The present invention relates to a stabiliser system for two wheeled vehicles, particularly vehicles which are powered by a rider. The invention relates most particularly, but not exclusively, to pedal bicycles and pedal-assisted bicycles. The rider of a bicycle experiences frequent stops and starts in urban areas due to road intersections, slow moving traffic and traffic congestion, road works and other obstructions. These conditions are a common occurrence for cyclists in towns and in urban areas and can result in potentially dangerous situations where the cyclist has to stop precipitately and may lose his or her balance in the process. In such traffic conditions, the cyclist has to put one or both feet on the ground at each stop and in many instances may have to dismount partially. The frequent and often abrupt stops and starts in traffic are highly inconvenient to the cyclist. They may also be potentially dangerous through loss of balance, impatient behaviour due to frustration and the like, particularly when the traffic includes heavy trucks. The design of the pedal bicycle and the physical dimensions of the rider often result in saddle seats which are set either too low for maintaining efficient pedal pressure or too high for remaining in the saddle when at the halt. This can lead to frequent dismounting and remounting. It is an object of the present invention to provide an improved stabilising system for a bicycle which enables the rider to bring the bicycle to a halt, without having to dismount.

There is described in WO92/02907 Al a stabiliser system, particularly for bicycles, which incorporates a stabiliser strut or arm pivoted at its upper end at or adjacent the rear wheel spindle of the vehicle and having at its lower end a cross shaft carrying stabilisers and a wheel-engaging roller, and means for lowering the arm to draw the cross shaft beneath the wheel, so that the tyre on the wheel engages the roller and the wheel is lifted off the ground. With this arrangement a large part of the weight of the rider is transferred to the ground through the wheel, the roller, the cross shaft and the stabilisers. According to one aspect of the present invention, the connection between the arm and the cross shaft incorporates a buffer. The buffer may be provided in various ways but in one arrangement there is a telescopic connection between the cross shaft and arm and the buffer is fixed within the outer member of the telescoping parts. Thus there may be provided a socket on the cross shaft which telescopingly receives the end of the arm, either the socket or the end of the arm having fixed thereto the buffer. In the preferred arrangement the arm is afforded by a tube having fixed at the outer end thereof a buffer block which engages, and preferably surrounds, the cross shaft. The socket may be fixed to the cross shaft in various ways but in one possible arrangement it forms part of a jacket which also has oppositely extending journals extending transversely to the socket and receiving the cross shaft. A retaining member such as a bolt may extend through the cross shaft and the buffer block and be secured to the arm. In a preferred arrangement, there is an abutment plate secured to the lower end of the

arm and through which the bolt passes and there may be a second abutment plate between an abutment such as the head of the bolt and the buffer block. Preferably the jacket has a hollow interior which is downwardly open to receive the buffer block and, where present, the upper and lower abutment plates. The jacket is preferably a fibre-reinforced polymer moulding. ^* The means for lowering the arm described in WO93/02908 Al comprises a rotary member such as a roller, rider-actuatable means for moving the rotatable member into engagement with a tyre on the said rear wheel of the vehicle to cause the rotary member to rotate, a spool rotatable by the rotary member, and a flexible element such as a cable windable on the spool and connected to the arm so that rotation of the spool draws the flexible element onto the spool and draws the roller beneath the wheel. In the preferred construction described, the shaft carries a second spool to rotate with the first spool, a length of cable running from each spool to the arm, the rotary member and the spools are carried on a common shaft to rotate together, and the rotary member and the spools are located ahead of the rear wheel. Although the construction described in WO93/02908 Al is perfectly satisfactory, it has been found that the geometry dictates a spool diameter which is smaller than is ideal for the multi-strand stainless steel cables which are commercially available. According to a second aspect of the present invention, the flexible element is reeved to provide a multi-part tackle between the spool and the arm. This enables the spool to have a substantially greater diameter while providing the same movement to the arm with the same

