Abstract:
A high-performance tire for a motor vehicle includes a carcass and tread band. The tire may be, for example, of the asymmetrical or directional type. The tread band includes a pattern including a central region, first and second shoulder regions, and first and second circumferential grooves. The first circumferential groove divides the first shoulder region from the central region, while the second circumferential groove divides the central region from the second shoulder region. The shoulder regions include shoulder blocks, separated from each other by transverse grooves, but joined to each other along axially inner ends of the shoulder blocks by respective circumferential portions. The central region includes rows of blocks and first and second annular projections or a central annular projection. The blocks of the central region, the shoulder blocks, the circumferential grooves, the transverse grooves, and the one or more annular projections help define the tread pattern.

Description:
This application is a continuation application of International Application No. PCT/EP00/05994, filed Jun. 28, 2000, in the European Patent Office; additionally, Applicants claim the right of priority under 35 U.S.C. § 119(a)–(d) based on patent application Ser. No. MI99A 001447, filed Jun. 30, 1999, in the Italian Patent Office; further, Applicants claim the benefit under 35 U.S.C. § 119(e) based on prior-filed, now abandoned provisional application No. 60/155,142, filed Sep. 22, 1999, in the U.S. Patent and Trademark Office the contents of all of which are relied upon and incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a high-performance tire for a motor vehicle. 
   2. Description of the Related Art 
   British Patent Document No. GB 1,212,795 discloses a radial tire having a tread provided with a central circumferential groove, two circumferential side grooves, one on each side of the central groove, disposed substantially equidistantly between the central groove and the edges of the tread, and transverse grooves extending from opposite side of the central groove toward, but not as far as, one of the side grooves. 
   In said tread, the circumferential side grooves are flanked on both sides by circumferential ribs. 
   The invention disclosed by this document has the aim of reducing the stiffness of the tread. 
   U.S. Pat. No. 4,446,901 discloses a heavy-duty pneumatic radial tire comprising a carcass of a substantially radial construction composed of at least one rubberized ply layer containing cords embedded therein and a belt superimposed about said carcass for stiff reinforcement beneath a tread and composed of at least two rubberized ply layers each containing metal cords embedded therein, said metal cords of which being crossed with each other at a relatively small angle with respect to the circumferential direction of the tire, and said tread being provided with a plurality of continuous or discontinuous zigzag circumferential ribs defined along the widthwise direction of the tire by at least three substantially zigzag main grooves extending circumferentially of said tread, said main grooves comprising one or a pair of central circumferential grooves located at a substantially central region of said tread and a pair of outside circumferential grooves defining each of the outermost ribs of said tread. In this tire, the central circumferential groove has such a symmetrical cross-sectional shape with respect to a centerline of said groove that an inclination angle of a groove wall of said groove with respect to a normal line drawn from an outer surface of said tread and passing an edge of said groove in the cross-section perpendicular to said groove wall is made relatively large in a region extending from the groove bottom to at least 50% of groove depth, and the outside circumferential groove has such an unsymmetrical cross-sectional shape with respect to a centerline of said groove that an inclination angle of an outer groove wall of said groove in the rotation axial direction of the tire is made relatively large, and an inclination angle of an inner groove wall of said groove in a region extending from the outer surface of said tread to at least 10% of groove depth is made smaller than that of said outer groove wall. 
   U.S. Pat. No. 4,773,459 discloses a low-section tire having a tread pattern comprising 5 a plurality of main grooves substantially extending in a circumferential direction of the tire in parallel to each other and a plurality of transverse grooves intersecting the main circumferential grooves at an inclination angle also in parallel to each other, said transverse grooves are formed in upwardly-sloping, raised-bottom fashion along a longitudinal direction thereof between two main grooves, bottoms of said transverse grooves are raised in a substantially equilateral-triangle shape in cross-section in such a way that a depth of said transverse grooves is shallowest at substantially the middle portion of each transverse groove and the deepest at the bottom of said main circumferential groove. 
   SUMMARY OF THE INVENTION 
