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Title:
HEAVY TRUCK TIRE
Document Type and Number:
WIPO Patent Application WO/2018/118479
Kind Code:
A1
Abstract:
The invention provides for a heavy truck tire (500) having a casing and a rubber tread (600) attached thereto, the tread extending axially between tread edges over a rolling tread width (RTW), the tread comprising a lower rubber layer (611) and an upper rubber layer (612), the upper rubber layer being intended to come into contact with the ground and the lower rubber layer being attached to the casing, the upper rubber layer consisting in an upper layer compound and the lower rubber layer consisting in a lower layer compound, the lower layer compound being different from the upper layer compound, wherein the lower layer compound has a max tan(δ) not greater than 0.07 and the upper layer compound has a max tan(δ) of at least 0.15.

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JP2011116319PNEUMATIC TIRE
WO/2020/256082TIRE
Inventors:
MAYNI PAUL (US)
TROWBRIDGE JEREMY (US)
Application Number:
PCT/US2017/065560
Publication Date:
June 28, 2018
Filing Date:
December 11, 2017
Export Citation:
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Assignee:
MICHELIN & CIE (FR)
MAYNI PAUL ANDREW (US)
TROWBRIDGE JEREMY (US)
International Classes:
B60C11/00
Domestic Patent References:
WO2015158871A12015-10-22
Foreign References:
US20120298271A12012-11-29
US9352615B22016-05-31
US20150158338A12015-06-11
US6196288B12001-03-06
EP0799854A11997-10-08
Attorney, Agent or Firm:
PIEROTTI, Neal, P. (US)
Download PDF:
Claims:
CLAIMS

What is claimed is:

1. A heavy truck tire (300; 500) having a casing and a rubber tread (600) attached thereto, the tread extending axially between tread edges over a rolling tread width (RTW), the tread comprising a lower rubber layer (411; 611) and an upper rubber layer (412; 612), the upper rubber layer being intended to come into contact with the ground and the lower rubber layer being attached to the casing, the upper rubber layer consisting in an upper layer compound and the lower rubber layer consisting in a lower layer compound, the lower layer compound being different from the upper layer compound, wherein the lower layer compound has a max tan(5) not greater than 0.07 and the upper layer compound has a max tan(5) of at least 0.15.

2. A heavy truck tire according to Claim 1, wherein a boundary (410; 610) between the upper and lower rubber layers is not higher than 6 mm above the tread bottom profile (BP).

3. A heavy truck tire according to any of the preceding Claims, wherein the boundary between the upper and lower rubber layers is higher than 2 mm above the tread bottom profile within at least 90% of RTW.

4. A heavy truck tire according to any of the preceding Claims, wherein the lower layer compound has a max tan(5) not greater than 0.065 and the upper layer compound has a max tan(5) of at least 0.17.

5. A heavy truck tire according to any of the preceding Claims, wherein the lower layer compound has a max tan(5) not greater than 0.06 and the upper layer compound has a max tan(5) of at least 0.18.

6. A heavy truck tire according to any of the preceding Claims, wherein the upper layer compound has a complex shear modulus for 25% strain (G*25) at 60°C not greater than 2.1 MPa.

7. A heavy truck tire according to any of the preceding Claims, wherein the upper layer compound has a complex shear modulus for 25% strain (G*25) at 60°C not greater than 1.9 MPa.

8. A heavy truck tire according to any of the preceding Claims, wherein the lower layer rubber compound has a complex shear modulus for 25% strain (G*25) at 60°C not greater than 1.9 MPa.

9. A heavy truck tire according to any of the preceding Claims, wherein the lower layer rubber compound has a complex shear modulus for 25% strain (G*25) at 60°C not greater than 1.7 MPa.

10. A heavy truck tire according to any of the preceding Claims, wherein the tread has no sacrificial ribs.

11. A heavy truck tire according to any of the preceding Claims, wherein the tread has no directional sipes.

12. A heavy truck tire (500) according to claim 1 or 2, wherein the lower rubber layer (611) is fully covered by the upper rubber layer (612) and wherein the lower layer compound has a max tan(5) not greater than 0.055 and the upper layer compound has a max tan(5) of at least 0.18.

13. A heavy truck tire according to Claim 12, wherein the lower layer compound has a max tan(5) not greater than 0.05 and the upper layer compound has a max tan(5) of at least 0.20.

