A STEERING ASSEMBLY

The present invention relates to a steering assembly suitable for a vehicle, such as a mountain board. The present invention also relates to frame and sub- frames for a steering assembly.

A mountain board comprises a deck on which three or four wheels are mounted. The mountain board is typically larger than a skateboard. For example, the deck may be 120cm in length and the diameter of the wheels may be between 20cm and 30cm. The three main styles of riding are 'borderX', 'freestyle' and 'freeride'. Mountain boards are sometimes called landboards^

The wheels on a mountain board are generally mounted on trucks which are spring-loaded to stiffen turning of the mountain board. A common type of truck comprises a frame fixedly mounted on the deck and a sub-frame carrying an axle. The sub-frame is typically attached to the frame by two bolts, one in front of the axle and the other behind the axle. The frame may be located between rubber bushes to allow it to rotate relative to the sub-frame. This relative rotation causes the sub-frame, and hence the axle, to turn in response to changes in the forces applied to the deck.

There are, however, certain limitations associated with known mountain board trucks. The sub-frame is typically offset vertically from the axle and the resultant forces do not act through the axle. The offset may also result in movement of the axle backwards and forwards relative to the frame. The efficiency with which forces are transferred from the deck to apply a turning force to the sub-frame may thereby be reduced. The prior art truck assemblies are typically made of steel and in order to withstand the forces experienced during use of the mountain board they are relatively heavy. The mounting of the frame between rubber bushes also adds weight to the mountain board.

Furthermore, known trucks typically comprise a single elongate frame which is mounted on the deck by mechanical fasteners. The transfer of forces

through the frame may damage the frame or deck over time and ultimately may result in component failure.

The present invention at least in preferred embodiments ameliorates or overcomes the problems and limitations associated with known steering assemblies, such as mountain board trucks.

Viewed from a first aspect, the present application relates to a sub-frame for carrying at least one axle having a longitudinal axis, the sub-frame comprising first and second members for mounting the sub-frame, wherein the first and second members are offset relative to each other in a direction perpendicular to said longitudinal axis and the first member is provided above the longitudinal axis and the second member is provided below the longitudinal axis.

The first and second members are preferably vertically offset from each other. When the first member and/or the second member is/are substantially horizontal, the first member is preferably above the longitudinal axis of said at least one axle and the second member is below the longitudinal axis of said at least one axle. In use, the offset of the first and second members may advantageously induce a turning moment about the longitudinal axis of the axle when turning forces are applied to the sub-frame. This turning moment can increase or decrease the downward force applied to the outside wheel in a turn depending on the orientation of the sub-frame.

Preferably, the first member is provided on a first side of the longitudinal axis and the second member is provided on a second side of the longitudinal axis. The first member is preferably provided above the longitudinal axis and the second member is preferably provided below the longitudinal axis. The first and second members are preferably substantially parallel.

The sub-frame could be made of metal, such as stainless steel, but is preferably made of carbon fibre. An insert is preferably provided in the first member and/or the second member. The insert is preferably made of stainless steel or Kevlar (RTM). The sub-frame may also include a grind plate. The grind plate is preferably made of stainless steel or Kevlar (RTM). Alternatively, the grind plate

may be reinforced with Kevlar (RTM) layers, for example as an outer coating to carbon fibre. It will be appreciated that this type of construction can be used in all areas of the frame and/or sub-frame requiring reinforcement.

The present invention further relates to a steering assembly comprising a sub-frame as described herein.

Viewed from a further aspect, the present application relates to a sub- frame for carrying at least one axle having a longitudinal axis, the sub-frame comprising first and second members for mounting the sub-frame, wherein the first and second members are offset relative to each other in a direction perpendicular to said longitudinal axis.

The present invention also relates to a vechicle such as a mountain board or a land board comprising one or more sub-frames as described herein. The vehicle comprises a deck or board on which the steering assemblies are mounted. When the deck is substantially horizontal, the first member of said sub-frame is above said longitudinal axis of said at least one axle and the second member is below the longitudinal axis of said at least one axle.

Viewed from a further aspect, the present invention relates to a steering assembly comprising a frame for mounting the assembly and a sub-frame carrying at least one axle; the sub-frame having first and second members for mounting the sub-frame on the frame, the first member being provided on a first side of the axle and the second member being provided on a second side of the axle; the axle having an axis and the first member being provided above said axis and the second member being provided below said axis. When the first member and/or the second member is/are substantially horizontal, the first member is above the longitudinal axis of said axle and the second member is below the longitudinal axis of said axle.

The first and second members are preferably each provided with a reinforcing insert. The reinforcing inserts preferably provide reinforcement for supporting one or more fasteners for attaching the sub-frame to a frame. The frame may be a substantially rectangular member, but it is preferably

Y-shaped.

The steering assembly preferably comprises first and second resilient members provided between the frame and the sub-frame. The resilient members enable the frame and the sub-frame to move relative to each other. The resilient members may be substantially circular, rectangular, elliptical or oval in transverse cross-section.

