TIRE COMPRISING A SINGLE CARCASS LAYER

Abstract

The tire (11) for a passenger vehicle comprises a crown (12), two beads (32), two sidewalls (30) each connecting each bead (32) to the crown (12), and a carcass reinforcement (34) anchored in each bead (32). The tire (11) has a load index L1 such that LILI+1, LI being the load index of an EXTRA LOAD tire of the same size according to the manual of the ETRTO 2019 standard. The tire (11) has a sidewall height H defined by H=SWAR/100, where SW is the nominal section width and AR the nominal aspect ratio of the tire according to the manual of the ETRTO 2019 standard such that H<95. The carcass reinforcement (34) comprises a single carcass layer (36).

Claims

1.-14. (canceled)

15. A tire (11) for a passenger vehicle, the tire comprising a crown (12), two beads (32), two sidewalls (30) each connecting each bead (32) to the crown (12), and a carcass reinforcement (34) anchored in each bead (32), the crown (12) comprising a crown reinforcement (16) and a tread (14), the carcass reinforcement (34) extending in each sidewall (30) and in the crown (12) radially on an inside of the crown reinforcement (16), wherein the tire (11) has a load index LI such that LILI+1, where LI being a load index of an EXTRA LOAD tire having a same size in accordance with standard ETRTO 2019, wherein the tire (11) has a sidewall height H defined by H=SWAR/100, where SW is a nominal section width and AR is a nominal aspect ratio of the tire in accordance with standard ETRTO 2019 such that H<95, and wherein the crown reinforcement (34) comprises a single carcass layer (36).

16. The tire (11) according to claim 15, wherein LI+1LILI+4.

17. The tire (11) according to claim 15, wherein the single carcass layer (36) forms a winding around a circumferential reinforcing element (33) of each bead (32) such that an axially inner portion (3611, 3621) of the single carcass layer (36) is arranged axially on an inside of an axially outer portion (3612, 3622) of the single carcass layer (36) and such that each axial end (361, 362) of the single carcass layer (36) is arranged radially on an outside of each circumferential reinforcing element (33).

18. The tire (11) according to claim 17, wherein each axial end of the single carcass layer (36) is arranged radially on an inside of an equator (E) of the tire.

19. The tire (11) according to claim 15, wherein the single carcass layer (36) has a portion arranged axially between two circumferential reinforcing elements of each bead (32) and each axial end of the single carcass layer (36) is arranged radially on an inside of each radially outer end of each circumferential reinforcing element of each bead (32).

20. The tire (11) according to claim 15, wherein the single carcass layer (36) is axially delimited by two axial edges (361, 362) of the carcass layer (36) and comprises carcass textile filamentary reinforcing elements (360) extending axially from one axial edge to an other axial edge of the carcass layer (36) along a main direction forming an angle ranging from 80 to 90 in terms of absolute value with a circumferential direction (X) of the tire (11).

21. The tire (11) according to claim 15, wherein the nominal section width SW ranges from 205 to 315, the nominal aspect ratio AR ranges from 25 to 55, the load index LI ranges from 98 to 116, and the tire has a nominal rim diameter ranging from 17 to 23.

22. The tire (11) according to claim 15, wherein 0.82H/LI0.92.

23. The tire (11) according to claim 15, wherein the tire (11) has a size and a load index LI selected from among the following sizes and load indexes: 205/40R17 88, 205/40ZR17 88, 255/35R18 98, 255/35ZR18 98, 245/35R20 98, 245/35ZR20 98, 265/35R20 102, 265/35ZR20 102, 245/35R21 99, 245/35ZR21 99, 255/35R21 101, 255/35ZR21101,265/35R21 103, 265/35ZR21 103, 285/30R21103,285/30ZR21 103, 315/30R21109,315/30ZR21 109, 315/30R23 111, and 315/30ZR23 111.

24. The tire (11) according to claim 15, wherein the crown reinforcement (16) comprises a working reinforcement (20) comprising a radially inner working layer (24) and a radially outer working layer (26) arranged radially on an outside of the radially inner working layer (24).

