WO2018115701A1

WO2018115701A1 - Tyre with reinforced sidewalls

Info

Publication number: WO2018115701A1
Application number: PCT/FR2017/053675
Authority: WO
Inventors: Hervé FERIGO
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2016-12-20
Filing date: 2017-12-19
Publication date: 2018-06-28
Also published as: FR3060455A1; CN110290944A; EP3558720A1

Abstract

The invention relates to a tyre for a wheel assembly comprising a rim and a tyre, said tyre including at least one carcass reinforcement (2) topped radially on the outside by a crown reinforcement (3), which is in turn radially inside a tread (4) having two axially outermost ends, said crown reinforcement (3) being made up of at least one layer of reinforcement elements, said tread (4) being connected to two beads (5) via two sidewalls (6), said beads (5) being intended for engaging with a rim (7) having gutter tops (7a), each bead (5) including at least one circumferential reinforcement element, said sidewalls (6) including, on the outer surface thereof, a series of projections (8) alternating with recesses (9), the projections (8) being arranged on the surface of the sidewall (6) in a regular or irregular manner, each projection (8) having a substantially longitudinal shape with two side walls extending over a continuous or discontinuous neutral axis length (Fn), wherein each side wall comprises an undercut portion extending from a point V of said side wall to a point U of said side wall, such that a straight line passing through the points V and U forms, with a straight line (Pn) perpendicular to the neutral axis extending in a plane tangential to the neutral axis from said side wall towards the recess (9) adjacent to said side wall, an angle β other than zero and strictly less than 90°, said undercut portion extending over a surface making up at least 20% of the surface of the side wall, and in which, in the area of said sidewall (6) in which the projections (8) alternate with the recesses (9), the surface fill rate is higher than 60%.

Description

Pneumatic with reinforced flanks

FIELD OF THE INVENTION

The invention relates to radial carcass or cross-carcass tires.

STATE OF THE ART

Radial-carcass tires have gradually taken hold in various markets, including the tire market for passenger vehicles. This success is due in particular to the endurance, comfort and low rolling resistance qualities of radial technology.

The main parts of a tire are the tread, the sidewalls and the beads. The beads are intended to come into contact with the rim. In a tire of radial technology, each of the main parts constituting the tire, namely the tread, the sidewalls and the beads, has functions well separated from each other, and therefore has a specific constitution well known.

The radial tire is substantially reinforced by a carcass reinforcement comprising at least one carcass ply having an angle substantially equal to 90 ° with respect to the circumferential direction of the tire. This carcass reinforcement is surmounted radially on the outside, and under the tread, reinforcing plies forming a belt.

The cross-carcass tire is distinguished from a radial tire by the presence of at least two crossed carcass plies whose angle is different from 90 ° with respect to the circumferential direction of the tire. The tablecloths are said

"Crossed" because the angles are of opposite signs from one tablecloth to another.

It is recalled that, according to the invention, the circumferential direction of the tire is the direction lying in a plane perpendicular to the axis of rotation of the tire and tangent to the belt reinforcement of the tire.

Following the appearance of radial tire, some cross-carcass tires have also been provided with belt reinforcement under the tread.

In these two types of tire, the tread, in contact with the ground, has the particular function of ensuring contact with the road and must adapt to the shape of the ground. The flanks, meanwhile, absorb the irregularities of the ground while transmitting the mechanical forces necessary to carry the load of the vehicle and ensure its movement. The belt reinforcement is an armature which must, on the one hand, be sufficiently rigid with respect to the deformations on edge so that the tire develops the drift thrusts necessary for its guidance, and transmit the engine or braking torque, and on the other hand, be very flexible in bending, that is to say allow variations in curvature of its plane to ensure a contact surface of the tire on the ground sufficient.

Therefore, the belt reinforcement generally has a composite structure, allowing it to have the rigidity required for a relatively low weight. The belt reinforcement generally consists of at least two plies with different angles, including reinforcements, cable-shaped, coated with rubber. The reinforcing elements are crossed from one sheet to the other with respect to the circumferential direction and are symmetrical or not with respect to this direction.