The first and second resilient members may be springs but they are preferably bushes. Different grades of polyurethane may be used in the same bush to alter its characteristics. A higher density polyurethane may be used to form an outer portion of the bush while a lower density polyurethane is used proximal the centre of the bush. Alternatively, a higher density polyurethane may be used to form the centre of the bush and a lower density polyurethane provided around the higher density polyurethane. A bush formed from a plurality of grades of polyurethane is believed to be independently patentable.

The width of the first resilient member may be greater than or less than the width of the second resilient member.

The steering assembly may be provided with a single axle. Alternatively, a first axle may be provided at a first end of the sub-frame and a second axle provided at a second end of the sub-frame. A reinforcing rod may be provided between the first axle and the second axle. The at least one axle may be formed separately from the sub-frame.

Preferably, the at least one axle is formed with an end-piece for fitting over an end of the sub-frame. The end-piece is preferably made of metal.

Alternatively, the at least one axle may be formed integrally with the sub- frame. The frame and/or the sub-frame may be made of metal. Preferably, however, the frame and/or the sub-frame is/are formed from carbon fibre.

The frame is preferably provided with one or more reinforcing inserts.

The steering assembly preferably also comprises a first fastener and a second fastener to mount the sub-frame on the frame. Additional fasteners may be provided, if required.

The fasteners to mount the sub-frame are preferably adjustable bolts. The adjustable bolts preferably each have a head with a rounded underside to facilitate relative movement between the bolt and the frame and/or sub-frame. The fasteners are preferably made of phosphor bronze or sinted bronze. The underside of the heads of the adjustable bolts preferably define a portion of a sphere. The head of each adjustable bolt is preferably received in a collar having a cooperating surface. The cooperating surface is preferably coated with polytetrafluoroethylene.

The sub-frame may be provided with a grind plate. The grind plate is preferably made of Kevlar (RTM).

The present invention further relates to a vehicle such as a mountain board or a land board comprising one or more steering assemblies as described herein. The steering assembly may be mounted on a deck of the vehicle. When the deck is substantially horizontal, the first member of said sub-frame is above said longitudinal axis of the axle and the second member is below the longitudinal axis of the axle.

The vehicle preferably comprises first and second steering assemblies as described herein. A first steering assembly is preferably provided at a first end of the vehicle and a second steering assembly provided at a second end. The first member of each steering assembly (i.e. the member provided below the longitudinal axis of the associated axle) is preferably provided between the axles of the first and second steering assemblies. Thus, the second member of each steering assembly (i.e. the member provided above the longitudinal axis of the associated axle) is provided at the front or back of the vehicle. Viewed from a further aspect, the present invention relates to a steering assembly comprising a frame for mounting the assembly and a sub-frame carrying at least one axle; a first fastener and a second fastener being provided to attach the sub-frame to the frame; the frame being rotatable relative to the sub-frame about a first axis; and said at least one axle defining a second axis; wherein rotation of the frame about said first axis causes the first fastener to apply a first turning force to the sub-frame and the second fastener to apply a

second turning force to the sub-frame, the first and second turning forces occurring in a plane and said second axis being substantially coincident with said plane.

This arrangement is particularly desirable since the turning forces are applied directly through the axle. At least in preferred embodiments this improves the control characteristics of the steering assembly. The present invention may advantageously reduce or minimise translation of the axle which may otherwise occur as a result of the plane in which the turning forces occur being offset from the axle. The first and second turning forces are preferably substantially parallel to the second axis. It will be appreciated that the rotation of the frame about the first axis will generate forces which are not parallel to the second axis. The application of these non-parallel forces to the sub-frame causes the sub-frame also to rotate about the first axis. The first and second fasteners are preferably offset from each other along said first axis. The first fastener or the second fastener may be substantially coincident with the second axis. Preferably, however, the first fastener is provided on a first side of the second axis and the second fastener is provided on a second side of the second axis. The first and second fasteners are preferably substantially equi-distant from the second axis.

The first fastener is preferably attached to a first member provided on the sub-frame and the second fastener is preferably attached to a second member provided on the sub-frame. The first and second members may be co-planar or they may be parallel to each other.

The first and second members may be provided at the same level as the second axis. Preferably, however, the first and second members are vertically offset from each other (preferably along a third axis substantially perpendicular to the first and second axes). The first member is preferably provided above the second axis and the second member is preferably provided below the second axis. The vertical offset of the first and second members advantageously

induces a turning moment about the first axis when the first and second turning forces are applied to the sub-frame. In use, this turning moment can increase or decrease the downward force applied to the outside wheel in a turn depending on the orientation of the sub-frame. For example, if the sub-frame is arranged such that front member is higher than the rear member, the downward force applied to the outside wheel will be reduced. Conversely, if the sub-frame is arranged such that front member is lower that the rear member, the downward force applied to the outside wheel will be increased. Thus, the turning characteristics may be adjusted to suit different individuals or conditions. It will be appreciated that the magnitude of the turning moment is related to the size of the offset between the first and second members.