25. The tire (11) according to claim 24, wherein each working layer (24, 26) is axially delimited by two axial edges (241, 242, 261, 262) of the working layer (24, 26) and comprises working filamentary reinforcing elements extending axially from one axial edge to an other axial edge of the working layer (24, 26), substantially parallel to one another.

26. The tire (11) according to claim 25, wherein each working filamentary reinforcing element extends in a main direction forming an angle which, in terms of absolute value, is strictly greater than 10, with a circumferential direction (X) of the tire (11).

27. The tire (11) according to claim 15, wherein the crown reinforcement (16) comprises a hoop reinforcement (22) that is axially delimited by two axial edges (281, 282) of the hoop reinforcement and comprises at least one hooping filamentary reinforcing element wound circumferentially in a helix so as to extend axially between the axial edges (281, 282) of the hoop reinforcement (22).

28. The tire (11) according to claim 27, wherein the or each hooping filamentary reinforcing element extends along a main direction forming an angle which, in terms of absolute value, is less than or equal than 10, with a circumferential direction (X) of the tire (11).

29. A mounted assembly (10) comprising: a mounting support (100) comprising a rim (200); and a tire (11) according to claim 15, mounted on the rim (200).

30. The mounted assembly (10) according to claim 29, wherein, with the crown reinforcement (16) being arranged radially between the tread (14) and the carcass reinforcement (34) and comprising a working reinforcement (20) comprising at least one axially narrowest working layer (26), the axially narrowest working layer (26) having an axial width T2 expressed in mm, and the rim (200) having a rim width A according to standard ETRTO 2019 and expressed in mm, a ratio T2/A is such that T2/A1.00.

31. A passenger vehicle comprising at least one tire (11) according to claim 15.

32. A passenger vehicle comprising at least one mounted assembly (10) according to claim 29.

Description

[0094] The invention will be understood better on reading the following description, which is given purely by way of non-limiting example and with reference to the drawings, in which:

[0095] FIG. 1 is a view, in a meridian section plane, of a mounted assembly according to a first embodiment of the invention,

[0096] FIG. 2 is a view, in a meridian section plane, of the tyre of the mounted assembly in FIG. 1,

[0097] FIG. 3 is a view in section on the plane III-III in FIG. 2 illustrating the carcass reinforcement of the tyre in FIG. 1, and

[0098] FIG. 4 is a view similar to the one in FIG. 1 comparing the deflection of a mounted assembly of the prior art and that of the mounted assembly in FIG. 1.

[0099] A frame of reference X, Y, Z corresponding to the usual axial (Y), radial (Z) and circumferential (X) directions, respectively, of a tyre or of a mounted assembly is shown in the figures.

[0100] In the following description, the measurements taken are taken on an unladen and non-inflated tyre or on a section of a tyre in a meridian plane.

[0101] FIG. 1 shows a mounted assembly according to the invention, denoted by the general reference 10. The mounted assembly 10 comprises a tyre 11 and a mounting support 100 comprising a rim 200. The tyre 11 is in this case inflated to a pressure ranging from 200 to 350 kPa, preferably from 250 to 330 kPa and in this case equal to 270 kPa.

[0102] The tyre 11 has a substantially toric shape about an axis of revolution R substantially parallel to the axial direction Y. The tyre 11 is intended for a passenger vehicle. In the various figures, the tyre 11 is depicted as new, i.e. when it has not yet been run.

[0103] The tyre 11 comprises two sidewalls 30 bearing a marking indicating the size of the tyre 11, and also a speed rating and a speed code. In this instance, the tyre 11 has a nominal section width SW ranging from 205 to 315, preferably from 225 to 315, more preferentially ranging from 245 to 315 and here equal to 255. The tyre 11 also has a nominal aspect ratio AR ranging from 25 to 55, preferably ranging from 30 to 45, and here equal to 35. The tyre 11 has a nominal rim diameter ranging from 17 to 23, preferably from 18 to 23, and here equal to 18. The tyre 11 therefore has a sidewall height H defined by SWAR/100=89<95.