   In the present description and in the claims, the term “continuous track” denotes a portion of tread band of a tiredelimited continuously on only one of its sides, and the term “sipe” denotes a notch having a width of not more than 1 mm. 
   None of said documents recognizes the problem of the “saw tooth” wear arising in a tire, particularly on the edges of the transverse grooves of the shoulders. This problem has been resolved by a high-performance tire according to claim  1 . 
   In one embodiment, said continuous lateral wall of said circumferential groove has an inclination in the range from approximately 14° to 24° with respect to said centre-line axis and a bottom radius R within a range from approximately 2 mm to 5 mm, while said facing lateral wall has an inclination in the range from approximately 3° to 10° with respect to said centre-line axis and a bottom radius R 1  in the range from approximately 4 mm to 7 mm. 
   Advantageously, said continuous lateral wall of said circumferential groove has an inclination of approximately 19° with respect to said centre-line axis and a bottom radius R of approximately 3.5 mm, while said facing lateral wall has an inclination of approximately 5° with respect to said centre-line axis and a bottom radius R 1  of approximately 5 mm. 
   Preferably, at least one of said shoulder blocks has a sipe which is approximately transverse with respect to an equatorial plane. 
   Advantageously, said central region comprises at least a first and a second circumferential row of central blocks, delimited by one of said circumferential grooves and by another deep circumferential groove. 
   Preferably, said central blocks are of approximately rhomboid shape. 
   Advantageously, said central blocks are approximately cusp-shaped. 
   Preferably, said central region also comprises a third circumferential row of inner central blocks, adjacent to an annular projection, said third row of blocks and said projection being delimited by said other circumferential grooves. 
   Advantageously, said inner central blocks have an approximately semi-parabolic shape. 
   The tireaccording to the invention provides high performance, both when it is new and when it is partially worn. This high performance consists primarily in a high plastic and acoustic travelling comfort and a high resistance to aquaplaning, both in straight travel and when cornering, together with good handling properties on dry and wet ground. 
   In particular, the presence of a continuous track which joins the shoulder blocks reduces the appearance of the typical irregular and premature deformations known as “saw tooth” wear phenomenon on the edges of the transverse grooves and of the adjacent circumferential groove during the rolling of the tire, and thus improves its mileage yield. 
   Moreover, the invention makes it possible to control certain design characteristics of a tire, such as the possibility of optimizing the flow and consequent distribution of the tread compound along the crown of the tire. 
   Therefore, the invention makes it possible to control certain behaviour characteristics of a tire, particularly a high-performance tire, such as the possibility of controlling the wear degree and rate of the tread band in use, as well as the roadholding in both dry and wet conditions, the plastic comfort and/or quietness of running in severe conditions of use at high running speeds. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the invention will now be illustrated with references to embodiments illustrated by way of example and without restriction in the attached figures, in which 
       FIG. 1  is a perspective view of a tire according to the invention; 
       FIG. 2  is a partial plan view of a tread of the tire shown in  FIG. 1 ; 
       FIG. 3  is a view in partial section, in a radial plane, of the tire shown in  FIG. 1 ; 
       FIG. 4  is a perspective view of another tire according to the invention; 
       FIG. 5  is a partial plan view of a tread of the tire shown in  FIG. 4 ; 
       FIG. 6  is a view in partial section, in a radial plane, of the tire shown in  FIG. 4 ; 
       FIGS. 7 and 8  are diagrams which show the variation of the noise level as a function of speed, measured in a vehicle fitted with tires according to the invention and with conventional tires; 
       FIG. 9  shows the profile of blocks of a tread of a tire according to the invention along an axial sequence of meridian planes, reconstructed by a laser beam after a certain period of use. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a high-performance tire  1  for a motor vehicle. Tyre  1  is of the asymmetrical type. In other words, it has a tread pattern that appears different (i.e. asymmetric) on one side of equatorial plane  10  from the other side ( FIG. 2 ). 
   The structure of the tire is of the conventional type and comprises a carcass, a tread band located on the crown of said carcass, a pair of axially superimposed sidewalls terminating in beads reinforced with bead wires and corresponding bead fillers, for securing said tire to a corresponding mounting rim. The tire preferably also comprises a belt structure interposed between the carcass and the tread band. More preferably, the tire of the type with a markedly flattened section, for example in the range from 0.65 to 0.30, where these figures express the percentage value of the ratio between the height of the cross right section of the tire and the maximum chord of said section. In the art this ratio is usually referred to as H/C. 