The first and second members preferably each have reinforcing inserts for contacting the first and second fasteners respectively. The frame preferably also has reinforcing inserts for contacting the first and second fasteners. The reinforcing inserts may be made of Kevlar (RTM) but they are preferably made of stainless steel.

The first fastener and/or the second fastener is/are preferably provided along the first axis. The first and second fasteners preferably have substantially parallel longitudinal axes. The longitudinal axes of the first and second fasteners are preferably substantially perpendicular to the first axis.

The frame preferably comprises a member having three or more arms. Although the frame may be an X-shaped member, it is preferably a Y-shaped member. Two or more of the arms are preferably suitable for mounting on the deck and the sub-frame is mounted on the remaining arms. The steering assembly is preferably arranged such that the first turning force and the second turning force are applied in opposite directions. The first and second turning forces are preferably applied in directions substantially parallel to the second axis.

The first and second axes are preferably substantially perpendicular when no load is applied to the frame and/or sub-frame.

The steering assembly preferably also includes first and second resilient members. The resilient members are preferably provided between the frame and the sub-frame. The first and second resilient members are preferably secured in place by the first and second fasteners respectively. The first and second resilient members could be springs, such as coil springs, but are preferably bushes.

The bushes are preferably made of rubber or polyurethane.

The sub-frame may carry a single axle. The axle may extend across the sub-frame to allow a wheel to be mounted at each side of the sub-frame. Preferably, however, the sub-frame carries a first axle at a first end thereof and a second axle at a second end thereof. Wheels are preferably mounted on the first and second axles.

The sub-frame may further comprise a reinforcing member. The reinforcing member preferably extends between the first axle and the second axle. The reinforcing member is preferably a rod. Most preferably, the reinforcing member is a carbon rod.

The at least one axle may be formed integrally with the sub-frame. Preferably, however, the at least one axle is formed separately from the sub- frame. The at least one axle is preferably formed with an end-piece for fitting over an end of the sub-frame. The end-piece is preferably made of metal.

The frame and/or the sub-frame could be made of metal. Preferably, however, the frame and/or the sub-frame is/are formed from carbon fibre.

The first fastener and the second fastener are preferably adjustable bolts. The adjustable bolts preferably each have a head having a rounded underside to facilitate relative movement between the bolt and the frame and/or sub-frame. The underside of the head of each adjustable bolt preferably defines a portion of a sphere. The head of each adjustable bolt is preferably received in a collar having a cooperating surface. The cooperating surface may be coated with polytetrafluoroethylene to help reduce friction between the bolt head and the collar. The first and second fasteners may be made of phosphor bronze which is a self-lubricating metal or sinted bronze.

The sub-frame is preferably provided with a grind plate. The grind plate is preferably provided on an underside of the sub-frame. The grind plate is preferably made of Kevlar (RTM).

The present invention further relates to a mountain board having at least one steering assembly as described herein. Preferably, the mountain board has two of the steering assemblies, one to carry a front set of wheels and a second to carry a rear set of wheels.

The present invention also relates to a frame or a sub-frame for a steering assembly as described herein. Furthermore, the present invention relates to a kit of parts for a steering assembly as described herein.

Viewed from a still further aspect, the present application relates to a steering assembly comprising a frame for mounting the assembly and a sub- frame carrying at least one axle, a first fastener and a second fastener being provided to attach the sub-frame to the frame; a resilient mount being provided to enable the frame to rotate about a first axis relative to the sub-frame; wherein the resilient mount consists of a first resilient member and a second resilient member provided between the frame and the sub-frame. Thus, the frame is not mounted between resilient members. Rather, the resilient mount consists of only first and second resilient members and these are provided between the frame and the sub-frame. Although the first and second resilient members could be springs or other resilient members, they are preferably bushes.

Viewed from a yet further aspect, the present application relates to a frame for a mountain board steering assembly, the frame having first and second elongate members for mounting on a deck and a third elongate member for carrying a sub-frame. This arrangement is particularly effective for transferring forces from the deck to a sub-frame carrying at least one axle. The frame is preferably y-shaped.

The frame cold be made of metal, such as stainless steel, but is preferably made of carbon fibre. Alternatively, the frame could be made from a fibreglass/carbon fibre composite. The frame preferably also has at least one reinforcing insert.

Viewed from a still further aspect, the present invention relates to a sub- frame for a mountain board steering system, the sub-frame comprising first and second mounting members and a tubular member for supporting at least one axle, wherein the sub-frame is made of carbon fibre. The first member is preferably provided with at least one reinforcing insert.

The second member is preferably provided with at least one reinforcing insert.

The sub-frame is preferably also provided with a grind plate. The grind plate is preferably made of Kevlar (RTM).

Viewed from a still further aspect, the present application relates to a fastener comprising a head and a shaft, wherein at least part of the head of the fastener is defined by a portion of a sphere. This arrangement is particularly suitable for allowing relative movement, and especially rotational movement, between components fastened together by the fastener. This arrangement is desirable in a range of applications, for example the mounting of a sub-frame to a frame in a mountain board steering assembly. The shaft is preferably threaded.

