Run-flat tire and rim assembly for ATV

The invention relates to a run-flat tire and rim assembly for all-terrain vehicles (ATV), wherein the rubber thickness of the tire sidewall is at leat 10 times the diameter of the ply cords of a carcass; the height of the radially outermost end of a tire bead apex from the tire bead base is within a range of 20 to 40% of the section height of the tire; each tire bead has a toe with a protrusion protruded radially inwardly from the bead base and a hump groove axially outward of the protrusion; the bead toe comprises a toe strip having a JIS A hardness of 65 to 95; and the rim is provided with a well in the center portion, a pair of bead seats one on each side of the well, a pair of humps one formed axially inward and adjacent to each bead seat to be engaged with the hump grooves of the tire beads and a pair of grooves one formed axially inward of each hump to receive the protrusions of the tire bead toes.

The present invention relates to a run-flat tire and rim assembly for 
all-terrain vehicles (ATV), wherein the tire is safely prevented from 
slipping out of the rim, even if the air is released by puncture or the 
like during running, and which is able to run with a deflated tire. 
In a conventional run-flat tire and rim assembly for an ATV, as shown in 
FIG. 3, the tire 25 is fixed to the rim in such a manner that the bottom 
surface and outside surface of each bead 20 are pressed against the bead 
seat and flange of the rim by mean of internal air pressure. Accordingly, 
when the pressure is lowered, its power of holding the tire on the rim is 
also lowered. In particular, when the internal pressure is suddenly 
lowered owing to puncture and the like, if the tire is additionally 
subjected to a lateral force by the operation of a handler and the like, 
the beads 20 of the tire would slip out of the bead seats of the rim, 
which remarkably imperils safety. Furthermore, as the normal air pressure 
for ATV tires is very low, the slipping-out of the bead from the bead seat 
occurs easily due to a lateral force owing to an eventual sharp cornering 
during operation to avoid a possible accident. The above mentioned 
slipping-out leads to not only a lack of the maneuver stability but also 
to such a dangerous situation that the tire drops off completely from the 
rim, particularly a rim which has a rim well. 
While in cornering operation, the tire is subjected to a lateral force, 
which shifts the tread 27 laterally with respect to the rim, and the force 
is transferred to the tire bead 20 through the carcass 29. Accordingly, 
the part of the bead adjacent to the ground contacting patch is subjected 
to an axial force and a moment around the bead, and the heal 20A of the 
bead would be lifted if the inner air pressure is low. Under such 
condition, the frictional force between the bead base 20B and the seat, or 
the only force that holds the beads on the seats would become remarkably 
reduced, which easily causes the bead to slip off the bead seat and to 
fall into the rim well. 
It is therefore, an object of the present invention to provide a run-flat 
tire and rim assembly for ATV which can solve the above mentioned problems 
caused by a sharp cornering operation by the handler, as being a major 
cause of car accident, under a low inner pressure, and continue to run 
after puncture. 
According to one aspect of the present invention, an assembly comprises a 
rim and a run-flat tire mounted thereon, wherein the tire comprises a pair 
of beads with a substantially inextensible bead core; a toroidal carcass 
of a radial or a bias construction extended across the beads and turned up 
in both edge portions around the bead cores; a tread disposed radially 
outward of the carcass; a pair of sidewalls disposed on the outside of the 
carcass and each extended from each buttress region to the bead region of 
the tire, the rubber thickness of each sidewall being at least 10 times 
the diameter of ply cords of the carcass; a pair of bead apexes one 
disposed radially outside each bead core and extended radially outwardly 
from the bead core, the radially outward height of the radially outermost 
end thereof from the bead base being within a range of 20 to 40% of the 
section height of the tire; and the beads each having a toe disposed 
axially inward of the bead core, the toe having a protrusion protruded 
radially inwardly from the bead base at the axially inside of the bead 
core, and each bead provided with a hump grove (Q) at the axially outside 
of the protrusion (R), and the rim has a well in the center portion of the 
rim; a pair of bead seats one on each side of the well; a pair of humps 
one formed axially inward and adjacent to each bead seat to be engaged 
with the hump grooves of the tire beads; and a pair of grooves one formed 
axially inward of each hump to receive the protrusions of the tire bead 
toes.

In the drawings, the run-flat tire and rim assembly comprises a run-flat 
tire 1 and a rim 2 on which the tire 1 is mounted. 
In FIG. 1, the tire 1 comprises a pair of bead cores 3 one disposed in each 
bead 9, a toroidal carcass 4 extending across the beads 9, a tread 5 
disposed radially outside the crown part of the carcass 4, a pair of 
sidewalls SW on the outside of the carcass, a belt 6 disposed between the 
carcass and the tread. Further, each bead region 9 is provided with a toe 
T with a dove's tail-like protrusion R, and the bead base is grooved to 
form a hump groove Q. 