In a collision with a sidewalk or pothole, the tire may be damaged, particularly by wedging it between the rim and the obstacle. Following the impact of the reinforcing elements of the sidewall of the tire may be damaged or broken. The tire may locally deform and / or lose its inflation pressure.

To overcome this drawback, several different solutions have been proposed. For example, it has been proposed to increase the breaking strength of the cables of the carcass ply, or even to increase the number of reinforcement layers, typically with two-ply solutions. Another solution is to have on the sidewall of the tire a set of protuberances and recesses which limit the stress of the cables during shocks. The international applications WO 2014/207093 and WO 2014/207094 published on December 31, 2014 describe exemplary embodiments of tires incorporating alternations of protuberances and recesses on the sidewalls to increase the resistance of these tires to side impacts.

The solutions proposed in these documents are effective with regard to the protection against lateral shocks but can sometimes increase the rolling resistance of the tire, in particular because tire flattening is less easy.

There is a need for a robust tire, particularly on the sidewall, resistant to physical attacks such as side impacts, and has improved rolling resistance over existing solutions.

Another object of the present invention is to provide a tire having increased resistance against shocks at the sidewalls and which has increased marking features on the sidewalls of said tire.

SUMMARY OF THE INVENTION For this purpose, a tire for a wheel assembly comprising a rim and a tire is proposed, said tire comprising at least one carcass reinforcement surmounted radially on the outside of a crown reinforcement, itself radially inside. a tread having two axially outermost ends, said crown reinforcement consisting of at least one layer of reinforcing elements, said tread being connected to two beads via two sidewalls, said beads being intended to come into contact with a rim having rim hook heights, each bead having at least one circumferential reinforcing element,

said flanks having, on their outer surface, a series of alternating protuberances with recesses, the protuberances being disposed at the surface of the sidewall in a regular or irregular manner, each protuberance having a substantially longitudinal shape with two side walls extending over a length continuous or discontinuous neutral fiber (Fn),

wherein each sidewall comprises an undercut portion extending from a point V of said sidewall to a point U of said sidewall such that a line passing through the points V and U forms with a straight line (Pn perpendicular to the neutral fiber extending in a plane tangent to the neutral fiber from said side wall to the recess adjacent to said side wall a non-zero angle β strictly less than 90 °, said undercut portion extending over a surface representing at least 20% of the surface of the side wall.

Preferred but non-limiting aspects of this tire, taken alone or in combination, are the following:

- The angle β of the undercut portion is strictly less than 85 °, preferably strictly less than 80 °, and more preferably less than or equal to 65 °.

the angle β of the undercut portion is between 30 ° and 75 °, and preferably between 35 ° and 65 °.

the undercut portion extends over a surface representing at least 50% of the surface of the lateral wall.

the undercut portion extends over a surface representing at least 75% of the surface of the sidewall.

the undercut portion extends over a surface representing the entire surface of the sidewall.

the area of said flank where the protuberances alternate with the hollows, the full surface area is greater than 60%, preferably between 70% and 95%. the undercut portion of the side wall is straight or curved.

each protuberance has a cross section having a trapezoidal, pentagonal or hexagonal shape.

each recess has a cross section having a first rectangular or trapezoidal portion positioned outwardly of the tire, and a second circular portion extending inwardly of the tire.

each side wall of the protuberance comprises a recessed portion complementary to the undercut portion, the undercut portion being located radially innermost relative to the recess portion.

each protuberance extends over a length of at least 10 mm.

the protuberances have variable heights, the maximum height being between 3 mm and 10 mm, and preferably between 4 mm and 8 mm.

