To increase the stability of such vehicles, there have been several proposals to duplicate either the front wheel or the rear wheel and to connect the two wheels to opposite ends of a balancing beam member pivoted to the vehicle frame at its mid point, thereby permitting equal movement of the wheels, one upwardly and the other downwardly as the vehicle tilts. Such an arrangement can provide greater stability when only one of the two wheels meets an obstruction on the road. The vehicle is, however, still at risk of toppling if the wheels lose adhesion to the road.

According to one aspect of the present invention, there is provided a motorcycle-type vehicle comprising a body structure, and rear and front ground-engaging wheels, in which the rear or front wheel or both is or are duplicated to form a pair of wheels, each wheel of the or each pair being connected to the body structure through a suspension having a first end linked to the associated wheel and a second end, the second ends being interconnected by connecting means constraining equal and opposite movements of the said opposite ends relative to the body structure, characterised by stabilizing braking means operable to

arrest movements of the said first ends of the suspensions relative to the body structure in the event of excessive lateral acceleration of the vehicle associated with incipient instability and in that limited movement is allowed in the path between each wheel and the body structure in the engaged state of the stabilizing braking means to provide a limited range of suspension.

With this arrangement, a small range of suspension movement will still be available when the stabilizing brakes are engaged so as to accommodate unevenness in the road's surface.

According to a further aspect of the invention, there is provided a suspension system for a front wheel of a motorcycle-type vehicle, comprising a swing arm for the front wheel, the swing arm being pivotally mounted at one end for angular movement about a first transverse axis of the vehicle, a stub axle assembly supporting the other end of the swing arm on its respective wheel, and a parallelogram linkage being formed by the swing arm, an upper arm pivotally mounted at a rear end for angular movement about a second common transverse axis of the vehicle, spaced above the first axis and a strut articulated at its upper end to the upper arm and at its lower end to the said other end of the swing arm. This arrangement provides the front wheel with constant trail as the suspension operates.

The arrangement is particularly suitable for motorcycle-type vehicles having a pair of front wheels, preferably including upper and lower steering rod systems for interconnecting a rider-operated steering control with each stub axle to form an Ackermann-type steering geometry, the upper and lower rod systems being interconnected for the

transmission of torques therebetween along the length direct of the struts.

The invention will now be further described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of one form of a four- wheeled motorcycle-type vehicle in accordance with the invention, Fig. 2 is a simplified front view of the vehicle being ridden along a straight road, Fig. 3 is a similar view of the vehicle being ridden round a right-hand bend, Fig. 4 is a diagrammatic perspective view of the rear suspension of the vehicle with its wheels, driving motors and other components omitted for clarity, Fig. 5 is a rear view of the rear suspension with the left-hand wheel riding over a bump while the vehicle is being ridden along a straight road, Fig. 6 is a view similar to Fig. 5 when the vehicle is ridden round a right-hand curve, Fig. 7 is perspective exploded view of the connection between a brake sector and a suspension arm, Figs. 8-10 show diagrammatically the behaviour of three different forms of suspension in response to variations in road surface;, Fig. 11 shows diagrammatically in more detail a suspension of the kind shown in Fig. 10, Figs. 12 and 13 are respectively front and rear perspective views of the chassis of a vehicle having a suspension of the kind shown in Figs. 10 and 12, Fig. 14 shows a portion of Fig. 12 on an enlarged scale, Fig. 15 shows the portion shown in Fig. 14 in side elevation,

Fig. 16 is a view similar to Fig. 14 of a variation of front suspension and steering, Fig. 17 is a. diagrammatic side view of the driving arrangement for one of the rear wheels, Fig. 18 is an axial sectional view of the pivotal connection between a suspension arm and the chassis, Fig. 19 is a cross section of a variant of Fig. 18, Fig. 20 shows diagrammatically a hydraulic equivalent to the mechanical balance beam arrangement of the previous figures, Fig. 21 shows diagrammatically in side elevation a vehicle carrying two-wheeled load containers, Fig. 22 is a similar view of the vehicle with the containers removed, and Fig. 23 shows the containers with handles extended.