   The carcass is reinforced with one or more carcass plies fixed to said bead wires, while the belt structure comprises two belt strips, formed from lengths of rubberized fabric incorporating metal cords, parallel to each other in each strip and crossing over those of the adjacent strips, preferably inclined symmetrically with respect to the equatorial plane, and radially superimposed on each other. Preferably, the carcass also comprises a third belt strip, in a radially outermost position, provided with cords, preferably textile and even more preferably made from heat-shrinkable material, orientated circumferentially, i.e. at zero degrees with respect to said equatorial plane. 
   Tire  1  has a tread  2  made from a predetermined compound, provided with deep circumferential grooves  3 ,  4 ,  5  and  6 . Grooves  3  and  6  divide a central region  7  of the tread from two shoulder regions  8  and  9 , located respectively on the left and on the right of equatorial plane  10 . 
   Central region  7  comprises three circumferential rows of blocks  11 ,  12  and  13 . Shoulder region  8  comprises a circumferential row of blocks  14  and shoulder region  9  comprises a circumferential row of blocks  15 . 
   The row of blocks  14  comprises shoulder blocks  20 , of approximately rectangular shape, separated from each other by transverse grooves  21 . Each block  20  has a sipe  23  which is approximately transverse with respect to equatorial plane  10  and is aligned with a transverse recess  24  towards the outer edge of the tread. Blocks  20  are joined at one end by a continuous annular track  22  which terminates in a continuous wall  103  which forms a lateral wall of groove  3 . 
   The row of blocks  11  is delimited by circumferential grooves  3  and  4 . Row  11  comprises outer central blocks  26  of an approximately rhomboid shape, separated from each other by transverse grooves  27 . Blocks  26  are divided into three portions  26   a ,  26   b  and  26   c . The two portions  26   a  and  26   b  are separated by an approximately transverse sipe  28 , are axially adjacent to third portion  26   c  and are separated from the latter by a circumferential recess  29 . Blocks  26  terminate in walls  30  which form a notched lateral wall  203  of groove  3 . 
   For example, groove  3  has a width of approximately 10.5 mm and a depth of approximately 8 mm and its lateral walls  103  and  203  are inclined at approximately 5° with respect to a centre-line axis, and are joined by a bottom radius of approximately 4.5 mm. 
   The row of blocks  12  is delimited on one side by circumferential groove  4  and is adjacent, on the opposite side, to an annular projection  35 , which in turn is delimited by circumferential groove  5 . Row  12  comprises inner central blocks  36  of approximately semi-parabolic shape, separated from each other by approximately transverse grooves  37 , and separated from projection  35  by a circumferential groove  38  which has a half-wave harmonic course. 
   The row of blocks  13  is delimited by circumferential groove  6  and is adjacent to an annular projection  40 , which, in turn, is delimited by annular groove  5 . Row  13  comprises outer central blocks  41  of approximately rhomboid shape, separated from each other by transverse grooves  42 . Each block  41  is separated from projection  40  by a circumferential recess  43 . Blocks  41  terminate in walls  44  which form a notched lateral wall  206  of groove  6 . 
   The row of blocks  15  comprises shoulder blocks  120 , of approximately rectangular shape, separated from each other by transverse grooves  121 . Each block  120  has an approximately transverse sipe  123 , aligned with a transverse recess  124  towards the outer edge of the tread. Blocks  120  are joined at one end by a continuous annular track  122  which terminates in a continuous wall  106  which forms a lateral wall of groove  6 . 
   Preferably the two shoulder regions have different widths from each other; for example, the narrower shoulder  8  (on the vehicle side) has a width of approximately 25% of the total width of the tread, while the wider shoulder  9  (preferably on the outer side) has a width of approximately 28% of the total width of the tread. 
   Continuous lateral wall  106  of groove  6  has a profile, in the radial plane ( FIG. 3 ), which is more inclined with respect to a centre-line axis of the groove, in other words which is more bulky, than the profile of facing lateral wall  206 . For example, groove  6  has a width of approximately 10.5 mm and a depth of approximately 8 mm, and wall  106  has an inclination of approximately 19° with respect to its centre-line axis and a bottom radius R of approximately 3.5 mm, while wall  206  has an inclination of approximately 5° with respect to the centre-line axis and a bottom radius R1 of approximately 5 mm. 