EQ denotes the most axially outside point of the sidewall, Req being the radius at the point EQ, each protuberance having a height at the point

EQ less than the height of said protuberance at points EQ + and EQ- respectively at distances Req + 20mm and Req - 20 mm with respect to the axis of rotation of the tire.

the tread comprises at least one axially outermost end a circumferential groove, where at least one protuberance interrupts partially or totally or does not interrupt said circumferential groove, said circumferential groove having lateral walls also having a counter-shaped portion; stripping in a form identical to that of the protuberances,

at least two protuberances have a length different from each other, two adjacent protuberances are substantially parallel to each other.

the neutral fiber of each protuberance passes through a radially innermost end and a radially outermost end, and has an angle with respect to the radial direction ZZ 'of between -60 ° and + 60 °.

said protuberances are arranged continuously between a point A and a point E,

o said point A being disposed at the intersection of the radially outer surface of the tread and the sidewall, and a radial axis ZZ 'distant from the equatorial plane AA' with a length LA of between ½ ^* (L- 60mm) and ½ ^* (L-10mm), where L is the nominal flange size, and

o said point E being disposed in a radius such that R2 <Re <Ra-25mm, R2 being the radius of the top of the rim hook and Ra being the radius of the point A. each protuberance has an average height greater than 80% of the maximum height over at least 80% of the distance between points A and E.

the protuberances cover at least 40% of the total circumferential surface of the flank between points A and E.

DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will become apparent from the description which follows, which is purely illustrative and nonlimiting and should be read with reference to the accompanying drawings, in which:

- Figure 1 shows schematically the section of a tire in a radial plane;

Figure 2 schematically shows an enlarged portion of a tire sidewall comprising a series of protuberances and recesses;

FIG. 3 represents a sectional view of several adjacent protuberances of a tire according to the prior art, along the axis A-A of FIG. 2;

FIG. 4 represents a sectional view of several adjacent protuberances of a tire according to a first embodiment of the invention, along the axis A-A of FIG. 2;

FIG. 5 represents a sectional view of several adjacent protuberances of a tire according to a second embodiment of the invention, along the axis A-

A of Figure 2;

FIG. 6 represents a sectional view of several adjacent protuberances of a tire according to a third embodiment of the invention, along the axis A-A of FIG. 2;

FIG. 7 represents a sectional view of several adjacent protuberances of a tire according to a fourth embodiment of the invention, along the axis A-A of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

In this document, the term "running surface" means all the points of the tread of a tire which are likely to come into contact with the ground when the tire is rolling.

In the use of the term "radial" it is appropriate to distinguish several different uses of the word by the person skilled in the art.

First, the term refers to a radius of the tire. A "radial direction" is a direction intersecting the axis of rotation of the tire and perpendicular to it. It is in this sense that we say from a point P1 that it is "radially interior" to a point P2 (or "radially inside" of point P2) if it is closer to the axis of rotation of the tire than point P2. Conversely, a point P3 is said to be "radially external to" a point P4 (or "radially outside" of the point P4) if it is farther from the axis of rotation of the tire than the point P4. We will say that we are advancing "radially inwards (or outwards)" as we move towards smaller (or larger) radii. When it comes to radial distances, this sense of the term also applies. On the other hand, the radius X of the tire X is the radial distance between the axis of rotation of said tire and the point X.

On the other hand, a wire or a reinforcement is said to be "radial" when the wire or reinforcing elements of the reinforcement make with the circumferential direction an angle greater than or equal to 80 ° and less than or equal to 90 °. Clarification that in this paper, the term "wire" is to be understood in a very general sense and includes threads in the form of monofilaments, multifilament, cable, twisted or equivalent assembly, and this regardless of the material constituting the wire or the surface treatment to promote its connection with the rubber.

Finally, by "radial section" or "radial section" here means a section or section along a plane which contains the axis of rotation of the tire. A "radial or meridian plane" is a plane that contains the axis of rotation of the tire.

The "median plane or equatorial plane" of the tire is the plane which is perpendicular to the axis of rotation of the tire and which is equidistant from the annular reinforcing structures of each bead. This plane divides the tire into two substantially equal halves, that is to say which passes through the middle of the tread.

