CA1115199A - Tire mounting and demounting apparatus and method - Google Patents

Abstract

Abstract of the Disclosure Apparatus for mounting and demounting tires and methods of mounting and demounting tires. The apparatus may include a clamp for holding a wheel as well as a tire clamp and pushing device for gripping a tire and applying a moving force thereto. The tire clamp is mounted for move-ment toward and away from the wheel clamp and toward and away from a support for the wheel clamp. It is operated, during tire mounting, to nonaxially urge a tire having one part of one bead received in the drop center of a wheel away from the wheel to draw that part into the drop center while axially moving the tire at a remote location toward the wheel so that the beads at the remote location are disposed between the flanges of the wheel. Both beads at the remote location are also brought towards each other into sufficient proximity so that both may enter the drop center of the wheel and thereafter, the tire is nonaxially urged at the remote lo-cation toward the wheel to dispose both the beads at the remote location within the drop center of the wheel. There-after, the tire is axially moved toward the wheel causing the remaining part of the bead to be received between the wheel flange. In demounting the tire, the tire clamp is uti-lized to bring the beads at one location into sufficient proximity such that both may enter the drop center of the wheel and thereafter, the tire is nonaxially urged in a direction to cause both of the beads to enter the drop center of the wheel. Oppositely therefrom, the tire is axially moved away from the wheel until both beads at the opposite location, are moved from between the wheel flanges.

Description

TIRE MOUNTING AND DEMOUNTING
APPAR~TUS AND METHOD
. _ _ Background o~ the Invention .

This invention relates to methods-and apparatus for mounting and demounting tires, particularly large tires as are typicallY employed with oversized vehicles as off the road vehicles~
While automobiles have utilized tires mounted on one-piece wheels having drop centers for-decades, little use of such wheels has been made in connection with larger vehi-cles requiring tiressignificantly larger than those used on automobiles. Rather, where large tires have been required, conventionally so-called "split-rim" type wheels have been utilized.
The latter type of wheel has been favored over the former for mounting large tires because due ~to the sti~fness of large tires, it has been virtually impossible to mount the same on one piece wheels. However, split-rim type wheels are not without their disadvantages for they are formed of multiple components including two wheel halves, a locking ring and one or more sealing gaskets at the very least. ~nd, it is necessarY to disassemble a split-rim type wheel for the purpose of either mounting a tire thereon or removing a tire therefrom. The seals or gaskets require replacement and a certain degree of hazard is present when the locking ring is applied to the wheel or removed therefrom.
In order to avoid these disadvantages, and attain the advantages normally associa~ed with one-piece type wheels in connection with larger tires, there have been proposed methods and apparatuS for mounting and demounting large tires on one-piece wheels. Such proposals are exemplified by, for example, the following United State5 Letters Patents: 3,4~9,198 issued 1 -- ., ... . . . . . ..... . . .... . =, ., . =.,= _~ .. ..... . .

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January 13, 1970 to Malinski; 3,612,140 issued October 12, 1971 to Malinski; 4,014,375 issued March 29, 1977 to Malinski et al;
and 4,031,941 issued E'ebruary 17, 1976, also to Malinski et al.
Apparatus stated to be manufactured under one or more of the above patents is commercially available and has made it possible to mount large tires, such as those used on off the road vehicles, on one-piece rims. However, the apparatus utilized is quite complex utilizing numerous pushing devices for distorting a tire during the mounting or demounting process as well as rotating bead deflector mechanisms. The methods by which the tires are mounted or demounted are relatively complex in terms of the number of steps which must be performed.
And the locale in which the equipment is used, of necessity, cannot be utilized for non-mounting or demounting purposes by reason of the construction of the equipment preventing such use.
_ummary o__the Invention A principal object of the invention is to provide new and improved apparatus for mounting and demounting large tires . 20 on one-piece rims. Another principal object of the invention is to provide new and improved methods for mounting and demounting such tires.
The invention in one aspect pertains to a tire servicing apparatus including a bed and wheel clamp means mounted on the bed for movement between a wheel clamping position above the bed and a retracted position below the bed to free -the bed of obstructions to enable use of the same for other purposes. Tire clamp and urging means are provided for gripping a tire and for applying a moving force to a tire, and means are provided for mounting the tire clamp and urging means adjacent the bed, such mounting providing for movement toward and away from the wheel clamp means, and toward and away from the bed. The tire clamp and urging means comprise a pair of opposed jaws and a pusher

