JP2003165303A - Pneumatic tire and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of preventing remarkable increases in manufacturing cost and weight and manufacturing method therefor. <P>SOLUTION: Durability of the tire 10 can be improved by making thickness (an oblique line part A) of an inner liner 16 from the vicinity of a shoulder part 22 to the vicinity of a buttress part 26 and thickness (an oblique line part B) of the inner liner 16 in the vicinity part 36 of a carcass end part comparatively thicker than that of other parts. Since thickness of the other parts is not made thick, the remarkable increase of the weight of the whole of the inner liner 16 can be prevented, and thereby an increase in weight of the whole of the pneumatic tire 10 can be prevented. By preventing a remarkable increase in rubber amount to be used, the remarkable increase in the manufacturing cost can be prevented. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire provided with an inner liner in which necessary portions are thickened and unnecessary portions are thinned, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Generally, a pneumatic tire has an inner liner formed inside a carcass layer in the tire radial direction.

Here, in order to improve the durability of the tire, in particular, it is necessary to make the inner liner relatively thick in the portion from the shoulder portion to the buttress portion and in the portion near the end portion of the carcass.

By making the inner liner of such a portion relatively thick, the rigidity of such a portion can be increased, and the pressure inside the tire allows the air inside the tire to permeate (deteriorate by oxygen) through the inner liner. Can be prevented. As a result, it is possible to suppress the rubber deterioration of the above-mentioned portion, and it is possible to suppress the belt end separation, the shoulder part separation, and the ply end separation.

By the way, in order to prevent the above-mentioned separations, increasing the gauge of the inner liner at the above-mentioned portion (improvement of the wall thickness) is one solution, but in the conventional technology, the gauge is increased only at the necessary portions. It was difficult to do.

For example, in the conventional pneumatic tire manufacturing method, it is difficult to partially increase the wall thickness of the inner liner because of the vulcanization bladder method. There was a problem that the thickened rubber would flow to other parts and eventually the gauge would become uniform.

Further, assuming that the rubber of the thickened inner liner flows to other portions, if a very thick sheet is put in the portion to be thickened, the rubber on the outer side of the carcass layer in the axial direction of the tire will be changed. It will flow to other parts and change the case line of the tire, which will adversely affect other performance.

Therefore, in order to avoid the above problems, the gauge of the entire inner liner is made thick according to the gauge of the portion to be made thick. Therefore, there has been a further problem that the weight of the tire is increased and the manufacturing cost is increased.

[0009]

Therefore, in consideration of the above facts, the present invention makes the thickness of a necessary portion thicker and the thickness of an unnecessary portion thinner, thereby significantly increasing the manufacturing cost and weight. It is an object of the present invention to provide a pneumatic tire capable of preventing the above-mentioned problems and a method for manufacturing the same.

[0010]

A pneumatic tire according to claim 1, wherein a pair of left and right bead cores, a carcass straddling the bead cores in a toroidal shape, an inner liner formed inside the carcass, A tread portion constituted by a tread rubber arranged on the tire radial direction outer side of the carcass, a shoulder portion located at a tire axial outer side end portion of the tread portion, a tire axial maximum width portion of the shoulder portion and the carcass. A buttress portion located substantially in the middle of, and a pneumatic tire having
The thickness of the inner liner from the shoulder portion to the buttress portion is 1.2 times or more and 5.0 times or less the thickness of other portions of the inner liner.

Next, the function and effect of the pneumatic tire according to claim 1 will be described.

According to the pneumatic tire of the present invention, the thickness of the inner liner from the shoulder portion to the buttress portion is set to 1.2 times or more and 5.0 times or less the thickness of the other portions of the inner liner. ing.

According to the present invention, by making the thickness of the inner liner from the shoulder portion to the buttress portion thicker than the thickness of other portions, the strength of the portion is increased and the air inside the tire has its pressure increased. This can prevent the inner liner from penetrating. For this reason, the amount of bending (bending deformation) of the portion from the shoulder portion to the buttress portion of the tire can be reduced, and belt end separation and shoulder portion separation can be prevented more effectively. As a result, the durability of the tire can be improved.

