GB2433478A

GB2433478A - Traction device

Info

Publication number: GB2433478A
Application number: GB0625780A
Authority: GB
Inventors: Antonio Syamak Eshragh
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-12-24
Filing date: 2006-12-22
Publication date: 2007-06-27
Also published as: GB0526472D0; GB0625780D0

Abstract

The device (31) is detachably mountable to a wheel of a vehicle and comprises a pair of terrain-engaging elements (4), each comprising a generally planar pad (5) of semi-rigid material, e.g plastics, rubber, with several terrain-engaging studs (9) extending from its outer face or a grooved tread, and an adjustment mechanism (38) to draw the terrain-engaging elements (4) together so as to grip the wheel tyre at diametrically opposite points. The adjustment mechanism (38) is connected to the terrain-engaging elements (4) by support struts (36), which are displaced longitudinally by means of rack-and-pinion arrangements so as to draw the terrain-engaging elements (4) together. Hook elements (10) extend from an inner edge of each pad (5) to contact an inner sidewall of the tyre, locating the device (31) securely on the wheel. The traction device (31) is used to travel over snow, ice, mud or other soft surfaces. It may also be mounted to a wheel that has already bogged down.

Description

TRACTION DEVICE

The present invention relates to apparatus mountable to one or more wheels of a vehicle to increase traction on surfaces such as snow, ice or mud. More particularly but not exclusively, it relates to a device that is detachably mountable to a pneumatic tyre of a vehicle to augment S... * S *5**

the grip of at least part of its tread. *5 S * . * * *5

*. : Conventional pneumatic tyres for motor vehicles have a tread that is designed to give a good * grip both on a dry road surface and on a wet one. However, such a tread pattern does not S.....

* give as good traction on soft surfaces, such as mud or snow. "Off-road" vehicles are usually provided with tyres having a tread optimised for traversing grass and mud, and tyres with a so-called snow tread are available for ordinary motor cars. However, such snow tyres are expensive and in most of the UK would only be of use on a few days of each year. Due to the cost and/or inconvenience of having to change tyres whenever there is snow or a threat of snow, snow tyres are very little used in the UK, south of the Scottish Highlands.

An additional problem when snow has fallen on a road is that it may become ice. Studded tyres have been produced, provided with studs extending radially outwardly from the tread surface to bite into packed snow or ice to provide a grip. However, use of such tyres on a clear road is generally consisted as illegal in the UK, on the grounds that the studs are liable to damage the road surface. Such tyres are hence seldom used.

"Snow chains" are available, which may be wrapped around a tyre such that lengths of chain extend across the tread surface, improving grip on snow and (to an extent) ice. However, these are not particularly convenient to fit and remove, not all cars have sufficient clearance between the tyre and adjacent bodywork to fit and use snow chains, and they have to be fItted before a vehicle encounters deep snow. For example, if a vehicle drives into a snowdrift, or deep snow accumulates around it while it is parked, it is too late to fit snow chains.

: 0 * As a result, there remains an unfulfilled need for a device that can easily be fitted to and ** * ** removed from a wheel or tyre, to provide increased grip in snowy, icy or even muddy *: : conditions. Various more or less elaborate devices have been proposed, but none of these appears to have achieved widespread adoption. As in the case of snow chains, they appear difficult or impossible to fit to a wheel that is already partly buried in snow.

S..... * .

It is hence an object of the present invention to provide a device, one or more of which may be detachably mounted to a respective wheel of a vehicle so as to provide increased traction on snow, ice, mud or the like, while obviating the above problems and providing the above advantages.

According to the present invention, there is provided a traction device, detachably mountable to a wheel of a vehicle, comprising a pair of terrain-engaging elements each comprising a generally planar body of semi-rigid material having a plurality of terrain-engaging protrusion means extending from an outer face thereof, and operating means to draw said terrain-engaging elements one towards the other so as to be in gripping contact with said wheel at substantially diametrically opposite zones thereof.

Preferably, said protrusion means are defined by a plurality of intersecting groove means.