[0104] In accordance with the invention, the marking also comprises a load index LI ranging from 98 to 116, such that LI>LI+1 with LI being the load index of an EXTRA LOAD tyre of the same size according to the manual of the ETRTO 2019 standard. Preferably, LI+1LILI+4, and even LI+2LILI+4.

[0105] A tyre of size 255/35R18 in its EXTRA LOAD version has a load index equal to 94 as indicated on page 36 of the part Passenger Car TyresTyres with Metric Designation of the manual of the ETRTO 2019 standard. Thus, the load index LI of the tyre 11 is such that LI95, preferably 95LI98 and even 96LI98 and in this case LI=98. This load index equal to 98 corresponds to the load index of a HIGH LOAD CAPACITY tyre of size 255/35R18 as indicated in the ETRTO 2021 manual. Thus, the tyre 11 is clearly of the HIGH LOAD CAPACITY type.

[0106] The tyre 11 is such that 0.82H/LI0.92 and in this case H/LI=0.91.

[0107] For such a size, the manual of the ETRTO 2019 standard indicates, on page 36 of the part Passenger Car TyresTyres with Metric Designation, a measuring rim with a rim width code equal to 9. The rim 200 of the mounted assembly 10 is thus selected from: [0108] a rim having a rim width code equal to the measuring rim width code for the size of the tyre and defined according to the manual of the ETRTO 2019 standard, and [0109] a rim having a rim width code equal to the measuring rim width code for the size of the tyre minus 0.5, and [0110] a rim having a rim width code equal to the measuring rim width code for the size of the tyre plus 0.5.

[0111] In this case, the rim 200 of the mounted assembly 10 is the rim having a rim width code equal to the measuring rim width code for the size of the tyre minus 0.5 and therefore in this case equal to 8.5. The rim 200 has a profile of type J and a rim width A according to the manual of the ETRTO 2019 standard. In this instance, with the profile of the rim 200 being of type 8.5 J, its rim width A expressed in mm is equal to 215.90 mm.

[0112] With reference to FIG. 2, the tyre 11 comprises a crown 12 comprising a tread 14 intended to come into contact with the ground when the tyre is running and a crown reinforcement 16 extending in the crown 12 in the circumferential direction X. The tyre 11 also comprises a layer 18 that is airtight with respect to an inflation gas and is intended to delimit an internal cavity closed with the mounting support 100 for the tyre 11 once the tyre 11 has been mounted on the mounting support 100.

[0113] The crown reinforcement 16 comprises a working reinforcement 20 and a hoop reinforcement 22. The working reinforcement 16 comprises at least one working layer and in this case comprises two working layers comprising a radially inner working layer 24 arranged radially on the inside of a radially outer working layer 26. Of the radially inner layer 24 and the radially outer layer 26, the axially narrowest layer is the radially outer layer 26.

[0114] The hoop reinforcement 22 comprises at least one hooping layer and in this case comprises one hooping layer 28.

[0115] The crown reinforcement 16 is surmounted radially by the tread 14. In this case, the hoop reinforcement 22, in this case the hooping layer 28, is arranged radially on the outside of the working reinforcement 20 and is therefore interposed radially between the working reinforcement 20 and the tread 14.

[0116] The two sidewalls 30 extend the crown 12 radially towards the inside. The tyre 11 also has two beads 32 radially on the inside of the sidewalls 30. Each sidewall 30 connects each bead 32 to the crown 12.

[0117] The tyre 11 comprises a carcass reinforcement 34 that is anchored in each bead 32 and, in this instance, forms a winding around a circumferential reinforcing element, in this case a bead wire 33. The carcass reinforcement 34 extends radially in each sidewall 30 and axially in the crown 12, radially on the inside of the crown reinforcement 16. The crown reinforcement 16 is arranged radially between the tread 14 and the carcass reinforcement 34. The carcass reinforcement 34 comprises at least one carcass layer 36 and in this case a single carcass layer 36.