number of revolutions of the rotatable member. Preferably, there is a three-part tackle on one side of the vehicle with the flexible element anchored at the arm end, passing around a pulley at the forward end, round a pulley at the arm end and leading to the spool at the forward end. In a preferred arrangement, there is a second spool on the other side of the vehicle and a second three-part tackle running in a corresponding way to the first. In this arrangement, the rotary member may have a bore extending therethrough at a radius spaced from the axis of rotation with the flexible element passing through the bore from one tackle to the other. In this way the lengths of the parts of the flexible element making up the two tackles can self-adjust by longitudinal movement of the flexible element through the bore. The bore may be in a sleeve which is rotatably located in an aperture in the rotary member, the bore preferably having flared ends. The or each anchor may be rotatable on the cross shaft so that it is self-aligning, thus avoiding sharp flexing of the flexible element as the arm and cross shaft are lowered. There is described in WO 93/02907 a construction in which the arm is pivoted to a rearwardly extending portion of a bracket having an aperture intermediate its length to receive the rear wheel spindle, a spring extends between a forwardly extending portion of the bracket and a point on the arm below the point at which the arm is pivoted to the bracket, and the bracket carries means preventing rotation of the bracket about the rear wheel spindle in a direction to raise the forwardly extending portion.

While this arrangement is satisfactory, the present invention provides an alternative means for preventing rotation of the bracket about the rear wheel spindle in a direction to raise the forwardly extending portion. Thus, according to a third aspect of the present invention, there is a connecting element extending between a point on the bracket and a point on the frame of the vehicle, a tendency of the bracket to rotate in the said direction increasing tension in the connecting element. Thus, the bracket may have a point of connection for one end of the connection element spaced upwardly and/or forwardly of the axis of the rear wheel spindle. Preferably, where the vehicle is a bicycle, the other end of the connecting element is connected to an anchorage adjacent the bottom bracket, for example to a clamp on the chain stays preferably by a connection permitting relative lateral adjustment to accommodate lateral variations in vehicle configurations. Preferably, both ends of the connecting element are able to pivot about horizontal axes transverse to the vehicle. To provide a bias to the arm in the retracting direction, there is preferably provided a gas spring, the outer end of the piston rod being pivotally connected to a forwardly and preferably downwardly extending portion of the bracket and the cylinder being pivotally connected intermediate its length to the arm, by being pivotally connected to a mounting component by which the arm is pivoted to the first bracket. The bracket may comprise a first generally flat portion containing the aperture and the forwardly extending portion, a second generally flat portion containing the said point on the bracket offset from

the first portion and a shelf portion joining the first and second portion. This construction enables the point of connection of the connecting element to the bracket (and hence the connecting element itself) to be spaced outwardly from the centre plane of the vehicle and so more easily clear other components and in addition provides a stiffer or stronger construction. The bracket may comprise two partially nesting components such as flanged pressings or may, for example, be a moulding, forging or casting. These features of the bracket may have applications independent of the connecting element. Preferably, where the vehicle is a bicycle, the other end of the connecting element is connected to an anchorage adjacent the bottom bracket, for example to a clamp on the chain stays. Preferably, the bracket comprises two partially overlapping components, the overlapping parts affording an aperture for the rear wheel spindle of the vehicle and a pivot for the arm, and a non-overlapping part of one of the components affording the connection between the bracket and the connecting element. In an advantageous construction, one of the components has peripheral flanges around portions of the overlapping part thereof and the overlapping part of the other component is located by the flanges. The overlapping construction gives the bracket strength in the section which is most heavily stressed, namely that containing the pivots. These features of the bracket may also have applications independent of the connecting element. Thus, in a preferred construction for use with a bicycle and according to a fourth aspect of the