The motorcycle-type vehicle shown in Figs. 1 and 2 is of generally conventional design insofar as it includes a frame supporting a fairing 1 within which is housed an engine and gearbox (not shown in detail), handlebars 2 for steering the vehicle, a seat 3 for the rider and an additional seat 4 for a pillion passenger.

The vehicle differs, however, from conventional design in that it has a pair of front wheels 4 and a pair of rear wheels 5. The spacing between the pair of front wheels 4 and also the spacing between the rear wheels 5 is sufficiently small to allow them to lie within the overall envelope of the vehicle as can be seen in Fig. 2.

As can be seen in Fig. 3, the rider. can, normally, tilt the vehicle to counteract the effect of centrifugal force when rounding a bend. For this purpose, each wheel 4,5 is mounted on the end of a respective swing arm. Fig. 4 shows diagrammatically the arrangement for the rear swing arms 6 which are each independently pivotally mounted at their

forward ends on the frame F for pivotal movement about the same transverse axis 7 which is horizontal when the vehicle is upright. At its trailing end, each swing arm 6 carries an axle 8 in which the respective rear wheel 5 is mounted.

As can be seen in Fig. 7, each swing arm 6 (here shown as being of tubular form) is secured to a cylindrical boss 9 formed with an internal bore 10 by means of which it is pivotally mounted on a shaft 11 which in turn is pivotally mounted in lugs 12 secured to the frame F. At its outer end (relative to the vehicle) the boss 9 is formed with a pair of dogs 13 interposed (with substantial angular clearance) between a pair of dogs 14 carried by a disc 15 secured to the shaft 11. The dogs 13 and 14 thus provide a lost-motion connection between the swing arm 6 and the shaft 11.

Cushioning elements 16, for example, of rubber, may be interposed between the dogs 13 and 14. These are retained by a cylindrical sleeve portion 17 of the disc 15.

The inner end of the shaft 11 carries a disc sector 21 which forms part of the disc brake assembly including a brake caliper 22 (Fig. 4) which can be engaged to arrest the disc 21 and shaft 11 and thereby limit the swinging movement of the swing arm 6 to the small range permitted by the clearance between the dogs 13 and 14 as further limited by the cushioning elements 16.

As shown in Fig. 4, each of the rear swing arm 6 is articulated to the lower end of a conventional suspension strut 25 at a point near but spaced from the axis 7. The upper ends of the two suspension struts 25 are articulated to the opposite ends of a beam 26 which is pivoted at its mid point on a shaft 27 carried by the frame F. Each suspension strut 25 is of the conventional kind having an internal spring and damping arrangement.

Under normal riding conditions, the brake 22 is disengaged so that the swing arms 6 are free to swing up and down under the control of the two suspension struts 25 and the beam 26. Thus, the suspension can accommodate a bump 28 encountered by one wheel as shown in Fig. 5. Further, as shown in Fig. 6, the rider can lean at an appropriate angle when rounding a bend. If, however, the wheels lose their grip on the ground, the brake caliper 22 can be quickly energised to arrest the two brake discs 21, for example, the position shown in Fig. 6 so that the vehicle is then prevented from tipping over further, apart from the small movement allowed by the lost motion connection 13,14,16.

Figs. 8a-c show the response of the suspension shown in Figs. 1-7 to three different road surface situations. Fig.

8a shows a smooth road surface with the two spring units 25 equally compressed. In Fig. 8b, only the right-hand wheel has encountered a bump in the road surface (hereinafter referred to as a b situation) resulting in the beam 26 turning through a sufficient angle to cause approximately equal compression in the two spring units 25 which are thus acting in series. When both wheels meet a bump of corresponding height as shown in Fig. c (hereinafter referred to as a c situation), both wheels are raised simultaneously thereby compressing both suspension units 25 equally without turning the beam 26 about its pivot 27. In this situation, the two spring units act in parallel giving an effective spring rate approximately four times greater than that in the case of Fig. 8b.

