases.

The front wheel 48a may also be moved into the lower pair of fork ends 46b so as to raise the front of the balance bicycle <NUM>.

Alternatively, as shown in <FIG> and <FIG>, a replacement connecting member <NUM> may be used which does not project past the connection with the rear portion <NUM>. The connecting member <NUM> may be provided with a detachable lower section which carries the bottom bracket shell <NUM> and may be removed to form the replacement connecting member <NUM> (utilising guide pins located in an appropriate position).

Alternatively, as shown in <FIG>, the connecting member <NUM> may be removed and the front and rear portions <NUM>, <NUM> prevented from rotating relative to one another by an arrangement comprising a hook <NUM> (i.e. a connecting member) and a notch <NUM> (or hole). The hook <NUM> projects from an underside of the top tube <NUM> at a position which is rearward of the mounting holes 14a, 14b and the notch <NUM> is formed in the base plate <NUM> of the mounting bracket <NUM>. The hook <NUM> is formed by a tubular portion which extends from the top tube <NUM> and is provided with an enlarged head at its distal end. The base plate <NUM> is received between the top tube <NUM> and the enlarged head of the hook <NUM> such that the tubular portion sits in the notch <NUM>. The enlarged head of the hook <NUM> therefore prevents the base plate <NUM> and thus the rear portion <NUM> from moving away from the top tube <NUM>. The enlarged head of the hook <NUM> and the notch <NUM> may be chamfered to allow for different mating angles.

The hook <NUM> may engage in separate notches <NUM> provided in the base plate <NUM> at appropriate positions for the smaller and larger configurations of the balance bicycle <NUM>. Alternatively, the hook <NUM> may be moved along the top tube <NUM> to positions which conform to the position of the notch <NUM> when the rear portion <NUM> is connected to the front portion <NUM> via the front and middle mounting holes 14a, 14b. For example, the underside of the top tube <NUM> may be provided with a pair of threaded bosses which are spaced from one another, so that the hook <NUM> can be screwed into the appropriate boss for the desired configuration of the balance bicycle <NUM>.

The transition from the smaller configuration to the larger configuration simultaneously increases both the wheelbase and the height of the seat pad <NUM>. The balance bicycle <NUM> is thus able to grow with the child. The balance bicycle <NUM> is generally suitable for children aged <NUM> to <NUM> years old and of a height of between <NUM> and <NUM>.

The transition from the smaller configuration to the larger configuration also decreases the angle of the top tube <NUM> and increases the angle of the head tube <NUM> (from horizontal). In the smaller configuration, the slack head angle increases the trail of the front fork <NUM>, thereby providing slower steering characteristics and thus improved stability for younger users. As described previously, during the transition from the smaller configuration to the larger configuration, the front wheel 48a may be moved into the lower pair of fork ends 46b so as to raise the front of the balance bicycle <NUM>. Accordingly, the change in the angles of the top tube <NUM> and the head tube <NUM> brought about by the change in position of the front and rear portions <NUM>, <NUM> also offsets the change in these angles resulting from the change in wheel position.

After the child has become proficient with balance and steering and has outgrown the larger configuration, the balance bicycle <NUM> can be converted into a pedal bicycle <NUM>, as shown in <FIG>.

To convert the balance bicycle <NUM> into the pedal bicycle <NUM>, the connecting member <NUM> is attached between the front and rear portions <NUM>, <NUM>. The wheels 48a, 48b are replaced by a larger pair of wheels 54a, 54b, preferably <NUM>" wheels. The front wheel 54a is again located in the upper pair of fork ends 46a. Front and/or rear brakes (not shown) are also fitted.

The seat tube <NUM> of the connecting member <NUM> receives a seat post <NUM> (see <FIG>) which carries a saddle <NUM>. The seat post <NUM> is telescopically received in the seat tube <NUM> and thus can slide relative to the seat tube <NUM> to vary the height of the saddle <NUM>. The saddle <NUM> is connected to the seat post <NUM> by a pair of rails <NUM> which are received by a clamp <NUM> of the seat post <NUM>. The rails <NUM> are curved along their length such that, at the front of the saddle <NUM>, the rails <NUM> are substantially parallel to an upper surface of the saddle <NUM> and, at the rear of the saddle <NUM>, the rails <NUM> are angled away from the saddle <NUM>. Similarly, the clamp <NUM> is curved along its length to conform to the curvature of the rails <NUM>.

The bottom bracket shell <NUM> of the connecting member <NUM> receives a crankset <NUM> which in turn receives a pair of pedals (not shown). The crankset <NUM> carries a front sprocket.