invention, the arm is mounted on a mounting component which is pivoted to a point on a bracket having an aperture through which the rear spindle of the bicycle passes, and a spring is secured between the bracket and the mounting component. The mounting component thus serves both to mount the arm on the bracket and to provide a mounting for the spring. The mounting of the arm on the mounting component may afford axial adjustment of the arm relative to the component, for example to accommodate different wheel sizes. Since the part of the bracket between the wheel spindle and the pivot for the mounting component will be highly stressed the construction referred to above and comprising two overlapped components, particularly when incorporating a shelf or offset, will be particularly suitable. it should be appreciated that many of the features referred to above, described below in more detail in relation to the drawings and included in the claims are individually inventive other than in combination with other features with which they are associated herein and, in particular, the four aspects of the invention referred to above may be considered as having the possibility of representing separate inventions. The invention may be carried into practice in various ways but one stabiliser system constructed in accordance with the invention will now be described by way of example with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a diagrammatic and fragmentary side elevation of the rear part of a bicycle with the stabiliser system fitted thereto and to a smaller scale than the subsequent Figures;

Figure 2 is a fragmentary plan view to an enlarged scale approximately on the plane II-II in Figure 1 with certain parts omitted; Figure 3 is a side elevation of the parts of the system shown in Figure 2,* Figure 4 is a rear elevation of the pendant arm shown in Figure 3; Figure 5 is a side elevation of the pendant arm; Figure 6 is a section through the pendant arm on the plane VI-VI in Figure 5; Figure 7 is a fragmentary side elevation of parts of the system shown in Figure 1 and extending from the region of the bottom bracket to the region of the rear wheel spindle; Figure 8 is a plan view of the part of the system shown in Figure 7; Figure 9 is a rear end elevation, partly in section, of the lower part of the system; Figure 10 is a detailed plan view of a plate member; Figure 11 is a detailed plan view of a buffer block; Figure 12 is an end elevation of the part of the system shown in Figure 9; Figure 13 is a detailed view of the anchorage system for one end of the cable shown in Figures 2 and 3; and Figure 14 is a section on the line XIV-XIV in Figure 13. Figure 1 shows, in simplified form, the rear wheel 111 of a bicycle having a rear wheel spindle 112 carried on each side in a gusset plate which is welded to the ends of a seat stay 114 and a chain stay 115.

The bicycle includes a bottom bracket 116 to which is connected the seat tube 117 and the down tube 118 and which provides bearings for the pedal spindle 119. The pedal spindle carries, on the far side as viewed in Figure 1, a chain wheel, not shown, and a chain passes around the chain wheel and the drive sprocket on the rear wheel hub. The bicycle includes a derailleur change speed gear which is not shown in the drawing but, alternatively, the bicycle could include a hub-type change speed gear or no gear change means. Attached to the frame of the bicycle in the vicinity of the rear wheel spindle 112 and on the side of the frame opposite to that of the drive sprocket is a bracket 124 the detailed construction of which is shown in Figures 7 and 8. The bracket consists of two generally flat but flanged pressings 125,126 which are coupled back to back. Each pressing has a rectangular section 127 containing an aperture through which the rear wheel spindle 112 passes so that the two rectangular sections are clamped together by the spindle nut and by a stub shaft 140 (described below) ; they are further prevented from rotating relative to one another by the rectangular section of the pressing 125 being nested within the flanges of the pressing 126. The pressing 125 has a section 128 which is of obtuse-angled isosceles triangle shape in elevation which lies in a vertical plane parallel to that of the rectangular sections 127 and is connected thereto and offset laterally outwardly therefrom by a horizontal shelf section 129. Adjacent the upper corner of the pressing 125 is an aperture receiving a bolt 131 through which passes a diametral bore 132 for one end of a rod 133 which is fixed in position by a nut 134.