Where this variation in spring rate depending on whether one or both wheels encounters a bump is considered unacceptable, the arrangement shown in Fig. 9 may be used.

Here the swing arms 6 are connected to the respective ends of the balance beam 26 by links 31 of constant length having a ball joint 32,33 at each end. The pivot 27 or the

balance beam 26 is movable along a rectilinear guide way 34 secured to the vehicle frame. A single suspension unit 35 acts between the movable pivot 27 and the frame of the vehicle.

The arrangement shown in Fig. 9 gives the same spring rate for both b and c type situations but does not alter the potential wheel movement ratio of about 2: 1. In practice, this ratio would probably be reduced due to the b situation involving half the moving mass of the c situation, resulting in the b situation requiring less damping and in that the pivot point in the b situation has half the acceleration of the pivot point in the c situation so that there is less damping in the b situation than in the c situation. The reduced mass and reduced pivot point acceleration in the b situation tend to achieve similar damping characteristics with the possibility of a damping design being able to cope satisfactorily with both b and c type situations.

Where, however, it is essential that the wheel movements and damping characteristics in the b type situation should be as close as possible to those in the c type situation, the arrangement shown in Figs. 10 and 11 may be used. In this arrangement, a hydraulic ram 41 is interposed between the spring unit 35 and the vehicle frame.

The pivot 27 of the balance beam 26 is carried by a cross- head 42 which is slidable on one or a pair of guide rods 43 secured to the vehicle. The ram 41 is supplied with hydraulic fluid by a pump 42 and a valve 43 which is under the control of a processor 44, a sensor 45 measures the extension of the ram 41 and supplies a corresponding signal to the processor 44 along the line 46. A further linear sensor 47 determines the position of the cross-head 42 and thus of the pivot 27 and delivers a corresponding signal to the processor 44 along a line 48.

The processor 44 determines the acceleration of the pivot point 27 by analysis of the output signal from the sensor 47 and thus can cause the ram 41 to be. extended in the event of detection of a b type situation. The inventor acknowledges the help given by Dr. Y. H. Au and Dr. S.

Sivaloganathan of Brunel University in verifying the feasibility of this arrangement.

The incorporation of the hydraulic ram 41 has other advantages. It can be used to ensure a constant ride height of the vehicle despite variations in the load being carried.

By the provision of a suitable rider-operated control, the rider can raise the ride height when traversing rough terrain. The rider may reduce the ride height when travelling in slippery conditions. The ride height may be automatically reduced when the suspension locking brake is engaged. This could be modified in accordance with the angle of lean of the vehicle as determined by appropriate sensors such as a rotary sensor measuring the angle between the two suspension arms 6 or between the beam 26 and the cross-head 42.

At very low speeds, the processor could be programmed to lower the vehicle's ride height automatically to increase low speed stability and also for parking. When parked, the stabilising brake as well as one or more road wheel brakes would be engaged by a handbrake. In severe emergency, for example, when all wheels have lost grip and the vehicle is about to collide with something, a manual command could quickly lower the vehicle sufficiently to bring a large friction pad on the underside of the vehicle into contact with the ground to give a greater area of frictional contact than that provided by the tyres and thereby help to decelerate the vehicle. The vehicle could also rest on the pad when parked. The pad may be pivotally connected to the vehicle about a longitudinal axis, with centring springs.

In the preferred form of vehicle which has a pair of front wheels and a pair of rear wheels, the rams of the front and rear suspensions could be coordinated to help keep the vehicle level over uneven ground thus, where the front linear sensor 47 detects an upward movement of its associated pivot point 27, the rear ram could be instructed to extend correspondingly.

