Patent Publication Number: US-9840115-B2

Title: Tyre for a vehicle wheel including a tread-band pattern

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of pending application Ser. No. 10/533,927, filed Dec. 2, 2005, which is a national stage entry of International Application No. PCT/IT02/000814, filed Dec. 19, 2002, both of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a tyre for vehicle wheels. 
     In more detail, the invention concerns a tyre of the winter type for high performance and ultra high performance cars, i.e. cars provided with particular performance qualities and generally having a rear-wheel drive. 
     Description of the Related Art 
     By winter tyre it is intended a tyre provided with a tread band suitable for running on surfaces of reduced compactness in particular snow-covered roadways. 
     Tyres having the above qualities are usually required to possess, together with optimal features in terms of traction power, braking and handling on a snow-covered roadway, a good behaviour on dry and wet roads and a satisfactory resistance to wear. Noiseless running also helps in elevating or worsening the qualitative evaluation of a winter tyre. 
     Usually, the above mentioned behavioural and operational features are determined through formation in the tread band of appropriate circumferential and transverse grooves suitably sized and oriented, which grooves give rise to creation of blocks usually aligned in rows disposed consecutively in side by side relationship and extending circumferentially of the tyre itself. 
     In addition, of decisive importance as regards the behavioural running features of a car on a snow-covered roadway is the presence of an appropriate lamelliform arrangement of cuts in the blocks, i.e. a thick series of narrow cuts disposed consecutively in side by side relationship in a circumferential direction and oriented substantially transversely with respect to the rolling direction. The task of these narrow cuts, which are currently referred to as sipes, is substantially that of effectively collecting and retaining the snow, since friction of snow against snow is known to be greater than rubber-on-snow friction. 
     In the international patent, application WO 02/068222 in the name of the same Applicant it is described a winter tyre for vehicle wheels comprising a tread band provided with three circumferential grooves and a plurality of transverse grooves that together delimit four circumferential rows of blocks: two axially external shoulder rows and two central rows disposed to the sides of the equatorial plane of the tyre. The transverse grooves converge to the equatorial plane towards a predetermined tyre-rolling direction. On the tread band, each transverse groove belonging to the central rows is provided with an enlarged area in its section having an essentially circular profile, the function of which is to entrap snow. In addition, for obtaining rolling with less noise on dry roads as well, each transverse edge of the blocks comprises at least two successive curvilinear portions. These curvilinear portions are differently shaped and have opposite bends in the two portions to mitigate noise generated by the impact of the blocks when the tyre is rolling on the ground. 
     The Applicant has perceived the increasing requirement of ensuring more handling on snow-covered roadways to all motor-vehicles and above all to those of the above mentioned high performance type, while at the same time affording more safety and comfort on dry and wet roads. 
     In fact many automobile houses during their winter tests have begun to regularly carry out behavioural tests on snow, beside the traditional acceleration and braking tests. 
     These tests are subjective behavioural tests and consist in the tyre being run on a mixed roadway, characterised by straight stretches and bends to be taken at different speeds, as well as by uphill and downhill portions, on the basis of which a test driver gives his/her opinion on different car handling parameters. 
     SUMMARY OF THE INVENTION 
     In this connection the Applicant has found that the winter tyres of the known art have a side (lateral) grip on snow-covered roadways that is not quite satisfactory. This phenomenon, present on both the car axles, is more marked on the driving wheels and is highlighted to a greater degree on rear-wheel drive cars provided with engines of high power. In fact, to ensure high performance on dry roadways, the cars of this type usually have low-section tyres, very large and stiff, having a footprint which is narrow in the circumferential direction and elongated (i.e. wide) in the axial direction of the tyre. All these features however have the opposite effect when running on snow is concerned. 
     The lack of side grip adversely affects the traction power on leaving a bend, giving rise to loss of grip of the rear axle of the car. 
     In addition, traditional block patterns for snow result in high noise when the tyre rolls on dry and compact road surfaces, reaching peaks of high intensity at given frequencies connected with the number of blocks disposed on each circumferential row of the tread band. 
     The Applicant has found that these problems particularly arise on vehicles in which the geometry of the suspensions imposes rather marked camber angles, for instance included between 0°, 5′ and 2°, typical of the above mentioned high performance cars. In more detail, the camber angle is the inclination of the equatorial plane of a tyre from a direction normal to the road plane. In cars with a negative camber the tyre footprint has an amplitude increasingly growing towards the axially internal edge of the tyre, contrary to what happens to tyre footprints of cars with a Positive camber. 
     The Applicant has further noticed that known winter tyres do not ensure the same performance level on dry roads as that obtainable with tyres expressly planned for use on such types of roadway. 
     While trying to find a solution to the problems set out hereinabove, the Applicant has perceived that the presence of transverse cuts substantially extending over the whole axial size of the tread band creates a forced correlation between the number of blocks present in the different circumferential rows, which greatly contributes to the origin of the above described problems. 