The end portion of the rod 133 is threaded to improve the grip of the bolt on the rod when the nut is tightened. The effect of the shelf 129 is to laterally offset the section 128, thus taking it further from the centre plane of the bicycle to enable the rod 133 to clear any mudguard carrier or other fixings to the top of the chain stay gusset. If a further offset is required, the rod 133 may be passed through the bore 132 on the outside of the pressing 125. The shelf 129 also provides lateral stiffness to the bracket 124 and strengthens the cantilever beam which is constituted by the part of the bracket extending between the rear wheel spindle 112 and the stub shaft 140. The pressing 126 has a triangular section 135 similar to the triangular section 128 but downwardly directed and adjacent one corner of this section there is an aperture receiving the shank of a spherically headed bolt 136. The stub shaft 140 which is fixed to the bracket 124 pivots a further bracket or mounting component 137 which has a U-shaped upper portion, the two limbs of the U being drawn together by bolts passing through apertures 138 to clamp between them one end of a tubular stabiliser strut or arm 139. A gas spring 120 having a cylinder 142 and a piston 143 biases the arm 139 in an anticlockwise direction as seen in Fig. 1. A clamp 141 grips the cylinder 142 and carries a peg 141a which is rotatable in a bore 141b in the bracket 137; the outer end of the piston 143 of the spring carries a cup 144 which embraces the head of the bolt 136. It will be seen that the arm 139 and the spring 120 are both mounted to the bracket 137; in each case this mounting is afforded by a clamp which permits adjustment during installation to accommodate to

different wheel sizes and other variations in the geometry of the vehicle to which the system is to be attached. The forward end of the rod 133 is turned through almost a right angle and is inserted into an aperture 145a in a block 145 which overlies the forward ends of the chain stays 115; these are clamped between the block 145 and a lower block 146 by means of a nut and bolt 147. The purpose of the rod 133 is to prevent rotation of the bracket 137 about the axis of the spindle 112 under the loads imposed on it by operation of the arm 139 as will be described. In practice, it is believed that the majority of these loads - and almost certainly the largest of these loads - will be in a direction tending to turn the bracket in a clockwise direction as viewed in Figure 1 so that the rod 133 will normally be in tension. The effective length of the rod 133 can be adjusted by sliding it through the diametral bore 132 prior to tightening the nut 134. The fixings at both ends of the rod 133 allow both rotational and lateral adjustment during installation to adapt it to the geometry of the vehicle to which it is to be attached. As seen in Figure 9, the lower end of the strut 139 carries a coupling component 151 which is preferably of unreinforced nylon but could be of another material such as a light alloy moulding or a fibre-reinforced resin structure. The component 151 has a sleeve section 152 in which the lower end of the arm 139 is a sliding fit and two journal sections 153 through which passes a hollow cross shaft 154. Reinforcing flanges 166,167 extend between the sleeve section 152 and the journal sections 153. Between the

journal sections 153 is a square section buffer housing 155 into which the lower end of the arm 139 extends. This lower end has a plate 156 (Figure 10) welded to it. Beneath the plate 156 is a pair of resilient buffers 161,162 having semi-cylindrical grooves on their facing surfaces to receive the cross shaft 154. A second plate 159 engages the lower side of the buffer 162 and the buffers 161,162 are compressed by a bolt 158 which passes through the lower plate 159, the lower buffer 162, a diametral bore in the cross shaft 154, the upper buffer 161, the upper plate 156 and a nut 157 which is welded to the upper plate 156. Each of the buffers 161,162 has an inner section adjacent the cross shaft which is a push fit in the housing 155 and has chamfered vertical edges and an outer section which is of square cross section and is rather smaller than the cross section of the housing to allow for expansion under compression. The pre-compression of the buffers 161,162 by the bolt 158 copes with oscillations in load on the buffers during operation. The plates 156 and 159 are shaped as seen in Figure 10, to afford guidance within the buffer housing while minimising friction during relative movement. The plate 156 moving in the square section housing 155 prevents relative rotation of the shaft 154 about the longitudinal axis of the arm 139. Opposite ends of the shaft 154 carry freely rotatable moulded plastic ground engaging stabiliser wheels 171,172 held in place by circular spring clips. In the central region of the cross shaft 154 there is a freely rotatable roller 173 which is generally aligned with the plane of the bicycle wheel 111 and has flanges 174 which are spaced apart so as snugly to engage the