An "axial" direction is a direction parallel to the axis of rotation of the tire. A point P5 is said to be "axially inner" at a point P6 (or "axially inside" of the point P6) if it is closer to the median plane of the tire than the point P6. Conversely, a point P7 is said to be "axially outside at" a point P8 (or "axially outside" of the point P8) if it is farther from the median plane of the tire than the point P8.

A "circumferential direction" or "longitudinal direction" is a direction that is perpendicular to both a tire radius and the axial direction. This corresponds to the rolling direction of the tire.

A "circumferential cut" or "circumferential section" is respectively a section or a section in a plane perpendicular to the axis of rotation of the tire. A "circumferential plane" is a plane perpendicular to the axis of rotation of the tire.

In Figure 1 is shown the section of a tire 1 in a radial plane. In a conventional manner, the tire 1 comprises at least one carcass reinforcement 2 surmounted radially on the outside of a crown reinforcement 3, itself radially inside a tread 4 having two axially most opposite ends. exterior.

The crown reinforcement 3 consists of at least one layer of reinforcement elements, and generally of several reinforcement layers.

The tread 4 is connected to two beads 5 via two sidewalls 6.

The beads 5 are intended to come into contact with a rim 7 having rim hook tops 7a. Each bead 5 preferably comprises at least one circumferential reinforcing element.

In order to reinforce the tire 1 and in particular to prevent the reinforcing elements of the sidewalls from being damaged or broken by side impacts, the sidewalls 6 comprise, on their outer surface, a series of alternating protuberances 8 with recesses 9, the protuberances 8 being disposed at the surface of the flank 6 in a regular or irregular manner.

Each protrusion 8 has a substantially longitudinal shape and extends along a length of neutral fiber (Fn), continuously or discontinuously. By neutral fiber is meant a neutral axis which passes substantially in the center of the volume of each protrusion 8, and which undergoes neither shortening nor elongation when it is subjected to compression and / or depression.

In Figure 1 we can see a protrusion 8, in section, extending continuously along the neutral fiber. The protuberances 8 may however also be arranged on the surface of the sidewall 6 in a discontinuous manner along the neutral fiber (Fn).

In the example illustrated in FIG. 1, each protuberance 8 extends continuously between a point A and a point E, where:

the point A is disposed at the intersection of the radially outer surface of the tread 4 and the sidewall 6, and a radial axis ZZ 'distant from the equatorial plane AA' of a length LA of between ½ ^* (L -60mm) and ½ ^* (L-10mm), where L is the nominal coil size, and

the point E being arranged in a radius Re such that R2 <Re <Ra-25mm, R2 being the radius of the top of the rim hook and Ra being the radius of the point A.

Figures 2 and 3 show protuberances as they exist in the prior art. As can be seen in particular in FIG. 3, such protuberances 8 have a profile with flanking side walls, that is to say that the lateral walls are inclined so as to facilitate demolding of the mold used to form the protuberances 8 on the flank 6. The draft angle denoted a is shown in FIG. 3. In the prior art, a clearance angle α is chosen which allows the tire to be demolded after firing without deformation of the final structure of the protuberances, this clearance angle α being for example of the order of 6 ° to 8 °.

According to the invention and contrary to the teachings of the prior art, it is proposed to form protuberances which have at least one portion undercut.

By undercut portion is meant a portion which - in contrast to a flush shape - comes to oppose the withdrawal movement of the mold once the structure has been formed.

An undercut portion is generally caused by problematic shapes such as cavities and retentions or specific wall inclinations, these types of shapes may generate additional stress during demolding after firing.

Provided that a protuberance 8 has a longitudinal shape with two side walls extending over a length of neutral fiber (Fn), it is proposed to form protuberances where each side wall comprises an undercut portion.