The resilient and damped suspension units 25 in Fig. 4 and 8 and 35 in Figs. 9-11, may be of any appropriate type whether resilience is supplied either by a spring or a compressed gas.

In the suspensions discussed so far, the suspension units have been shown acting at right angles to the swing arm 6 and thus. vertical in the drawings. However, by connecting them to integral lugs or projections on the swing arms, they may be placed substantially horizontally (or an any other desired angle) with corresponding space saving and lowering of the centre of gravity of the vehicle..

Figs. 12 and 13 are perspective views from the front and rear respectively of the chassis and suspensions of a four-wheel motorcycle-type vehicle, incorporating suspensions of the kind shown in Figs. 10 and 11, for the front and rear wheels. Parts corresponding to those shown in Figs. 10 and 11 are indicated by the same reference numerals increased by 100 and with the suffix F for the front suspension and R for the rear suspension.

The chassis shown in Figs. 12 and 13 has a mainframe 100 defining a location 101 for a prime move such as an internal combustion engine and a housing 102 for a transmission which may include a mechanical gearbox or a generator. The rear, trailing suspension arms 106R are each independently pivoted at their front ends to the rear of the

frame 100. The suspension arms 106F at the front of the vehicle are of an inverted U or J shape and are each independently pivoted to the front of the frame 100 again about a common transverse axis as leading suspension arms.

Suspension locking brakes 121F and 121R enable the suspension arms 106F and 106R to be locked to each other and/. or to the frame in an emergency. Each of the front swing arms 106F has a short lateral extension connected by the ball joint 132F to the connecting link 131F which is connected at its other end by the ball joint 133F to an arm of the beam 126F which is pivotally mounted on the cross- head 142F. The cross-head 142F is slidable along parallel guide rods 143F which have their ends secured in brackets 150F secured to the frame 100 at each end.

One end of the front resilient suspension unit 135F is secured to the cross-head 142F while its other, rear end is connected by the ram 141F and a clevice to an upstanding lug 152F to a portion of the frame 100.

Each of the rear swing arms 106R carries an upstanding lug 153R which are connected by the ball joints 132R, constant length links 131R and ball joints 133R to the opposite ends of the rear suspension beam 126R which is pivoted again about a vertical axis on the rear cross-head 142R. The guide rods 143R for the cross-head 142R are fixed at each end in brackets 150R. The rear end of the rear suspension unit 135R is secured to the cross-head 142R while the rear ram 141R interconnects the front of the rear unit 135R with an upstanding lug 152R on the frame 100.

It will be noted that the two suspension units 135F and 135R are side by side and offset from the centre line of the vehicle to produce a compact arrangement with a low centre of gravity.

At the front end, the frame has an upstanding bridge portion extending over the front connecting links 131F to form a support for the steering linkage which is shown on an enlarged scale in Figs. 14 and 15.

In Fig. 14, an Ackermann-type linkage is located above an upper wishbone member 171 and a stub axle assembly 172 is formed integrally with a vertical strut 173. At its free end, the swing arm 106F carries a bracket 160 on which the lower end of the stub axle assembly 172 is articulated by means of a ball joint 164. The centre of the ball joint 164 lies in the central plane of the tyre (not seen), thereby providing wheel centre steering. Above the stub axle assembly 172, the strut 173 is offset at 174. Near its upper end, the strut 173 carries an arm 175. The arm 175 is articulated to the leading end of the wishbone member 171 by means of a ball joint 176. The rear, base portions 161 of the wishbone members are pivotally mounted on cross-shafts 162 in the bridge portion 163. A drag link 177 is articulated to-the upper end of the strut 173 by means of a ball joint 178. At its rear end, the drag link 177 is articulated by a ball joint 179 to one arm of a bell-crank lever 180 which is pivotally mounted on the bridge at 180 and has its other arm 182 articulated at 183 to the outer end of a track rod 184. The inner end of each track rod 184 pivots at 185 to an arm 186 on the stem 187 of the handle bars 2 (Fig. 1), (or a steering wheel) thereby forming an Ackermann steering linkage.