   The presence of continuous track  122  imparts optimal rolling to tire  1 , since it prevents the formation, as a result of wear, of “saw tooth” wear deformations on the edges of transverse grooves  121  and of sipes  123 , which would give rise to noise and discomfort in travel. 
   The particular shape of groove  6 , located on the outer edge of the tread, i.e. on the side which is on the exterior of the vehicle when fitted, also makes it possible to improve the wear-resistance of the shoulder of the tire during severe use in cornering (at high speeds and radii), thus significantly reducing premature wear, particularly of the “saw tooth” wear phenomenon type, on the edges of the circumferential groove. This minimizes the usual degradation of the performance of the tire due to wear. 
   Transverse grooves  27  of the row of blocks  11  have a bottom wall  127  ( FIG. 3 ) which has a cambered profile in a radial plane. 
   Preferably, this profile is of the curvilinear type and extends approximately along an arc whose shape is chosen in such a way as to promote the migration of the compound according, for example, to the viscosity of said compound, which is preferably in the range from 40 ML(1+4) to 110 ML(1+4) (Mooney viscosity), according to information which will be familiar to those skilled in the art. Preferably, this curvilinear profile has a radius of curvature in the range from 25 to 110 mm. 
   Transverse grooves  37  of the row of blocks  12  have a bottom wall  137  with an inclined profile decreasing towards circumferential groove  4 . Preferably, this inclined profile has a moderately curvilinear form with a radius of curvature in the range from 90 to 120 mm. 
   Also transverse grooves  42  of the row of blocks  13  have a bottom wall  142  with an inclined profile decreasing towards groove  6 . Preferably, said inclined profile has a moderately curvilinear form with a radius of curvature in the range from 90 to 120 mm. 
   This configuration with variable depths of the profiles of bottom walls  127 ,  137  and  142  of transverse grooves  27 ,  37  and  42  promotes a uniform distribution of the tread compound during vulcanization in an suitable mould, since it facilitates the longitudinal migration of said tread compound along the pitch sequence of the pattern. In this way, non-homogenous and unbalanced distributions of the masses are prevented. 
   For example, in a 225/40 ZR 18 tire, tread  2  has a width L of approximately 243 mm, shoulder region  8  has a width of approximately 61.5 mm, and shoulder region  9  has a width of approximately 67.5 mm. 
   Each block  120  of row  15  is produced by rotating of 180° a block  20  of row  14  about an axis lying in the plane of the sheet and passing through equatorial plane  10 . The block thus produced is then turned over through 180° with respect to an axis lying in the plane of the sheet and perpendicular to equatorial plane  10 . 
   The pattern of tread  2  has four different pitch values distributed along the extension of the tread according to a predetermined pitch sequence. Each pitch represents the length, in a predetermined circumferential direction, of one block and of the adjacent transverse groove; for example, a block  20  or  120  and adjacent groove  21  or  121 . The pitch sequence is produced according to the invention of U.S. Pat. No. 5,371,685, in order to modulate the noise emitted by the tire and, in particular, to avoid a siren effect (the presence of resonant phenomena, particularly at high frequency). 
     FIG. 4  shows a high-performance tire  51  for a motor vehicle. Tyre  51  is of the directional type in other words, it has a tread pattern which is symmetrical about equatorial plane  50  ( FIG. 5 ). 
   Tyre  51  has a tread  52  made from a predetermined compound, provided with deep, circumferential grooves  53 ,  54 ,  55  and  56 . Grooves  53  and  56  divide a central region  57  of the tread from two shoulder regions  58  and  59 , located respectively on the left and on the right of equatorial plane  50 . Circumferential grooves  54  and  55  have a half-wave harmonic course. 
   Central region  57  comprises two circumferential rows of blocks  60  and  61 . Shoulder region  58  has a circumferential row of blocks  62  and shoulder region  59  has a circumferential row of blocks  63 . 
   The row of blocks  62  comprises shoulder blocks  64 , of approximately rectangular shape, separated from each other by transverse grooves  65 . Each block  64  has an approximately transverse sipe  68  aligned with a transverse recess  69  towards the outer edge. Blocks  64  are joined at one end by a continuous annular track  66  which terminates in a continuous wall  153  which forms a lateral wall of groove  53 . 
   The row of blocks  60  is delimited by circumferential grooves  53  and  54 , and comprises central blocks  70  which are approximately cusp-shaped. Blocks  70  are separated from each other by approximately transverse grooves  71  and are divided into two portions  70   a  and  70   b  by a curved notch  72 . Portion  70   a  has an approximately transverse sipe  73 . Blocks  70  terminate in walls  74  which form a notched wall  253  of groove  53 . Transverse grooves  71  have a bottom wall  271  with an inclined profile decreasing towards circumferential groove  53 . 