14. A heavy truck tire according to Claim 12, wherein the lower layer compound has a max tan(5) not greater than 0.04 and the upper layer compound has a max tan(5) of at least 0.22.

15. A heavy truck tire according to any of Claims 12 to 14, wherein the boundary (610) between the upper and lower rubber layers is higher than 2 mm below the tread bottom profile and is not higher than 4 mm above the tread bottom profile within at least 90% of RTW.

16. A heavy truck tire according to any of Claims 12 to 15, wherein a distance "d" separates the lower rubber layer from the groove surfaces, d being greater than 1 mm.

Description:
HEAVY TRUCK TIRE

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] This invention relates generally to tires. More specifically, this invention relates to tires for heavy trucks, in particular tires for free-rolling wheels thereof (so-called steer axle positions and trailer axle positions), especially tires for steer positions.

Description of the Related Art

[0002] Manufacturers of heavy commercial vehicle tires have made huge progress in developing tire architectures and tire materials that allowed them to increase the wear resistance of tire treads and reduce the rolling resistance of tires while in the same time improving their level of grip and resistance to road hazard.

[0003] Irregular tread wear (also called "uneven wear" or "abnormal wear") is a great concern for heavy commercial vehicle tires as it can progressively induce tire vibrations that become sensed by the driver through the steering wheel. It can also make for a poor looking wear pattern. Both of these undesired effects often lead to the tire being removed from service at an early stage of its wear life. Generally, the more the tire is put through a slow-wearing usage, the more irregular wear is affecting the removal mileage. This is why resistance to irregular wear is of paramount importance for truck tires in the so-called long haul steer usage.

[0004] Two examples of successful long haul steer tires on the North American market are the tires sold under the names MICHELIN ® XZA3 ® + EVERTREAD ® and MICHELIN ® X LINE™ ENERGY Z. The tread of those tires combine features that make them perform at a very good level in term of rolling resistance, wear rate, resistance to irregular wear and resistance to aggression in the long haul steer usage.

[0005] The tread of those tires use a combination of two main layers of different rubber compounds laid on top of each other. The ground contacting upper layer being a more hysteretic compound than the lower layer. [0006] Those treads also feature a directional tread pattern including partial sipes on the side of the tread ribs. The partial sipes are inclined relative to the radial direction of the tire (that is to say relative to the thickness direction of the tread). As discussed in more detail in US patent 6196288, the resistance to irregular wear is increased by having the partial sipes inclined by an angle of between 5° and 15° in a given direction relative to the rolling direction of the tire. The performance of such tires is therefore sensitive to the direction they are mounted on the vehicle and later used on the road. This is why they are called directional tires (or directional treads) and marked with an indicator on their side to help install them properly on the wheels of the vehicle. Such rolling direction indicators are generally arrows pointing in the direction in which the tread should be moving towards while the tire is rolling during forward displacement of the vehicle.

[0007] However, directional treads impose constraints to the user when it comes to rotating the tires from one side of the vehicle to the other side. Each tire needs then to be removed from its wheel, flipped, remounted on the same or another wheel and the tire-wheel assembly needs to be balanced again before it can be bolted to the other side of the vehicle.

[0008] Therefore, it may be desirous to propose a novel way to design tire treads that would not require directional partial sipes to deliver very good performances regarding wear and resistance to irregular wear in a long haul usage.

SUMMARY OF THE INVENTION

[0009] The invention provides for a heavy truck tire having a casing and a rubber tread attached thereto, the tread extending axially between tread edges over a rolling tread width (RTW), the tread comprising a lower rubber layer and an upper rubber layer, the upper rubber layer being intended to come into contact with the ground and the lower rubber layer being attached to the casing, the upper rubber layer consisting in an upper layer compound and the lower rubber layer consisting in a lower layer compound, the lower layer compound being different from the upper layer compound, wherein the lower layer compound has a max tan(5) not greater than 0.07 and the upper layer compound has a max tan(5) of at least 0.15. [0010] In an embodiment, a boundary between the upper and lower rubber layers is not higher than 6 mm above the tread bottom profile.

[0011] In an embodiment, the boundary between the upper and lower rubber layers is higher than 2 mm above the tread bottom profile within at least 90% of RTW.

[0012] In an embodiment, the lower layer compound has a max tan(5) not greater than 0.065 and the upper layer compound has a max tan(5) of at least 0.17.