The fastener has a longitudinal axis and the centre of the sphere defining at least part of the head of the fastener is preferably located on said longitudinal axis. The at least part of the head of the fastener is preferably substantially hemispherical. The at least part of the head of the fastener defined by a portion of a sphere is preferably provided on an underside of the head nearest the shaft.

The threaded shaft preferably has a male thread or a female thread extending over at least a portion of its length.

A portion of the shaft proximal the head of the fastener is preferably unthreaded. The un-threaded portion is preferably provided between the head of the fastener and the threaded portion of the shaft. The un-threaded portion of the shaft may provide support in a transverse direction whilst helping to protect the threaded portion of the shaft from damage.

The head of the fastener preferably has a keyed recess. The keyed recess is typically suitable for receiving an Allen key, a hexagonal key or a screwdriver.

The fastener is preferably made of phosphor bronze or sinted bronze. The fastener may be oil impregnated to provide additional lubrication.

The fastener may be machined but is preferably moulded. The fastener is preferably a bolt. The present invention also relates to a collar for receiving a fastener as described herein. The collar preferably has a cup portion for receiving the head of the fastener and an aperture for allowing the threaded member to project out of the collar. The aperture is preferably conical to facilitate movement of the threaded member relative to the collar. Viewed from a further aspect, the present invention relates to an adjustable fastener comprising a first bolt and a second bolt, the first bolt having a first head and the second bolt having a second head; the first and second bolts having cooperating threads; wherein at least part of the first head is defined by a portion of a first sphere. The adjustable fastener preferably has a longitudinal axis. The centre of the first sphere defining at least part of the first head is preferably located on said longitudinal axis.

The at least part of the second head is preferably defined by a portion of a second sphere. The centre of the second sphere defining at least part of the second head is preferably located on the longitudinal axis of the adjustable fastener.

The adjustable fastener preferably also comprises a first collar for the first bolt and/or a second collar for the second bolt. The first collar preferably has a first cup portion for receiving said first head. The second collar preferably has a second cup portion for receiving said second head.

Viewed from a still further aspect, the present invention relates to a steering assembly as described herein, wherein at least one of the first and second fastener(s) is an adjustable fastener of the type described herein.

Viewed from a yet further aspect, the present invention relates to a steering assembly comprising a frame for mounting the steering assembly and a sub-frame for carrying at least one axle, a first resilient member and a second

resilient member being provided between the sub-frame and the frame, wherein the width of the first resilient member is greater than the width of the second resilient member. The term "width" in this context refers to the dimension of the resilient member measured in a direction substantially parallel to a longitudinal axis of said at least one axle. The first resilient member may be provided at the front or at the back of the steering assembly. The first and second resilient members are preferably provided along a first axis.

The resilient members may be circular in transverse cross-section, but equally may be substantially oval, elliptical or rectangular. The resilient members may be springs but are preferably bushes.

The present invention also relates to a vehicle comprising a board and at least one steering assembly as described herein. The at least one steering assembly is typically provided at an end of the board. The second resilient member may be provided closer to the middle of the board, but preferably the first resilient member is provided closer to the middle of the board.

Preferably, the vehicle comprises first and second steering assemblies of this type provided at first and second ends respectively of a board. The resilient members having the largest width in each steering assembly are preferably provided towards the middle of the board. Viewed from a still further aspect, the present invention relates to a steering assembly comprising a frame for mounting the steering assembly and a sub-frame for carrying at least one axle, a first resilient member and a second resilient member being provided between the sub-frame and the frame, wherein the resilience of said first resilient member is greater than the resilience of said second resilient member. The first and second resilient members are preferably bushes. The resilience of the bushes may be determined by the grade or density of the material from which they are made. The first resilient member may be provided at the front or at the back of the steering assembly.

Viewed from a still further aspect, the present invention relates to a steering assembly comprising a frame for mounting the steering assembly and a sub-frame for carrying at least one axle, a first resilient member and a second

resilient member being provided between the sub-frame and the frame, wherein the height of said first resilient member is greater than the height of said second resilient member.

Viewed from a further aspect, the present invention relates to a steering assembly comprising a frame for mounting the steering assembly and a sub- frame for carrying at least one axle, a first fastener and a second fastener being provided to attach the sub-frame to the frame, the first fastener having a first longitudinal axis, the second fastener having a second longitudinal axis and said sub-frame having a third longitudinal axis; wherein the first axis transects the third axis.

The first and second longitudinal axes are preferably substantially parallel when there is no load on the frame and/or sub-frame. Alternatively, the first and second longitudinal axes may be substantially perpendicular when there is no load on the frame and/or sub-frame. Viewed from a still further aspect, the present invention relates to a sub- frame for supporting an axle, the sub-frame comprising a tubular member, wherein the transverse cross-section of said tubular member defines an aerofoil for generating lift or a down force.

