Tire Having Optimized Sidewalls and Crown Reinforcement Made up of Two Working Crown Layers and a Layer of Circumferential Reinforcing Elements

Abstract

A tire having a radial carcass reinforcement, made up of a single layer of reinforcing elements anchored in each of the beads by being turned up around a bead wire, reinforced by a stiffener. The two working crown layers are the only ones present to form the crown reinforcement over at least 75% of the width of the tread, the absolute value of the difference between the absolute values of the angles α2 and α1 being greater than 7°, α2 being greater than α1 in terms of absolute value, the mean angle α satisfying the relationship 13+131*exp(−L/100)<α<28+110*exp(−L/100), the reinforcing elements of the carcass reinforcement being cords which, in the test referred to as the permeability test, yield a flow rate of less than 20 cm.sup.3/min, a rubber compound being present within the cords, and, in the sidewall of the tire, the profile of the outer surface of the tire is at a constant distance from the carcass reinforcement layer between the points F and A, and meets the outer surface of the bead at the point C, forming two successive circular arcs.

Claims

1. A tire intended to be fitted on a drop-center rim of the “15° drop-center” type, comprising a radial carcass reinforcement made up of a single carcass reinforcement layer formed of reinforcement elements, said tire comprising a crown reinforcement, comprising two working crown layers of reinforcing elements that are crossed from one layer to the other, making with the circumferential direction angles (α1, α2) greater than 8°, said angles α1 and α2 being oriented on either side of the circumferential direction, and at least one layer of circumferential reinforcing elements, the crown reinforcement being radially capped by a tread, said tread being connected to two beads via two sidewalls, the carcass reinforcement layer being anchored in each of the beads by being turned up around a bead wire to form a main part of the carcass reinforcement layer extending from one bead wire to the other, and a turn-up of the carcass reinforcement layer in each of the beads, said turn-up of the carcass reinforcement being reinforced by at least one layer of reinforcement elements or a stiffener, wherein: said two working crown layers and said at least one layer of circumferential reinforcing elements are the only ones present to form the crown reinforcement over at least 75% of the axial width of the crown reinforcement, the reinforcing elements of the radially outermost working crown layer (52) form an angle (α2) with the circumferential direction that is greater in terms of absolute value than the angle (α1) formed by the reinforcing elements of the radially innermost working crown layer (51) with the circumferential direction, the absolute value of the difference between the absolute values of the angles (α2) and (α1) is greater than 7°, the mean angle α satisfies the relationship:
13+131*exp(−L/100)<α<28+110*exp(−L/100), α being defined by the relationship α=Arctan((tan(|α1|)*tan(|α2|)).sup.1/2), L being the maximum width of the tire measured in the axial direction and expressed in mm, the metal reinforcing elements of said carcass reinforcement layer are cords that, in the test referred to as the permeability test, yield a flow rate of less than 20 cm.sup.3/min, and a rubber compound is present at least locally within the structure of said cords, in each of the beads, in a meridian section of said tire: any point of the profile of the outer surface (S) of the tire, between a first point (F), itself defined by the intersection of an axially oriented straight line, passing through the axially outermost point (E) of the main part of the carcass reinforcement layer and the outer surface (S) of the tire, and a point (A), is at a constant distance (T) from the main part of the carcass reinforcement layer, said distance being measured at any point in a direction normal to the main part of the carcass reinforcement layer, wherein the point (A) is radially on the outside of a first circle (C1) of radius (R1) that is centered on the end of the turn-up of the carcass reinforcement layer, (R1) being between 8 and 13 mm, radially on the inside of the point (A), the outer surface (S) of the tire extends by an arc of a circle of radius (R2), the center of which is axially on the outside of the surface (S) of the tire, the circular arc of radius (R2) is tangential at its radially innermost end (B) to a circular arc of radius (R3), the center of which is axially on the inside of the surface (S) of the tire, and continues the outer surface (S) of the tire radially inwards as far as the point (C), said point (C) being a point of tangency between the circular arc of radius (R3) and the circle (C2) of radius (R1) centered on the radially outermost end of the stiffener, and wherein said point (C) being radially on the inside of the axially outermost point (D) of the circle (C2).