The rear wheel 54b is provided with a rear sprocket assembly <NUM> which will be described in further detail below. The crankset <NUM> and rear sprocket assembly <NUM> are connected by a toothed belt <NUM>, chain or the like.

<FIG> shows the bicycle <NUM> in a first, small configuration. In this configuration, the connecting member <NUM> is connected to the front portion <NUM> via the front pivot hole 20a. The orientation of the connecting member <NUM>, and thus the relative positions of the front and rear portions <NUM>, <NUM>, is fixed by the link formed by the connection of the rear portion <NUM> to the front portion <NUM>.

In this configuration, the connecting member <NUM> is angled furthest away from vertical, thus reducing the vertical and horizontal distances between the front and rear portions <NUM>, <NUM>. As a result, the frame <NUM> is at its minimum size as defined by its vertical and horizontal dimensions.

Specifically, the orientation of the connecting member <NUM> draws the rear wheel 54b (i.e. rear axle) and crankset <NUM> (i.e. bottom bracket) horizontally towards the front wheel 54a and the head tube <NUM>. This minimises the horizontal dimensions of wheelbase (the separation between the front and rear axles), reach (the horizontal separation between the bottom bracket and the top of the head tube) and axle-reach (as per reach, but measured from the rear axle rather than the bottom bracket).

The orientation of the connecting member <NUM> also draws the crankset <NUM> (i.e. bottom bracket) vertically towards the head tube <NUM>. This increases the angle of the top tube <NUM> and decreases the angle of the head tube <NUM> (from horizontal). As a result, the vertical dimensions of stack (the vertical separation between the bottom bracket and the top of the head tube), axle-stack (as per stack, but measured from the rear axle rather than the bottom bracket), head tube height, top tube height (both at the front and rear), standover height and minimum saddle height (defined by the top of the seat tube) are all minimised.

The angle of the connecting member <NUM> also results in the crankset <NUM> being located forward of the saddle <NUM> which is more suitable for learners. In addition, the slack head angle increases the trail of the front fork <NUM>, thereby providing slower steering characteristics and thus improved stability. The orientation of the connecting member <NUM> also raises the height of the bottom bracket so as to reduce the vertical distance between the bottom bracket shell <NUM> and the saddle <NUM>.

In this configuration, the saddle <NUM> is located towards the front of the bicycle <NUM> such that the clamp <NUM> of the seat post <NUM> connects towards the rear of the rails <NUM>. Accordingly, the angle between the upper surface of the saddle <NUM> and the seat post <NUM> (measured from the front of the saddle <NUM> downwards to the seat post <NUM>), and thus the seat tube <NUM> of the connecting member <NUM>, is reduced so that the upper surface of the saddle <NUM> is substantially level. This also reduces the distance between the saddle <NUM> and the handlebar <NUM>.

The orientation of the connecting member <NUM> can be finely adjusted by translating the guide pins 42a, 42b along the guide slots 34a, 34b. Specifically, as shown, the guide pins 42a, 42b are translated forward along the guide slots 34a, 34b so as to reduce the distance between the second and third connecting points. This also controls the distance between the crankset <NUM> and the rear sprocket assembly <NUM> (which may be used to maintain a constant distance) in order to maintain an appropriate tension in the belt <NUM>. A lead screw arrangement (not shown) may be provided to drive the guide pins 42a, 42b forward along the guide slots 34a, 34b for this purpose. Alternatively, the tension of the belt <NUM> may be adjusted by altering the position of the rear wheel 54b.

The guide slots 34a, 34b may be provided with a visual or tactile indication of the appropriate position for the guide pins 42a, 42b for each size configuration. For example, the guide slots 34a, 34b may be provided with a visual marker which indicates the position for each size configuration. Alternatively, the guide slots 34a, 34b may be provided with a plurality of recesses which receive the nuts screwed onto the guide pins 42a, 42b when positioned appropriately.

Once the child has outgrown the small configuration, the bicycle <NUM> can be transitioned to a medium configuration, as shown in <FIG>.

In the medium configuration, the connecting member <NUM> is pivoted toward vertical about the front pivot hole 20a and the rear portion <NUM> is connected to the front portion <NUM> via the middle mounting hole 14b to fix the orientation of the connecting member <NUM>. This reduces the distance between the first and third connecting points and increases the vertical and horizontal distances between the front and rear portions <NUM>, <NUM>. As a result, the previously described vertical and horizontal dimensions of the bicycle <NUM> are increased simultaneously. The crankset <NUM> is also brought more underneath the saddle <NUM> giving a more efficient riding position. In addition, the angle of the top tube <NUM> decreases and the angle of the head tube <NUM> increases.