     The Applicant has therefore found the possibility of achieving important improvements in tyre behaviour as regards most of the problems found in the known art and correlated with side grip, handling, traction power and braking on snow as well as in terms of noiseless running on a dry road, through accomplishment of a tread band pattern in which the number of blocks arranged in each circumferential row is not strictly conditioned by the number of blocks present in other circumferential rows, for example in the shoulder rows. 
     Therefore, in accordance with the present invention, it is proposed a tyre for vehicle wheels comprising a tread band having a tread band pattern defined by at least two circumferential portions disposed in axial side by side relationship, at least one of which has a first geometric module repeated many times along a circumferential-extension direction of the tyre and comprising: a land portion or elongated ridge delimited by two grooves oblique to the circumferential-extension direction and divided into a plurality of intermediate blocks with respect to an axial-extension direction of the tread band, which are bounded by a plurality of cuts substantially transverse to the elongated ridge; at least two shoulder blocks associated with the elongated ridge and circumferentially aligned along a side edge of the tread band and delimited by grooves oriented transversely to the circumferential extension of the tyre. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages will become more apparent from the detailed description of a preferred but not exclusive embodiment of a tyre for vehicle wheels in accordance with the present invention. 
       This description will be set out hereinafter with reference to the accompanying drawings given by way of non-limiting example, in which: 
         FIG. 1  is a fragmentary plan view showing a tread band of a tyre made in accordance with the present invention; 
         FIG. 2  shows in enlarged scale one geometric module of the tread band pattern of a first circumferential portion of the tread band shown in  FIG. 1 ; 
         FIG. 3  shows in enlarged scale a second geometric module of the tread band pattern of a second circumferential portion of the tread band of  FIG. 1 ; 
         FIG. 4  shows a second embodiment of the tread band of  FIG. 1 ; 
         FIG. 5  shows a third embodiment of the tread band of  FIG. 1 ; 
         FIG. 6  shows a fourth embodiment of the tread band of  FIG. 1 ; and 
         FIG. 7  shows the longitudinal-section outline of a cut sectioned along line VII-VII of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Referring particularly to the above drawings, generally denoted at  1  is a tread band of a tyre made in accordance with the present invention; the remaining parts of the tyre are not highlighted since they can be made in any manner convenient for a person skilled in the art. 
     The tread band  1  has a tread band pattern  2  defined by at least two circumferential portions  3   a ,  3   b  disposed in axial side by side relationship. 
     In at least one of the circumferential portions  3   a ,  3   b , the tread band pattern is substantially defined by a first geometric module  4   a  repeated many times along the circumferential extension direction X of the tyre. 
     It is pointed out that by the term “geometric module” it is herein meant a predetermined shape that is repeated along the circumferential extension X of the tyre. Geometric figures having the same shape, although with different circumferential and/or axial sizes, are at all events ascribable to a unique geometric module. In particular, on repeating the geometric module, different circumferential sizes following each other in a predetermined sequence along the circumferential extension of the tyre can be attributed to the shape identifying the module so as to distribute the rolling noise on a wider spectrum of frequencies, according to a predetermined so-called “pitch sequence”. 
     Advantageously, the first geometric module  4   a  has at least two shoulder blocks  5  that are circumferentially aligned along a side edge  6  of the tread band  2  and bounded by grooves  7  oriented transversely to the circumferential extension of the tyre. 
     The first geometric module  4   a  further has an elongated ridge  8  delimited between two oblique grooves  9  with respect to the circumferential extension direction X. The elongated ridge  8  is divided into a plurality of intermediate blocks  10  with respect to an axial extension direction Y of the tread band  1 , bounded by cuts  11  substantially transverse to the elongated ridge  8 . 
     In the embodiment shown in  FIGS. 1 and 2 , six intermediate blocks  10  are provided in each elongated ridge  8 . However ridges  8  with a different number of blocks  10  can be made by suitably varying the sizes of the blocks  10  themselves or the length of ridge  8  in compliance with the nominal width of the tyre. 
     By way of example, each transverse groove  7  and each oblique groove  9  has a depth P1 included between 6 mm and 10 mm, and a width L1 included between 4 mm and 13 mm, measured on an outer rolling surface of the tread band  1 . The depth and/or width of the transverse grooves  7  can not be the same as that of the oblique grooves  9 . 
     Cuts  11  have a depth P2 preferably smaller than that of grooves  7 ,  9  and included just as an indication between 2 mm and 10 mm, and a width L2 included, by way of example, between 2 mm and 10 mm, and preferably lower than that of grooves  7  and  9 . 
     In addition, to give the intermediate blocks  10  greater structural steadiness to the advantage of handling, running noiselessness and wear evenness, the blocks themselves can be connected with each other by reinforcing elements  12  placed in cuts  11 . In more detail, taking into account the longitudinal section of a cut  11 , as shown in  FIG. 7 , each reinforcing element can be defined by a portion of reduced depth arranged at the central region of the respective cut  11 . The depth of cut  11  at the central region can be included, by way of example, between 1.5 mm and 9.5 mm. 