2. A tire intended to be fitted on a drop-center rim of the “15° drop-center” type, comprising a radial carcass reinforcement made up of a single carcass reinforcement layer formed of reinforcement elements, said tire comprising a crown reinforcement, comprising two working crown layers of reinforcing elements that are crossed from one layer to the other, making with the circumferential direction angles (α1, α2) greater than 8°, said angles α1 and α2 being oriented on either side of the circumferential direction, and at least one layer of circumferential reinforcing elements, the crown reinforcement being radially capped by a tread, said tread being connected to two beads via two sidewalls, the layer of reinforcing elements of the carcass reinforcement being anchored in each of the beads by being turned up around a bead wire to form a main part of the carcass reinforcement layer extending from one bead wire to the other, and a turn-up of the carcass reinforcement layer in each of the beads, said turn-up of the carcass reinforcement being reinforced by at least one layer of reinforcement elements or a stiffener, wherein: said two working crown layers and said at least one layer of circumferential reinforcing elements are the only ones present to form the crown reinforcement over at least 75% of the axial width of the crown reinforcement, the reinforcing elements of the radially outermost working crown layer form an angle (α2) with the circumferential direction that is greater in terms of absolute value than the angle (α1) formed by the reinforcing elements of the radially innermost working crown layer with the circumferential direction, the absolute value of the difference between the absolute values of the angles (α2) and (α1) is greater than 7°, the mean angle α satisfies the relationship:
13+131*exp(−L/100)<α<28+110*exp(−L/100), α being defined by the relationship α=Arctan((tan(|α1|)*tan(|α2|)).sup.1/2), L being the maximum width of the tire measured in the axial direction and expressed in mm, the metal reinforcing elements of said carcass reinforcement layer being cords, preferably non-wrapped cords, having at least two layers, at least one inner layer being sheathed with a layer consisting of a non-crosslinkable, crosslinkable or crosslinked rubber composition, preferably based on at least one diene elastomer, and in each of the beads, in a meridian section of said tire: any point of the profile of the outer surface (S) of the tire, between a first point (F), itself defined by the intersection of an axially oriented straight line, passing through the axially outermost point (E) of the main part of the carcass reinforcement layer and the outer surface (S) of the tire, and a point (A), is at a constant distance (T) from the main part of the carcass reinforcement layer, said distance being measured at any point in a direction normal to the main part of the carcass reinforcement layer, the point (A) is radially on the outside of a first circle (C1) of radius (R1) that is centered on the end of the turn-up of the carcass reinforcement layer, (R1) being between 8 and 13 mm, radially on the inside of the point (A), the outer surface (S) of the tire extends by an arc of a circle of radius (R2), the center of which is axially on the outside of the surface (S) of the tire, the circular arc of radius (R2) is tangential at its radially innermost end (B) to a circular arc of radius (R3), the center of which is axially on the inside of the surface (S) of the tire, and continues the outer surface (S) of the tire radially inwards as far as the point (C), said point (C) being a point of tangency between the circular arc of radius (R3) and the circle (C2) of radius (R1) centered on the radially outermost end of the stiffener, and wherein said point (C) being radially on the inside of the axially outermost point (D) of the circle (C2).