It will be appreciated that the steering assembly described herein is suitable for use with a variety of wheeled vehicles and is not limited to use with a mountain board.

Preferred embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 shows a mountain board having front and rear trucks in accordance with a first embodiment of the present invention;

Figure 2 shows the front truck of the mountain board shown in Figure 1 ;

Figure 3 shows a perspective view of the truck according to the first embodiment;

Figure 4A shows a perspective view of a frame for the truck according to the first embodiment;

Figure 4B shows a side view of the frame shown in Figure 4A;

Figure 4C shows a plan view of the underside of the frame; Figure 4D shows a cross sectional view of the frame; Figure 5 shows an exploded view of a sub-frame for the truck according to the first embodiment; Figure 6A shows a perspective view of the sub-frame shown in Figure 5;

Figure 6B shows an end view of the sub-frame;

Figures 6C shows a perspective view of the underside of first and second mounting brackets provided on the sub-frame;

Figure 6D shows a cross-sectional view of the sub-frame mounting bracket;

Figure 6E shows a perspective view of a grind plate provided on the underside of the sub-frame;

Figure 6F shows a side view of the grind plate shown in Figure 6E; Figure 7A shows a perspective view of first and second axles and a reinforcing rod for the truck;

Figure 7B shows a cross-sectional view of the first axle; Figure 8 shows a perspective view of a bush for the truck according to the first embodiment of the present invention;

Figure 9A shows a female fastener and a collar for mounting the sub- frame on the frame;

Figure 9B shows a male fastener and a collar for cooperating with the female fastener shown in Figure 10A;

Figure 9C shows the male and female fasteners assembled; Figure 9D shows a cross sectional view of the assembly shown in Figure 10C;

Figure 10 illustrates the relative movement of the female fastener relative to the collar;

Figures 11 A to 11 F show the different stages in the assembly of the truck according to the first embodiment of the present invention; Figure 12A illustrates the response of the truck to a force applied to the frame member;

Figure 12B illustrates the deformation of one of the rubber bushes in response to the application of a force;

Figure 13 shows a plan view of the sub-frame according to the first embodiment; Figure 14 shows a side view of the steering assembly according to the first embodiment;

Figure 15 shows a modified mounting arrangement for the steering assembly according to the first embodiment;

Figure 16 shows a modified version of the steering assembly according to the first embodiment;

Figure 17 shows a modified version of the frame according to the first embodiment;

Figure 18 shows a steering assembly according to a second embodiment of the present invention; Figure 19 shows a truck according to a third embodiment of the present invention; and

Figure 20 shows a truck according to a fourth embodiment of the present invention.

A mountain board 1 in accordance with the present invention is shown in Figure 1. The mountain board 1 comprises a front truck 3 and a rear truck 5 mounted on a deck 7. A pair of bindings 9 is provided on the deck 7 to attach a rider's feet to the mountain board 1. The front and rear trucks 3, 5 are the same and for brevity only the front truck 3 will now be described. As shown in Figures 2 and 3, the front truck 3 comprises a frame 11 for mounting the truck 3 on the deck 7 and a sub-frame 13 for carrying a pair of axles. The frame 11 and the sub-frame 13 are both moulded from carbon fibre.

The frame 11 is a Y-shaped member having first and second arms 15, 17. A series of holes 19 are provided in the frame 11 for receiving bolts to mount the frame 11 fixedly on the underside of the deck 7. First and second apertures 21 , 23 are provided along a longitudinal first axis X of the frame 11 for receiving first and second mechanical fasteners 25, 27 to mount the sub-frame 13.

The sub-frame 13 comprises a tubular member 29, a front bracket 31 and a rear bracket 33. The sub-frame 13 carries first and second axles 35, 37 on which wheels 39 are mounted. The wheels 39 are rotatable about a longitudinal second axis Y defined by the first and second axles 35, 37. The front and rear brackets 31 , 33 are offset vertically relative to each other, i.e. spaced apart along a third axis Z, perpendicular to the first and second axes X, Y.

The first and second axles 35, 37 are formed separately from the sub- frame 13. The first axle 35 is formed integrally with a first end piece 40 and the second axle 37 is formed integrally with a second end piece 41. The first and second end pieces 39, 41 are machined from stainless steel and mounted over the ends of the sub-frame 13. The ends of the first and second axles 35, 37 are threaded to receive a locking nut to retain the wheels 39 in place.

The front and rear brackets 31 , 33 on the sub-frame 13 are provided with third and fourth apertures 43, 45, corresponding to the first and second apertures 21 , 23, to mount the mechanical fasteners 25, 27. First and second rubber bushes 47, 49 are provided around the first and second fasteners 25, 27 respectively to facilitate movement of the sub-frame 13 relative to the frame 11. The first and second bushes 47, 49 are primarily intended to allow the frame 11 to rotate about the first axis X. A perspective view of the frame 11 is shown in Figure 4A and a side view is shown in Figure 4B. The frame 11 has a dogleg configuration to match the vertical offset of the front and rear brackets 31 , 33 on the sub-frame 13. First and second inserts 51 , 53 are provided in the first and second apertures 21 , 23. The first and second inserts 51 , 53 are made of stainless steel and provide bearing surfaces on the top of the frame 11 for the first and second mechanical fasteners 25, 27. As shown in Figure 4C, a first circular recess 55 and a second circular recess 57 are defined in the underside of the frame 11 , around the first and second apertures 21 , 23 respectively, for receiving the first and second bushes 47, 49. A cross section of the second aperture 23 in the frame 11 is shown in Figure 4D.