     In the embodiment herein illustrated, all intermediate blocks  10  are connected with each other by reinforcing elements  12  but the possibility of providing that only part of blocks  10  are connected with each other is not excluded. 
     Cuts  11  transverse to the elongated ridge  8  preferably comprise first cuts  11   a  substantially perpendicular to the circumferential extension X and second cuts  11   b  substantially perpendicular to the oblique grooves  9 . As a matter of fact, the transverse cuts  11  have a curved shape the concavity of which is turned in the same direction. Ascribed to each of them can be a median (meridian) line M 1  defined as a series of points spaced apart the same distance from the respective edges of the cut. 
     The second cuts  11   b  have an inclination included between 25° and 55° with respect to the axial direction Y, wherein this inclination is represented by angle α 1  formed between the median line M 1  and the axial direction Y. 
     Advantageously, the first cuts  11   a  and second cuts  11   b  are disposed in an alternate sequence along a major extension direction Z of the elongated ridge  8 , so that each of the intermediate blocks  10  has a substantially trapezoidal shape. 
     Transverse cuts  11  all having the same inclination may be also provided. 
     The oblique grooves  9  have an inclination included between 15° and 35° relative to the circumferential direction X, wherein this inclination is represented by angle α 2  formed between the median line M 2 , spaced apart the same distance from the edges  9   a  of the oblique groove  9 , and the circumferential direction X. 
     The transverse grooves  7  are slightly curved and have an inclination included between 75° and 105° relative to the circumferential direction X, wherein this inclination is represented by angle α 3  formed between the median line M 3  as defined for the transverse cuts  11  of the elongated ridge  8 , and the circumferential direction X. 
     In the embodiments shown the oblique grooves  9  each have an orientation concordant with the transverse grooves  7  and run in the extension of one of the transverse grooves  7  themselves. 
     In particular, the elongated ridge  8  has an axially external end  13  located close to the tyre shoulder and substantially in alignment, in an axial direction, with one of the shoulder blocks  5 . The axially external end  13  of the elongated ridge  8  is defined by an end block  14  having a substantially trapezoidal shape. 
     The first geometric module  4   a  further comprises an auxiliary block  15  disposed circumferentially close to the axially external end  13  of the elongated ridge  8  and substantially having a trapezoidal shape. 
     The auxiliary block  15  is bounded by a first branch  16  and a second branch  17  of the oblique groove  9  each terminating at one of the transverse grooves  7 . Preferably, both the first branches  16  and the second branches  17  are substantially aligned with one of the transverse grooves  7 , and the auxiliary block  15  is substantially aligned, in an axial direction, with one of the shoulder blocks  5 . 
     More specifically, the first branch  16  extending from an axially external end  18  of the oblique groove  9  delimits the end block  14  of the elongated ridge  8 , on one side  16   a , and the auxiliary block  15 , on the opposite side  16   b.    
     The second branch  17  extending from an intermediate point  19  located between the axially external end  18  and an axially internal end  20  of the oblique groove  9 , delimits the auxiliary block  15 , on one side  17   a , and the end block  14  of the adjacent elongated ridge  8 , on the opposite side  17   b.    
     The end block  14  and auxiliary block  15  appear as appendices of the respective shoulder blocks  5  spaced apart therefrom by a circumferential shoulder groove  21  separating the elongated ridges  8  from the shoulder blocks themselves. The shoulder groove  21  has a width included, just as an indication, between 1.5 mm and 6 mm and a depth included, by way of example, between 2 mm and 10 mm, preferably smaller than that of the transverse groove  7  over at least part of the circumferential extension of each shoulder block  5 . The first and second branches  16 ,  17  and the respective transverse grooves  7  open into the circumferential shoulder groove  21 . 
     The elongated ridge  8  further has a swollen axially internal end  22  in which at least two centre blocks  23 ,  24  are defined; said blocks are circumferentially aligned and each have a substantially trapezoidal shape. 
     The centre blocks  23 ,  24  are bounded by transverse cuts  25  converging into a circumferential separating groove  26  interposed between the circumferential portions  3   a ,  3   b  of the tread band pattern. 
     In particular, a first centre block  23  is separated from one of the intermediate blocks  10  by one of the second transverse cuts  11   b . Also associated with the first centre block  23  is a second centre block  24  separated from the first centre block  23  by one of the transverse cuts  25  converging into the circumferential separating groove  26 . Finally, the first centre block  23  is also delimited by one of the second centre blocks  24  which is circumferentially consecutive by means of one of the transverse cuts  25 . 
     Advantageously, as shown in  FIGS. 1 to 4 , the shoulder blocks  5  do not all have the same circumferential size C along the circumferential tyre extension. The elongated ridges  8  too have a varying transverse size depending on the size of the shoulder blocks  5  associated therewith. This is due to the fact that, as above mentioned, in repeating the geometric module along the circumferential tyre extension, the module shape is preferably proposed again in several different forms mainly differentiated from each other in the size of the circumferential extension so that at least one of the two shoulder blocks  5  associated with one of the elongated ridges  8  has different circumferential sizes C with respect to those of at least one of the two shoulder blocks  5  associated with at least one of the adjacent elongated ridges  8 . 