3. The tire according to claim 1, wherein the rupture potential index F2/FR2 of the radially outermost working crown layer is less than ⅙, where: FR2 is the breaking force in uniaxial extension of each of the cords of the radially outermost working crown layer,
F2=p.sub.2*Tc*[(tan(|α1|)/((tan(|α1|)+tan(|α2|)))/cos.sup.2(|α2|)+C.sub.F], where
Tc=0.078*P*R.sub.S*(1−(R.sub.S.sup.2−R.sub.L.sup.2)/(2*Rt*R.sub.S)), P is the nominal inflation pressure of the tire according to the ETRTO,
C.sub.F=0.00035*(min((L−80)/sin(|α1|),(L−80)/sin(|α2|),480)−480), p.sub.2 is the pitch at which the reinforcing elements of the radially outermost working crown layer are laid, measured perpendicularly to the reinforcing elements at the circumferential median plane,
Rs=Re−Es, Re is the external radius of the tire, measured at the radially outermost point on the tread surface of the tire, said surface being extrapolated in order to fill any voids there might be, Es is the radial distance between the radially outermost point of the tire and the orthogonal projection thereof onto the radially exterior face of a reinforcing element of the radially innermost working crown layer, RL is the mean of the radii of the axially outermost points on each side of the tire, Rt is the radius of the circle passing through three points situated on the exterior surface of the tread outside of the voids, defined from a shoulder end at respective axial distances equal to ¼, ½ and ¾ of the width of the tread.

4. The tire according to claim 1, wherein the rupture potential index F2/FR2 of the radially outermost working crown layer is less than ⅛.

5. The tire according to claim 1, wherein the rupture potential index F1/FR1 of the radially innermost working crown layer is less than ⅓, where: FR1 is the breaking force in uniaxial extension of each of the cords of the radially innermost working layer,
F1=p.sub.1*Tc*[(tan(|α2|)/((tan(|α1|)+tan(|α2|)))/cos.sup.2(|α1|)+C.sub.F], where p.sub.1 is the pitch at which the reinforcing elements of the radially innermost working crown layer are laid, measured perpendicularly to the reinforcing elements at the circumferential median plane.

6. The tire according to claim 5, wherein the rupture potential index F1/FR1 of the radially innermost working layer is at least 30% higher than the rupture potential index F2/FR2 of the radially outermost working layer.

7. The tire according to claim 1, wherein the two working crown layers and said at least one layer of circumferential reinforcing elements are the only ones present to form the crown reinforcement over the entirety of the axial width of the crown reinforcement (5).

8. The tire according to claim 1, wherein the radius (R2) is between 50% and 125% of the distance between the point (F) and the center of gravity of the bead wire.

9. The tire according to claim 1, wherein the radius (R3) being between 50% and 125% of the distance between the point (F) and the center of gravity of the bead wire.

10. The tire according to claim 1, wherein the distance (T), measured in a direction normal to the main part of the carcass reinforcement layer, is greater than 3 mm and preferably less than 7 mm.

11. The tire according to claim 1, wherein the radial distance between the point (F) and the point (A) is greater than 70% of the radial distance between the point (F) and the radially outermost point (G) of the outer surface (S) of the tire, for which the distance, measured in a direction normal to the main part of the carcass reinforcement layer, between said main part of the carcass reinforcement layer and the surface (S), is equal to (T), said distance between any point, on the outer surface (S) of the tire, radially between the points (F) and (G) and the main part of the carcass reinforcement layer being constant.

12. The tire according to claim 1, wherein the radially outermost end of the stiffener is radially on the outside of the end of the turn-up of the carcass reinforcement layer.

13. The tire according to claim 1, wherein in any meridian plane, in each bead, the tire has a retention reinforcement surrounding the bead wire and a volume of rubber compound in direct contact with the bead wire.