- 2 -member extending between the jaws and pivotally mounting the jaws for movement toward and away from each other.
Another aspect of the invention comprehends a tire changer for changing large tires mounted on drop center wheels including an elongated frame and a plurality of wheel clamps mounted on the frame for engaging a wheel and clamping the same to same frame. ~t least one of the clamps is mounted on the frame for movement relative to at least one other clamp between wheel clamping and unclamping positions. A tire grasping and urging means is on the frame and has opposed jaws movable towards and away from each other for gripping a tire on opposed side walls and compressing the same. Means are provided for movably mounting the grasping and urging means on the frame so - that the jaws will move in concert toward and away from the wheel clamps in a first direction generally transverse -to the rotational axis of a wheel engaged by the clamps and in a second direction generally parallel to the axis in addition to being movable toward and away from each other to grip a tire. Thus a tire gripped by the jaws through movement thereof toward each . 20 other may be urged in the first direction to locate one or both tire beads on one edge of the tire in the drop center of a wheel engaged by the clamps and urged in tne second direction to effect relative movement between the tire and the wheel generally along the axis to mount and/or demount the tire from the wheel.
Disclosed is a method of mounting a tire having opposed, normally spaced beads on a drop center wheel comprising the steps of disposing the tire partly on the wheel such that part of one of the beads is between the flanges of the wheel, non-axially urging at a location remote from the bead part, the tireaway from the wheel to draw the bead part into the drop center while axially moving the tire at the remote location toward the wheel so that the beads at the remote location are disposed between the flanges of the wheel, bringing both beads a-t the , . .
~ - 3 -remote location toward each other into sufficient proximity such that both may enter the drop center of the wheel, non-axially urging the tire at the remote location toward the wheel to dispose both beads at the remote location within the drop center of the wheel, and axially moving the tire adjacent the first mentioned bead part toward the wheel to cause the part of the bead opposite -the bead part to be disposed between the wheel flanges.
~ccording to another aspect of the disclosed invention, there is provided a method of demounting a tire from a drop center wheel including the steps of bringing the beads at one location about the periphery of the tire, into sufficient proximity such that both beads at that location may enter the drop center of the wheel, non-axially urging the tire in a direction to cause both of the beads at that location to enter the drop center of the wheel, and axially moving the tire away from the wheel at a location generally opposite the first mentioned location until both beads at the opposite location are moved from between the wheel flanges.
.20 Other aspects and advantages will become apparent from the following specification taken in connection with the accompanying drawings.
Description of the_Draw~
Fig. 1 is a side elevation of a tire serviclng apparatus made according to the invention and mounted on a vehicle;
Fig. 2 is a plan view of the apparatus omitting vehicle structure;
Fig. 3 is an enlarged, sectional view of a wheel clamping apparatus taken approximately along the line 3 - 3 in Fig. 4i Fig. 4 is an enlarged, fragmentary view of the clamping apparatus with parts broken away for clarity;
Fig. 5 is an enlarged side elevation of the tire servicing apparatus with parts broken away for clarity;