The protrusion means and groove means may then comprise a tread pattern of the terrain engaging element.

Additionally or alternatively, said protrusion means may comprise a plurality of stud means.

*.* Said stud means are preferably substantially rigid. S... * *

*: . Advantageously, said stud means are detachably mounted to a respective generally planar S.. body. *5 a * * . * .*

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a.....

* The stud means may be mounted to socket means embedded in the generally planar body.

Each generally planar body may comprise an elastomeric material, such as rubber, optionally rubber filled with a particulate material such as carbon black.

Each generally planar body may comprise a semi-rigid plastics material.

Each generally planar body may comprise substantially rigid reinforcement means, optionally of metal.

Said reinforcement means may extend generally around a periphery of the generally planar body.

Each generally planar body may be so curved as to conform generally with a profile of a ground contact surface of the wheel to which it is to be mounted.

Optionally, the semi-rigid material may be sufficiently resilient substantially to comply with said profile when so mounted.

Preferably, the traction device comprises a respective elongate connecting member extending : ... between each terrain-engaging element and said operating means. * S S...

*: Said connecting members may extend substantially collinearly. a..

S S. S

* Alternatively, said connecting members may extend parallelly spaced each from the other.

S..... * S

The connecting members may be disposable generally diametrically across an outwardly-facing side of the wheel.

Preferably, the operating means is selectably operable to displace each connecting member longitudinally of itself.

Each connecting member may be independently so displaceable.

The operating means may comprise rack-and-pinion means.

The operating means may comprise single pinion means cooperating with respective rack means mounted to each connecting member.

The operating means may be operable by means of handle means detachably attachable thereto.

The operating means may be operable by hand tool means, such as socket wrench means.

The operating means may comprise ratchet means.

S I. * S.. S.,

The operating means may comprise selectably releasable latch means or other locking means.

S * S * * S. IS.

Preferably, each terrain-engaging element is provided with detent means disposable to bear S* S on an inwardly-facing side of the wheel.

S..... * .

Advantageously, said detent means comprise finger means, optionally a plurality thereof, extending from a periphery of a respective generally planar body, generally towards, in use, an axle of the wheel.

Said finger means may be slightly re-entrantly hooked.

Said finger means may be foldably mounted to a respective terrain-engaging element.

Said finger means may be mounted to the reinforcement means of the generally planar body.

Each terrain-engaging element may be provided on a surface contactable with the wheel with grip-enhancing means.

In a preferred embodiment, the device is adapted to be mountable to a tyre of a wheel of a vehicle without contacting a remainder of the wheel.

A pair of said traction devices may be provided to be mounted to a pair of wheels on a common axle.

n... An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which; * S S * S. *5* Figure 1 is a side elevation of a wheel of a vehicle with a first traction device *. . embodying the present invention mounted thereto; S...'.

* Figure 2 is a plan view from above of the wheel and first traction device shown in Figure 1; Figure 3 is a side elevation of a tread pad of the first traction device shown in Figure 1; Figure 4 is a schematic cross-section of the tread pad shown in Figure 1, taken generally along the line IV-IV; Figure 5 is a scrap elevation of an adjustment mechanism of the first traction device shown in Figure 1, partially disassembled; Figure 6 is a scrap elevation of the adjustment mechanism shown in Figure 5, fully assembled; Figure 7 is a side elevation of a wheel of a vehicle with a second traction device embodying the present invention mounted thereto; Figure 8 is a plan perspective view of the second traction device as shown in Figure 7; Figure 9 is a perspective view of an adjustment mechanism of the second traction device shown in Figure 7, partially disassembled; Figure 10 is a scrap perspective view of a rack and pinion mechanism of the adjustment mechanism shown in Figure 9; and Figure 11 is a scrap perspective view of a tread pad of the second traction device in place on a wheel. * .**

Referring now to the Figures and to Figure 1 in particular, a first snow traction device I embodying the present invention is shown mounted to a vehicle wheel 2 provided with a conventional pneumatic tyre 3 having a tread pattern adapted for use on a standard road *..: surface (such as tarmac) in fine weather or in rain. The first traction device 1 comprises two S.....