14. The tire according to claim 2, wherein the rupture potential index F2/FR2 of the radially outermost working crown layer is less than ⅙, where: FR2 is the breaking force in uniaxial extension of each of the cords of the radially outermost working crown layer,
F2=p.sub.2*Tc*[(tan(|α1|)/((tan(|α1|)+tan(|α2|)))/cos.sup.2(|α2|)+C.sub.F], where
Tc=0.078*P*R.sub.S*(1−(R.sub.S.sup.2−R.sub.L.sup.2)/(2*Rt*R.sub.S)), P is the nominal inflation pressure of the tire according to the ETRTO,
C.sub.F=0.00035*(min((L−80)/sin(|α1|),(L−80)/sin(|α2|),480)−480), p.sub.2 is the pitch at which the reinforcing elements of the radially outermost working crown layer are laid, measured perpendicularly to the reinforcing elements at the circumferential median plane,
Rs=Re−Es, Re is the external radius of the tire, measured at the radially outermost point on the tread surface of the tire, said surface being extrapolated in order to fill any voids there might be, Es is the radial distance between the radially outermost point of the tire and the orthogonal projection thereof onto the radially exterior face of a reinforcing element of the radially innermost working crown layer, RL is the mean of the radii of the axially outermost points on each side of the tire, Rt is the radius of the circle passing through three points situated on the exterior surface of the tread outside of the voids, defined from a shoulder end at respective axial distances equal to ¼, ½ and ¾ of the width of the tread.

Description

[0130] Further details and advantageous features of the invention will become apparent hereinafter, from the description of exemplary embodiments of the invention, in particular with reference to FIGS. 1 to 3, in which:

[0131] FIG. 1 shows a schematic meridian view of a tire according to the invention,

[0132] FIG. 2 shows an enlarged schematic depiction of the outer surface of the tire between the bead region and the point F,

[0133] FIG. 3 shows an enlarged schematic depiction of the region of a bead of a reference tire.

[0134] In order to make them easier to understand, the figures are not shown to scale.

[0135] FIGS. 1 and 3 show only a half-view of a tire, which extends symmetrically with respect to the axis XX′, which represents the circumferential median plane, or equatorial plane, of the tire.

[0136] In FIG. 1, the tire 1 is of size 315/70 R 22.5. Said tire 1 comprises a radial carcass reinforcement 2 anchored in two beads 3. The carcass reinforcement 2 is formed of a single layer of metal cords. It further comprises a tread 6.

[0137] The carcass reinforcement 2, formed by a single layer of metal cords, is wound, in each of the beads 3, around a bead wire 4 and forms, in each of the beads 3, a turn-up 7 of the carcass reinforcement layer having an end 8.

[0138] Located axially on the outside of the turn-up 7 is a stiffener 9, the radially outermost end 10 of which is radially on the outside of the end 8 of the turn-up 7 of the carcass reinforcement layer.

[0139] The radially innermost end 11 of the stiffener 9 is radially on the outside of the radially innermost point of the bead wire 4.

[0140] The reinforcing elements of the carcass reinforcement layer 2 are non-wrapped layered cords of 1+6+12 structure, made up of a central nucleus formed of one thread, of an intermediate layer formed of six threads, and of an outer layer formed of twelve threads.

[0141] They exhibit the following characteristics (d and p in mm): [0142] structure 1+6+12; [0143] d.sub.1=0.20 (mm); [0144] d.sub.2=0.18 (mm); [0145] p.sub.2=10 (mm) [0146] d.sub.3=0.18 (mm); [0147] p.sub.3=10 (mm); [0148] (d.sub.2/d.sub.3)=1;
with d.sub.1 being the diameter of the nucleus thread, d.sub.2 and p.sub.2 respectively being the diameter and the helical pitch of the threads of the intermediate layer and d.sub.3 and p.sub.3 respectively being the diameter and the helical pitch of the threads of the outer layer.

[0149] The core of the cord, composed of the central nucleus formed of one thread, and of the intermediate layer formed of six threads, is sheathed with a rubber composition based on non-vulcanized diene elastomer (in the raw state). The sheathing is obtained via a head for extrusion of the core, followed by a final operation in which the 12 threads that form the outer layer are twisted or cabled around the core thus sheathed.

[0150] The cord, in the test referred to as the permeability test, as described hereinabove, yields a flow rate equal to 0 cm.sup.3/min and therefore less than 2 cm.sup.3/min Its penetration by the rubber composition is greater than 98%.