Fig, 6 is a fragmentary plan view o~ the apparatus shown in Fig. 5;
Figs. 7-9 are schematics illustrating se~uential steps in one method of mounting a tire;
Fig. 10 is a schematic illustratïng one method of de-mounting a tire;
Figs. 11-14 ~re schematics illustrating sequential steps in another method of mounting a tire; and Figs. 15-18 are schematics illustrating sequential steps in ano~her method of demounting a tire.
Description of the Preferred Embodimen_s An exemplary embodiment of a tire servicing apparatus made according to the invention is illustrated in the environment of a vehicle such as a service truck 10 (Fig.l) having wheels 12 by which the truck 10 can traverse the underlying terrain to move the servicing apparatus to a point of use. Mounted on the truck just to the rear of a cab 16 is an articulated, tire handling crane 18 made according to United States Patent ~,927,778, issued ~ecember 23, 1975 to Zrostlik. For present pur~oses it is sufficient to note that the crane 18 has hydraulically operated, opposed grippers 19 which can grasp a tire on a diameter thereof to be (a) elevated or lowered, (b) rotated about its cylindrical axis (c) swing to either side of th~ truck, or (d) rotated about an axis extending between the yrippers 25.
Rearwardly of the crane 18, the truck mounts a bed 20 which can be alter;~ately used for transporting ~ires and/or wheels or for receiving a tire and wheel for mounting or delllounting purposes. As illustrated in Fig. 1, a large tire 22 mounted on a one-piece rinl 24 i~ secured to the bed 20 by clamp n,eans 26 for demounting. The crane 18 may be used for loading or unloading the bed 20 and f~r mounting and demounting tires.

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Adjacent one side of the bed, a tire clamp and urging means, generally designated 28 is provided and, as will be seen, is utilized during tire mounting and demounting operations in connection with the clampinq means 26.
The tire clamp and urging means 28 includes a generally vertically oriented post 30 mounted for rotation about a generally vertical axis in a conventional ring bearing 32 secured to the truck 10 to one side of its center line. Thus, as can be de-termined from Fig. 2, the tire clamp and urging means 28 can be swung from the position shown whereat it is disposed for tire mounting or demounting operations in a counterclockwise direction just short of 90 in the direction of an arrow 34 so as not to overlie the bed 20 thereby making the bed 20 fully available for receipt of materials to be transported.
For stabilization purposes during loading or unloading of the bed 20 by the crane 18, a plurality of outriggers 36 (only one of which is shown) of conventional construction may be provided.
Turning now to Figs. 3 and 4, the nature of the clamping means 26 will be described in greater detail. The upper surface of the bed is designated 38 and just below the same, a pair of spaced, parallel pivot shafts 40 are provided. Each pivot shaft 40 journals a tube 42 which in turn mounts spaced clamping plates 44 at its opposite ends. As seen in Fig. 3, the plates 44 are somewhat elongated and the tubes join thereto intermediate the ends of each plate 44.
One end of each of the plates 44 is provided with a hook formation 46 which is adapted to engage the one-piece rim - 24 at the inturned end 48 of the lowermost rim flange 50.
The lower ends of the plates 44 associated with each shaft 40 are interconnected by a tube 52 having a rectangular cross-section for strengthening purposes and the same i,nter-mediate its ends mounts spaced ears 54 which receive a pivot pin 56. The pivot pins 56 are coupled to the rods 58 of correspondinghydraulic cylinders 60 which are in turn pivotally connected as at 62 to a cross-member 64 of the frame of the vehicle 10.
When the cylinders 60 are retracted, the clamping plates 44 will assume the dotted line position illustrated in Fig. 3 and it will be observed that no part thereof ex-tends above the upper surface 38 of the bed 20. Preferably,the surface 38 is generally imperforate save for slots (not shown) aligned with the plates 44 through which the plates 44 may be elevated to the solid line position illustrated in Fig. 3.
Adjacent each of the hook formations 26, each of the plates 44 is provided with an arcuate cam surface 70 leading to the hook formation 46. It will be appreciated that when the plates 44 are in their retracted position illustrated in dotted lines, a tire and wheel or simply the wheel 24 may be approximately centered over the clamps 26. As the plates 44 are elevated to their solid line positions, the cam surfaces 70 cam the wheel 24 into a precisely centereA position to be firmly gripped by the hook formations 46.
By reason of the foregoing construction, when a tire mounting or demounting operation is not to be performed, the clamps 26 may be fully retracted below the surface 38 of the bed 20 so as to not obstruct the same. Thus, the surface of the bed 20 may be used to receive articles as, for example, tires and/or wheels so as to enable the same to be transported 3n to a desired point of use or to a location for servicing if P~,~