The undercut portion extends from a point V of said side wall to a point U of said side wall such as a straight line passing through the points V and U forms with a straight line (Pn) perpendicular to the neutral fiber (Fn) extending in a plane tangent to the neutral fiber in the direction of the recess (9) adjacent to said side wall a non-zero angle β strictly less than 90 °. More precisely, the angle β is the angle formed between the vector Pn and the vector VU, the vector Pn being oriented along the line (Pn) so as to go from the material of the protuberance to the recess between two adjacent protuberances .

The point V corresponds to the point of the lateral wall of the protuberance 8 which is the most axially inward with respect to the cross-section of the said protuberance 8.

The point U is a point on the side wall of the protuberance 8 being axially more outward with respect to the point V. Preferably, the point U corresponds to the point of the side wall of the protuberance 8 most axially to the outside relative to the cross section of said protuberance 8.

The point V is radially further inland than the point U. It can also be said that the point V is closer to the base of the protrusion 8, that is to say closer to the hollow 9 adjacent to the protuberance 8, that point U.

Preferably, the angle β of the undercut portion is strictly less than 85 °, or even strictly less than 80 °.

According to a preferred embodiment, the angle β of the undercut portion is between 30 ° and 75 °. The undercut portion extends over a surface representing at least 20% of the surface of the sidewall. Thus, at least 20% of the total lateral surface of all the protuberances is undercut.

Preferably the undercut portion extends over a surface representing at least 30% of the surface of the side wall, more preferably at least 50% of the surface of the side wall, or even at least 75% of the surface area. of the side wall.

According to a still preferred embodiment, the undercut portion extends over a surface representing the entire surface of the side wall.

The fact of having an undercut portion at the walls of the protuberance 8 allows to have protuberances with more flexibility. This makes it possible to reduce the overall stiffness of the protuberances with iso-volume of material. Thus, the rolling resistance is reduced since flat tire is easier.

Another advantage of this particular shape of the protuberances with an undercut enables the marking surface to be increased on the sidewall 6. In fact, the undercut portions make it possible to maintain an upper surface of the protuberances 8 extended, which comes even cover a large part of the free space of the hollows 9.

In the area of said sidewall 6 where the protuberances 8 alternate with the recesses 9, the full surface area is greater than 60%, preferably between 70% and 95%.

Finally, this particular shape also highlights the protuberances 8 compared to the hollows which are darker.

FIG. 4 illustrates an embodiment in which the protuberances 8 have a trapezoidal cross-section, the small base corresponding to the base of the protuberance 8, that is to say the connection with the surface of the sidewall 6, while that the large base corresponds to the outer surface of the protuberance 8. According to this example, the side wall of the undercut portions is straight.

According to the example of Figure 4, the two side walls of the protuberance 8 have identical undercut portions, that is to say that the side walls form with the bottom Pn of the hollow 9 the same angle β. The cross section of the protrusion is according to this example an isosceles trapezium. These angles could however be different, thus forming two portions undercut with different inclinations.

In Figure 5 is precisely presented an embodiment of protuberances, wherein each of the two side walls (8a, 8b) of the protuberance 8 has portions undercut different from each other. Such a design will for example facilitate the demolding of the mold during the formation of the protuberances.

In particular, the angles of inclination β and β 'of the side walls with respect to the bottom

Pn and Pn 'of the recesses 9 adjacent to the protuberance 8 are different. According to the example of Figure 5, the protuberance has a pentagonal cross section. According to this example, the side wall of the undercut portions is straight.

Indeed, the wall 8a of the side walls (8a, 8b) of the protuberance 8 has not only an undercut portion extending from the point U to V, but also a recess portion.

The wall 8b of the lateral walls (8a, 8b) of the protuberance 8 has for its part only an undercut portion which extends from a point U 'situated at the base of the wall 8b to the point V situated at the upper surface of the protuberance 8.

One embodiment could be envisaged (not shown) where the protuberance has a cross section of hexagonal shape, that is to say where each of the two side walls comprises an undercut portion and a recess portion.

Figures 6 and 7 illustrate examples where the protuberances have undercut portions formed by curved walls. The undercut portion of the side wall is curved.