[0151] The cord has a diameter equal to 0.95 mm.

[0152] The elastomer composition that makes up the rubber sheath is made from a composition as described hereinabove.

[0153] In FIG. 1, the carcass reinforcement 2 is hooped in accordance with the invention by a crown reinforcement 5 formed radially, from the inside to the outside: [0154] of a first working layer 51 formed of metal cords oriented at an angle equal to 16°, [0155] of a layer of circumferential reinforcing elements 53, formed of 21.23 steel metal cords, of the “bimodulus” type, [0156] of a second working layer 52 formed of metal cords oriented at an angle equal to 34° and crossed with the metal cords of the first working layer 51, the cords of each of the working layers 51, 52 being oriented on each side of the circumferential direction.

[0157] The metal cords that constitute the reinforcing elements of the two working layers are cords of formula 9.35. They are distributed within each of the working layers with a distance between the reinforcing elements, measured along the normal to the direction of the mean line of the cord, equal to 2 mm.

[0158] The tire is inflated to a pressure of 9 bar.

[0159] The axial width L.sub.51 of the first working layer 51 is equal to 246 mm.

[0160] The axial width L.sub.52 of the second working layer 52 is equal to 227 mm.

[0161] The axial width L.sub.53 of the layer of circumferential reinforcing elements 53 is equal to 200 mm.

[0162] The axial width L.sub.6 of the tread is equal to 268 mm.

[0163] The axial width L is equal to 315 mm.

[0164] The combined mass of the two working layers 51, 52 and of the layer of circumferential reinforcing elements 53, including the mass of the metal cords and of the skim compounds, thus amounts to 9.5 kg.

[0165] The difference between the angles formed by the cords of the first working crown layer and the circumferential direction, and those of the cords of the second working crown layer is equal to 18°.

[0166] The mean angle is equal to 23.7° and is clearly between 18.6° and 32.7°.

[0167] The measured value of Re is equal to 508.6 mm.

[0168] The measured value of Es is equal to 22.5 mm.

[0169] The mean value RL of the measured radii is equal to 399 mm.

[0170] The value Rt determined on the tire is equal to 755 mm.

[0171] The calculated value of Tc is equal to 305 N/mm.

[0172] The calculated value of C.sub.F is equal to −0.021.

[0173] The value of F1 is equal to 563.9 N.

[0174] The value of F2 is equal to 315.5 N.

[0175] The breaking forces of the reinforcing elements of the working crown layers FR1 and FR2 are equal to 2600 N.

[0176] The rupture potential index F2/FR2 is equal to 12.1%.

[0177] The rupture potential index F1/FR1 is equal to 21.7%.

[0178] The rupture potential index F1/FR1 is 79% higher than the rupture potential index F2/FR2.

[0179] FIG. 2 schematically illustrates the outer surface S of the tire between the point F and the region of the bead 3 in a meridian cross section of the tire, which is defined such that the centers of mass of the bead wires 4 form an axially oriented straight line, said centers of mass being distant from each other by a distance equal to the width of the nominal rim increased by 20 mm and decreased by twice the distance measured axially between a center of mass of a bead wire 4 and a point on the outer surface of the tire.

[0180] The axially outermost point E of the carcass is, for example, determined by tomography, the tire being mounted/inflated under nominal conditions.

[0181] The point F is then determined by axial projection of the point E onto the outer surface S of the tire.

[0182] The outer surface S of the tire describes a first portion, from the point F to the point A, the latter being radially on the outside of the circle C1 of radius R1 centered on the end 8 of the turn-up of the carcass reinforcement layer.

[0183] The distance T measured between any point on the outer surface S of the tire and the main part of the carcass reinforcement layer, said distance being measured at any point in a direction normal to the main part of the carcass reinforcement layer, is equal to 4.7 mm and is substantially constant over this portion between the points F and A.