     Furthermore, the two shoulder blocks  5  associated with one individual elongated ridge  8  can have the same circumferential sizes C or different circumferential sizes C. 
     For example, denoted at  8   a  in  FIG. 1  is an elongated ridge the axially external end  13  of which is associated with a shoulder block  5  having a circumferential size C 1  greater than the circumferential size C 2  of the shoulder block  5  aligned with the auxiliary block  15  belonging to the same geometric module. In addition, denoted at  8   b  is an elongated ridge the axially external end  13  of which is associated with a shoulder block  5  having a circumferential size C 3  smaller than the circumferential size C 4  Of the shoulder block  5  aligned with the corresponding auxiliary block  15 . 
     A further elongated ridge identified with  8   c  is also provided in which the shoulder blocks  5  all have the same circumferential size C 5 . 
     The tread band  1  also has a plurality of sipes  27  formed in the different blocks  5 ,  10 ,  15 ,  23  and  24  and mainly extending in an axial direction. 
     Advantageously, each sipe  27  may extend following a sawtoothed profile the depth of which is in the range of 1.5 mm to 9.5 mm and the width of which does not exceed 1 mm. Furthermore, sipes  27  are circumferentially spaced apart from each other by a value D included between 4 mm and 8 mm. 
     The tread band  1  further has a plurality of notches  28  connecting sipes  27 . In particular, two adjacent sipes  27  are connected by at least one connecting notch  28  having a substantially circumferential extension with a depth in the range of 1 mm to 3 mm and a width in the range of 1 mm to 2 mm, measured in an axial direction. 
     The connecting notches  28  generally do not connect more than two consecutive sipes  27  and do not open into the grooves  7 ,  9  and the cuts  11  delimiting the blocks. 
     In more detail, each of the shoulder blocks  5  has a first series  29  of sipes  27  disposed according to an extension substantially parallel to the transverse grooves  7 . 
     The intermediate blocks  10  each have a second series  30  of sipes  27  disposed parallel to each other mainly in an axially-extending direction. 
     The centre blocks  23 ,  24  each have a third series  31  of sipes  27  disposed parallel to each other mainly in an axially-extending direction. 
     Finally, the end blocks  14  and auxiliary blocks  15  each have a fourth series  32  of sipes  27  disposed according to an extension substantially parallel to the transverse grooves  7 . 
     In the embodiments shown, each of the shoulder blocks  5 , end blocks  14  and auxiliary blocks  15  is provided with three or four sipes  27 . Each of the centre blocks  23 ,  24  has four or five sipes  27 . The intermediate blocks  10  each have four sipes  27 . 
     Advantageously, as shown in  FIGS. 1 to 4 , the tread band pattern  2  comprises a first circumferential portion  3   a  and a second circumferential portion  3   b  disposed in side by side relationship and spaced apart from each other by the circumferential separating groove  26 . 
     Advantageously, the separating groove  26  can be spaced apart from the equatorial plane E of the tyre ( FIGS. 1  and  4 ) towards one or the other of the tyre shoulders, by an amount for example included between 2% and 8% of the overall width of the tread band  1 . 
     In the second circumferential portion  3   b , the tread band is defined by a second geometric module  4   b  repeated many times along the circumferential tyre extension. 
     In accordance with the embodiment shown in  FIG. 1 , the first circumferential portion  3   a  of the tread band pattern  2  has the same structure as hitherto described whereas the second geometric module  4   b  of the second circumferential portion  3   b  comprises two shoulder blocks  34  and four inner blocks  35  ( FIG. 3 ). 
     Repeating the second geometric module  4   b  along the circumferential extension X gives origin to a plurality of shoulder blocks  34  arranged along a single row, and to a plurality of inner blocks  35 . 
     Also the shoulder blocks  34  and inner blocks  35  of the second geometric module  4   b  in accordance with the embodiments shown in  FIGS. 1, 3 and 4  do not all have the same circumferential size C along the tyre extension. 
     The shoulder blocks  34  of the second circumferential portion  3   b  in accordance with the preferred embodiment are circumferentially aligned along a side edge  36  of the tread band  1 , axially opposite to the side edge  6  of the first circumferential portion  3   a , and confined by grooves  37  oriented transversely of the circumferential tyre extension. 
     More specifically, the transverse grooves  37  are slightly curved and have an inclination included between 75° and 105° with respect to the circumferential direction X, wherein said inclination is represented by angle α 4  formed between the medial line M 4 , as defined for the transverse cuts  11  of the elongated ridge  8 , and the circumferential direction X itself. 
     The inner blocks  35  are distributed along at least one first circumferential row  38  separated from the shoulder blocks  34  of the second circumferential portion  3   b  by a circumferential shoulder groove  39  and are delimited by grooves  40  oriented transversely to the circumferential tyre extension. 
     Preferably, the second circumferential portion  3   b  of the tread band pattern  2  further comprises a second circumferential row  41  of inner blocks  35  disposed in axial side by side relationship with the first row  38  and separated therefrom by a circumferential groove  42 . 
     In further embodiments not shown, the tyre can be provided with more than two circumferential rows of inner blocks  35 , for example along the nominal chord of the tyre itself. 
     Just as an indication, grooves  37 ,  39 ,  40 ,  42  of the second circumferential portion  3   b  and the separating groove  26  do not necessarily have the same depth P3, said depth being preferably included between 6 mm and 10 mm. 