By the way, in the pneumatic tire of the present invention,
Since the thickness of the other parts of the inner liner is not made thick, it is possible to prevent a significant increase in the weight of the entire inner liner, and thus to prevent an increase in the weight of the entire pneumatic tire. Further, by preventing a large increase in the amount of rubber used, it is possible to prevent a large increase in manufacturing cost.

Particularly, if the thickness of the inner liner from the shoulder portion to the buttress portion is 1.2 times or more the thickness of the other portion of the inner liner, if it is less than 1.2 times, Sufficient effect to suppress the permeation of air through the inner liner cannot be expected. On the other hand, the reason why it is 5.0 times or less is that it is not preferable if it is more than 5.0 times, since the thickness becomes unnecessarily thick and the weight and the manufacturing cost increase significantly.

The other parts of the inner liner are
For example, it means a portion other than a portion from the shoulder portion of the inner liner to the buttress portion, such as a portion near the tire equator line or a portion near the carcass maximum width.

In the present specification, the "tread portion" means a portion that comes into contact with the road surface in a state where the pneumatic tire of the present invention is mounted on a standard rim, a regular internal pressure is filled, and a regular load is applied. To do. In particular, in the tire axial direction, it refers to a region between the tire axially outer end portions that has the maximum tire ground contact width.

The "shoulder portion" means the outer end portion of the tread portion in the tire axial direction.

"Butless portion" means a substantially intermediate portion between the shoulder portion and the tire axial maximum width portion of the carcass.

The "wall thickness of the inner liner at the shoulder portion" means the thickness of the inner liner measured along the normal direction passing through the shoulder portion.

The "wall thickness of the inner liner in the buttress portion" means the thickness of the inner liner measured along the normal direction passing through the buttress portion.

Here, the pneumatic tire is used by being attached to a rim defined by a standard issued by JATMA (Japan) or the like according to each size, and this rim is usually called a regular rim.

Similarly, "normal load" and "normal internal pressure" mean
The maximum load and the air pressure for the maximum load in the applicable size and ply rating specified in the standard.

Further, in the present specification, the "maximum width of tire contact with the ground" means that the tire is assembled to the "regular rim", the "regular internal pressure" is filled, and the "regular load" is statically applied. Refers to the maximum contact width of the tread in the axial direction of the tire.

The load is the maximum load (maximum load capacity) of a single wheel in the applicable size listed in the following standard, and the internal pressure is the maximum load of the single wheel in the applicable size described in the following standard ( Air pressure corresponding to the maximum load capacity), and the rim is a standard rim in the applicable size described in the following standard.

The standard is defined by an industrial standard effective in the region where the tire is produced or used. For example, in Japan, "JATMA" of the Japan Automobile Tire Manufacturers Association
"Year Book".

In the pneumatic tire according to claim 2, a pair of left and right bead cores, a carcass straddling the bead core in a toroidal shape, and both ends thereof folded back outward in the tire axial direction with respect to the bead cores, A pneumatic tire having an inner liner formed inside a carcass, wherein a thickness of the inner liner at an end portion of the carcass is 1.2 times or more a thickness of other portions of the inner liner. It is characterized by being 5.0 times or less.

Next, the function and effect of the pneumatic tire according to claim 2 will be described.

In the pneumatic tire of the present invention, the thickness of the inner liner at the end of the carcass (ply end) is set to 1.2 times or more and 5.0 times or less the thickness of the other parts of the inner liner. Has been done.

According to the present invention, the thickness of the inner liner at the end of the carcass is made thicker than the thickness of the other portions, so that the strength of those portions is increased and the air inside the tire is pressurized by the inner liner. Can be prevented. Therefore, the amount of bending (bending deformation) of the carcass end portion of the tire can be reduced, and the carcass end separation can be prevented more effectively. As a result, the durability of the tire can be improved.

By the way, in the pneumatic tire of the present invention,
Since the thickness of the other parts of the inner liner is not made thick, it is possible to prevent a significant increase in the weight of the entire inner liner, and thus to prevent an increase in the weight of the entire pneumatic tire. Further, by preventing a large increase in the amount of rubber used, it is possible to prevent a large increase in manufacturing cost.