The carcass 4 is turned up in both edge portions around the bead cores 3 
from the inside to the outside thereof to be secured thereto, whereby two 
turnup portions and a main portion therebetween are formed. In the tire 1 
of FIG. 1, the carcass is of a radial construction in which at least one 
rubberized parallel cord ply is arranged so that the cords are laid at an 
angle of 70 to 90 degrees with respect to the equatorial plane of the 
tire. 
The carcass ply cords are made of organic fibers such as nylon, polyester, 
rayon and aromatic polyamide. However, the carcass can also employ a bias 
construction in which at least two rubberized parallel cord plies are 
arranged so that the cords of one ply intersect with those of the other 
ply. 
The belt 6 is composed of rubberized cords laid at an angle of 10 to 30 
degrees with respect to the equatorial plane of the tire. The belt cords 
are made of inextensible material such as steel. The belt 6 is preferably 
extended all over the width of the tread to increase the rigidity of the 
ground contacting region of the tire, whereby the stability at straight 
running is improved and the resistance to puncture is increased. 
Each sidewall SW is made of rubber and extended from each edge of the tread 
5 in the tire buttress portion BT to the clincher part FR of the bead 
region which contacts with a rim flange 13 when mounted. The thickness of 
the sidewall is so set that the thickness C at the buttress portion BT, 
the thickness E at the maximum tire section width portion, and the 
thickness F at the clincher part FR are at least 10 times the diameteer of 
the carcass ply cord, whereby the vertical stiffness of the sidewall SW is 
maintained at a certain level, even if the internal air is released. When 
they are less than 10 times, it is impossible to get a enough vertical 
stiffness to run under deflation. The elastic modulus at 100% elongation, 
of the sidewall rubber is preferably more than 12 kg/sq.cm. 
In each bead region 9, a bead apex BE is disposed radially outside the bead 
cores 3 between the turnup portion and main portion of the carcass 4. The 
bead apex BE is made of a rubber compound preferably having a JIS A 
hardness of 65 to 95. 
The bead apex BE extends radially outwardly from the bead core, and the 
height h2 of the radially outermost end thereof from the bead base L is 
within a range of 20 40%, more preferably within a range of 20 to 30% of 
the tire section height h1 from the same bead base L. When it is less than 
20%, the lateral stiffness of upper bead part over the rim flange 13 
becomes low, and the bead portion of the deflated tire will fatique 
remarkably. On the contrary, when it is more than 40%, under the normal 
state, the stress concentrate is apt to occur at the radially outermost 
end of the bead apex BE, which causes the separation of rubber. 
Further, as mentioned above, in each bead region 9, the bead toe T is 
formed axially inside the bead core 3 along the axially inside of the 
carcass main portion, and extended radially inwardly therefrom. The bead 
toe T of FIG. 1 includes a toe strip (hatched part) as a core of the toe 
being harder than the surrounding elastomer. 
The toe strip is preferably made of a hard rubber compound having JIS A 
hardness of 65 to 95. For the toe strip, one made of a plastic material, 
or one having fibers or the likes may be used to further increase the 
engagement of the tire with the rim. Further, for the bead toe T, one made 
of a single elastomer without any core may be employed. 
The toe strip is disposed axially inside the bead core 3 along the axially 
inside of the carcass main portion, and extended radially and axially 
inwardly therefrom, that is, obliquely to the bead base level L. 
Therefore, in this example, the surrounding elastomer is protruded from 
the bead base L, and this protrusion R forms the tip of the bead toe. 
Accordingly, the protrusion R becomes softer than the toe strip. 
Further, the bead toe T is prferably reinforced by a fiber cord reinforcing 
layer disposed along the profile of the whole bead, that is, including the 
toe from the inside to the outside thereof. 
FIG. 2 shows a rim according to the present invention. In FIG. 2, the rim 2 
is provided with; a well 11 in a central portion of the rim; a pair of 
bead seats 12 one on each side of the well; a pair of rim flanges 13 
extending radially outwardly one from the axially outward end of each bead 
seat 12. And further, in each of the portions between the well and the 
bead seats, a hump HP adjacent to the axially inner end of the bead seat 
12 and a circumferentially extending groove P located axially inward of 
the hump are formed to fit with the hump groovw (Q) and the protrusion (R) 
of the tire bead toe T, respectively. 
The bead seat 12 is tapered at an angle (alfa), and the resultant down 
slope is smoothly connected with the hump HP by an arc, and also the hump 
HP and the groove P are connected smoothly with each other. 
The outer diameter DH of the hump HP is set to be larger 1.5 to 5 mm than 
the bead diameter DB or the rim diameter, that is, the diameter of the 
above-mentioned bead base L. 
The width BSW of the bead seat 12 is set to be substantially equal to the 
width of the bead of a standard tire of the identical size, so that such 
standard tires as shown in FIG. 3 can be mounted on the rim 2. 