* terrain contact portions 4, each comprising a tread padS which extends across the tread of the tyre 3. Each tread pad 5 is connected to a respective elongate support strut 6 by a respective support plate 7. Each support strut 6 is connected to an adjustment mechanism 8, such that it is longitudinally moveable with respect thereto (see Figures 5 and 6 for details). The tread pads 5 are each provided with a plurality of studs 9 extending radially outwardly of the wheel 2. In this embodiment, the studs 9 are removably mounted to the tread pads 5, for example by means of a screw thread connection.

The two terrain contact portions 4 are mounted to diametrically opposite regions of the tyre 3, and the support struts 6 each extend radially of the wheel 2, close to an Outer face of its hub and close to or touching an outer sidewall of the tyre 3. The adjustment mechanism 8 is located substantially on an axis of the wheel 2, although in this embodiment there is no direct connection between the hub of the wheel 2 and the adjustment mechanism 8.

As shown in Figure 2, each terrain contact portion 4 is provided with a plurality of hook elements 10, extending from a side of the tread pad 5 remote from the support plate 7 and curving inwardly so as to contact an inner sidewall of the tyre 3. In Figure 2, the support plates 7 are shown spaced from the other sidewall of the tyre 3 for clarity, but in practice the tyre 3 is gripped between the respective support plate 7 (and/or the support strut 6) and hook elements 10, so as to locate the tread padS securely over the tread of the tyre 3. * S * a..

The adjustment mechanism 8 is operated as described below with regard to Figures 5 and 6, so as to draw the tread pads 5 firmly into contact with the tread of the tyre 3.

S

* : * One of the tread pads 5 is shown in more detail in Figures 3 and 4. Its contact surface is *SSSSI * provided with a tread pattern comprising a plurality of upstanding islands 11 defmed by a plurality of grooves 12. The exact tread pattern shown is for the purpose of example only; in practice, the islands 11 and channels 12 would be arranged similarly to those of the tread of a snow or off-road tyre. Thus, the tread pads 5 would have a more pronounced, coarse or "chunkier" pattern than the conventional road tyre 3 to which they are mounted. The studs 9 are shown secured into corresponding sockets in a proportion of the islands 11; they may be removed if it is believed that the tread pattern of the tread pads 5 alone will give sufficient extra grip. It may be necessary for the sockets to receive the studs to comprise a harder material than a remainder of the tread pad 5, and the sockets may be provided with anchoring plates to restrict deflection of the studs 9 under load.

The tread pad 5 comprises rubber of essentially the same composition as is used for the tread of a conventional tyre. To support this, the tread pad 5 also comprises a steel frame 13 extending around its periphery (shown in Figure 3 by a dotted line). This may be mounted to a face of the tread pad 5 opposite to the islands II and channels 12, or may, as shown in Figure 4, be partially or wholly encased in a rubber moulding. The support plate 7 is mounted to the steel frame 13 along a first edge of the tread pad 5, and the hook elements 10 extend from the frame 13 at a second edge of the pads, opposite to the first.

The tread pads 5 are curved to conform generally to a profile of the tyre 3 to which they are mounted. (It is envisaged that a single device I would be compatible with a range of tyre p...

diameters; for example, one model would be usable with tyres from fourteen to seventeen * : * inches in diameter). S..

: The adjustment mechanism 8 is shown in more detail in Figures 5 and 6. In Figure 5, only S.....