The distance. X1 between the pivotal axis 149 of the front swing arms 106F and that of the ball joint 164 is equal to the distance between the axis 162 and the ball joint 176. Further, the distance X2 between the ball joint 176 and the ball joint 164 is equal to the distance between the axis 162 and the axis 149. Accordingly, the axes represented by 162,149,164 and 176 form a first

parallelogram. A second parallelogram (X1, X4) is effectively formed by the axes of 176,178,179 and 162. As a result, the Ackermann-type steering developed by the members 184 and 182 is transmitted to the front road wheels by these two parallelogram linkages which also provide constant trail for the suspension irrespective of up and down movements of the wheel and without deflecting the handlebars. The arrangement is also suitable for a single front wheel vehicle.

The inverted U or J shape of the front swing arms 106 permits the rear portions of the front wheels to turn without obstruction under the underside of the rear limb 107 of the swing arm.

As shown in Fig. 18, each rear, trailing suspension arm 106R, which may be an aluminium alloy forging, has a bore 108 in which a steel sleeve 109 is fixedly secured. The two ends of the sleeve 109 are supported in lugs 112 carried by the vehicle body by means of appropriate bearings 112a, which may for example be double row roller or ball bearings.

Within the sleeve 109 is a shaft 111 supported in end caps 115 fixed in the internal bore of the sleeve 109 by screw threads. The shaft 111 projects from one of the end caps 115 to carry one element 121 such as the brake sector, of the suspension stabilising brake.

Where residual resilient movement is required between the shaft 111 and the sleeve 109, the shaft 111 has projections 113 interposed with clearance between internal projections 114 on the interior of the bore. As in the case of Fig. 7, resilient buffer elements, for example of rubber, are inserted in the spaces between the projections 113 and 114. Where such resilient residual movement is not required, the projections 113 and 114 are made sufficiently large to avoid any clearance and may in fact be replaced by

a splined connection between the shaft 111 and the sleeve 109.

With this construction, a variety of different types of residual resilient suspension can be obtained when the suspension stabilising brake is engaged. Such resilient residual suspension is desirable to avoid the tendency of the vehicle to bounce and lose stability.

The following variations can be achieved:- 1. Residual suspension for b type situations with full suspension for c type situations. Here, the brake would interconnect the two suspension arms of each suspension with the interposition of the resilient elements between the projections 113 and 114.

2. Zero suspension movement for b type situations with full suspension movement for c type situations. Here, the resilient elements would be omitted so that the shaft 111 is effectively solid with the sleeve 109 for each suspension arm.

3. Residual suspension movement for both b and c type situations. Here, the other portion of each suspension brake, typically the caliper, is rigidly mounted on the chassis or other sprung part of the vehicle and resilient elements are included between the projections 113 and 114.

4. If the resilient residual suspension provided by the vehicle tyres is considered sufficient, the stabilising brakes may be arranged to effectively lock each suspension arm to the chassis without the interposition of the resilient elements.

5. Zero suspension movement for b type situations with residual suspension movements for c type situations.

This would be achieved by omitting the resilient elements, thereby locking the two suspension arms of each pair to each other but mounting the brake assembly to a member 118 (Fig.

19) which can make small angular movements about the shafts

111 under the constraint of resilient blocks 119 engaged between it and the elements of the chassis 100.

If it is not feasible to insert the brake to act between the two arms of the pair, with or without residual resilience, the construction shown in Fig. 18 may be used between the balance beam and the cross-head. This situation may occur where a differential unit is required in the position shown for the brake 121R in Fig. 13. Where zero suspension movement for b type situations and residual suspension movement for c type situations is required, an electrically-stiffened suspension damper would be used which is automatically activated when the suspension brake is engaged.