[0118] The hoop reinforcement 22, in this case the hooping layer 28, is axially delimited by two axial edges 281, 282 and comprises one or more hooping filamentary reinforcing elements that are wound circumferentially in a helix between each axial edge 281, 282 along a main direction forming an angle AF which, in terms of absolute value, is less than or equal to 10, preferably less than or equal to 7 and more preferably less than or equal to 5 with the circumferential direction X of the tyre 10. In this case, AF=5.

[0119] Each radially inner working layer 24 and radially outer working layer 26 is axially delimited by two axial edges 241, 242, 261, 262, respectively, of each working layer 24, 26. The radially inner working layer 24 has an axial width T1=223.00 mm and the radially outer working layer 26 has an axial width T2=209.00 mm, making the radially outer working layer 26 the axially narrowest working layer.

[0120] It will be noted that SW=255 and T2=209 satisfy the following relationships T2SW75, preferably T2SW70 and T2SW=27, preferably T2SW30.

[0121] As illustrated in FIG. 1, the mounted assembly 10 is such that the tyre 11 has radially straightened sidewalls. Specifically, the ratio T2/A is such that 0.85T2/A1.00, preferably 0.90T2/A1.00, and more preferably 0.93T2/A0.97 and in this case T2/A=0.97.

[0122] Each working layer 24, 26 comprises working filamentary reinforcing elements extending axially from one axial edge 241, 261 to the other axial edge 242, 262 of each working layer 24, 26, substantially parallel to one another along main directions forming oppositely oriented angles AT1 and AT2, respectively, which, in terms of absolute value, are strictly greater than 10, preferably ranging from 15 to 50 and more preferably ranging from 20 to 35, with the circumferential direction X of the tyre 10. In this case, AT1=26 and AT2=+26.

[0123] The single carcass layer 36 is delimited axially by two axial edges 361, 362, respectively, and comprises carcass textile filamentary reinforcing elements 360 extending axially from one axial edge 361 to the other axial edge 362 in a main direction D3 forming an angle AC which, in terms of absolute value, ranges from 80 to 90, in this case AC=+90, with the circumferential direction X of the tyre 10.

[0124] The single carcass layer 36 forms a winding around each circumferential reinforcing element 33 of each bead 32 such that an axially inner portion 3611, 3621 of the first carcass layer 36 is arranged axially on the inside of an axially outer portion 3612, 3622 of the first carcass layer 36 and such that each axial end 361, 362 of the first carcass layer 36 is arranged radially on the outside of each circumferential reinforcing element 33.

[0125] Each axial end 361, 362 of the single carcass layer 36 is arranged radially on the inside of the equator E of the tyre. More specifically, each axial end 361, 362 of the first carcass layer 36 is arranged at a radial distance RNC of less than or equal to 30 mm from a radially inner end 331 of each circumferential reinforcing element 33 of each bead 32. In this case, RNC=23 mm.

[0126] Each working layer 24, 26, hooping layer 28 and carcass layer 36 comprises a calendering matrix for the filamentary reinforcing elements of the corresponding layer. Preferably, the calendering matrix is polymeric and more preferably elastomeric, like those usually used in the field of tyres.

[0127] Each hooping filamentary reinforcing element conventionally comprises two multifilament plies, each multifilament ply being made up of a spun yarn of aliphatic polyamide, in this instance nylon, monofilaments, with a thread count equal to 140 tex, these two multifilament plies being twisted in a helix individually at 250 turns per metre in one direction and then twisted together in a helix at 250 turns per metre in the opposite direction. These two multifilament plies are wound in a helix around one another. As a variant, use could be made of a hooping filamentary reinforcing element comprising one multifilament ply made up of a spun yarn of aliphatic polyamide, in this case nylon, monofilaments with a thread count equal to 140 tex, and one multifilament ply made up of a spun yarn of aromatic polyamide, in this case aramid, monofilaments with a thread count equal to 167 tex, these two multifilament plies being twisted in a helix individually at 290 turns per metre in one direction and then twisted together in a helix at 290 turns per metre in the opposite direction. These two multifilament plies are wound in a helix around one another. In yet another variant, use could be made of a hooping filamentary reinforcing element comprising two multifilament plies each made up of a spun yarn of aromatic polyamide, in this case aramid, monofilaments with a thread count equal to 330 tex, and one multifilament ply made up of a spun yarn of aliphatic polyamide, in this case nylon, monofilaments with a thread count equal to 188 tex, each of the multifilament plies being twisted in a helix individually at 270 turns per metre in one direction and then twisted together in a helix at 270 turns per metre in the opposite direction. These three multifilament plies are wound in a helix around one another.