The sub-frame 13 is formed from an upper part 59 and a lower part 61 , as shown in Figure 5. The upper and lower parts 59, 61 are moulded from carbon fibre in aluminium moulds (not shown). The assembled sub-frame 13 is shown in Figure 6A. The front and rear brackets 31 , 33 are substantially parallel to each other but are offset along the third axis Z, as shown in Figure 6B. The front and rear brackets 31, 33 have third and fourth circular recesses 63, 65, formed around the third and fourth apertures 43, 45 respectively, for receiving the first and second bushes 47, 49. A third insert 67 and a fourth insert 69 are provided in the third and fourth apertures 43, 45 on the underside of the front and rear brackets 31 , 33. Again, the third and fourth inserts 67, 69 are made of stainless steel and provide bearing surfaces for the mechanical fasteners 25, 27. A cross- section of the front bracket 31 is shown in Figure 6D.

As shown in Figure 6E, a grind plate 71 is provided on the underside of the sub-frame 13. The grind plate 71 is made of Kevlar (RTM) and is moulded integrally with the lower part 61. The grind plate 71 helps protect the tubular member 29 from damage. A side view of the grind plate 71 is shown in Figure 6F.

As shown in Figure 7A, a reinforcing rod 73 is provided between the first and second axles 35, 37. The reinforcing rod 73 may be made of steel but is preferably made of carbon to reduce weight. The first and second axles 35, 37 are hollow cylinders and the reinforcing rod 73 is received inside of them. The reinforcing rod 73 is preferably a friction fit inside the axles 35, 37 to help secure them in position. As shown in Figure 7B, the first end piece 40 has a first cylindrical aperture 75 for receiving a first end of the tubular member 29. The second end piece 41 has a second cylindrical aperture (not shown) for receiving the second end of the tubular member 29.

The first bush 47 for mounting between the frame 11 and the sub-frame 13 is shown in Figure 8. The first bush 47 is cylindrical and made of rubber. The second bush 49 is the same as the first bush 47. The colour of the rubber or polymer used to make the bushes 47, 49 may be varied to represent different stiffness. The bushes are moulded in aluminium moulds (not shown).

The first and second fasteners 25, 27 are the same and for brevity only the first fastener 25 will now be described. The components making up the first fastener 25 are shown in Figures 9A to 9D. The first fastener 25 comprises a first bolt 77 (shown in Figure 9A) having a female thread and a second bolt 79 (shown in Figure 9B) having a male thread. The first fastener 25 also comprises first and second collars 81 , 83 for receiving the first and second bolts 77, 79.

The first bolt 77 comprises a first head 85 and a first shaft 87 having an internal thread. The second bolt 79 comprises a second head 89 and a second shaft 91 having an external thread. The threads on the first and second shafts 87, 89 are matching to allow the second bolt 79 to be screwed into the first bolt 77, as shown in Figure 9C. The first and second heads 85, 89 each have a hexagonal recess (not shown) to allow the first fastener 25 to be adjusted using an Allen key or other suitable tool.

The underside of the first and second heads 85, 89 are substantially hemispherical and are received in first and second hemispherical cups 93, 95 formed in the first and second collars 81 , 83. The first and second collars 81 , 83 also have first and second conical apertures 97, 99 to facilitate rotation of the first and second shafts 87, 89 about a transverse axis. The bolts 77, 79 form ball and socket joints with the collars 81 , 83 and this allows rotation of the frame 11 relative to the sub-frame about the first axis X. The first and second cups 93, 95 may optionally be coated with polytetrafluoroethylene to help prevent the bolt heads 85, 89 bonding with their respective collars 81 , 83.

The first collar 81 has a first flange 101 for engaging the bearing surface of the first insert 51 provided in the first aperture 21. The remainder of the first collar 81 is received inside the first aperture 21. Similarly, the second collar 83 has a second flange 103 for engaging the bearing surface of the third insert 67 provided in the rear bracket 33. Again, the remainder of the second collar 83 is received inside the second aperture 43.

A cross-sectional view of the second bolt 79 and the second collar 83 is shown in Figure 10. The conical aperture 97 facilitates rotation of the second bolt 79 through an angle α about a transverse axis, as illustrated by arrow 105.