Particularly, the thickness of the inner liner at the end of the carcass is set to be 1.2 times or more the thickness of the other parts of the inner liner, when the thickness inside the tire is less than 1.2 times. It cannot be expected to have a sufficient effect of suppressing permeation through the liner. On the other hand, the reason for setting it to 5.0 times or less is that if it is more than 5.0 times, it will be unnecessarily thick, and the weight and manufacturing cost will increase significantly.
This is because it is not preferable.

The other parts of the inner liner are
For example, it means a portion other than the portion corresponding to the carcass end portion of the inner liner, such as a portion near the tire equator line and a portion near the carcass maximum width.

In the present specification, "wall thickness of the inner liner at the end of the carcass" means a straight line passing through a point on the outer surface of the tire located at the shortest distance from the end of the carcass and the end of the carcass. Means the thickness of the inner liner measured along.

In the pneumatic tire according to the present invention, a pair of left and right bead cores, a carcass straddling the bead core in a toroidal shape, both ends of which are folded back to the outside in the tire axial direction around the bead core, and the carcass An inner liner formed on the inner side of the carcass, a tread portion constituted by a tread rubber arranged on the tire radial outside of the carcass, a shoulder portion located at the tire axial outer end of the tread portion, and the shoulder Portion and a buttress portion located substantially in the middle of the tire axial maximum width portion of the carcass, a pneumatic tire having, wherein the thickness of the inner liner from the shoulder portion to the buttress portion, the It is 1.2 times or more and 5.0 times or less the wall thickness of the other part of the inner liner, and at the end of the carcass. Serial thickness of the inner liner, or 1.2 times the thickness other portion of the inner liner 5.
It is characterized by being 0 times or less.

Next, the function and effect of the pneumatic tire of claim 3 will be described.

According to the pneumatic tire of the present invention, the durability of the tire can be improved for the same reason as described in claims 1 and 2.

Further, it is possible to prevent an increase in weight of the pneumatic tire as a whole and a significant increase in manufacturing cost.

The pneumatic tire manufacturing method according to claim 4 is the pneumatic tire manufacturing method according to any one of claims 1 to 3, wherein the inner liner has a thick wall portion. Inner liner forming step of winding the inner liner so as to fill the concave portion on the core in which the concave portion is formed in the corresponding portion, a carcass forming step of forming a carcass on the inner liner by pressure bonding, and a carcass on the carcass The method further comprises a belt forming step of forming the belt by pressure bonding, and a tire outer shape forming step of winding an elastic member on the belt to form an outer shape of the tire.

Next, the function and effect of the method for manufacturing a pneumatic tire according to claim 4 will be described.

According to the method for manufacturing a pneumatic tire of the present invention, in the inner liner forming step, the concave portion is filled on the core in which the concave portion is formed in the portion corresponding to the thick portion of the inner liner. The inner liner is rolled up.

In the carcass forming step, the carcass is pressure-bonded and formed on the inner liner.

In the belt forming step, the belt is pressure-bonded on the carcass.

In the tire contour forming step, an elastic member is wound around the belt to form the contour of the tire.

A raw tire is manufactured through the above steps,
A pneumatic tire is manufactured by vulcanizing this in a vulcanization process. The core is removed after vulcanization.

According to the method of manufacturing a pneumatic tire of the present invention, since the core is provided with the recessed portion, the thick portion of the inner liner, for example, the portion extending from the shoulder portion to the buttress portion or the end portion of the carcass is formed. The thickness of the inner liner corresponding to the portion can be made relatively thick.
On the contrary, the wall thickness of the other parts of the inner liner does not become thick because the core has no recessed portion.

Therefore, according to the method for manufacturing a pneumatic tire of the present invention, it is possible to make the thickness of the necessary portion relatively thick and the thickness of the unnecessary portion relatively thin, thereby reducing the manufacturing cost and weight. Can be prevented from increasing significantly.

[0048]

BEST MODE FOR CARRYING OUT THE INVENTION A pneumatic tire according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, the pneumatic tire 10
Includes a pair of left and right bead cores 12. The bead core 12 has a hexagonal cross section.

A carcass 14 is provided between the bead cores 12.
Spans in a toroidal shape, and the end portion of the carcass 14 in the tire axial direction is folded back outward in the tire axial direction with the bead core 12 as a reference.