     The inner blocks  35  of each row  38 ,  41  can advantageously be connected with each other by reinforcing elements  12  similar to the reinforcing elements  12  used for the intermediate blocks  10  of the elongated ridges  8 . 
     In addition, the transverse grooves  37  of the shoulder blocks  34 , the circumferential grooves  39 ,  42  and separating groove  26  do not necessarily have the same width L3, said width being preferably included between 4 mm and 13 mm, measured on an outer rolling surface of the tread band  1 . 
     Finally, the transverse grooves  40  of the inner blocks  35  have a width L4 included between 2 mm and 10 mm, generally smaller than the width L3 typical of grooves  37  in the shoulder blocks  34 , as well as of the circumferential grooves  39 ,  42  and separating groove  26 . Advantageously, the transverse grooves  40  bounding the inner blocks  35  of the first row  38  are circumferentially offset with respect to the transverse grooves  37  of the shoulder blocks  34  of the second circumferential portion  3   b  and, where the second row  41  is also provided, with respect to the transverse grooves  40  bounding the inner blocks  35  of the second row  41 . 
     Between the transverse grooves  40  delimiting the inner blocks  35  are provided first grooves  40   a  that are inclined to the axial direction Y and second grooves  40   b  substantially perpendicular to the circumferential tyre extension. The first grooves  40   a  and second grooves  40   b  are disposed in an alternate sequence along the respective circumferential row  38 ,  41 , so as to give the inner blocks  35  a substantially trapezoidal shape. 
     More specifically, the transverse grooves  40  have a curved shape the concavity of which is turned in the same direction. A median line defined as the series of points spaced apart the same distance from the respective edges of the groove can be ascribed to each of said grooves. 
     The first grooves  40   a  are inclined to the axial direction Y by an angle included between 25° and 55°, wherein said inclination is represented by angle α 5  formed between the median line M 5  and the axial direction Y. 
     The second grooves  40   b  too are inclined to the axial direction Y by an angle included between 5° and 20°, wherein this inclination is represented by angle α 6  formed between the median line M 6  and the axial direction Y. 
     Preferably, the first grooves  40   a  delimiting the inner blocks  35  of the first circumferential row  38  and the first grooves  40   a  delimiting the inner blocks  35  of the second circumferential row  41  are parallel to each other. 
     Alternatively, according to an embodiment not shown, the first grooves  40   a  delimiting the inner blocks  35  of the first circumferential row  38  and the first grooves  40   a  delimiting the inner blocks  35  of the second circumferential row  41  symmetrically converge towards the circumferential groove  42  separating the first row  38  from the second row  41 . 
     The possibility of providing grooves  40  all having the same inclination is not to be excluded. 
     Advantageously, the inner blocks  35  and shoulder blocks  34  have their longitudinal sides  35   a ,  34   a , i.e. those sides substantially oriented in the circumferential direction X, inclined to the circumferential direction X itself by an angle α 7  included between 1° and 5° so as to generate widened portions  45  in the circumferential grooves  39 ,  41  belonging to the second circumferential portion  3   b  and in the separating groove  26 . The transverse grooves  40  delimiting the inner blocks  35  open into these widened portions  45 . In addition, to increase amplitude of the widened portions  45 , at least one of the corners of the inner blocks  35  facing said portion  45  is rounded off at  46  so as to offer more room for snow entrapping. 
     In accordance with the embodiment shown in  FIG. 1 , the transverse grooves  37  in the shoulder blocks  34  of the second circumferential portion  3   b  and the transverse grooves  7  of the shoulder blocks  5  of the first circumferential portion  3   a  are substantially parallel, to give origin to a tyre of the asymmetric and non-directional type. 
     Alternatively, according to a second embodiment shown in  FIG. 4 , the transverse grooves  37  of the shoulder blocks  34  of the second circumferential portion  3   b  and the transverse grooves  7  of the shoulder blocks  5  of the first circumferential portion  3   a  converge towards each other, to give origin to a tyre of the asymmetric-directional type. 
     In both the embodiments shown in  FIGS. 1 and 4  the second circumferential portion  3   b  too is provided with a plurality of sipes  27  extending according to a sawtoothed profile and mutually connected by a plurality of notches  28  in the same manner as described for the first geometric module  4   a . Sipes  27  of the second circumferential portion  3   b  have a depth included between 1.5 mm and 9.5 mm and a width not exceeding 1 mm. 
     In particular, each of the shoulder blocks  34  of the second circumferential portion  3   b  has a fifth series  47  of sipes  27  disposed substantially parallel to the transverse grooves  37  delimiting the shoulder blocks  34  themselves. The shoulder blocks  34  of the second circumferential portion  3   b  as well have circumferential sizes different from each other and are provided with three or four sipes  27  depending on their circumferential size. 
     In addition, advantageously, each of the inner blocks  35  of the first circumferential row  38  has a sixth series  48  of sipes  27  disposed parallel to each other and the extension of which is oblique to the axial direction Y and parallel to the first grooves  40   a  in the inner blocks  35  of the first circumferential row  38 . 
     Preferably, as shown in  FIGS. 1, 3 and 4 , the first row  38  has inner blocks  35  with five sipes  27 , and inner blocks  35  with four sipes  27 . 
     The inner blocks  35  of the second circumferential row  41  each have a seventh series  49  of sipes  27  disposed parallel to each other and having an extension oblique to the axial direction Y and parallel to the first grooves  40   a  in the inner blocks  35  of the second circumferential row  41 . 