opposite sides of the tyre when the stabiliser is in operation as will be described below. On each side of the roller 173 is a rear pulley 170 and outside each pulley 170 is a cable anchorage 175, the pulleys and anchorages being rotatably mounted on the shaft 154. The anchorages are identical and therefore only one will be described. The anchorage is shown in detail in Figures 12 to 14. The anchorage is formed as a die-casting or moulding and is generally pear-shaped in elevation, having a cylindrical section 178 from which extends a radial flange 179. In the narrow part of the pear the flange 179 is thickened and an opening 180, extending generally radially of the cylindrical section 178 and flaring towards the cylindrical section provides a passage for a cable 181. The cable enters the opening 180, is wound twice around the outside of the cylindrical section 178 and then exits again through the opening 180, one end 181a of the cable being located just beyond the end of the opening. The cable is anchored by clamping by a nut and bolt 182; the nut is prevented from turning by being seated in the opening 180 and its escape is prevented by a nib 183 at the outer end of the opening 180. The facing surfaces of the opening 180 are grooved to a depth less than the diameter of the cable, the entrance groove being fractionally deeper than the exit groove so that the nut pressure is greater on the tail of the cable. A part - circumferent ial flange 207 on the respective anchorage 175 partially shrouds the adjacent pulley 170. The lower block 146 adjacent the bottom bracket 116 has a horizontal aperture receiving a pivot pin 191

on which is pivoted the upper end of a swing arm 192 (Figures 1, 2 and 3) which is able to pivot in the plane of the rear wheel 11. A stator arm 193 is also pivoted to the aperture 191 but is held in position by a strut 190 the upper end of which is connected to the down tube 118 by a clamp 189. The swing arm 192 is a moulding of complex shape, consisting essentially of a forwardly facing channel having a web 220 and forwardly directed flanges 221,222. In its lower part the web extends outwardly and rearwardly to form two generally triangular fins 223,224, the lower rear corners of which are formed as journals for a spindle 194. As can be seen from Figures 4 to 6, the stator arm 193 is a moulding of complex shape but is generally of channel form having a web 230 and rearwardly extending flanges 231 and 232. The upper end is formed with a journal section 233 by which the stator arm is pivoted to the pin 191 and the lower end is formed with a journal section 234 for a purpose to be described. A tyre engaging rotary member or drive wheel 195 and a pair of spools or winches 196 are rigidly secured to the spindle 194 between the two arms 223,224 of the swing arm 192. The wheel 195 may be toothed to ensure good contact with the tyre of the wheel 111. It is desirable to make the wheel 195 and the spools 196 as large as convenient but the size is of course limited by the geometry of the surrounding parts of the bicycle. Large diameters reduce the speed of rotation, increase the torque available, reduce the risk of the wheel 195 slipping on the tyre and ensure that the cable 181 lays neatly on the spools as will be described.

A transverse pin 235 extending through holes 236 in the flanges of the stator arm 193 carries a cam 237 (Figure 3) which has a lobe 238 engaging a pad 239 on the swing arm 192 and an arm 241 receiving one end of the core 242 of a Bowden cable 243. This cable extends to a manually operable control lever (not shown) on the handlebars of the bicycle. The sheath of the Bowden cable is secured to a bracket 244 secured at an adjustable position along the length of the strut 190. For purposes to be described below, the actuator lever on the handlebars is of the known construction which has a latching operative position and can be released by applying further pressure to the lever. Alternatively, a second lever could be provided to effect release. The lower end of the strut 190 is bifurcated and embraces the cam 237, the pin 235 passing through apertures in the limbs of the bifurcation. The cam extends through a slot 245 in the web 230 of the stator arm 193. Extending from each side of the stator arm 193 adjacent its bottom are housings 197 each of which contains a moulded pulley wheel 198 having an inner tapered flanged section 199 and an outer simple flanged section 200. The pulley wheels 198 are rotatable on a cross-shaft 201. The wheel 195 has a pair of opposed bosses 202 and a bore 203 extends through the wheel and bosses parallel with the axis of rotation of the wheel. The ends of the bore have trumpet- or bell-shaped flares through which the cable 181 can slide freely. The run of the cable 181 can be seen from Figures 2 and 3 and is as follows. One end is anchored as described in the anchorage 175 on one side. From there