Therefore, the end of the carcass 14 folded back by the bead core 12 is located outside the bead core 12 in the tire radial direction. The carcass 14 is formed by coating a plurality of cords (not shown) with rubber.

On the other hand, an inner liner 16 is formed inside the carcass 14 in the radial direction of the tire. The thickness of the inner liner 16, which is a feature of the present invention, will be described later.

A belt layer 18 is arranged outside the carcass 14 in the tire radial direction. The belt layer 18 includes three belts 18A and 18B that are laminated in the tire radial direction.
It is composed of 18C.

A tread rubber is arranged outside the belt layer 18 in the tire radial direction.

As shown in FIG. 1, the pneumatic tire 10 is a portion in which the pneumatic tire 10 is mounted on a standard rim and is in contact with the road surface in a state where a regular internal pressure is filled and a regular load is applied, that is, In terms of the tire axial direction, it has a tread portion 20 which is a region L between the tire axially outer ends which has the maximum width of contact with the tire.

Further, the pneumatic tire 10 has a shoulder portion 22 which is an outer end portion in the tire axial direction of the tread portion 20.
have.

Further, the pneumatic tire 10 has a buttress portion 26 which is a substantially intermediate portion between the shoulder portion 22 and the tire axial maximum width portion 24 of the carcass 14.

Further, the pneumatic tire 10 has a bead portion 28 containing the bead core 12.

Here, the main part of the present invention will be described in detail.

As shown in FIG. 2, in the pneumatic tire 10 of the present invention, the thickness of the inner liner 16 from the portion 34 near the end portion in the tire axial direction of the belt layer 18 to the portion near the maximum width portion 24 of the carcass (FIG. 2). The middle hatched portion A) is 1.2 times or more the thickness of the inner liner 16 at other portions (for example, the portion 30 near the tire equator line CL, the quarter portion 32 near the tread portion 20, etc.) 5 It is formed so as to be 0.0 times or less.

In the present specification, the "1/4 portion of the tread portion" means the distance from the shoulder portion 22 to the inner side in the tire axial direction of 1/4 of the axial width of the tread portion 20. Means a point.

Similarly, the thickness of the inner liner 16 in the portion 36 near the folded end of the carcass 14 (hatched portion B in FIG. 2) is the same as that of the other portions.
The thickness is 1.2 times or more and 5.0 times or less.

Next, a method of manufacturing the pneumatic tire 10 will be described.

As shown in FIGS. 2 and 3, in the inner liner forming step, the inner liner 16 is wound on the hard core 40. The winding operation of the inner liner 16 in the inner liner forming step is performed by a conventionally known device (not shown).

Here, a recess 42 is formed on the outer surface of the hard core 40, which corresponds to the portion where the wall thickness of the inner liner 16 is increased. The depth of the recess 42 is such that the thickness of the inner liner 16 from the portion 34 near the end portion in the tire axial direction of the belt layer 18 to the portion near the maximum width portion 24 of the carcass 14 and the portion 36 near the folded end portion of the carcass 14 is the With respect to the wall thickness of the inner liner 16 at a portion (for example, the portion 30 near the tire equator line CL, the quarter portion 32 of the tread portion 20, etc.),
It is preset so as to be 1.2 times or more and 5.0 times or less.

As described above, in the inner liner forming step, the inner liner 40 is wound so as to fill the recess 42 of the hard core 40. As a result, the inner liner 40 is formed.

In the conventional manufacturing method, the maximum thickness of the inner liner 40 was 2.5 mm, but according to the manufacturing method of the pneumatic tire 10 of the present invention, it is 4.0 mm.
The above thickness can be added.

Next, in the carcass forming step, the carcass 14 is pressure-bonded and formed on the inner liner 16.

After the carcass 14 is pressure-bonded and formed, the bead cores 12 are fitted and pressure-bonded from both sides. After that, the tire axial end portion of the carcass 14 is bent outward in the tire axial direction with the bead core 12 as a reference.

Next, as shown in FIG. 4, in the belt forming step, the three belts 18 are pressed from the top of the carcass 14.

Next, in the tire contour forming step, an elastic member such as rubber is wound around the belt 18.