The protuberances 8 according to the examples of Figures 6 and 7 have walls both having an undercut portion and a recess portion, the undercut portion being positioned radially innermost relative to the portion bare.

The shape of the protuberances 8 can be defined from the shapes of the recesses 9 separating two adjacent protuberances.

Thus, according to these examples, each recess 9 has a cross section having a first portion 9a rectangular or trapezoidal positioned outwardly of the tire, and a second portion 9b circular extending from the first portion 9a.

The first portion 9a defines the flank portion of the protuberance 8, while the circular portion 9b defines the curved undercut portion of the protuberance 8.

In Figure 6 is illustrated an example of a protuberance with a large undercut portion relative to the undercut portion, both in terms of relative heights that radius of curvature of the undercut portion.

In Figure 7, the protuberance has a recess portion having a height substantially greater than the height of the undercut portion.

In the examples of Figure 6 and Figure 7, the circular portion 9b has optimized dimensions to prevent cracking in the bottom of the hollow. Thus the diameter of the circular portion 9b is chosen according to the curvature of the sidewall. In addition to the particular shapes of the protuberances as presented above, with in particular the presence of an undercut portion, one can characterize these protuberances by their general dimensions.

Thus, each protuberance 8 preferably extends over a length of at least 10 mm.

Each protuberance 8 preferably has an average width of between 4 mm and 12 mm.

Each protuberance for example has an average height of between 3 mm and 10 mm, preferably between 5 mm and 8 mm.

The protuberances can have variable heights, the maximum height being between 3 mm and 10 mm, and preferably between 4 mm and 8 mm.

By designating by EQ the most axially outside point of the flank 6 and Req being the radius at the point EQ, and if the protuberance has a variable height along its length, then said protrusion 8 preferably has a height at the point EQ less than the height of said protuberance 8 at the points EQ + and EQ- respectively located at distances Req + 20mm and Req - 20 mm with respect to the axis of rotation of the tire

1.

The protuberances 8 of the same sidewall 6 may have different lengths.

Preferably, two adjacent protuberances 8 are substantially parallel to one another.

The neutral fiber of each protrusion 8 passes through a radially innermost end and a radially outermost end, and has an angle with respect to the radial direction ZZ 'between -60 ° and + 60 °.

In one possible embodiment, the tread 4 comprises at least one axially outermost end a circumferential groove, where at least one protrusion 8 interrupts partially or totally or does not interrupt said circumferential groove.

In this case, it is advantageous for the circumferential groove to comprise side walls that also have an undercut portion in a shape identical to that of the protuberances 8.

BIBLIOGRAPHIC REFERENCES

- WO 2014/207093

- WO 2014/207094

Claims

1. A pneumatic tire for a wheel assembly comprising a rim and a tire, said tire comprising at least one carcass reinforcement (2) surmounted radially on the outside of a crown reinforcement (3), itself radially inside a tire. tread (4) having two axially outermost ends, said crown reinforcement (3) consisting of at least one layer of reinforcing elements, said tread (4) being connected to two beads (5) by means of two sidewalls (6), said beads (5) being intended to come into contact with a rim (7) having rim hook heels (7a), each bead (5) comprising at least one element of circumferential reinforcement,

said flanks (6) having, on their outer surface, a series of alternating protuberances (8) with recesses (9), the protuberances (8) being arranged on the surface of the flank (6) in a regular or irregular manner, each protuberance (8) having a substantially longitudinal shape with two side walls extending over a continuous or discontinuous neutral fiber length (Fn),

each side wall including an undercut portion extending from a point V of said side wall to a point U of said side wall such as a straight line passing through points V and U forms with a perpendicular line (Pn) to the neutral fiber extending in a plane tangent to the neutral fiber from said side wall to the recess (9) adjacent to said side wall a non-zero angle β strictly less than 90 °, said undercut portion extending on a surface representing at least 20% of the surface of the side wall,

wherein in the area of said flank (6) where the protuberances (8) alternate with the recesses (9), the full surface area is greater than 60%.