[0128] In general, the use of a high load leads to a reduction in the acceptable limit speed of the tyre and also a deterioration of its behaviour, for example its cornering stiffness. Thus, by using one or more high-modulus hooping filamentary reinforcing elements, for example like those described in the last two variants above comprising one or more aromatic polyamide plies, it is possible to increase the limit speed acceptable by the tyre and to improve the behaviour, in particular its cornering stiffness.

[0129] Each working filamentary reinforcing element is an assembly 4.26 of four steel monofilaments, comprising an internal layer of two monofilaments and an external layer of two monofilaments wound together in a helix around the internal layer at a pitch of 14.0 mm, for example in the S direction. Such an assembly 4.26 has a force at break equal to 640 N, a diameter equal to 0.7 mm. Each steel monofilament has a diameter equal to 0.26 mm and a mechanical strength equal to 3250 MPa. As a variant, use could also be made of an assembly of six steel monofilaments having a diameter equal to 0.23 mm, comprising an internal layer of two monofilaments wound together in a helix at a pitch of 12.5 mm in a first direction, for example the Z direction, and an external layer of four monofilaments wound together in a helix around the internal layer at a pitch of 12.5 mm in a second direction, opposite to the first direction, for example the S direction.

[0130] As shown in FIG. 3, each carcass textile filamentary reinforcing element 360 comprises an assembly of at least two multifilament plies 363, 364. Each multifilament ply 363, 364 is selected from a polyester multifilament ply, an aromatic polyamide multifilament ply and an aliphatic polyamide multifilament ply, preferably is selected from a polyester multifilament ply and an aromatic polyamide multifilament ply. In this instance, the assembly is selected from among an assembly of two polyester multifilament plies and an assembly of a polyester multifilament ply and an aromatic polyamide multifilament ply, and in this case is made up of two PET multifilament plies, these two multifilament plies being twisted in a helix individually at 270 turns per metre in one direction and then twisted together in a helix at 270 turns per metre in the opposite direction. Each of these multifilament plies has a thread count equal to 334 tex such that the total thread count of the assembly is greater than or equal to 475 tex and in this case equal to 668 tex. Each carcass textile filamentary reinforcing element 360 has an average diameter D, expressed in mm, such that D0.85 mm, preferably D0.90 mm, and such that D1.10 mm, preferably D1.00 mm. In this instance, D=0.95 mm.

COMPARATIVE TESTS

Running Test Simulations

[0131] In a first simulation, in order to demonstrate the advantage of the invention, the inventors simulated the running of a tyre according to the invention and having a sidewall height H<95 and the running of a tyre having a sidewall height H95. These two tyres have substantially equal ratios T2/A.

[0132] For each tyre described above, a mounted assembly comprising each tyre described above mounted on a mounting support comprising the measuring rim was simulated for the tyre size defined according to the manual of the ETRTO 2019 standard. For each of these mounted assemblies, a simulation of a running test similar to the load/speed performance test described in Annex VII of UN/ECE Regulation No 30 was carried out, but under even more demanding conditions.

[0133] Thus, a tyre inflated to a pressure equal to 250 kPa, under a load that the EXTRA LOAD version of the tyre must normally be able to bear but at a pressure of 290 kPa in accordance with the manual of the ETRTO 2019 standard, was simulated. Thus, these conditions reproduce overloaded and underinflated use of the tyre.