The raw tire manufactured by the above respective steps is
The pneumatic tire 10 is manufactured by being vulcanized with the hardcore 40 attached. The hardcore 40 is
After vulcanization, it is divided and removed.

Next, the operation and effect of the pneumatic tire 10 of this embodiment and the manufacturing method thereof will be described.

As shown in FIG. 2, according to the method of manufacturing the pneumatic tire 10 of the present invention, the recess 42 is formed in the hard core 40.
Are formed, the portion 34 near the end portion in the tire axial direction of the belt layer 18 to the portion near the maximum width portion 24 of the carcass (hatched portion A), particularly from the shoulder portion 22 to the buttress portion 2
It is possible to make the thickness of the inner liner 16 corresponding to the portion reaching 6 and the portion 36 (shaded portion B) near the folded end of the carcass 14 relatively thick. Further, the wall thickness of the other portions of the inner liner 16 does not become thick because the recess 42 is not formed in the hard core 40.

As described above, the pneumatic tire 10 of the present invention
According to the manufacturing method of 1, the thickness of the necessary portion can be made relatively thick and the thickness of the unnecessary portion can be made relatively thin.

Further, according to the pneumatic tire 10 manufactured by the method for manufacturing the pneumatic tire 10 of the present invention, in particular, the wall thickness of the inner liner 16 from the vicinity of the shoulder portion 22 to the buttress portion 26 (hatched portion A) By making () thicker than the thickness of other portions, the strength of such portions can be increased and the air inside the tire 10 can be prevented from passing through the inner liner 16 due to the pressure.

Therefore, the shoulder portion 22 of the tire 10 is
The amount of bending (bending deformation) of the portion from the buttress portion 26 can be reduced, and the belt end separation and the shoulder portion separation can be more effectively prevented. As a result, the durability of the tire 10 can be improved.

Similarly, a portion 36 near the end of the carcass
By making the thickness of the inner liner 16 (hatched portion B) in FIG. 2 thicker than the thickness of other portions, the carcass 1
The amount of bending (bending deformation) of the portion (bead portion 28) near the end portion of No. 4 can be reduced. As a result, the ply end separation can be prevented more effectively, and the durability of the tire 10 can be improved.

By the way, in the pneumatic tire 10 of the present invention, since the thickness of the other parts of the inner liner 16 is not thick, it is possible to prevent a large increase in the weight of the inner liner 16 as a whole. 1
It is possible to prevent an increase in the weight of the entire body. Further, by preventing a large increase in the amount of rubber used, it is possible to prevent a large increase in manufacturing cost. (Test Example) Next, a performance test using the tire of the present invention and a conventional tire will be described.

In this test, both tire sizes were 1200R24.

The thickness of the inner liner 16 in each part was set as shown in Table 1 below. The thickness of the inner liner 16 at each portion is shown in FIG.

As a test method, the durability is ETR.
TO regular internal pressure / load (775 kPa / 4000 kg (3
Indoor drum test 100,000km under the condition of 9.2N))
In the running product, each failure position (belt end, shoulder,
The deterioration rate (Eb retention rate) of the rubber member at the bead portion) was evaluated.

On the other hand, the wear resistance and uneven wear resistance were tested by the user in an actual vehicle.

[0084]

[Table 1] Here, the “conventional tire A” in Table 1 above is a tire in which the hard core 40 is not used as a manufacturing method and the inner liner has a uniform wall thickness of 0.9 mm.

"Conventional tire B" means that the inner core liner has a thickness of 1.5 without using the hard core 40 as a manufacturing method.
It is unified so as to be relatively thick with mm.

The "tire A of the present invention" means that the hard core 40 is not used as a manufacturing method and only a part of the inner liner 16 (in the vicinity of the belt end portion, the shoulder portion, the buttress portion) has a wall thickness of 1.5 mm. It is made thicker.

The “invention tire B” is the tire of the present invention, which uses the hard core 40 as described above, and compares the thickness of the inner liner 16 from the vicinity of the belt end portion to the buttress portion and the ply end portion with 1.5 mm. It is designed to be thicker.