a run 204 of the cable extends forwards, around the simple section 200 of pulley 198, rearwardly as a run 205 and around the pulley wheel 170 and forwardly again as the run 206. It then passes around the tapered pulley section 199 and passes through the bore 203 in the wheel 195. On the other side of the bicycle, the cable 181 is reeved in the equivalent manner and its other end is anchored to the anchorage 175 on the other side of the bicycle. By passing the cable through the bore 203 in the wheel 195 it is possible to avoid the necessity of anchoring the cable to the spools 196 as would be the case if a separate cable was used on each side of the bicycle. Also, when the cable is fully unwound from the spools 196, the cable will be able to move longitudinally through the bore 203 to equalise tensions between the parts of the cable on each side of the bicycle. The tapers on the pulley sections 199 bias the cable towards the outboard sides of the pulleys to ensure that the parts of the cable extending between the pulleys 198 and the pulley wheels 170 on the cross shaft 154 are kept clear of other components such as the tyre. Operation of the stabiliser is as follows. During normal riding, the stabiliser system is in the condition shown in Figure 1 with the strut 139 in the raised position. It is maintained in this position by the gas spring 120 tending to pivot the strut 139 in the anti-clockwise direction as seen in Figure 1, such movement being resisted by tension in the cable 181. When the rider comes near to stopping and wishes to be supported by the stabiliser system when he comes to a halt, he operates the control lever on the handlebars by moving it from the inoperative position to the

operative position. This causes the cam 237 to rotate so that the cam lobe 238 causes the swing arm 192 to swing counter-clockwise as seen in Figures 1 and 4 to bring the drive wheel 195 into engagement with the tyre of the rotating wheel 111. This causes the wheel 195 to rotate in the opposite direction, the spools 196 rotating in the same direction and winding in the cable 181. This causes the strut or swing arm 139 to move from the inoperative position seen in Figure 1 to an operative position beneath the wheel 111 causing the stabiliser wheels 171,172 to engage the ground. Also, because of the eccentric mounting of the upper end of the arm 139 relative to the axis of rotation of the wheel 111, the roller 173 comes into engagement with the tyre on the wheel 111. As the ground engaging wheels 171,172 and the tyre-engaging roller 173 move under the wheel 111 the bicycle wheel 111 is lifted off the ground, the arm 192 continuing to move clockwise until the arm is at approximately vertical or rearwardly inclined to the vertical at up to about 15°. The rider will time this to occur substantially at the time the bicycle comes to a halt. The weights of the rider and of the bicycle are largely transferred to the ground through the wheel 111, the roller 173 and the stabiliser wheels 171,172 but a small proportion of this weight will be transmitted through the arm 139. It will be seen that the stabiliser device will, provided that the bicycle is maintained approximately upright, support the bicycle in the upright position without the rider having to place a foot on the ground. It is also possible for the rider to dismount and to leave the bicycle in a parked condition. When the rider wishes to move off, the control

lever on the handlebars is released, thus releasing the cam 237 to allow the swing arm 192 to move clockwise as seen in Figures 3 and 4 to release the wheel 195 from the tyre of the wheel 111 and removing the restraint on rotation of the spools 196 under the influence of the tension in the cable 181 maintained by the gas spring 142,143. It will be seen that because the pulleys 198 on the stator arm 193 are located ahead of the spools 196, tension in the parts of the cable between the pulleys and the spools will tend to move the spools forwardly to retract the drive wheel 195 from the tyre. The arm 139 then moves back towards the retracted position under the influence of the gas spring 120 and the tendency of the bicycle to move forwards pressure is applied to the pedals. The rider rotates the pedals and rides away smoothly. Since the cable 181 is able to move longitudinally in the bore 202 in the wheel 195, the stabiliser system will be stressed approximately evenly by the portions of the cable on opposite sides of the bicycle so that it is not necessary to ensure that initially the two portions are of exactly equal length and any differential takeup between the two spools 196 or any differential stretch in the two portions of the cable will be self compensated. To facilitate this balancing effect by movement of the cable 181 through the bore 202, the cable should be so anchored that when the arm is in its retracted condition there are no turns of the cable on the spools 196. During initial setting up of the stabiliser system, the nut 134 is loosened and the effective length of the rod 133 is adjusted to position the bracket 124 appropriately so that, because of the