The width BW of the tire bead base is set within a range of 2.4 to 2.7 
times the width BSW of the bead seat 12, and the axial distance WP between 
the rim flange 13 and the groove P is set to be substantially equal to, 
but little shorter than the bead base width BW to fit the protrusion R of 
the tire bead toe T with the groove P. 
The radially inward height TR of the protrusion R of the bead toe T from 
the bead base level L is set to be in a range of 2 5% of the tire section 
height h1. 
The height TH of the radially outermost end of the above-mentioned toe 
strip is in a range of 120 to 150% of the flange height FH. When it is 
under 120%, the rigidity in the longitudinal direction thereof becomes 
insufficient for maintaining the force to push the protrusion R into the 
groove P. On the other hand, when it is over 150%, the work of mounting 
the tire on the rim becomes difficult. 
As the tire 1 is constructed as above, it can be mounted on the rim 2 by a 
conventional way, for example, setting the beads 9 into the rim well 11 
over the rim flange 13, and then applying air through the value. 
Accordingly, the air presses the beads 9 against the bead seats 12 and 
flanges 13 over the hump HP, and the protrusion R of the bead toe T is 
pushd into the groove P, whereby the beads are firmly held on the rim 2. 
Further, by disposing the hard toe strip in the bead region, the bead toe 
becomes rigid in the longitudinal direction of the toe strip, but in a 
direction perpendicular to the longitudinal direction, the bead toe 
becomes flexible. And further, the protrusion R is softer than the toe 
strip, and the toe strip is terminated at the bead base level L, which 
allows a easy tire fitting work, but the tire beads are not allowed to be 
easily unseated under low pressure, because when an axially inward force 
is act on the bead, the toe strip gives a substantially radially and 
axially outward force to the bead core 3, which prevents the axially 
inward movement of the bead and increases the retaining force of the bead 
on the rim. 
In addition, it is possible for the wheel-rim according to the invention to 
fit not only the above-mentioned run-flat tire but also a standard tire by 
only setting its bead on the bead seat 12 of the rim as usual. Even in 
case the standard tire, the wheel rim is safely used therefor. 
Assemblies A and B of which the specifications are given in Table 1, were 
tested for the resistance to unseating (a force by which the bead is 
slipped out from the bead seat), the plunger resistance (a resistance to 
puncture), the rolling resistance and the ability to run flat (a runable 
distance under a deflation of air pressure 0 kg/sg.cm). 
The test results are set out in Table 2, wherein each value is expressed by 
an index based on the assumption that the assembly B of a conventional 
tire of FIG. 3 and the rim of FIG. 2 is 100, and the larger the value the 
better the performance. 
TABLE 1 
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ASSEMBLY A B 
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TIRE FIG.1 FIG. 3 
Size 25 .times. 12.00-9 
25 .times. 12.00-9 
Section height mm 
180 180 
Sidewall 
Thickness 
C mm 7.0 4.5 
E mm 7.0 4.5 
F mm 9.0 5.0 
100% modulus kg/sq .multidot. cm 
15 12 
Bead 
Height mm 54 15 
Hardness JIS-A 85 85 
Belt non 
Cord steel/2 
Cord angle deg 15 
Carcass ply radial bias 
Cord polyester polyester 
1000d/2 1000d/2 
Cord angle deg 90 45 
Toe strip non 
Hardness JIS-A 85 
Height TH mm 20 
BW/BSW 27/11 = 2.45 
WQ/BSW 15/11 = 1.36 
RIM FIG. 2 FIG. 2 
Size 9 .times. 9.0 
9 .times. 9.0 
Flange height FH mm 
16 16 
WH/BSW 15/11 = 1.36 
WP/BSW 24/11 = 2.18 
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TABLE 2 
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ASSEMBLY A B 
______________________________________ 
Plunger resistance *1 
280 100 
Unseating resistance *2 
615 100 
Rolling resistance *3 
54 100 
Run flat over 100 km 
at 40 km/h 
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Test condition 
*1 - Internal air pressure: 
0.15 kg/sq .multidot. cm 
Diameter of plunger: 
8 mm 
*2 - Internal air pressure: 
0.15 kg/sq .multidot. cm 
Lubricant: Water 
*3 - Internal air pressure: 
0.15 kg/sq .multidot. cm 
Speed: 80 km/h 
Load: 80 kg 
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As described above, in the present invention, the rim is provided with 
grooves, and the tire is provided in the bead region with the toe strip to 
form a bead toe with a protrusion. Accordingly, the retaining force of the 
run-flat tire on the rim will be increased, and there is no possibility of 
the tire slipping out from the rim owing to a quick handling under low air 
pressure, and further, the ability to run-flat under the deflated state 
with no air pressure is improved by the stiff reinforced sidewalls of the 
tire. 
Further, the hump groove and the hump can be modified in various shape for 
the sake of the prevention of slipping out of the tire from the rim.