     The second row  41  too has inner blocks  35  with five sipes  27 , and inner blocks  35  with four sipes  27 . 
     Finally, as can be viewed from  FIGS. 1 and 4 , the number of the shoulder blocks  34  of the second circumferential portion  3   b  is the same as the number of the inner blocks  35  of the first circumferential row  38  and as the number of the inner blocks  35  of the second circumferential row  41 , and is twice the number of the elongated ridges  8  of the first circumferential portion  3   a.    
     In accordance with a third embodiment and a fourth embodiment, shown in  FIGS. 5 and 6  respectively, the second geometric module  4   b  of the second circumferential portion  3   b  of the tread band pattern  2  is similar in structure to the geometric module  4   a  of the first portion  3   a.    
     In particular, the second geometric module  4   b  too comprises at least two shoulder blocks  5  circumferentially aligned along a side edge  36  of the tread band  1  axially opposite to the side edge  6  belonging to the first geometric module  4   a  and bounded by grooves  7  oriented transversely to the circumferential tyre extension. The second geometric module  4   b  further comprises an elongated ridge  8  delimited by two oblique grooves  9  with respect to the circumferential extension direction X and divided into a plurality of blocks  10  disposed at an intermediate position in the axial extension of the tread band  1  and delimited by a plurality of cuts  11  substantially transverse to the elongated ridge  8 . 
     In the third embodiment shown in  FIG. 5 , the oblique grooves  9  of the second geometric module  4   b  converge towards the oblique grooves  9  of the first geometric module  4   a  to form a tyre of the directional type. In the particular embodiment shown, the second geometric module  4   b  is symmetric with the first geometric module  4   a  with respect to the equatorial plane E of the tyre and is also circumferentially offset relative to the first geometric module itself. 
     In a fourth embodiment shown in  FIG. 6 , the oblique grooves  9  of the second geometric module  4   b  are substantially parallel to the oblique grooves  9  of the first geometric module  4   a , to create a tyre of the symmetric type. 
     In the particular embodiment shown, the second geometric module  4   b  is identical to the first geometric module  4   a , but rotated of 180° in the plane of the figure and circumferentially offset relative to the first geometric module itself. 
     In further embodiments not shown the geometric modules  4   a ,  4   b  of the two, circumferential portions  3   a ,  3   b , while having the same structure, can advantageously have different sizes, particularly in relation to the length of the elongated ridges  8 . 
     The present invention thus achieves the intended purposes. 
     The innovative expedients proposed by the invention, in fact, give rise to important improvements in terms of side grip of the tyre on roadways of reduced compactness, in particular on snow-covered surfaces, together with excellent qualities in terms of traction power and braking due in particular to the conformation of the first geometric module  4   a  adopted for the circumferential portion  3   a  shown in  FIG. 1 , and to the synergic co-operation with the second geometric module  4   b.    
     In fact, due to the presence of cuts and grooves transverse to the axial direction, a remarkable surface for ground contact and snow accumulation is offered when the tyre is submitted to side forces. The presence of sawtoothed sipes also helps in achieving this result. Simultaneously, the transverse cuts and transverse grooves work, together with the cuts parallel to the axial direction, in order to supply traction power and grip on braking. 
     In addition, the oblique grooves ensure an efficient water ejection that helps in avoiding occurrence of the dangerous phenomenon known as “aquaplane”. 
     It should be also understood that distribution of the blocks internal to the elongated ridges and of the shoulder blocks, as well as the inclination of same relative to the circumferential direction give rise to a noise spectrum distributed over a wide frequency band and of reduced intensity, thereby greatly reducing the rolling noise felt both internally and externally of the car. In fact, the number of points belonging to the edges of the blocks simultaneously coming into contact with the ground during rolling of the tyre is very reduced. 
     Simultaneously, the particular pattern of the first geometric module  4   a  at all events ensures a large contact surface between tyre and asphalt and consequently a performance level on dry roadways comparable with that ensured by a tread pattern expressly designed for such conditions. 
     Referring particularly to the embodiment of  FIG. 1  and to the second embodiment of  FIG. 2 , differentiation of the two circumferential portions with the inner portion characterised by elongated ridges enables an optimised tyre for high performance cars with negative camber to be obtained. In fact, the two portions embody different features and, being applied simultaneously, ensure an optimal performance in all tests for tyre evaluation. 
     The outer portion works principally during changes of direction on snow-covered roadways, in particular on leaving a bend, since the snow bears against the shoulder blocks and inner blocks and is entrapped into the labyrinth path generated by them and into the greatly inclined sipes. The inner portion which, as already specified, represents the largest part of the footprint area, ensures a good behaviour on dry or wet roads as well. 
     Finally, distribution of the cuts and grooves following different inclinations over the whole extension of the tread band enables tendency of the tyre during rolling to rotate about an axis orthogonal to the rest surface to be minimised, which effect is known in the specific field as “torque steer”. 