[0013] In an embodiment, the lower layer compound has a max tan(5) not greater than 0.06 and the upper layer compound has a max tan(5) of at least 0.18.

[0014] In an embodiment, the upper layer compound has a complex shear modulus for 25% strain (G*25) at 60°C not greater than 2.1 MPa.

[0015] In an embodiment, the upper layer compound has a complex shear modulus for 25% strain (G*25) at 60°C not greater than 1.9 MPa.

[0016] In an embodiment, the lower layer compound has a complex shear modulus for 25% strain (G*25) at 60°C not greater than 1.9 MPa.

[0017] In an embodiment, the lower layer compound has a complex shear modulus for 25% strain (G*25) at 60°C not greater than 1.7 MPa.

[0018] In an embodiment, the tread has no sacrificial ribs.

[0019] In an embodiment, the tread has no directional sipes.

[0020] In an embodiment, the lower rubber layer is fully covered by the upper rubber layer and wherein the lower layer compound has a max tan(5) not greater than 0.055 and the upper layer compound has a max tan(5) of at least 0.18. tread has no sacrificial ribs.

[0021] In an embodiment, the lower layer compound has a max tan(5) not greater than 0.05 and the upper layer compound has a max tan(5) of at least 0.20. [0022] In an embodiment, the lower layer compound has a max tan(5) not greater than 0.04 and the upper layer compound has a max tan(5) of at least 0.22.

[0023] In an embodiment, the boundary between the upper and lower rubber layers is higher than 2 mm below the tread bottom profile and is not higher than 4 mm above the tread bottom profile within at least 90% of RTW.

[0024] In an embodiment, a distance "d" separates the lower rubber layer from the groove surfaces, d being greater than 1 mm.

[0025] The foregoing and other objects, features and advantages of the invention will be apparent from the following more detailed descriptions of a particular embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is schematic perspective section view of a tire according to the prior art.

[0027] FIG. 2 is a schematic view of a detail of the tire of FIG. I.

[0028] FIG. 3 is a schematic section view of a tire according to a first embodiment of the invention.

[0029] FIG. 4 is a schematic section view of a tire according to another embodiment of the invention.

[0030] The use of the same or similar reference numerals in the figures denotes identical or similar features or functions.

DESCRIPTION OF AN EXAMPLE FROM THE PRIOR ART

[0031] FIG. 1 is showing in a schematic way relevant features of a commercially available tire sold as MICHELIN ® XZA3 ® + EVERTREAD ® or MICHELIN ® X LINE™ ENERGY Z.

[0032] This tire 100 has a pair of beads (not shown), respective sidewalls 101, 102 and a belt structure 103 that together constitute what is generally referred to as a tire casing. A tread 200 is attached to this casing. The tire has a circumferential direction that corresponds to the longitudinal direction of the tread and is often represented as the oX direction in an oXYZ coordinate system. The tire and tread have an axial direction (also referred to as the lateral or transverse direction) that corresponds to the oY direction in said oXYZ coordinate system. The tire has a radial direction that corresponds to the thickness direction or depth direction of the tread and is represented as the oZ direction in said oXYZ coordinate system.

[0033] The tread of tire 100 has five longitudinal main ribs 201, 202, 203, 204 and 205. The main ribs are separated by main grooves 213, 214, 215 and 216. This tread also has so-called sacrificial ribs 206 and 207 outside the main ribs on either side of the tread. The sacrificial ribs are separated from the main ribs by respective sacrificial grooves 208 and 209. The ground contacting surface of the sacrificial ribs is offset from the ground contacting surface CS of the main ribs. Sacrificial ribs are known to improve the resistance of the tread to irregular wear in the shoulder areas.

[0034] A rolling tread width RTW is defined as the distance between tread edges. The tread edges are defined as the maximum axial locations where the tread of the tire no longer comes in contact with the ground under standard, straight rolling conditions (75% of the TRA load at standard pressure for the tire). These locations do not account for tread that may intermittently come in contact (such as is the case for a sacrificial rib).

[0035] Another feature of this prior art tire is that its tread 200 is made up of two tread rubber layers, a lower (radially internal) rubber layer and an upper (radially external) rubber layer. Each of said layers uses a different rubber compound. The lower rubber layer 211 consists in a lower layer compound and the upper rubber layer 212 consists in an upper layer compound. In the main ribs, the boundary between the two rubber layers is set parallel to the ground contacting surface CS about 4 mm above the bottom of the main grooves. The sacrificial ribs 206 and 207 are made exclusively from the lower layer compound.