[0184] The radius R1 of the circle C1 is equal to 8.8 mm.

[0185] The outer surface S of the tire then continues radially inwards through a circular arc 12 of radius R2, which is itself tangential at B to a circular arc 13 of radius R3, said circular arc continuing the outer surface S of the tire as far as the point C.

[0186] The point C is the point of tangency between the circular arc 13 and the circle C2 centered on the radially outermost end of the stiffener.

[0187] The point C is radially on the inside of the axially outermost point D of the circle C2.

[0188] The radius R2 is equal to 80 mm.

[0189] The radius R3 is equal to 105 mm.

[0190] The distance between the point F and the center of gravity of the bead wire is equal to 116.4 mm.

[0191] The radii R2 and R3 are thus clearly between 50% and 125% of this distance between the point F and the center of gravity of the bead wire.

[0192] The radial distance between the point F and the point A is equal to 29 mm.

[0193] The point G, which is visible in FIG. 1, is the point, radially on the outside of the point F, from which the distance between a point on the outer surface S of the tire and the main part of the carcass reinforcement layer, measured at any point in a direction normal to the main part of the carcass reinforcement layer, is greater than the distance T.

[0194] The radial distance between the point F and the point G is equal to 29 mm.

[0195] The radial distance between the point F and the point A is thus clearly greater than 70% of the radial distance between the point F and the point G.

[0196] Tires I according to the invention were compared with various reference tires of the same size.

[0197] First reference tires T1 differ from tire I according to the invention in terms of the nature of the reinforcing elements of the carcass reinforcement layer. The reinforcing elements of the carcass reinforcing layer of this first reference tire T1 are non-wrapped layered cords of 1+6+12 structure, identical to those of the tire I according to the invention, the core of these not being sheathed with a rubber composition.

[0198] Such cords, in the test referred to as the permeability test, as described hereinabove, yield a flow rate equal to 40 cm.sup.3/min Their penetration by the rubber composition is equal to 66%.

[0199] Second reference tires T2 differ from the reference tires T1 in terms of their crown reinforcement, which is formed radially, from the inside to the outside: [0200] of a first working layer formed of metal cords oriented at an angle equal to 26°, on the same side as the cords of the triangulation layer with respect to the circumferential direction, [0201] of a layer of circumferential reinforcing elements, formed of 21.23 steel metal cords, of the “bimodulus” type, [0202] of a second working layer formed of metal cords oriented at an angle equal to 18° and crossed with the metal cords of the first working layer, the cords of each of the working layers being oriented on either side of the circumferential direction, [0203] of a protective layer formed of elastic 6.35 metal cords, in which the distance between the reinforcing elements, measured along the normal to the direction of the mean line of the cord, is equal to 2.5 mm, oriented at an angle equal to 18° on the same side as the cords of the second working layer.

[0204] The metal cords of the two working layers are cords of formula 9.35. They are distributed within each of the working layers with a distance between the reinforcing elements, measured along the normal to the direction of the mean line of the cord, equal to 2.5 mm.

[0205] The reference tire is inflated to a pressure of 9 bar.

[0206] The axial width of the first working layer is equal to 252 mm.

[0207] The axial width of the second working layer is equal to 232 mm.

[0208] The axial width of the layer of circumferential reinforcing elements 53 is equal to 194 mm.

[0209] The axial width of the protective layer is equal to 100 mm.

[0210] The combined mass of the working layers, of the protective layer and of the layer of circumferential reinforcing elements of the reference tires T2, including the mass of the metal cords and of the skim compounds, amounts to 10.9 kg.

[0211] The absolute value of the difference between the absolute values of the angles formed by the cords of the first working crown layer and the circumferential direction, and those of the cords of the second working crown layer is zero, the angles being identical, unlike in the invention.

[0212] The mean angle is equal to 21.7°.

[0213] The value of F1 is equal to 371 N.