     In confirmation of the above mentioned advantages, two tables are reproduced hereinafter which relate to comparison tests between the tyre (P) of the present invention and three different tyres of the known art (Pr, P1, P2) having the same sizes 205/55 R16. Tyre Pr is a reference tyre produced by the Applicant and has the same structure and elastomer composition, in the different component elements thereof, of the inventive tyre. Tyres P1 and P2 are two reference tyres representing the two best tyres available from competitor firms and presently on the market. 
     The tyres were tested both on a snow-covered roadway and a dry road, using the same motor-vehicle and under the same environmental conditions. In particular, tests were conducted utilising a BMW 328i car (rear-wheel drive) and an Audi A3 1.8T car (front-wheel drive). 
     The values reproduced in the following tables represent a mean value between those obtained in several test sessions (5-6 tests, for example) using both the above mentioned cars. 
     In particular, tyres were submitted to instrument tests on traction, braking and slalom on a snow-covered roadway; to braking tests on a dry roadway; to noise tests; to aquaplane tests on a bend and on a straight stretch. 
     The above tyres were further submitted to subjective tests on traction, braking and handling on a snow-covered roadway; to handling tests on a dry and a wet roadway; and to noise tests, writing down the test drivers&#39; subjective evaluations (expressed through a point system). 
     Table 1 refers to instrument tests, whereas Table 2 reproduces the test drivers&#39; subjective evaluations. 
     The traction tests on a snow-covered roadway were conducted carrying out first-gear standing starts. With reference to Table 1, the maximum traction force of tyres P, P1, P2 was measured and expressed as a percentage of the maximum traction force of the reference tyre Pr. 
     Braking tests on a snow-covered roadway were carried out with deceleration from 50 to 5 km/h by using both the antilock braking system (ABS) and locked-wheel system. 
     Braking tests on dry asphalt were conducted with decelerations from 100 to 5 km/h by using the ABS system. 
     The average deceleration of tyres P, P1, P2 was measured and expressed as a percentage of the maximum deceleration of the reference tyre Pr. 
     The slalom test on a snow-covered roadway was conducted between ten traffic cones placed at a distance of eighteen meters from each other and at a speed included between 35 and 45 km/h; the maximum side acceleration of tyres P, P1, P2 during the slalom test was measured and expressed as a percentage of the maximum acceleration of the reference tyre Pr. 
     The aquaplane test on a straight stretch was carried out on a smooth asphalt stretch (100 m long, for example) covered with a water layer of constant depth (7 mm). The water layer was restored after each passage so as to ensure the same conditions during each test. The test was conducted by making the vehicle to enter the asphalt stretch at a constant speed (70 km/h, for example) under optimal grip conditions and by progressively accelerating the vehicle until reaching conditions of complete grip loss. During the test the speed at which all wheels lose grip was measured and this speed was expressed as a percentage of the maximum speed of the reference tyre Pr. 
     The aquaplane test on a bend was carried out on a curvilinear path of constant radius (of 100 m) the final stretch of which (over a portion 20 m long, for example) was covered with a water layer of constant depth (7 mm deep). The test was conducted at a constant speed and repeated for different speed values. The maximum speed and maximum acceleration of the car on the bend were measured before grip loss and these values were expressed as a percentage of the maximum speed and maximum acceleration of the reference tyre Pr. 
     The outdoor noise test (the term “outdoor” being used to distinguish it from the indoor noise test carried out in a semi-anechoic chamber) was conducted in order to evaluate both the internal noise of the car and the external noise of same. 
     In order to evaluate the internal noise of the car, the test consisted in driving the car at a predetermined constant speed and subsequently making the car to run a straight stretch with a switched-off engine and in neutral (this test is called “coast by noise”). The test is repeated driving the car at different speeds. When cars were run on this straight stretch with a switched-off engine and in neutral, the internal noise of the car was instrumentally measured by use of a so-called “acoustic head” simulating the driver/passenger position within the car by means of microphones positioned at the ear height. The test further consisted in a subjective evaluation (expressed through a point system) carried out by the test driver having the task of evaluating the noise level perceived within the car. 
     This test was further conducted making the car to travel over said straight stretch at constant speed, without switching the engine off. In addition, this test was repeated on different asphalt typologies. 
     In order to evaluate the noise external to the car, the test consisted in causing the car to run over a straight stretch provided with microphones disposed on opposite sides of said stretch. 
     The test was conducted following two different modalities: a) imposing an acceleration to the car while said car was covering the above mentioned stretch (this test is called “pass by noise”); b) bringing the vehicle to a constant speed, by switching the engine off and putting it in neutral at the above mentioned straight stretch. 
     The handling tests were conducted on a track and the test driver simulated some characteristic manoeuvring (change of lane, entering a bend, leaving a bend, for example) carried out at constant speed, in acceleration and in deceleration. Then test driver judged the tyre behaviour and assigned a score depending on the tyre performance during said manoeuvring. 
     The average scores given by several test drivers to the different performance tests taken into account are reproduced in Table 2. 
     In the tables it is possible to see that the tyre of the present invention has higher, scores than the tyres of the known art. 
     The values reproduced in the tables are expressed in relation to the value of 100 given to the reference tyre Pr. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Instrument tests 
               