2. A tire according to claim 1, wherein the angle β of the undercut portion is strictly less than 85 °, preferably strictly less than 80 °.

3. The tire of claim 1, wherein the angle β of the undercut portion is less than or equal to 65 °.

4. A tire according to claim 1, wherein the angle β of the undercut portion is between 30 ° and 75 °.

5. A tire according to claim 1, wherein the angle β of the undercut portion is between 35 ° and 65 °.

A tire according to any one of claims 1 to 5, wherein the undercut portion extends over a surface representing at least 50% of the surface of the sidewall.

A tire according to any one of claims 1 to 5, wherein the undercut portion extends over a surface representing at least 75% of the surface of the sidewall.

A tire according to any one of claims 1 to 5, wherein the undercut portion extends over a surface representing the entire surface of the sidewall.

9. A tire according to any one of claims 1 to 8, wherein in the area of said sidewall (6) where the protuberances (8) alternate with the recesses (9), the full surface area is between 70% and 95 %.

A tire according to any one of claims 1 to 9, wherein the undercut portion of the side wall is straight or curved.

1 1. Tire according to any one of claims 1 to 10, wherein each protuberance (8) has a cross section having a trapezoidal, pentagonal or hexagonal shape.

Tire according to any one of claims 1 to 10, wherein each recess (9) has a cross-section having a first rectangular or trapezoidal portion positioned towards the outside of the tire, and a second circular portion extending towards the outside. inside the tire.

13. A tire according to any one of claims 1 to 12, wherein each side wall of the protrusion (8) comprises a recess portion complementary to the undercut portion, the undercut portion being located radially. the innermost in relation to the undercut portion.

14. A tire according to any one of claims 1 to 13, wherein each protrusion (8) extends over a length of at least 10 mm.

15. A tire according to any one of claims 1 to 14, wherein the protuberances (8) have variable heights, the maximum height being between 3 mm and 10 mm, and preferably between 4 mm and 8 mm.

16. A tire according to any one of claims 1 to 15, wherein EQ denotes the most axially outside point of the sidewall (6), Req being the radius at the point EQ, each protuberance (8) having a height. at the level of the EQ point lower than the height of said protuberance (8) at the points EQ + and EQ- respectively at distances Req + 20mm and Req - 20 mm with respect to the axis of rotation of the tire.

17. A tire according to any one of claims 1 to 16, wherein the tread (4) comprises at least one axially outermost end a circumferential groove, where at least one protuberance (8) interrupts partially or totally or does not interrupt said circumferential groove, said circumferential groove having walls laterally also having an undercut portion in a shape identical to that of the protuberances (8).

18. A tire according to any one of claims 1 to 17, wherein at least two protuberances (8) have a length different from each other.

19. A tire according to any one of claims 1 to 18, wherein two adjacent protuberances (8) are substantially parallel to each other.

20. A tire according to any one of claims 1 to 19, wherein the neutral fiber of each protrusion (8) passes through a radially innermost end and a radially outermost end, and has an angle to the radial direction ZZ 'between -60 ° and + 60 °.

21. Tire according to any one of claims 1 to 20, wherein said protuberances (8) are arranged continuously between a point A and a point E, said point A being disposed at the intersection of the radially outer surface of the tread (4) and the sidewall (6), and a radial axis ZZ 'distant from the equatorial plane AA' with a length LA of between ½ ^* (L-60mm) and ½ ^* (L-10mm), Where L is the nominal strand size, and

said point E being disposed in a radius such that R2 <Re <Ra-25mm, R2 being the radius of the top of the rim hook and Ra being the radius of the point A.

22. A tire according to claim 21, wherein each protuberance (8) has an average height greater than 80% of the maximum height over at least 80% of the distance between points A and E.

23. A tire according to any one of claims 21 or 22, wherein the protuberances (8) cover at least 40% of the total circumferential surface of the sidewall between points A and E.