* those parts of the mechanism 8 linked to a first 6A of the support struts 6 are shown. The mechanism 8 comprises a back plate 14, to which is mounted a cog wheel 15 and two rollers 16. The first support strut 6A extends between the cogwheel 15 and the rollers 16, and has a toothed portion 17 which engages with the teeth of the cog wheel 15. The cog wheel 15 has an outstanding axially-extending stud 18, to which a key or wrench may be attached to turn the cog wheel 15. The cog wheel 15 and support strut 6A thus comprise a rack-and-pinion mechanism, by which the support strut 6A (and hence the terrain contact portion 4 mounted thereto) may controllably be displaced, longitudinally of the strut 6A. -.10-

The second 613 of the support struts 6 is provided with a very similar rack-and-pinion mechanism, its cog wheel (not shown) being mounted to the back plate 14 at a point 19 on an opposite side of the struts 6 to the cog wheel 15 linked to the first strut 6A. The second strut 68 hence has its toothed portion 17 along an opposite edge to that of the first strut 6A.

As shown in Figure 6, the mechanism 8 is provided with a front plate 20 provided with two apertures 21 to provide access for the key or wrench to the stud 18 of each cog wheel 15.

Each of the support struts 6 is provided with a terminal stop 22, extending transversely therefrom towards the other of the struts 6, which prevents excessive displacement of either strut 6. *0 * I0* 000I

* * To prevent the support struts 6 from moving relative to the adjustment mechanism 8, as a 0: : result of jolts or vibrations experienced while the first device 1 is mounted to a moving wheel ** 2, manual latches 23 are provided which may be brought into engagement with the respective toothed portion 17 of each support strut 6A, 6B (N.B. only one said latch 23 is shown in S... S Figure 5 for simplicity).

To mount the first device 1 to a wheel 2, the adjustment mechanism 8 is operated to move the terrain contact portions 4 sufficiently far apart that the first device I may be placed over the wheel 2 without the hook elements 10 fouling the tyre 3. The adjustment mechanism 8 is disposed substantially on the axis of the wheel 2, with the support struts 6 extending between them substantially across a diameter of the wheel 2. Although it is not vital that the first device 1 is aligned horizontally, as shown in Figure 1, this is usually convenient, and when the wheel 2 is deep in snow may be the sole practical alignment. The adjustment mechanism 8 also allows the first device I to be fitted to wheels 2 of differing diameters.

The adjustment mechanism 8 is then operated to draw the terrain contact portions 4 in turn towards the axis of the wheel 2. The hook elements 10 come into contact with an inner sidewall of the tyre 3, maintaining the alignment of the tread pad S with the tread of the tyre 3 beneath. When both tread pads 5 are in contact with the tread of the tyre 3 at diametricaLly opposite points, the adjustment mechanism 8 is operated further so that the tyre 3 is securely gripped between the tread pads 5. The latches 23 are then engaged with the toothed portions of the support struts 6, locking them in position to prevent the first device 1 loosening its grip on the tyre 3 while in use.

ri.. While it is not essential that the first device I is completely symmetrically aligned, the S...

adjustment mechanism 8 should remain as close as possible to the axis of the wheel 2, to u.: avoid unbalancing the wheel 2. e

S

e The first device 1 is removed after use by reversing the above procedure.

S..... a

The wheel 2 is thus provided around roughly a quarter of its circumference with zones having a tread providing a better grip than that of the tyre 3, and optionally having ice-engaging studs or spikes. The tread pads 5 will stand slightly proud of the tyre 3, so that a bumpy ride may ensue at speed. However, the device I is intended for use in conditions when only low speeds should be employed in any case, and the simplicity of mounting and removal means that the device 1 can be taken off the wheel 2 as soon as conditions allow use of the un-augmented tyre 3.

A second snow traction device 31 embodying the invention is shown in Figures 7 to 11.

In Figure 7, the second traction device 31 is shown mounted to a wheel 2 provided with a conventional pneumatic tyre 3. In general layout, it resembles the first device 1, since it comprises two terrain contact portions 4, each comprising a tread pad 5 extending across the tread of the tyre 3. Each tread pads is provided with a plurality of studs 9 extending radially outwardly with respect to the wheel 2. In this particular embodiment, steel studs 9 provided with a threaded portion are screwed permanently into tread pads 5 that are made from rubber :. having essentially the same composition as is used for the tread portion of a conventional tyre * 3. (In an alternative embodiment, plastics-coated studs, similar to those used on football ***. * S S...

boots or the like, are used. These are mounted detachably, using fastenings similar to those S. used on the soles of football boots). S.. * .