[0036] The lower layer compound has a substantially lower loss factor than the upper layer compound. It also has a slightly lower complex dynamic shear modulus than the upper layer compound. Because the lower layer compound has a very low electrical conductivity, a central projection 217 from the upper rubber layer in the center main rib is designed to create a permanent electrical conduction path between the ground and the metallic belt structure 103 for allowing the discharge of static electricity.

[0037] The example tread of the prior art also includes partial sipes 218 on the sides of its main ribs.

[0038] FIG. 2 is showing more details of those partial sipes 218 in a schematic partial section view taken in a plane parallel to the meridian plane (XoZ plane) of the tire of FIG. 1 and next to a main groove. The partial sipes extend from the ground contact surface CS, through the full upper layer 212 and down into the lower layer 211. This detail view illustrates the fact that the partial sipes of this tread are inclined relative to the radial direction Z by an angle a in the order of 9°. As shown on FIG. 2, the partial sipes are inclined from the radial direction Z in the direction opposite to the rolling direction RD of the tread. As discussed earlier, such directional siping has proven to be effective against irregular wear.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0039] Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the drawings. These examples are provided by way of explanation of the invention.

[0040] FIG. 3 shows in a detailed section view the crown portion of a tire 300 according to a first embodiment. Only half of the crown portion is shown as clearly illustrated by the equatorial plane EP. Relative to equatorial plane EP, the other half of the tire may be substantially symmetric to the one shown. The other half may also be notably different form the first one as long as it remains within the scope of the invention as limited by the claims.

[0041] The tread has five main ribs and four longitudinal grooves. A shoulder groove 413 separates the shoulder rib 401 from the intermediate rib 402 and an intermediate groove 414 separates the intermediate rib 402 from the center rib 403. The tread 400 is made from two different layers, a lower rubber layer 411 and an upper rubber layer 412. The boundary 410 between the two layers runs substantially parallel to the contact surface CS of the tread.

[0042] The rubber compound for the upper layer 412 is much more hysteretic than the compound for the lower layer 411. The upper layer compound has a loss factor "max tan(5)" of 0.19 while the lower layer compound has a max tan(5) of 0.06. As explained above, because low- hysteresis compound often have insufficient electrical conductivity, a projection 417 of the upper layer compound is connecting the tire casing 303 through the lower layer 411 as part of the center rib 403.

[0043] The outer profile OP of a tread is defined as the curved line that follows the tread contact surface CS in a radial section. The bottom profile BP of a tread is generally defined as the translation of the outer profile OP down to the bottom of the deepest grooves of that tread (ignoring wear bars). The position of the boundary 410 between the upper and lower layers can then be described relative to the position of the bottom profile BP. Here the boundary between the two layers is in the order of 4 mm above the tread bottom profile and substantially parallel to it (with the exception of the conductive projection 417 of course). The lower layer 411 is apparent at the bottom of the grooves 413, 414.

[0044] FIG. 4 shows the tread portion of a tire 500 according to another embodiment. Here, the lower layer 611 of tread 600 is not surfacing at the bottom of the grooves. The grooves are fully embedded in the upper layer 612. A distance "d" can be measured between the surface of the grooves and the boundary 610. The boundary does not run parallel to bottom profile BP but remains between within about 2 mm below and about 4 mm over BP within 90% of RTW. Beyond this limit of 90%, that is to say adjacent the tread edges, the boundary may be more distant from BP, for instance due to manufacturing constraints or variations.

[0045] In this second embodiment, the lower layer compound has a max tan(5) of 0.03, being substantially less hysteretic than in the first embodiment. On the other hand, the upper layer compound has a max tan(5) of 0.22 being substantially more hysteretic than in the first embodiment. [0046] FIG. 4 also shows a different groove type for the intermediate groove 614. This groove is a hidden groove where a channel 615 is running below the contact surface CS and is connected to the surface by an undulated sipe 616. The channel may run parallel to the surface around the whole circumference of the tire or undulate between a lower position as shown in this section view and a higher position where it is surfacing at the contact surface CS.

[0047] FIG. 4 also shows a different approach to ensuring the right level of electrical conductivity through the tread. Here a conductive rubber strip 617 is inserted in the center of the tread. This rubber strip may use the same or a different compound compared to the upper layer 612.