To counteract the change in angle of the connecting member <NUM>, the saddle <NUM> is moved rearward so as to increase the angle between the upper surface of the saddle <NUM> and the seat post <NUM> (measured from the front of the saddle <NUM> downwards to the seat post <NUM>). As a result, the upper surface of the saddle <NUM> remains substantially level. This also increases the distance between the saddle <NUM> and the handlebar <NUM>. The saddle <NUM> is also raised to allow for the longer legs of the child.

Again, the orientation of the connecting member <NUM> can be finely adjusted by translating the guide pins 42a, 42b along the guide slots 34a, 34b to reduce the distance between the second and third connecting points and to maintain appropriate tension in the belt <NUM>.

Once the child has outgrown the medium configuration, the bicycle <NUM> can be transitioned to a large configuration, as shown in <FIG>.

In the large configuration, the connecting member <NUM> is instead connected to the rear pivot hole 20b so as to move the connecting member <NUM> (and saddle <NUM>) rearward. The rear portion <NUM> is connected to the front portion <NUM> via the rear mounting hole 14c to fix the orientation of the connecting member <NUM>. This further reduces the distance between the first and third connecting points and further increases the vertical and horizontal distances between the front and rear portions <NUM>, <NUM>. As a result, the previously described vertical and horizontal dimensions of the bicycle <NUM> are further increased to their maximum values. The crankset <NUM> is also brought further underneath the saddle <NUM> giving a more efficient riding position. In addition, the angle of the top tube <NUM> further decreases and the angle of the head tube <NUM> further increases.

Moving the connecting member <NUM> between the pivot holes 20a, 20b minimises the change in angle of the connecting member <NUM> as the frame <NUM> transitions from the small to the large configurations. This avoids the pedals being located too far in front of the saddle <NUM> when in the small configuration.

To counteract the change in angle of the connecting member <NUM>, the saddle <NUM> is moved further rearward so as to increase the angle between the upper surface of the saddle <NUM> and the seat post <NUM> (measured from the front of the saddle <NUM> downwards to the seat post <NUM>). As a result, the upper surface of the saddle <NUM> remains substantially level. This also increases the distance between the saddle <NUM> and the handlebar <NUM>. The saddle <NUM> is also raised further to allow for the longer legs of the child.

In this configuration, the front wheel 54a may also be replaced by a larger wheel (i.e. a <NUM>" wheel). This may be located in the lower pair of fork ends 46b. The upper and lower pairs of fork ends 46a, 46b are offset from one another by a distance which corresponds to the difference in size (the radius) between the wheels. Consequently, the position of the rim remains constant between the wheels so that no (or very little) adjustment of the front brake is required.

When in the small configuration, the bicycle <NUM> is generally suitable for children aged <NUM> to <NUM> years old and of a height of between <NUM> and <NUM>. In the medium configuration, the bicycle <NUM> is generally suitable for children aged <NUM> to <NUM> years old and of a height of between <NUM> and <NUM>. In the large configuration, the bicycle <NUM> is generally suitable for children aged <NUM> to <NUM> years old and of a height of between <NUM> and <NUM>.

As described, the relative positions of the front and rear portions <NUM>, <NUM> and the orientation of the connecting member <NUM> are altered simply by changing the mounting hole 14a, 14b, 14c used to connect the rear portion <NUM> to the front portion <NUM> (possibly with an additional transition between the pivot holes 20a, 20b). The direct connection between the front and rear portions <NUM>, <NUM> restricts the frame <NUM> to predefined, optimised positions of the front and rear portions <NUM>, <NUM> relative to one another. These optimised positions are designed to provide a frame which replicates a purpose-built frame of the desired size.

As the child grows and increases in strength, they will not only outgrow the physical size of the frame <NUM> (requiring conversion between the different size configurations), but will also outgrow the gearing of the bicycle <NUM>, as defined by the crankset <NUM> and rear sprocket assembly <NUM>. Accordingly, at each size transition, there is also an associated change in the gearing of the bicycle <NUM>. This may be achieved using the rear sprocket assembly <NUM> shown in <FIG>.

As shown, the rear sprocket assembly <NUM> comprises an inner sprocket <NUM> which is connected to or integrally formed with a back plate <NUM>. The inner sprocket <NUM> is provided with a number of teeth (<NUM> are shown) which project radially.