As shown in Fig. 16, the front suspension has a swing arm 231 for each front wheel. Each swing arm 231 is of inverted J shape having its shorter limb pivotally mounted on the frame F by the arrangement shown in Fig. 7 and connected, by the lost motion arrangement shown in Fig. 7 to a further brake sector 232. Approximately horizontal suspension struts 233 are articulated to the swing arms 231 at 234 at one end and to a beam 235 at the other end. The beam 235 is pivotally mounted on the frame in the manner of the beam 26 of the rear suspension but in this case the pivotal axis is approximately vertical.

As in the case of the rear suspension, the brake discs 232 can be arrested by a brake caliper 237 secured to the frame.

At the lower front end of each swing arm 231 is pivotally mounted a cross shaft 241 carrying at one end, a stub axle assembly 242 with an axle 243 for the front wheel (not shown). The stub axle assembly 242 can turn on the shaft 241 by means of a king pin 244.

The shaft 241 extends inwardly of the vehicle beyond the inner face of the swing arm 231 and is secured in a block 245 at the lower end of a tubular strut 246. Near its upper end, the strut 246 is. pivoted about a transverse axis 247 to the front end of a wishbone member 248, the rear end of which is pivotally mounted on a shaft 249 carried in lugs 250 secured to the frame F.

The handlebars 202 are carried on an upwardly extending shaft 251 which is supported in a bearing assembly 252 secured to the frame F. A shaft 251 carries short lever arms 253. Upper steering rods 254 are articulated at one end 255 to the lever 253 and at their forward ends at 256 to crank levers 257 which are of the same effective length as the levers 253.

The crank levers 257 are mounted on the upper ends of steering shafts 258 extending downwards through the struts 246 to terminate in lower crank arms 259 to which are articulated at 260 lower steering rods 261 articulated at their other ends 262 to steering lever 263 secured to the stub axle assemblies 242.

The distance between the axis of each shaft 241 and the pivotal axis 264 of the swing arm 231 is equal to the distance between the axis 247 and the axis of the shaft 249.

Further, the distance between the axis of the shaft 249 and pivotal axis 264 of the swing arm is equal to the distance between the axis 247 and the axis of the shaft 241, thereby resulting in a parallelogram linkage maintaining the strut 46 parallel to a particular axis of the frame. By making the arms 259 and 263 of appropriately unequal length, an Ackermann-type steering is obtained.

By using linear guiding for the pivot point of the balance beam as shown in Figs. 12-14, the variations in the

effect of the spring rate and damping can be reduced.

During movements of the suspension mechanism, the connecting links and swing arms in a b type situation, the force exerted by the suspension unit is not equally divided between the suspension arms, although the difference is likely to be small or negligible. Nevertheless, by repositioning the two balance beam ends above or below the pivot point axis, and/or by arranging the point of application of the suspension unit on a short projection on the beam, the force exerted by the suspension unit on the pivot point through the cross-head can be biased towards either suspension arm in a b type situation. This could also be used to counter the momentum of the suspension arm during a b type encounter, thereby improving stability.

Locating the suspension brakes on the pivotal axes of the swing arms reduces the unsprung weight and keeps the centre of gravity of the vehicle low. The links connecting the swing arms may be arranged to be in tension rather than compression, for example, by mounting the ? lugs 153 on the underside of their swing arms.

Fig. 17 shows an arrangement for driving one of the rear wheels. The front portion of the rear trailing suspension arm 106 forms a mounting for a hydraulic or electric motor 192 which drives a toothed pulley 193. A further toothed pulley 194 mounted on the axle 108 at the rear end of the suspension arm 106 is secured to the rear wheel. A toothed belt 195 extends around the pulleys 193 and 194 so that the motor 192 drives the rear wheel. The pulleys 193 and 194 and belt 195 could of course be replaced by a convention chain and sprocket drive.