[0048] There are no sacrificial ribs or directional features like inclined sipes or partial sipes in these embodiments and still the tires can show strong performances in resistance to irregular wear. The other performances like wear rate, rolling resistance or grip are maintained at a very good level, making the tires for instance fully compliant with EPA SmartWay requirements.

[0049] The rubber compounds used for the lower and upper layers may be based upon natural rubber or upon synthetic polyisoprene with a majority of cis-1,4 chains and possibly on at least one other diene elastomer and of a reinforcing filler consisting:

- (i) either of a white filler of the silica and/or alumina type having SiOH and/or AIOH surface functions, selected from the group formed by precipitated or pyrogenic silicas, aluminas or aluminosilicates, with a specific surface area in the range between 120 and 200m2/g, used in a loading between 0 phr and 70 phr,

- (ii) or of a blend of carbon black having a CTAB specific surface area of between 20 and 120 m2/g in a loading greater than or equal to 0 phr and less than or equal to 25 phr and of a white filler described in (i), in which the overall content of filler is between 40 phr and 70 phr.

[0050] As used herein, "phr" is "parts per hundred parts of rubber by weight" and is a common measurement in the art wherein components of a rubber composition are measured relative to the total weight of rubber in the composition, i.e., parts by weight of the component per 100 parts by weight of the total rubber(s) in the composition. [0051] The CTAB specific surface area is determined according to AFNOR Standard NFT 45-007 (November 1987, method B).

[0052] If a clear filler or white filler is used, a coupling and/or coating agent, chosen from agents known to those skilled in the art, must be used. Examples of preferred coupling agents that may be mentioned are sulphurized alkoxysilanes of the bis-(3-trialkoxysilylpropyl) polysulphide type, and of these, notably, the bis(3-triethoxysilylpropyl) tetrasulphide marketed by Degussa under the trade names Si69 for the pure liquid product and X50S for the solid product (blended 50/50 by weight with N330 black). Examples of coating agents that may be mentioned are fatty alcohol, alkylalkoxysilane such as hexadecyltrimethoxy or triethoxy silane marketed by Degussa under the trade names Si 116 and Si216 respectively, diphenylguanidine, polyethylene glycol, and silicone oil, modified by means of the OH or alkoxy functions if required. The coating and/or coupling agent is used in a proportion of between 1/100 and 20/100 by weight to the filler, and preferably in the range from 2/100 to 15/100 if the clear filler forms the whole of the reinforcing filler and in the range from 1/100 to 20/100 if the reinforcing filler is formed by a blend of carbon black and clear filler.

[0053] Other examples of reinforcing fillers, having the morphology and SiOH and/or AIOH surface functions of the materials of the silica and/or alumina type described above and suitable for use according to the invention in total or partial replacement of these, that may be mentioned include carbon blacks modified either during synthesis by the addition of a silicon and/or aluminium compound to the oil supplied to the furnace, or after synthesis by the addition of an acid to an aqueous suspension of carbon black in a sodium silicate and/or aluminate solution so as to coat at least part of the surface of the carbon black with SiOH and/or AIOH functions. Some non- limiting examples of this type of carbonated filler with SiOH and/or AIOH surface functions that may be mentioned are the CSDP fillers described at Conference No. 24 of the ACS Meeting, Rubber Division, Anaheim, Calif., 6-9 May 1997, and those mentioned in patent application EP-A-0 799 854.

[0054] If a clear filler is used as the sole reinforcing filler, the properties of hysteresis and cohesion are obtained by using a precipitated or pyrogenic silica or a precipitated alumina or an aluminosilicate with a CTAB specific surface area in the range from 120 to 180 m2/g. Some non- limiting examples of this type of filler that may be mentioned are the silicas: KS404, marketed by Akzo, Ultrasil VN2 or VN3 and BV3370GR marketed by Degussa, Zeopol 8745 marketed by Huber, Zeosil 175MP or Zeosil 11 65M marketed by Rhodia, HI-SIL 2000 marketed by PPG, etc.