The assembly of the front truck 3 will now be described with reference to Figures 11 A to 11 F. The upper and lower parts 59, 61 are first brought together, as shown in Figure 11 A. The first and second end pieces 39, 41 are then provided over the ends of the tubular member 29 to clamp the upper and lower parts 59, 61 of the sub-frame 13 together. The reinforcing rod 73 is provided through the centre of the sub-frame 13 and is received inside the first and second axles 35, 37 to retain the end pieces 39, 41 in position.

As shown in Figure 11 F, the first and second bushes 47, 49 are located on the front and rear brackets 31 , 33. The frame 11 is then located on top of the first and second bushes 47, 49, as shown in Figure 11 D. The first and second mechanical fasteners 17, 19 are then located in the respective apertures 21 , 23, 41 , 43 in the frame 11 and the sub-frame 13, as shown in Figure 11 E. The mechanical fasteners 17, 19 are then tightened to retain the sub-frame 13 in position. The front truck 3 is then mounted on the deck 7. The steps shown in

Figures 11 A to 11 F are then repeated for the rear truck 5 and it is mounted on the deck 7.

The operation of the front truck 3 will now be described with reference to Figures 12A and 12B. Steering of the mountain board 1 is effected by the rider shifting their weight from one side of the deck 7 to the other. Shifting the rider's weight on to one side of the deck 7 causes a force A to be transferred to the frame 11 , as shown in Figure 12A. The force A causes the frame 11 to rotate about the first axis X. The rotation of the frame 11 relative to the sub-frame 13 applies a first turning force B to the rear bracket 33 and a second turning force C to the front bracket 31 of the sub-frame 13. The first and second turning forces B and C are substantially parallel to the second axis Y and cause the sub-frame 13 to rotate about the third axis Z, as illustrated by arrows 107, 109 in Figure 12A. The rotation of the sub-frame 13 rotates the axles 35, 37 about the third axis Z and hence the wheels 39. Thus, the mountain board 1 can be steered. Since the front and rear brackets 31 , 33 are offset from each other vertically, the first and second turning forces B and C induce a turning moment in

the sub-frame 13 about the first axis X. This turning moment varies the force applied to the inside and outside wheels 39 of the mountain board during a turn.

In the arrangement of the front truck 3, the turning moment increases the downward force applied to the inside wheel 39 and reduces the downward force applied to the outside wheel 39. Conversely, since the rear truck 5 is the reverse arrangement of the front truck 3, the downward force applied to the outside wheel

39 is increased and the downward force applied to the inside wheel is reduced.

Thus, the arrangement of the front and rear brackets 31 , 33 affects the handling of the mountain board 1. The front and rear trucks 3, 5 can be modified to provide the desired handling characteristics for a particular riding style or for certain conditions.

Figure 12B shows a cross-sectional view of the first bush 47 in an unloaded state and the resulting deformation when the force A is applied to the frame 11. Various changes and modifications may be made to the front and rear trucks 3, 5 to alter the handling characteristics of the mountain board 1. These will now be described with reference to Figures 13 to 16.

A plan view of the sub-frame 13 of the front truck 3 is shown in Figure 13.

The distances between the geometric centres of the third and fourth apertures 43, 45 and the second axis Y are labelled X1 and X2. By varying the distances

X1 , X2 relative to each other, the handling characteristics of the truck can be varied.

Increasing the distance X1 between the second axis Y and the centre of the third aperture 43 (coincident with the centre of the first bush 47) provided in the rear bracket 33 such that it is larger than the distance X2 between the second axis Y and the centre of the fourth aperture 45 (coincident with the centre of the second bush 49) provided in the front bracket 31 , reduces the angular rotation about the first axis X required to induce to a predetermined rotation about the third axis Z. Thus, arrangements in which the distance X1 is greater than the distance X2 typically require less rotation about the first axis X to induce a certain angle of turn than those arrangements in which the distance X1 is equal to or

less than the distance X2. To facilitate adjustment of the distances X1 and X2, one or more of the apertures 21 , 23, 43, 45 could be elongated along said first axis X; or a series of apertures could be provided along said first axis X in the frame 11 and sub-frame 13. The changes required to implement the same handling characteristics for the rear truck 5 are the opposite of those required for the front truck 3. In particular, the distance between the centre of the aperture in the front bracket and the second axis Y should be greater than the distance between the centre of the aperture in the rear bracket and the second axis Y to reduce the rotation about the first axis X required to induce a predetermined rotation about the third axis Z.

The first bush 47 is mounted on the second bracket 33 at the rear of the first truck 3 and the second bush 49 is mounted on the first bracket 31 at the front of the first truck 3. It has been recognised that varying the diameter D1 of the first bush 47 relative to the diameter D2 of the second bush 49 may alter the control characteristics. If the diameter D1 of the first bush 47 is larger than the diameter D2 of the second bush 49, the angular rotation about the first axis X required to induce to a predetermined rotation about the third axis Z is reduced. Thus, arrangements in which the diameter D1 is greater than the diameter D2 typically require less rotation about the first axis X to induce a certain angle of turn than those arrangements in which the diameter D1 is equal to or less than the diameter D2. Of course, it may be desirable to increase the rotation about the first axis X required to induce a certain angle of turn and the diameter D2 may be greater than the diameter Dl It will be appreciated that the first and second bushes 47, 49 are not necessarily circular in cross-section. In these arrangements, the width of the first and second bushes 47, 49 (i.e. their dimension measured in a transverse direction parallel to the second axis Y) relative to each other may be altered to affect handling characteristics. Again, if the width of the first bush 47 is greater than the width of the second bush 49, the responsiveness of the truck 13 to turning is increased.