that is required, Thus, full use of the bed 20 for transpor-tation purposes is maintained through the use of the retract-able clamps 26 while at the same time providing clamps which may hold a wheel during a mounting or demounting operation.
With reference now to Figs. 5 and 6, the tire clamp and urging means 28 will be described in greater detail~
The upstanding post 30, by means of a pivot pin 80 pivotally mounts a boom 82 for rotation about a generally horizontal axis. The boom 82 may be formed out of heavy duty rectangular tubing and telescopingly receives an extendable member 84. A cylinder (not shown) is disposed within the boom 82 and coupled between the same and the extendable member 84 so that the latter can be moved in a reciprocal fashion be-tween extended and retracted positions, Preferably, the boom 82, at an end remote from the post 30 mounts a collar 86 which in turn journals a roller 88 abutting the underside of the extendable member 84 to minimize friction during such movement.
~ hydraulic cylinder 90 has its head end pivoted at 92 to the post 30 and its rod 94 pivoted by a pin 96 to the collar 86. As a consequence, the cylinder 90 may be operated to pivot the boom 82 and the extendable member 84 about the pivot axis defined by pin 80 towards and away from the underlying bed 20. The aforementioned cylinder contained within the boom 82 may be operated to extend the extendable member 84 towards and away from the clamping means as can be ascertained from Fig. 2.
Returning to Figs. 5 and 6, two horizonally disposed, spaced tubes 100 are interconnected by spaced, vertically extending plates 102. A pivot pin 104 extends between the plates 102 and connects to the outer end of the extendable member 84 - 8 ~

P~

on a horizonal axis.
Elongated, rectangular tuhes 106 which serve as a pusher means for purposes to be described interconnect the tubes 104 and at their opposite ends journal pivot pins 108.
The uppermost pin 103 pivotally mounts an upper jaw, generally designated 110 while the lowermost pin 108 pivotally mounts a lower jaw, generally designated 112. Both of the jaws 110 and 112 are formed of two spaced elon~ated channels 114. The ends of the channels 114 of each jaw remote from the post 30 are interconnected by a cross-member formed of a tube 116 for gripping a tire without cutting the same by pivoting the jaws 110 and 112 towards each other about the pivot axis provided by pins 108.
Two cylinders 118 are pivotally connected by pivot 15 pins 120 to corresponding channels 114 of the upper jaw 110 and by pivot pins 122 to the lower of the cross-members 100.
Similar cylinders 124 are pivotally connected by pins 126 to corresponding channels 114 of the lower jaw 112 and by pins 128 to the upper one of the cross-members 100. Consequently, 20 by energization of the cylinders 118 and 124, the jaws 110 and 112 may be made to pivot towards and away from each other to grip or release the tire.
The upper surface of the boom 84 includes a notch 130 at its end adjacent to the jaws 110 and 112 and the extendable member 84, on its upper surface, mounts a pair of spaced up-standing eyes 132. When the extendable member 84 is fully re-tracted into the boom 82, interference between the eyes 132 and the boom 82 is avoided by the provision of ~he notch 130.
As best seen in Fig. 5, the eyes132 mount a pivot pin 30 134 which in turn is connected to the rod 136 of a cylinder 138.