[0055] Among the diene elastomers that may be used in a blend with natural rubber or a synthetic polyisoprene with a majority of cis-1,4 chains, mention may be made of polybutadiene (BR), preferably with a majority of cis-1,4 chains, stirene-butadiene copolymer (SBR) solution or emulsion, butadiene-isoprene copolymer (BIR), or even stirene-butadiene-isoprene terpolymer (SBIR). These elastomers may be elastomers modified during polymerization or after polymerization by means of branching agents such as divinylbenzene or star forming agents such as carbonates, tin halogens and silicon halogens, or alternatively by means of functionalizing agents causing oxygenated carbonyl, carboxyl functions or an amine function to be grafted on to the chain or at the end of the chain, by the action of dimethyl- or diethylamino-benzophenone for example. In the case of blends of natural rubber or synthetic polyisoprene with a majority of cis-1,4 chains with one or more diene elastomers, mentioned above, the natural rubber or synthetic polyisoprene is preferably used in a majority proportion and more preferably in a proportion of more than 70 phr.

[0056] For example, the two elastomeric main compounds that constitute the tread as in FIG. 3, may be as described in the table below.

Upper layer Lower layer

compound compound

(412) (411)

NR (phr) 35 100

BR (phr) 45

SBR (phr) 26

Carbon black 200 Series (phr) 67 7

Silica (phr) 40

Silane /covering agent (phr) 4

Processing aids (phr) 16

Anti-Degradants (such as Paraffin,

z 3.5

anti-oxidant) (phr)

Cure Package (such as Stearic acid,

7.4 10.58

ZnO, Sulphur, Accelerator) (phr) G* 25% @ 60°C (MPa) 2.0 2.0

Max Tan(5) @ 60°C 0.19 0.06

[0057] For example, the two elastomeric main compounds that constitute the tread as in FIG. 4, may be as described in the table below.

Upper layer Lower layer

compound compound

(612) (611)

NR (phr) 25 100

BR (phr) 75

Carbon black 200 Series (phr) 76

Carbon black - low surface area (phr) 49

Silica (phr) 6

Processing aids (phr) 45 15

Anti-Degradants (such as Paraffin,

3 1.8

anti-oxidant) (phr)

Cure Package (such as Stearic acid,

9 13.53

ZnO, Sulphur, Accelerator) (phr)

G* 25% @ 60°C (Mpa) 1.65 1.45

Max Tan(5) @ 60°C 0.22 0.03

[0058] The loss factor "tan(5)" is a dynamic property of the rubber compound. It is measured on a viscosity analyzer (Metravib VA4000) according to Standard ASTM D5992-96. The response of a test specimen consisting of two cylindrical pellets each 2 mm thick and one centimeter in diameter is recorded (the test specimen is made from samples taken from a tire mid-way up the height of the layer concerned as close as possible to the region of the equatorial plane in a region that is thick enough to be able to form the test specimen), the specimen being subjected to simple alternating sinusoidal shear loadings at a frequency of 10 Hz, at a temperature of 60° C. The sweep covers amplitude of deformation from 0.1% to 25% peak to peak (on the outbound cycle) then from 25% to 1% peak to peak (on the return cycle). The results that are used here are the loss factor tan(5) and the complex dynamic shear modulus. The complex dynamic shear modulus is denoted "G*25" in reference to the 25% strain applied during the test. During the outbound cycle, the maximum value of tan5 that is observed is denoted "max tan(5)". [0059] The terms "comprising," "including," and "having," as used in the claims and specification herein, shall be considered as indicating an open group that may include other elements not specified. The terms "a," "an," and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The terms "at least one" and "one or more" are used interchangeably. The term "single" shall be used to indicate that one and only one of something is intended. Similarly, other specific integer values, such as "two," are used when a specific number of things is intended. The terms "preferably," "preferred," "prefer," "optionally," "may," and similar terms are used to indicate that an item, condition or step being referred to is an optional (i.e., not required) feature of the invention. Ranges that are described as being "between a and b" are inclusive of the values for "a" and "b" unless otherwise specified.

[0060] While this invention has been described with reference to particular embodiments thereof, it shall be understood that such description is by way of illustration only and should not be construed as limiting the scope of the claimed invention. Accordingly, the scope and content of the invention are to be defined only by the terms of the following claims. Furthermore, it is understood that the features of any specific embodiment discussed herein may be combined with one or more features of any one or more embodiments otherwise discussed or contemplated herein unless otherwise stated. Also as explained earlier, a tire according to the invention may or may not be symmetric, that is to say that a tire according to the invention may or may not have the same configuration on both tire halves either side of its equatorial plane EP.