Again, the changes required to implement the same handling characteristics for the rear truck 5 are the opposite of those required for the front truck 3. In particular, the diameter of the bush at the front of the rear truck 5 should be larger than the diameter of the bush at the rear of the rear truck 5 to reduce the rotation about the first axis X required to induce a predetermined rotation about the third axis Z.

It has also been recognised that varying an effective steering angle α of the front and rear trucks 3, 5 can affect their handling characteristics. This will be described with reference to Figure 14. The steering angle α is the angle defined between the horizontal and a steering axis A extending between first and second points P1 , P2 on the first and second bushes 47, 49 respectively. The first and second points P1 , P2 are the geometric centres of the first and second bushes 47, 49 on their top surfaces. The steering angle α is determined by the vertical distance Ya between the first and second points P1 , P2 and the horizontal distance between the geometric centres of the third and fourth apertures 43, 45 (equal to the sum of X1 and X2). The steering angle α may be varied by changing the relative heights of the first and second bushes 47, 49 and varying the horizontal distance between the centres thereof. The steering angle α may also be varied by changing the first and second vertical distances Y1 , Y2 between the second axis Y and the base of the first bush 47 and the second bush 49 respectively.

As shown in Figure 15, the effective steering angle α may also be changed by varying the angle at which the truck 3 is attached to the deck 7. An insert or riser 111 is inserted between the first and second arms 15, 17 and the deck 7 to modify the steering angle α. In cross-section, the riser 111 is a triangular wedge defining an angle ψ1. The steering angle α is effectively increased by the angle ψ1 when the riser 11 is inserted. It will be appreciated that a range of risers 111 may be provided to allow the angle α to be adjusted to match an individual's particular preference. The riser is preferably made of a resilient material, such as polyurethane, suitable for providing damping.

Rather than provide a riser 111 between the first and second arms 15, 17 and the deck 7, the first and second arms 15, 17 may be inclined at an angle β relative to the regions in which the first and second apertures 21 , 23 are formed. The steering angle α is thereby increased by the angle β. As shown in Figure 16, a range of frames 11 defining different angles β1 , β2 may be provided.

A perspective view of the underside of a modified version of the frame 11 is shown in Figure 17. The frame 11 is provided with reinforcing ribs to provide additional strength.

A truck 3, 5 in accordance with a second embodiment of the present invention is shown in Figure 18. Like reference numerals have been used for like components.

The frame 11 is generally unchanged from the first embodiment but the sub-frame 13 has been modified to provide an aerofoil cross-section. The aerofoil cross-section may be provided simply to reduce the drag coefficient of the sub-frame 13. Alternatively, or additionally, the aerofoil may be inclined such that lift or a down-force is generated when the mountain board 1 is in use.

The sub-frame 13 is illustrated having an integrally formed aerofoil section. However, an aerofoil attachment may be mounted on the sub-frame 13. The angle of attack of the aerofoil attachment may be adjusted to vary the lift or down-force generated in use.

A third embodiment of the truck according to the present invention is shown in Figure 19. Like reference numerals have again been used for like components in the first and second embodiments. The sub-frame 13 according to the second embodiment has been modified to remove the front bracket 31. Instead, the second fastener 27 is attached directly to the sub-frame 13. The longitudinal fastener of the second fastener 27 is preferably substantially coincident with the third axis Z.

A fourth embodiment of the truck according to the present invention is shown in Figure 20. Like reference numerals have again been used for like components in the first and third embodiments. Again, the sub-frame 13 has been modified to remove the front bracket 31 and the second fastener 27

attached directly to the sub-frame 13. In this embodiment, the longitudinal fastener of the second fastener 27 is preferably substantially parallel to or coincident with the first axis X.

The first, second and third axes X, Y, Z are used herein for reference purposes only and are illustrated in their relative positions when there is no load applied to the mountain board 1. It will be appreciated that the orientation of these axes X, Y, Z varies depending on the forces applied to the mountain board 1. For example, rotation of the sub-frame 13 relative to the frame 11 , as illustrated in Figure 12A, varies the angular orientation of the first and second axes X, Y.

It will be appreciated that various changes to the preferred embodiments described herein are possible without departing from the scope of the present invention. Rather than form the sub-frame 13 in two parts, the sub-frame 13 may be formed in a single piece, for example using an inflatable bladder to form the sub-frame 13 in a mould.

Although the present invention has been described with reference to a mountain board, it will be appreciated that the invention is also suitable for use on other vehicles, such as a landboard for power kiting.