[0214] The value of F2 is equal to 451 N.

[0215] The values F1 and F2 are obtained by a finite element simulation, the high number of reinforcing plies in the crown not making it possible to use a simple analytical model.

[0216] The breaking forces of the reinforcing elements of the working crown layers FR1 and FR2 are equal to 2600 N.

[0217] The rupture potential index F2/FR2 is equal to 17.4%.

[0218] The rupture potential index F1/FR1 is equal to 14.3%.

[0219] The rupture potential index F1/FR1 is 22% higher than the rupture potential index F2/FR2.

[0220] Third reference tires T3 differ from the tire I according to the invention in that they have a more traditional exterior surface profile, and fourth reference tires T4 differ from the reference tires T2, again in that they have a more traditional exterior surface profile. Such a tire profile is shown in FIG. 3.

[0221] In this FIG. 3, which shows a tire 31 of the same size, it appears that the region of the bead 33 is similar to that of the tire according to the invention and that the structure of the carcass reinforcement layer 32 is identical, the latter being turned-up around a bead wire 34 in order to form a turn-up 37 reinforced by a stiffener 39. By contrast, the profile of the outer surface of the tire 31 is different from that of the tire according to the invention.

[0222] Tests were carried out with tires I produced according to the invention and with the reference tires T1, T2, T3 and T4.

[0223] Endurance tests were carried out by running two shaved tires one on the other with a regulated pressure of 5.5 bar and a load of 4571 daN at a speed of 50 km/h and at an ambient temperature of 15° C. for 20 000 km.

[0224] The tests were carried out for the tires according to the invention under conditions identical to those applied to the reference tires T1, T2, T3 and T4.

[0225] All of the reference tires and the tires according to the invention exhibit substantially identical results.

[0226] Second endurance tests were run on a test machine that forced each of the tires to run in a straight line at a speed equal to the maximum speed rating prescribed for said tire (the speed index) under an initial load of 3550 daN that was progressively increased in order to reduce the duration of the test.

[0227] Other endurance tests were carried out on a test machine that cyclically imposed a transverse loading and a dynamic overload on the tires. The tests were carried out for the tires according to the invention under conditions identical to those applied to the reference tires.

[0228] The tests thus carried out showed that the distances covered during each of these tests are substantially identical for the tires according to the invention and the reference tires T1, T2, T3 and T4. It is thus apparent that the tires according to the invention and the reference tires T1 and T3 exhibit performance, in terms of endurance of the bead regions of the tire and of the crown reinforcement, which is substantially equivalent to that of the reference tires T2 and T4, when running on bituminous surfaces.

[0229] Another type of test was carried out to test the performance capabilities in terms of resistance to impacts and/or rubbing against kerbs.

[0230] In order to carry out these tests, the tires are also provided with radial striations on their sidewalls.

[0231] These tests are carried out on a pavement with a 15 cm high kerb. The tire was mounted on a vehicle, the path of which drove the tire at a speed of 20 km/h with an angle of incidence of 10° with respect to the kerb.

[0232] The operation was repeated 6 times and then the sidewall was analyzed to detect any chunking.

[0233] All of the tires exhibited two instances of chunking.

[0234] As far as the surface that struck the kerb is concerned, it is 8% less on the tire according to the invention and on the reference tires T1 and T2 compared with the reference tires T3 and T4.

[0235] Tests aimed at characterizing the breaking strength of a tire crown reinforcement subjected to shock loadings were also carried out. These tests involve running a tire, inflated to a recommended pressure and subjected to a recommended load, over a cylindrical obstacle or indenting tool with a diameter equal to 1.5 inches, i.e. 38.1 mm, with a hemispherical head, and with a given height, pressing against the center of the tread. The breaking strength is characterized by the critical height of the indenting tool, i.e. the maximum height of the indenting tool that results in complete breakage of the crown reinforcement, i.e. in the breakage of all the crown layers. The values express the energy required to obtain breakage of the crown block. The values are expressed with reference to a base 100 that corresponds to the value measured for the reference tire T4.