The tread pads 5 of the second traction device 31 are each connected by a support plate 7 to a * S respective support strut 36. However, unlike the support struts 6 of the first device 1, the support struts 36 extend parallelly, each to the other, spaced on opposite sides of a line extending diametrically of the wheel 2. The adjustment mechanism 38 of the second traction device 31 is located substantially on an axis of the wheel 2, close to an outer face of its hub, and it is operatively connected to both support struts 36. However, its internal mechanism differs from that of its counterpart 8 in the first device I (see Figure 9 below).

Figure 8 shows the second traction device 31 separated from the wheel 2. (NB: this is a perspective view, so an interior, tyre-contacting surface of both tread pads 5 is visible). As can also be seen, the second traction device 31 is also provided with hook elements 10 -13 -extending from an edge of each tread pad 5 remote from the support struts 36 and support plates 7, generally radially inwardly of the wheel 2 when in use, and curved slightly inwardly so as to contact the inner sidewall of the tyre 3 in use (see also Figure 11 for more details).

While the support struts 36 and support plates 7 are intended to contact the outer sidewall of the tyre 3 in use, the adjustment mechanism 38 is intended to be spaced from the hub of the wheel 2. However, to avoid damage from inadvertent contact during attachment or removal of the second fraction device 31, a padding zone 32 of foam rubber or the like is provided on a corresponding surface of the adjustment mechanism 38.

Figure 9 shows the adjustment mechanism 38 with its front plate 20 removed, demonstrating :. how both support struts 36 are located on the same side of the back plate 14. The mechanism 38 comprises separate rack-and-pinion arrangements to engage with each support strut 36, : each rack-and-pinion being operable via a drive shaft 33 to displace the respective support 1.: : strut 36 longitudinally, and hence to move the respective terrain contact portion 4 relative to * the adjustment mechanism 38. The drive shafts 33 are turned using a complementary key 34 *..*** * * (shown in position on one shaft 33 in Figure 7) which fits concentrically over the shaft 33 and engages with a radial stud 35.

Figure 10 shows details of one of the rack-and-pinion arrangements, which are not visible in Figure 9. In this embodiment of the device 31, each support strut 36 has a generally U-shaped cross-sectional profile, and is provided with two arrays of teeth 37, extending parallelly, each with the other, along respective extremities of the U-section (see also the view from above in Figure 8). This is found to be more reliable and robust than a single array of teeth 17, as used in the first device 1. A pinion wheel 41 of the mechanism is therefore provided with two sets of gear teeth 42 (one set hidden in this perspective view, but see also Figure 8), each disposed to mesh with a respective array of teeth 37 on the support strut 36. Turning the drive shaft 33 thus turns the coaxially-mounted pinion wheel 41, whose gear teeth 42 engage with the teeth 37 on the support strut 36 to move it longitudinally.

Referring back to Figure 9, the adjustment mechanism 38 of the second traction device 31 is provided with a latch lever 39 to lock each support strut 36 (in place of the manual latches 23 used in the first device 1 to lock the adjustment mechanism 8, once the device was correctly mounted). The latch levers 39 are each pivotably mounted to the back plate 14. Adjacent a first end of each latch lever 39 is provided a transversely-extending locking pin 40, and the latch levers 39 are spring-biased towards a disposition as shown, in which this locking pin 40 : is located between adjacent teeth 37 of the respective support strut 36. The latch levers 39 S... * d

are so mounted, however, that they act as ratchet pawis. When the support strut 36 is moved *5 * to draw the respective terrain-contact portion 4 towards the adjustment mechanism 38, the *11 teeth 37 urge the lever 39 to pivot, pushing the locking pin 40 to one side so the support strut 36 may move past it. However, movement in the reverse direction brings the teeth 37 into S.... * .

contact with the pin 40 in such a way that there is little or no turning moment on the lever 39, and the pin 40 remains between the teeth 37, locking the support strut 36 in place. Manual operation of the latch lever 39 is necessary to displace the locking pin 40 out of engagement with the teeth 37, so that the terrain-contacting portions 4 may be moved outwardly from the tyre 3 (e.g. to remove the device 31).