The two motors 192 are mounted near the axis 7 and so do not greatly increase the unsprung mass of the rear suspension. The motors 192, if hydraulic are supplied by a

common swash-plate pump, or if electric by a generator, driven by an internal combustion engine. The drive is shared between the two motors in such a manner that they form a differential drive. The effective gear ratio between the engine and the rear wheels can be varied by varying the angle of the pump swash-plate or generator output. This may be controlled automatically in response to the torque encountered by each wheel and the road speed. As a result of using this transmission or other automatic transmission, the need for a hand operated clutch control on the left-hand handle bar is avoided. This control may be replaced by a manual control for the stabilising brakes. This control may be similar to the brake lever 88 (fig. 1) for controlling the front road wheel brakes.

In an alternative transmission, the rear wheels each incorporate an electric motor which is supplied by a common generator driven by the prime mover. Moreover, if desired, the front wheels may instead, or additionally, incorporate electric motors supplied by the generator ! In the modified suspension arrangement shown diagrammatically in Fig. 20, a hydraulic suspension unit 301 is connected by a respective link 302 to the suspension swing arm 306 for the respective wheel. The hydraulic chambers of the two hydraulic suspension units 301 are connected together by a line 307 which is also connected to the hydraulic oil chamber of an oleo pneumatic accumulator 308 in which a body of compressed gas 309 pressurises a body of oil 310 and thereby the oil in the two suspension units 301.

In the event of detection of a b situation, additional oil can be fed into the system through a line 311 supplied either directly from a system of the kind shown in Fig. 11

or by the use of a ram 312 to displace oil from a chamber 313.

Because the vehicle's components are mounted as low as practically possible to give the vehicle a low centre of gravity, perhaps with the fuel tank between the back wheels, a useful space is created on top of the main components either side of the seat post. These spaces could have racks on them for tying down transported items or for permanent or removable containers. If removable, the containers could have their own wheels and extendable handle for easy transportation to and from the vehicle as shown in the following diagram. Alternatively, the seat post could be mounted to one side or from the front or back of the vehicle to give an interrupted load space.

Thus, Figs. 21 and 22 are side views of a vehicle of the kind shown in Figs. 12 to 14. The vehicle has a fuel tank 320 mounted between the rear, trailing suspensions arms 106R which, as shown here can be of curved shape. An upstanding post 321 extends upwards from the body structure 100 between the suspension units 135F and 135R (Figs. 12 and 13) to carry a suitable seat or saddle 322. As can be seen from Fig. 22, a low centre of gravity is achieved. This enables containers for goods such as those shown at 323 to be carried one between the post 321 and the handlebars 2 and the other behind the post 321 as shown in Fig. 21.

Conveniently, the containers 323 have a pair of small wheels 324 and a retractable handle 325. In the vehicle shown in Figs. 12 to 14, the stabilising brake arrangement shown in Fig. 7 may be used for each of the suspension arms. When the stabilising brakes are engaged, limited residual suspension movement remains available in response to both b and c type situations. If no residual resilient suspension is required in response to b type situations when the stabilising brakes are applied, the stabilising brakes would

be arranged to act directly on the suspension arms without the interposition of any resilient elements. If residual resilience is required in such a case in response to c type situations, the brakes could be resiliently mounted to the vehicle.

In operation, the vehicle described above can be ridden under normal conditions like a conventional motor bicycle as shown in figs. 2 and 3. The maximum angle of tilt, however, allowed by the suspension need only be about 30° to accommodate cornering forces which would require a conventional two-wheel motorcycle to lean at an angle of 45°.

If the rider senses that the vehicle is losing control, the rider can engage the stabilising brakes to prevent further tilting of the vehicle (other than the relatively small residual angular movement where allowed by the lost- motion device such as shown in fig. 7). This control arrangement may be augmented by sensing means (for example an accelerometer arranged to detect abnormal lateral acceleration) for detecting incipient instability and reacting more quickly than the rider to apply the stabilising brakes. The rider then assumes manual control of the stabilising brakes and releases them when the dangerous condition has passed.