TABLE-US-00001 Reference T4 100 Reference T3 115 Reference T2 100 Reference T1 115 Invention I 115

[0236] These results show that, despite the lightening of the tire, notably by reducing the mass of the crown reinforcement thereof, the energy at break in the event of a shock loading on the surface of the tread of the tires according to the invention or of the reference tires T1 and T3 is significantly higher than that of the reference tires T4 and T2.

[0237] Final tests aimed at characterizing the breaking strength of a tire crown reinforcement subjected to specific loadings were also carried out. These tests involve running a tire, inflated to a nominal pressure according to the ETRTO, and subjected to a nominal load according to the ETRTO over 40 000 km at 40 km/h on a rolling road, over spherical obstacles of radius 26 mm, truncated at 21 mm and separated by approximately 2.50 metres, which press against the edge of the tread, the axial position of the center of the obstacles being situated 10 mm towards the center from a point beyond which the tangent to the outer surface of the tread makes an angle greater than or equal to 30° with the axial direction. Six pieces of cord of length 150 mm are extracted from the carcass reinforcement layer, the pieces being centered on the end of the axially widest working crown layer. The force at break of the cords is measured using a uniaxial tensile test, and the mean of the measurements taken across the six pieces of cord extracted from the tire is calculated. The values are expressed with reference to a base 100 that corresponds to the value measured for the reference tire T1.

TABLE-US-00002 Reference T1 100 Reference T2 105 Reference T3 105 Reference T4 100 Invention I 117

[0238] These results demonstrate that despite the lightening of the tire, notably by reducing the mass of the crown reinforcement thereof, the endurance performance of the cords of the carcass reinforcement layer of the tires according to the invention is significantly improved with their compression behavior having been modified in comparison with the reference tires T1, to the extent that they exhibit performance superior to that of the reference tires T2 and T4 which have more conventional crown reinforcements. Comparing the tires according to the invention against the reference tires T3, which differ only in terms of the exterior profile in the vicinity of the rim, reveals the benefit of combining carcass reinforcement cords having a sheathed core, with the bead-region exterior surface profile of the tire according to the invention.

[0239] Another tire 12 according to the invention was also tested. This tire 12 differs from tire I in terms of the nature of the reinforcing elements of the carcass reinforcement layer. The reinforcing elements of the carcass reinforcement layer of this tire 12 are non-wrapped layered cords of 1+6+11 structure, made up of a central nucleus formed of one thread, of an intermediate layer formed of six threads, and of an outer layer formed of eleven threads.

[0240] They exhibit the following characteristics (d and p in mm): [0241] structure 1+6+11; [0242] d.sub.1=0.20 (mm); [0243] d.sub.2=0.175 (mm); [0244] p.sub.2=7 (mm) [0245] d.sub.3=0.175 (mm); [0246] p.sub.3=10 (mm);

[0247] (d.sub.2/d.sub.3)=1;

with d.sub.1 being the diameter of the nucleus thread, d.sub.2 and p.sub.2 respectively being the diameter and the helical pitch of the threads of the intermediate layer and d.sub.3 and p.sub.3 respectively being the diameter and the helical pitch of the threads of the outer layer.

[0248] The core of the cord which is made up of the central nucleus formed of one thread, and of the intermediate layer formed of six threads, is not sheathed with a rubber composition.

[0249] Such cords, in the test referred to as the permeability test, as described hereinabove, yield a flow rate equal to 5 cm.sup.3/min Its penetration by the rubber composition is equal to 98%.

[0250] In the tests aimed at characterizing the breaking strength of the crown reinforcement of the tire subjected to particular impacts pressing against the edge of the tread, the measured force at break of the cords, expressed with reference to a base 100 that corresponds to the value measured for the reference tire T1, is equal to 110.