Strictly speaking, this is not a standard ratchet and pawl arrangement, since the teeth of a ratchet gear are usually asymmetrical, being "hooked" to improve their engagement with the pawl in a reverse direction. This (and most other) rack-and-pinion arrangement has symmetrical involuted teeth 37 to minimise wear and to give a smoother drive (a true ratchet operates in a series of discrete, possibly jerky steps). In practice, however, the latch-cum-ratchet arrangement shown is fully effective. (It is suspected that flexure of the tread pads 5 and the tyre 3, particularly in the final stages of tightening, assists smooth operation of the rack-and-pinion and latch lever arrangements).

Alternative arrangements to hold the device 31 in a desired confIguration are possible. For example, a wedge, insertable between the pinion wheel 41 and the teeth 37 (forming the rack) of the support strut 36, is showing promise as an infinitely adjustable locking arrangement (the fineness of adjustment possible with the latch lever 39 arrangement depends on the pitch of the teeth 37). It is also envisaged that an additional clamping mechanism might be * provided, wholly separate from the latcWratchet arrangement in case it ever failed. * 14 * * -I.. 0I

* Figure 11 shows how the hook elements 10 ensure that the terrain-contact portions 4 stay correctly in place over the tread of the tyre 3. Each hook element 10 extends from an edge of : the tread pad 5 towards an axle of the wheel 2. When the device 31 is in position, the hook S....-* I elements 10 contact an inner sidewall of the tyre 3. Indeed, as the device 31 is tightened into position and the tread pad 5 and the tyre 3 flex to conform with each other, the sidewalls will tend to expand outwardly into closer contact with the hook elements 10 (and with the support struts 36 on the outer face of the tyre 3). The tyre 3 is thus securely gripped. In some embodiments, a tyre-contacting surface of the hook elements 10 is provided with shallow knobs or is roughened to enhance grip on the tyre 3, particularly for when the device 31 is only loosely in position. Protrusions on an inner surface of the tread pad 5, to help it locate securely with respect to the underlying tread of the tyre 3, are also possible.

Mounting of the second traction device 31 to the wheel 2 is very similar to mounting the first device I thereto. The simplest approach is probably to adjust the position of one support strut 36 to approximately the correct length, to fit the device 31 over the wheel 2 (probably having first removed any hubcap or wheel trim to give sufficient clearance), then to draw in the other support strut 36 to fit. Final adjustments may then be made until the device 31 is securely and substantially symmetrically in place on the wheel 2. It has been found that the latch levers 39 will hold the device 31 in place under the planned conditions of use. To remove the device 31, it is preferable to tighten the adjustment mechanism 38 slightly, loosening the grip between the teeth 37 and the locking pin 40, before the latch lever 39 is operated fully to disengage the pin 40. The adjustment mechanism 38 is then loosened until the device 31 may be removed.

The second traction device 31 is largely constructed from mild steel and aluminium plate.

The tread pads 5 may be custom-moulded from a hard-wearing tyre-grade filled vulcanised * rubber, or may simply be made from sections of tyre tread, mounted to a suitable metal frame or backing pad.

S

* :..: Other embodiments are planned, providing further useful improvements over those *:** illustrated. For example, to reduce weight, aluminium would be used instead of steel wherever possible (e.g. the hook elements 10), and the overall dimensions of the adjustment mechanism would be reduced. The hook elements 10 may also be hingeably mounted to the tread pads 5, so that they may be folded inwardly for convenience in handling. Guides may be added to ensure that the movable components of the device do not collide in operation. A carrying handle may be provided.

In place of the bespoke key 34, it is planned to replace the drive shafts 33 with a standard socket or node that can be engaged by a conventional socket-wrench or the like. The latch lever 39 will be modified to conform more conveniently to the remainder of the adjustment mechanism 38; this may aho obviate any risk of the lever 39 being accidentally operated.