            
           
           
               
               
               
               
               
            
               
                   
                 P 
                 Pr 
                 P1 
                 P2 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Traction on snow 
                 105 
                 100 
                 101 
                 98 
               
               
                   
                 Braking on snow 
                 102 
                 100 
                 98 
                 100 
               
               
                   
                 Slalom on snow 
                 106 
                 100 
                 100 
                 97 
               
               
                   
                 Braking on dry asphalt 
                 101 
                 100 
                 101 
                 100 
               
               
                   
                 Aquaplane on a bend 
                 104 
                 100 
                 101 
                 98 
               
               
                   
                 Aquaplane in straight 
                 103 
                 100 
                 102 
                 97 
               
               
                   
                 stretch 
               
               
                   
                 Outdoor noise 
                 107 
                 100 
                 95 
                 98 
               
               
                   
                 (internal noise) 
               
               
                   
                 Outdoor noise 
                 105 
                 100 
                 98 
                 100 
               
               
                   
                 (external noise) 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Subjective tests 
               
            
           
           
               
               
               
               
               
            
               
                   
                 P 
                 Pr 
                 P1 
                 P2 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Traction on snow 
                 108 
                 100 
                 101 
                 99 
               
               
                   
                 Braking on snow 
                 103 
                 100 
                 98 
                 101 
               
               
                   
                 Handling on snow 
                 108 
                 100 
                 102 
                 102 
               
               
                   
                 Handling on a dry 
                 105 
                 100 
                 98 
                 100 
               
               
                   
                 roadway 
               
               
                   
                 Handling on a wet 
                 105 
                 100 
                 99 
                 98 
               
               
                   
                 roadway 
               
               
                   
                 Outdoor noise on 
                 108 
                 100 
                 96 
                 99 
               
               
                   
                 smooth/coarse asphalt