The cylinder 138 is in turn connected by a pivot pin 140 to :
spaced eyes 142 on the uppermost cross-m~mber 100. Thus, by extending and retracting the cylinder 138, the jaws 110 and 112 as well as the pusher means defined by the tubes 106 can be pivoted about the pivot axis provided by the pin 104.
Suitable valves and a source of hydraulic fluid under pressure are provided for selective operation of the various cylinders to sequence the operation of the tire clamp and urging means in a manner to be described to perform mounting and de-mounting operations.
The manner in which the previously described apparatus is utilized in mounting and demounting tires will now be de-scribed in connection with Figs. 7-10 inclusive.
A typical one-piece wheel 24 is illstrated in Figs. 7-10 ` and is seen to include a drop center 150 and upper and lower flanges 152 and 154 respectively. The wheel 24 is clamped in place by the wheel clamps 26 in a manner described previously.
A tire 22 having upper and lower, opposed, normally spaced beads 156 and 158 is disposed on the wheel 24, typically through use of the crane 18.
The tire 22 is first canted on the wheel 24 such that a part, shown at 160,of the lower bead 158 enters the drop center.
Oppositely therefrom, the tire 22 is gripped on its sidewalls by the jaws 110 and 112 and by retraction of the extenda~le member 84, a nonaxial urging force designated by an arrow 162 is exerted on the tire 22 to bring the part 160 into the drop center 150 of the wheel 24. This results in the inner edges 164 and 168 of the upper and lower beads adjacent the jaws 110 and 112 beina moved to a location whereat they will clear the upper wheel flange 152. By pivoting the boom 82 about the pivot 80 and/or the jaws 110 and 112 and pusher means 106 about the pivot 104, a generally axially moving force represented by an arrow 170 may be applied to the tire to move the tire 22 toward the wheel 24. Such movement is continued until the beadparts 164 and 168 are located between the wheel flanges 152 and 154 as shown in Fig. 8. At this point in time only a part 172 of the upper bead 156 immediately above the part 160 of the lower bead will not be disposed between the rim flanges. The jaws 110 and 112 are driven by their respective cylinders so as to cause the bead parts 164 and 168 to be brought into sufficient proximity to each other that both may simultaneously enter the drop center 150 of the wheel 24 and the extendable member 84 is then extended.
This causes the pusher means lQ6 to engage the tread of the tire and apply a nonaxial force in the direction of an arrow 180 to move the bead parts 164 and 168 into the drop center 150 by pushing the tire towards the wheel 24, As a consequence, the - bead part 172 will be moved away from the upper wheel flange 152 sufficiently to clear the same, The part of the tire 22 remote from the pusher means 106 may then move downwardly in the direction of an arrow 182 under the influence of gravity to a location whereat the entirety of both the upper and lower beads 156 and 158 are between the flanges 152 and 154. The mounting process is thereby completed.
While Fig. 8 illustrates the left-hand part of the tire 22 as being free from distortion by the jaws 110 and 112, it will be appreciated that the clamping action initiated by the steps illustrated in Fig. 7 can be maintained during this time.
The various lines of applied force can easily be obtained by suitably pivoting the boom and/or the jaw structure abnut pivots 80 and 104 as well as by extending and retracting the extendable member 84.

To demount a wheel, the jaws 110 and 112 are brought into engagement with the sidewall of the tire 22 sufficiently to bring the immediately adjacent bead parts 164 and 168 into suffi.cient proximi-ty so as to enable them to enter the drop center 150 of the wheel 24, The pusher means 106 may then be opera-ted as previously described to apply a force to the tire 22 in the direction of an arrow 184 to urge the bead parts 164 and 168 into the drop center 150 of the rim. As a consequence, both the bead part 160 of the lower bead and the head part 172 Of the upper beàd are displaced radially outwardly of the upper and lower wheel flanges 152 and 154 as shown in Fig. 10 suf-ficiently to enable a flexible strap 186 to be disposed under the tire 22 at a location directly oppositely of the pusher means 106 and through the space bet~een the wheel 24 and the adjacent part of the tire 22. By means of a hook 1~8 secured to one end of the strap, the innermost end of the strap 186 may be firmly affixed to the wheel 24. Thereafter, an upward force in the direction of an arrow 190 may be applied to the strap 186 at its end remote from the hook 188 to move the tire 22 in a generally axial direction as shown by an arrow 192 to completely pivot the tire off of the wheel 24. Frequently, the crane 99 may be utilized to raise the strap 186.
If desired, hydraulic cylinders 194 mounted on the bed 20 may be utilized to engage the lower tire side wall to par-tially elevate the tire with respect to the wheel so that thebeads are aligned with the drop center of the wheel.
An alternate, and highly preferred method of mounting a tire on a wheel is illustrated in Figs. 11-14 inclusive.
This method is preferred over that illustrated in Figs. 7-9 in that it may be effected more rapidly. However, the method .~ .
. ,~ .