[0134] During these simulations, the maximum volumetric energy dissipation DNRJ of the calendering matrix of a portion of the single carcass layer located in the sidewall was recorded, expressed in daN/mm2. The higher this value, the greater the energy dissipation by the tyre structure and the greater the rise in temperature. These values were expressed in relation to a relative value 100 below which the energy dissipation is controlled and above which the energy dissipation is not sufficiently controlled. These values are collated in Table 1 below.

TABLE-US-00001 TABLE 1 Tyre with H < 95 Tyre with H 95 DNRJ DNRJ < 100 DNRJ > 100

[0135] These tests show that the use of a single carcass layer in combination with a relatively short sidewall makes it possible to control the energy dissipation in the portion of the carcass reinforcement located in the sidewall, even under a relatively high load and at a pressure lower than the recommended pressure for bearing the corresponding load.

Maximum Meridian Curvature Simulations

[0136] In a second simulation, tyres of sizes 255/35 R21 and 275/30 R20, which are not in accordance with the invention and the carcass reinforcement of which comprises two carcass layers, were compared. Each of these tyres has a sidewall height H<95.

[0137] For each of these tyres, the maximum meridian curvature Cmax of the carcass layer which is axially innermost when the tyre is mounted on a rim that has a rim width code equal to the measuring rim width code and is defined in accordance with the manual of the ETRTO 2019 standard for the size of the tyre minus 0.5 was measured. These mounted assemblies were simulated while subject to a greater load than that described in the load/speed performance test described in Annex VII of UN/ECE Regulation No 30 and while inflated to a pressure lower than the recommended pressure for bearing the corresponding load. Beforehand, it was determined that the maximum meridian curvature limit above which relatively high compression of the axially innermost carcass layer in the sidewall and an increase in the energy dissipation are observed was equal to 0.30 mm.sup.1.

TABLE-US-00002 TABLE 2 255/35 R21 275/30 R20 H 89 83 Cmax 0.31 mm.sup.1 0.39 mm.sup.1

[0138] Thus, it was observed that these tyres, having a sidewall height H strictly less than 95, have an axially innermost carcass layer with a curvature greater than the acceptable maximum threshold in use conditions under high load and when underinflated.

[0139] It will also be noted that, as the sidewall height H increases, the curvature decreases and comes closer to the threshold of 0.30 mm.sup.1, which is reached for H=95.

Tensioning Simulations

[0140] In a third simulation, the inventors simulated the tension of each carcass filamentary reinforcing element of multiple tyres. For each of these tests, the tension of each carcass filamentary reinforcing element was simulated for tyres inflated to a pressure equal to 2.8 bar and subjected to a load much higher than that used for the load/speed performance test described in Annex VII of UN/ECE Regulation No 30.

[0141] Various tyres of the following sizes 255/35 R20, 235/60 R18, 255/60 R18 with carcass reinforcements comprising a single carcass layer were simulated.

[0142] The tension of each carcass filamentary reinforcing element is measured at the end of the single carcass layer.

[0143] The results of these simulations are collated in Table 3 below.

TABLE-US-00003 TABLE 3 Dimension 255/35 R20 235/60 R18 255/60 R18 H 89 141 153 Tension (daN) 0.46 0.71 0.79

[0144] It will be noted that, for sidewall heights greater than or equal to 95, the tension of the carcass reinforcement comprising a single carcass layer is not controlled.

Running Test Simulations

[0145] In a fourth simulation, in order to demonstrate the advantage of straightening the sidewalls of the tyre, which, although advantageous, is optional within the scope of the invention, the running of a Pilot Sport 4 tyre of the MICHELIN trade name and of size 255/35R18 in its EXTRA LOAD version, having a load index equal to 94 within the ETRTO 2019 standard, was simulated. This tyre comprises a crown reinforcement similar to that of the tyres described above, except that the value of T2 is equal to 226.00 mm.