For the small configuration, a large annular sprocket <NUM> is disposed over the inner sprocket <NUM>. Inner and outer surfaces of the large annular sprocket <NUM> are provided with teeth. The teeth of the inner surface conform to the teeth of the inner sprocket <NUM> such that the large annular sprocket <NUM> can be received over and engaged with the inner sprocket <NUM>. The teeth of the outer surface have the same profile and spacing as the teeth of the inner surface (and of the inner sprocket <NUM>), but, owing to the larger diameter of the outer surface, there are a greater number of teeth on the outer surface (<NUM> are shown) than on the inner surface of the large annular sprocket <NUM> (and on the inner sprocket <NUM>).

When converting the bicycle <NUM> from the small configuration to the medium configuration, the large annular sprocket <NUM> is removed, as shown in <FIG>. This is achieved by removing the rear wheel 54b from the frame <NUM> and sliding the large annular sprocket <NUM> axially relative to the inner sprocket <NUM>. The large annular sprocket <NUM> is then replaced with a medium annular sprocket <NUM>, as shown in <FIG>.

As per the large annular sprocket <NUM>, the medium annular sprocket <NUM> has an inner surface with teeth which conform to the teeth of the inner sprocket <NUM>. An outer surface of the medium annular sprocket <NUM> is also provided with teeth. The diameter of the outer surface of the medium annular sprocket <NUM> is smaller than that of the large annular sprocket <NUM> such that the medium annular sprocket <NUM> has fewer teeth (<NUM> are shown). This thus increases the gearing of the bicycle <NUM>.

When converting the bicycle <NUM> from the medium configuration to the large configuration, the medium annular sprocket <NUM> is removed, as shown in <FIG>, and the belt <NUM> engages directly with the inner sprocket <NUM>. This further increases the gearing of the bicycle <NUM>.

Alternatively, the medium annular sprocket <NUM> may be nested between the inner sprocket <NUM> and the large annular sprocket <NUM> such that the inner surface of the large annular sprocket <NUM> conforms to the outer surface of the medium annular sprocket <NUM>. The large annular sprocket <NUM> and medium annular sprocket <NUM> are therefore removed sequentially at each transition in size.

As shown in <FIG>, the large annular sprocket <NUM> may be formed as two semi-circular halves 70a, 70b (or more than two segments) which are connected to one another using a suitable interlocking joint, such as a dovetail joint. The two halves 70a, 70b may be retained using a grub screw or similar. The medium annular sprocket <NUM> may also be formed in this manner. This allows the large annular sprocket <NUM> and medium annular sprocket <NUM> to be removed from and attached to the inner sprocket <NUM> without removing the rear wheel 54b from the frame <NUM>.

To maintain a constant belt length while the gearing is adjusted as described above, the guide pins 42a, 42b are translated along the guide slots 34a, 34b to move the bottom bracket shell <NUM> of the connecting member <NUM> and thus the crankset <NUM> away from the rear sprocket assembly <NUM>. Once the belt <NUM> is under sufficient tension, the connecting member <NUM> and thus the front and rear portions <NUM>, <NUM> are in the desired position and orientation for that size configuration.

As an alternative (or in addition), a similar arrangement to the rear sprocket assembly <NUM> described above may be used at the crankset <NUM>. With this arrangement, the size of the sprocket at the crankset <NUM> would increase in size as the frame <NUM> is converted from the small to large. This may therefore offset the reduction in the distance between the crankset <NUM> and rear sprocket assembly <NUM>, maintaining a substantially constant belt tension without having to translate the guide pins 42a, 42b along the guide slots 34a, 34b.

The convertible sprocket assembly may be used to change the gear ratio in any bicycle and is not limited to the adjustable frame described above. It will be appreciated that the inner surface of the annular sprocket(s) may have fewer teeth compared to the inner sprocket such that the teeth provided on the inner surface of the annular sprocket(s) engage with only some of the teeth on the inner sprocket.

<FIG> show an alternative embodiment of the frame <NUM>. The frame <NUM> of this embodiment differs from the frame <NUM> in that the top tube <NUM> is provided with only a single pivot hole <NUM>. In the small and medium configurations, the connecting member <NUM> is arranged so that the boss <NUM> which connects the connecting member <NUM> to the pivot hole <NUM> is instead located behind the seat tube <NUM>.

During the transition between the medium and large configurations (shown in <FIG> and <FIG>), the connecting member <NUM> is rotated about its longitudinal axis so that the boss <NUM> lies in front of the seat tube <NUM>. As the boss <NUM> is offset from the axis of the seat tube <NUM>, this causes the connecting member <NUM> to be moved rearward.