1~

lllustrated in Figs. 11-14 requires the use of the crane 18 in addition to the clamping and urging means 28.
Initially, with the rim 24 clamped in place, the ~ire 22 is gripped by the grippers 19 and the crane 1~ operated such that the tire 22 is canted with respect to the horizontal as illustrated in Fig. 11. The crane 18 is then operated to urge the tire downwardly with force being applied along a line generally illustrated by the arrow 200. This will result in the tire 22 assuming the position illustrated in Fig. 11 10 with respect to the rim 50. That is, a part 202 of the lower bead of the tire 22 will be disposed within the drop center 150 of the rim 24.
At this point in time, the crane 18 is then operated so as to urge the tire 22 in a direction opposite from the lower 15 bead part 202 in the drop center 150 as well as downwardly.
This line of force application is shown by an arrow 204 in Fig. 12 and results in the remainder 206 of the lower bead being disposed between the flanges of the rim 24.
The tire clamp and urging means 28 is then brought into 20 play with the upper and lower jaws 110 and 112 squeezing the lower bead part 202 into contact with the corresponding upper bead part 210. The tire is moved by the tire clamp and urging means 28 oppositely from the lower ~ead part 206 cand downwardly as shown by an arrow 212 so that the upper bead part 210 clears the upper rim flange of the wheel 24 and is moved toward the drop center as illustrated in Fig. 13.
With the bead parts 202 and 210 still clamped together by the jaws 110 and 112, the same are urged by the ~ire clamp and urging means 28 in the direction of an arrow 214 into the 30 drop cen-ter 150 of -the rim 24 while at the same time the :
crane 18 may apply a force in generally the same direction as well as downwardly as shown by an arrow 216 at which time the part 21~ of the upper bead aligned with the part 206 will clear the upper rim flange of the wheel 24 to be located be-tween the flanges. The tire is then ready for inflation.
Figs. 15-18 inclusive illustrate a further method of demounting the tire from the wheel. The method illustrated in Figs. 15-18 is somewhat slower than that illustrated in Fig. 10 but m,ay be effected solely through the use of the crane 18, that is, without requiring the use of the tire clamp , and urging means 28.
Initially, the tire 22 is in the configuration illustra-' ted in Fig. 15 and the same is gripped by the grippers 19~
The crane 18 is operated to move aligned bead parts 240 and 242 towards the drop center while moving diametrically opposite 'bead parts 244 and 246 away therefrom. Because o~ the typical slant angle portions 248 and 250 intermediate the drop center 150 and the flallges 252 and 254 of the wheel 24, t~e bead parts 2ao will tend to be cammed inwardly and into the drop center ,~ 20 lS0 when such a force is applied.
At the same time, a canting or rotative force is applied to the tire by the crane and the combination of the forces ap-plied is generall~ designated by an arrow 256. As a conse-quence, part of the tire will assume the dotted line position illustrated in Fig. 15 at which time the upper bead part 244 will be free of the wheel 24.
Force application to the tire 22 radially of the wheel is then reversed such that the lower bead part 246 enters the drop center 150 of the wheel. At the same time, an upward force is applied to the tire 22 and a combination of the two forces is illustrated by an arrow 260. This results in the upper bead part 240 being freed from the wheel as illustrated in dotted lines in Fig. 16.
The force application radially of the wheel is again reversed as illustrated by an arrow 262 in Fig. 17 and a canting force again applied so that ~he tire 22 moves from the position illustrated in solid lines in Fig. 17 to one where both the bead parts 244 and 246 are free t~e wheel as shown in dotted lines as is the part 240 shown in solid lines.
Force direction is again reversed as illustrated in ; Fig. 18 by the arrow 264 with the consequence that the re-maining bead part 242 disposed between the wheel rims 248 and 250 is moved to the dotted line position illustrated in Fig. 18. At this time, the tire has been completely de-mounted.
Those skilled in the art will readily appreciate that tire mounting and demounting apparatus and methods according to the invention produce numerous advantages over those here-tofore employed.
For one, the apparatus utilizes unique clamping means which are fully retractable enables dual use of the environ-ment, that is, the bed of the servicing apparatus as, ~or example, storage purposes or when on a vehicle, for transpor-tation purposes.
It will also be appreciated that the invention elimi-nates the need for complex, rotatable bead deflecting devices for disposing the beads between the wheel ~langes. ~t the same time, the number of steps required for both mounting and demounting operations is reduced from those heretofore emplo~ed thereby providing a time savings in mounting and demounting operations as well.

Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Tire servicing apparatus comprising:
a bed;
wheel clamp means mounted on said bed for movement between a wheel clamping position above said bed and a retracted position below said bed to free said bed of obstructions to enable use of the same for other purposes;
tire clamp and urging means for gripping a tire and for applying a moving force to a tire; and means mounting said tire clamp and urging means adjacent said bed for movement a) toward and away from said wheel clamp means, and b) toward and away from said bed;
said tire clamp and urging means comprising a pair of opposed jaws and a pusher member extending between said jaws and pivotally mounting said jaws for movement toward and away from each other.

2. The tire servicing apparatus of claim 1 wherein said wheel clamp means comprise at least two spaced plates having oppositely directed hook formations, each plate being pivoted to said bed below the surface thereof and at a location spaced from its hook formation and rotatable between a position wherein its hook formation is above said surface and a position wherein its hook formation is below said surface, and a cam surface on each said plate leading to the associated hook formation whereby as a hook formation emerges from below said surface, the corresponding cam surface will cam a wheel edge toward the hook formation to be gripped thereby.

3. A tire changer for changing large tires mounted on drop center wheels comprising:
an elongated frame;
a plurality of wheel clamps mounted on said frame for engaging a wheel and clamping the same to same frame, at least one of said clamps being mounted on said frame for movement relative to at least one other clamp between wheel clamping and unclamping positions;
a tire grasping and urging means on said frame and having opposed jaws movable towards and away from each other for gripping a tire on opposed side walls and compressing the same;
and means movably mounting said grasping and urging means on said frame so that said jaws will move in concert toward and away from said wheel clamps in a first direction generally transverse to the rotational axis of a wheel engaged by said clamps and in a second direction generally parallel to said axis in addition to being movable toward and away from each other to grip a tire;
whereby a tire gripped by said jaws through movement thereof toward each other may be urged in said first direction to locate one or both tire beads on one edge of the tire in the drop center of a wheel engaged by said clamps and urged in said second direction to effect relative movement between the tire and the wheel generally along said axis to mount and/or demount the tire from the wheel.

4. The tire changer of claim 3 wherein said frame is horizontally disposed.

5. The tire changer of claim 4 wherein said frame comprises the bed of a vehicle.

6. A tire changer for changing large tires mounted on drop center wheels comprising:

an elongated frame defining a base for said tire changer;
a plurality of wheel clamps mounted at spaced locations on said frame for engaging a wheel and clamping the wheel to said frame to hold the wheel on the frame in a predetermined plane against movement relative to the frame, at least one of said clamps being movably mounted on said frame for movement relative to at least one other clamp between wheel clamping and wheel unclamping positions;
means on said frame for moving said one clamp between said clamping and unclamping positions;
tire grasping and urging means mounted on said frame to one side of said clamps for movement generally within said plane toward and away from said clamps and for movement toward and away from said plane, said tire grasping and urging means including opposed jaws mounted for movement toward and away from each other and said plane so as to be able to grip a tire and position it in or remove it from said plane to effect mounting and/or demounting of a tire on a wheel clamped in said plane by said clamps;
means for moving said tire grasping and urging means generally within said plane toward and away from said clamps;
means for moving said tire grasping and urging means toward and away from said plane; and means for moving said jaws toward and away from each other.

7. The tire changer of claim 6 wherein said frame comprises a horizontally disposed bed and all of said clamps are movably mounted thereon for movement between said clamping and unclamping positions, said clamps when in said clamping position having wheel engaging formations above said bed, said clamps when in said unclamping position being wholly below the upper surface of said bed.

8. The tire changer of claim 6 wherein said tire grasping and urging means further includes tire engaging pusher means in close proximity to said jaws and on the side thereof remote from said clamps, said pusher means including at least one elongated surface facing said clamps and extending generally transverse to said plane and movable toward and away from said clamps generally in said plane.

9. The tire changer of claim 6 in combination with a vehicle, said elongated frame comprising a bed on said vehicle, and a crane mounted on said vehicle for loading and unloading wheels and/or tires onto and from said bed, said clamps being movable relative to said bed to a stowed position freeing said bed for receipt of wheels and/or tires for transportation purposes.