In a further embodiment, the tread pads 5 are formed from a semi-rigid plastics material instead of vulcanised rubber. Peripheral portions of the plastics tread pads 5 would be of substantially increased thickness, to obviate the need for metal reinforcements or frames 13.

Such tread pads 5 would preferably be injection-moulded or cast in a desired form. This embodiment would probably be provided with plastics or plastics-covered "football boot" studs, detachably mountable to sockets in the tread pads 5. Indeed, materials and methods used to produce football boot outsoles, with integral sockets, could well be usable to produce such tread pads 5.

S * S * *5* * Another development that may be beneficial would be to employ a

single, centrally-mounted *:*. pinion wheel 41, directly or indirectly engaging with the rack teeth 37 of both support struts :. 36. Thus, turning a single drive shaft 33 (or socket) would simultaneously draw both terrain-contact portions 4 inwardly to grip the tyre 3. This would be more convenient than having to * operate two rack-and-pinion arrangements separately.

The devices described are of especial use as escape devices, e.g. being mountable to driving wheels of a car to enable it to escape a snowdrift or boggy ground, or to break the car free of snow that has built up around its wheels while parked.

Claims

CLAIMS

1. A traction device, detachably mountable to a wheel of a vehicle, comprising a pair of terrain-engaging elements each comprising a generally planar body of semi-rigid material having a plurality of terrain-engaging protrusion means extending from an outer face thereof, and operating means to draw said terrain-engaging elements one towards the other so as to be in gripping contact with said wheel at substantially diametrically opposite zones thereof.
2. A traction device as claimed in claim 1 wherein said protrusion means comprise a plurality of stud means.
3. A traction device as claimed in claim 2, wherein said stud means are detachably mounted to a respective generally planar body. * . S...

*:*.
4. A traction device as claimed in any one of the preceding claims, wherein said protrusion means are defined by a plurality of intersecting groove means, optionally * * such that the protrusion means and groove means comprise a tread pattern of the * * terrain engaging element.
5. A traction device as claimed in any one of the preceding claims, wherein each generally planar body comprises an elastomeric material, such as rubber, optionally rubber filled with a particulate material such as carbon black.
6. A traction device as claimed in any one of the preceding claims, wherein each generally planar body comprises a semi-rigid plastics material.
7. A traction device as claimed in any one of the preceding claims, wherein each generally planar body is so curved as to conform generally with a profile of a ground contact surface of the wheel to which it is to be mounted.
8. A traction device as claimed in any one of the preceding claims, comprising a respective elongate connecting member extending between each terrain-engaging element and said operating means.
9. A traction device as claimed in claim 8, wherein said connecting members are disposable generally diametrically across an outwardly-facing side of the wheel. * I * ***
10. A traction device as claimed in either claim 8 or claim 9, wherein the operating means is selectably operable to displace each connecting member longitudinally of itself. I..

I

* :.* *
11. A traction device as claimed in claim 10, wherein each connecting member is * : * independently so displaceable.
12. A traction device as claimed in any one of the preceding claims, wherein the operating means comprises rack-and-pinion means.
13. A traction device as claimed in any one of the preceding claims, wherein the operating means comprises selectably releasable latch means, ratchet means or other locking means.
14. A traction device as claimed in any one of the preceding claims, wherein each terrain- engaging element is provided with detent means disposable to bear on an inwardly-facing side of the wheel.
15. A traction device as claimed in claim 14, wherein said detent means comprise finger means, optionally a plurality thereof, extending from a periphery of a respective generally planar body generally towards, in use, an axle of the wheel.
16. A traction device as claimed in any one of the preceding claims, adapted to be mountable to a tyre of a wheel of a vehicle without contacting a remainder of the * * wheel. **.* ** * * * * * S.

* .
17. A traction device substantially as described herein with reference to the Figures of the * * accompanying drawings. * * * S