As per the boss <NUM>, the bottom bracket shell <NUM> is also offset in the same direction from the axis of the seat tube <NUM>. Accordingly, as the connecting member <NUM> is rotated during the transition from the medium to large configuration, the bottom bracket shell <NUM> and thus the crankset <NUM> translate forwards. This avoids the crankset <NUM> from moving too far underneath the saddle <NUM> and thus maintains a slightly crank-forward position. The rotation of the connecting member <NUM> also increases the distance between the crankset <NUM> and the rear sprocket assembly <NUM> which allows the inner sprocket <NUM> to be used so as to increase the gearing, as described previously.

The bracing of the rear portion <NUM> against the front portion <NUM> (the link) may be achieved in other manners than that described previously. For example, the front portion <NUM> may extend past the pivot with the connecting member <NUM> and connect to the rear portion <NUM>. The link must, however, restrict the relative positions of the front and rear portions <NUM>, <NUM>.

If desired, the frame <NUM> may be provided with a suitable shock absorbing arrangement. For example, one or more of the connections between the front portion <NUM>, the rear portion <NUM> and the connecting member <NUM> may comprise an elastomeric portion, such as a bushing, which provides some damping. Alternatively, a shock absorber may be provided, such as in-line with the connecting member <NUM>. Where any movement of the relative positions between the front portion <NUM>, the rear portion <NUM> and the connecting member <NUM> is permitted by such suspension designs, it will be appreciated that the different size configurations refer to the resting or static geometry of the frame without any load.

Although the frame <NUM> has been described as having discrete pivot holes 20a, 20b, they may instead each be embodied as a slot which allows the position of attachment to be continuously varied or an enlarged opening which houses an insert or carrier (a flip chip) which can be reoriented within the opening to allow the position of attachment to follow a linear or non-linear path. The guide slot 34a, 34b may instead be embodied as several discrete mounting holes (or slots in order to still provide some adjustment for tensioning the belt <NUM>). Again, the guide slot 34a, 34b may instead be formed as an enlarged opening which houses an insert or carrier (a flip chip) which can be reoriented within the opening to allow the position of attachment to follow a linear or non-linear path. Although the guide slot 34a, 34b has been described as being curved, it may instead be straight or may be formed by a series of portions which are angled with respect to one another to form a zigzag or stepped slot.

The connecting member <NUM> may be removed from the frame <NUM> in order to allow the frame <NUM> to be folded to a more compact size for transportation.

Although the saddle <NUM> and seat post <NUM> have been described as having curved rails <NUM> and a curved clamp <NUM>, it will be appreciated that this arrangement could be reversed. Further, a single central rail or other guide may be used having a slot-type arrangement. The seat post <NUM> may also be omitted and the saddle <NUM> connected directly to the top tube <NUM> or connecting member <NUM>. Where the saddle <NUM> is connected directly to the top tube <NUM>, only minimal (or no) adjustment of the angle of the saddle <NUM> may be required, so that the curved rails <NUM> and clamp <NUM> can be dispensed with.

As described, the front fork <NUM> may comprise first and second pairs of fork-ends 46a, 46b to accommodate wheels of different sizes. Although not shown, a similar arrangement may also be used at the rear fork.

Although the holes 20a, 20b have been described as pivot holes, it will be appreciated that the connecting member <NUM> may be removed from the front portion <NUM> and reattached in a new orientation so that the connecting member <NUM> does not actively pivot about the hole 20a, 20b. Similarly, the connection between the connecting member <NUM> and the rear portion <NUM> need not be a pivot in the conventional sense.

In other embodiments, the bottom bracket shell <NUM> may be provided on the rear portion <NUM> instead of the connecting member <NUM>.

Claim 1:
A bicycle frame (<NUM>, <NUM>) comprising:
a front portion (<NUM>) configured to receive a front wheel assembly;
a rear portion (<NUM>) configured to receive a rear wheel assembly; and
a connecting member (<NUM>) configured to receive a seat assembly and connected to the front portion (<NUM>) at a first connecting point and connected to the rear portion (<NUM>) at a second connecting point, the first and second connecting points being spaced from one another along the length of the connecting member (<NUM>);
wherein one of the front and rear portions (<NUM>, <NUM>) extends towards and is connected to the other of the front and rear portions (<NUM>, <NUM>) at a third connecting point to form a link;
characterized in that the frame is configured so as to allow a distance between at least two of the connecting points to be adjusted;
wherein adjustment of said distance increases or decreases the size of the frame;
wherein the link has a plurality of mounting positions which define said distance;
wherein the plurality of mounting positions are formed by a plurality of discrete holes (14a, 14b, 14c) provided on the front portion (<NUM>).