The "invention tire C" uses the hard core 40 as described above as a manufacturing method, and makes the inner liner 16 in the buttress portion from the vicinity of the belt end portion have a relatively large thickness of 1.5 mm. It was done.

The “invention tire D” uses the hard core 40 as described above as a manufacturing method, and further increases the wall thickness of the inner liner 16 from the vicinity of the belt end portion to the buttress portion to 2.5 mm. It is a thing.

The results of this test are shown in Table 2 below.

[0091]

[Table 2] The values in Table 2 above are based on the evaluation of the conventional tire A (10
It is shown by the index evaluation as 0).

Regarding the numerical values in Table 2, the smaller the manufacturing cost and the weight, the larger the belt durability, the shoulder separation, the bead portion durability, the wear resistance and the uneven wear resistance. Means good.

As shown in Table 2 above, in the tire of the present invention, the belt durability, the shoulder portion separation and the bead portion durability were significantly improved as compared with the conventional tire A.

However, the tire of the present invention is inferior to the conventional tire A in manufacturing cost and weight.

However, as compared with the pneumatic tire manufactured by the conventional manufacturing method like the conventional tire B, the tire of the present invention manufactured by the manufacturing method of the present invention can prevent a significant increase in manufacturing cost and weight. found.

[0096]

According to the present invention, it is possible to prevent a significant increase in manufacturing cost and weight by increasing the thickness of a necessary portion and reducing the thickness of an unnecessary portion.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a pneumatic tire according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a pneumatic tire according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a carcass forming step of the method for manufacturing a pneumatic tire according to the embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a tire outer shell forming step of the method for manufacturing a pneumatic tire according to the embodiment of the present invention.

[Explanation of symbols]

10 pneumatic tires 12 bead core 14 carcass 16 Inner liner 18 belts 20 tread section 22 Shoulder 24 Carcass maximum width in tire axial direction 26 Buttress Club 40 Hardcore 42 recess

Claims (4)

[Claims] 1. A pair of left and right bead cores, a carcass straddling the bead cores in a toroidal shape, an inner liner formed inside the carcass, and a tread rubber disposed outside the carcass in a tire radial direction. Air having a tread portion, a shoulder portion located at an outer end portion of the tread portion in the tire axial direction, and a buttress portion located substantially at an intermediate portion between the shoulder portion and the tire axial maximum width portion of the carcass. A filled tire, wherein the thickness of the inner liner from the shoulder portion to the buttress portion is 1.2 times or more and 5.0 times or less the thickness of other portions of the inner liner. Pneumatic tires. 2. A pair of left and right bead cores, a carcass that straddles the toroidal shape on the bead cores, both ends of which are folded back outward in the axial direction of the tire with respect to the bead cores, and an inner liner formed inside the carcass. And a wall thickness of the inner liner at the end of the carcass is 1.2 times the wall thickness of the other part of the inner liner.
A pneumatic tire characterized by being at least twice and at most 5.0 times. 3. A pair of left and right bead cores, a carcass straddling the bead core in a toroidal shape, and both ends thereof being folded back around the bead core in the axial direction of the tire, and an inner liner formed inside the carcass. A tread portion constituted by a tread rubber arranged on the tire radial direction outer side of the carcass, a shoulder portion located at a tire axial direction outer end portion of the tread portion, the shoulder portion and the tire axial direction maximum of the carcass. A pneumatic tire having a buttress portion located substantially in the middle of the substantial portion, wherein the thickness of the inner liner from the shoulder portion to the buttress portion is the thickness of the other portion of the inner liner. Is 1.2 times or more and 5.0 times or less, and the thickness of the inner liner at the end of the carcass is In other parts of the emissions toner liner having a thickness of 1.2
A pneumatic tire characterized by being at least twice and at most 5.0 times. 4. The method of manufacturing a pneumatic tire according to claim 1, wherein the inner liner has a recess formed in a portion corresponding to a thick portion of the inner liner. An inner liner forming step of winding an inner liner so as to fill the recess, a carcass forming step of forming a carcass on the inner liner by pressure bonding, a belt forming step of forming a belt on the carcass by pressure bonding, the belt A method for manufacturing a pneumatic tire, comprising: a tire outer shell forming step of forming an outer shell of a tire by winding an elastic member thereon.