[0146] A simulation was carried out for multiple mounted assemblies comprising the tyre described above mounted on multiple mounting supports comprising rims having three different rim width codes: 8.5, 9 and 10. For each of these mounted assemblies, a simulation of a running test similar to the load/speed performance test described in Annex VII of UN/ECE Regulation No 30 was carried out, but under even more demanding conditions of two different types.

[0147] With the first type of conditions reproducing use of the tyre in its EXTRA LOAD version, a tyre inflated to a pressure equal to 250 kPa under a load equal to 670 kg was simulated. It will be noted that the load applied corresponds to the load that the tyre must normally be able to bear but at a pressure of 290 kPa in accordance with the manual of the ETRTO 2019 standard. Thus, these first conditions reproduce underinflated, and therefore particularly demanding, use of the tyre.

[0148] With the second type of conditions reproducing use under a much higher load, a tyre inflated to a pressure likewise equal to 250 kPa under a load equal to 750 kg was simulated. It will be noted that the load applied corresponds to the load that a tyre having a load index 98 must normally be able to bear at a pressure of 290 kPa in accordance with the manual of the ETRTO 2019 standard. Thus, these two conditions reproduce overloaded and underinflated use of the tyre that is even more demanding than the first conditions.

[0149] During these simulations, just like in the first simulation, the maximum volumetric energy dissipation DNRJ of the calendering matrix of a portion of the single carcass layer located in the sidewall was recorded, expressed in daN/mm2. These values were expressed in relation to a relative value 100 that is different in terms of absolute value from the relative value 100 of the first simulation, below which the energy dissipation is controlled and above which the energy dissipation is not sufficiently controlled. These values are collated in Table 4 below. The indication NT means that the mounted assembly was not tested.

TABLE-US-00004 TABLE 4 Result of the test Result of the test at P = 250 kPa at P = 250 kPa and under a load and under a load A T2/A Z = 670 kg Z = 750 kg 8.5 1.05 DNRJ > 120 NT 9 0.98 DNRJ < 100 DNRJ < 100 10 0.89 NT DNRJ < 50

[0150] These tests show that the reduction in the ratio T/2A makes it possible to control the energy dissipation in the portion of the single carcass reinforcement located in the sidewall, even under a relatively high load and at a pressure lower than the recommended pressure for bearing the corresponding load. Thus, it is possible to change T2 and/or A in order to obtain a ratio T2/A making it possible to radially straighten the sidewalls and thus reduce the stresses exerted on the carcass reinforcement.

Static Test

[0151] In order to illustrate the effect of straightening the sidewalls, which, although advantageous, is optional within the scope of the invention, FIG. 4 illustrates the result of a static compression test on a tyre of size 255/35R18, which is identical to the tyre described above but for which the ratio T2/A is equal to 1.05 (tyre illustrated on the left-hand side) and the tyre described above for which the ratio T2/A is equal to 0.97 (tyre illustrated on the right-hand side). The load applied to each tyre is equal to 750 kg at a pressure of 250 kPa.

[0152] It will be noted that the deflection of the left-hand tyre is much greater than the deflection of the right-hand tyre. Specifically, the distance DR1 from the axis of rotation R to the ground in the left-hand tyre is less than the distance DR2 from the axis of rotation R to the ground in the right-hand tyre.

[0153] It will be noted in particular that the sidewalls of the right-hand tyre are radially straighter than the sidewalls of the left-hand tyre. This can be seen by comparing, at the same radial point on each sidewall, the distances DF1 and DF2 between the outer surface of the sidewall located on the opposite side to the contact patch and the plane SA that is perpendicular to the axis of rotation R of the tyre and passes through the bearing face of the rim delimiting the axial width A of the rim. This can also be seen by comparing, at the same radial point on each sidewall located in line with the contact patch, the distances DF1 and DF2 between the outer surface of the sidewall and the perpendicular plane SA. It will be observed that DF1>DF2 and that DF1>DF2.

[0154] The invention is not limited to the embodiments described above.