eccentricity between the pivotal axis of the strut 139 and the axis of the rear wheel hub 112, the roller 173 is sufficiently spaced from the tyre when the strut is in its retracted position but is sufficiently close to the axis of the rear wheel hub 112 when the strut is in the operative position for the bicycle wheel to be lifted off the ground by the roller 173, taking account of the compressibility of a properly inflated tyre. If the tyre should be partially deflated, the arm 139 will be able to move forwardly beyond the operative position and, in the case of a fully deflated tyre, reach a position in which the strut is forward of the vertical and the weight of the rider is transferred to the roller 173 essentially through the rim of the wheel 111 and the flattened walls of the tyre. Thus, the stabiliser system will still be operative and the arm 139 will not be excessively stressed. However, it may not be possible for the rider to move off from the halt at all easily as this will require the rear wheel to ride over the roller 173. This will provide the rider with a clear indication that the tyre is under-inflated. Although the bracket 124 has been described as being assembled from two pressings, it could alternatively be a reinforced plastic moulding, a metal forging or of some other construction. in order to prevent the arm 139 swinging too far to the left as seen in Figure 1 when the stabiliser device is operated, limiting means may be provided, preferably on the gas spring 120. Thus the cylinder of the gas spring may have an internal stop which is engaged by the piston or the piston rod may have a stop which engages the end of the cylinder of the gas

spring. In either case a compression spring may be provided to prevent excessive shock as the end position is approached. Although the cable 181 has been shown as having a three-part purchase on each side of the bicycle it would be possible to provide a purchase with only two parts or more than three parts. With reference to the coupling component 151 seen in Figures 9 to 11, it will be seen that this provides a rigid connection between the arm 139 and the cross shaft 154 except that it permits limited vertical movement of the swinging arm 139 when reacting with the buffer blocks 161,162. The buffer blocks are of a polymer having a low yield consistency to ensure stability in normal conditions, compressing only in conditions of overload when traversing a rough surface area or possibly when the bicycle is on the tilt with the rider in the saddle. It is intended to act as a damper in traversing rough surfaces and has minimum metal to metal contact for that purpose. The buffer provides for a reversal of the compressive forces as the cross shaft is lowered and comes under the rear tyre of the bicycle. Momentarily, when the stabiliser wheels 171,172 make contact with the ground and also when the rider is negotiating a bumpy surface, a downward load will be exerted on the buffer. However, when the cross shaft comes fully under the rear wheel of the bicycle, the load on the buffer will tend to be upward as the tyre of the bicycle is forced to compress onto the centre roller 173. The retaining bolt 157, while positioning the whole assembly, makes the essential connection with the lower end of the swinging arm 139. Limited

pre-compression is applied on installation by screwing up the bolt 158 to ensure that the lower flange plate 159 under head of the bolt always remains in contact with the buffer 162. To summarise, the double acting compressible connection is designed to minimise risk of distortion while providing a rigid connection between the swinging arm 139 and the cross shaft 154 through the buffer arrangement. Also, when the component 151 is made of polymer it has a modicum of flexibility and a capacity to recover from limited distortion. The telescoping connection between the arm 139 and the sleeve 155 and the compressibility of the buffer blocks 161,162 provide a degree of compressibility to the overall length of the arm 139 and are able to take up small misalignments and also shocks resulting from the wheels 171,172 travelling over bumps and to damp vibrations induced by irregularities in the road surface. It should be noted that the buffer blocks 161,162 which may be made of polyurethane are hard so that there will be little noticeable compression under normal conditions. However, the blocks can be compressed under exceptional loads such as bumps in the road surface and a significant tilting of the bicycle and rider when at the halt . With the two-part buffer arrangement described, it is possible to employ parts having different degrees of compressibility .