   Continuous lateral wall  153  of groove  53  has a profile in a radial plane which is more inclined with respect to a centre-line axis of the groove, in other words which is more bulky, than the profile of facing lateral wall  253 . For example, groove  53  has a width of approximately 12 mm and a depth of approximately 8 mm, and the wall  153  has an inclination of approximately 14° with respect to a centre-line axis and a bottom radius R of approximately 4.5 mm, while wall  253  has an inclination of approximately 5° with respect to the centre-line axis. 
   Central region  57  also comprises two annular projections  75  and  76  located on the left and on the right of equatorial plane  50 . Projection  75  is delimited by half-wave annular groove  54  and by a circumferential recess  77 . Projection  76  is delimited by circumferential recess  77  and by half-wave annular groove  55 . 
   The row of blocks  61  is delimited by circumferential grooves  55  and  56 , and comprises central blocks  170  which are mirror images of and out of alignment with blocks  70 . Blocks  170  are separated from each other by transverse grooves  171  and are divided into two portions  170   a  and  170   b  by a thin curved notch  172 . Portion  170   a  has an approximately transverse sipe  173 . Blocks  170  terminate in walls  174  which form a notched wall  256  of groove  56 . Transverse grooves  171  have a bottom wall  371  with an inclined profile decreasing towards circumferential groove  56 . 
   The row of blocks  63  comprises shoulder blocks  164  which are mirror images of and out of alignment with blocks  64 . Shoulder blocks  164  are of approximately rectangular shape and are separated from each other by transverse grooves  165 . Each block  164  has an approximately transverse sipe  168  aligned with a transverse recess  169  towards the outer edge. Blocks  164  are joined at one end by a continuous annular track  166  which terminates in a continuous wall  156  which forms a lateral wall of groove  56 . 
   Continuous lateral wall  156  of groove  56  has the same profile (identical and a mirror image) and the same dimensions as continuous lateral wall  153  of groove  53 . 
   For example, in a 225/40 ZR 18 tire, tread  52  has a width L of approximately 237 mm and shoulder regions  58  and  59  have each a width of approximately 73 mm. 
   Specimens of tires  1  and  51  were made and were shown to have excellent performance (comfort, quietness, resistance to aquaplaning and to wear) by tests of comparison with conventional tires conducted both in the laboratory (indoor tests) and on the road and track. 
   The tires according to the invention were compared with the PZero tire made by the Applicant, which at present is considered to be the reference standard by motor vehicle manufacturers, and with equivalent tires which represent commercially available alternative types of both asymmetric and directional tires. Furthermore, the tire of the present invention has been compared with two commercial tires selected among the most sold ones. The first was an asymmetric tire referred to hereinafter as C 1  and the second was a directional tire referred to hereinafter as C 2 . 
   The vehicle used for the tests was a Porsche Carrera 996 fitted, depending on the type of test to be conducted, with four asymmetric tires or, alternatively, with directional tires on the front wheels and asymmetric tires on the rear wheels. The tires fitted on the front wheels were of the 225/40 ZR 18 type, and those fitted on the rear wheels were of the 265/35 ZR 18 type. 
   The tires were fitted on standard rims and were inflated to the nominal operating pressure. 
   Comfort Test with Totally Asymmetric Fitting. 
   Given that the used assessment scale ran from −3 to +3 and represented a subjective judgement expressed by the test driver who tested and compared in sequence all the fittings on a route that was mixed in terms of the type of road layout (motorway, ordinary road, straight, twisting), the road surface (smooth, rough) and the speed of travel, the results were as follows: 
   
     
       
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
                 
             
             
                 
               Invention 
               PZero 
               C 1   
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
                 
               Plastic comfort 
               1.2 
               1.2 
               0.6 
             
             
                 
               Acoustic comfort 
               1 
               0.6 
               1 
             
             
                 
                 
             
           
        
       
     
   
   In this type of test, plastic comfort was evaluated according to the set of sensations perceived by the test driver with respect to the tire&#39;s capacity for absorbing rough areas of the road surface. 
   Also, in this type of test, “acoustic comfort” denotes the noise perceived by the test driver inside the passenger compartment. 
   Obstacle Test. 
   The test consisted in making the tire, loaded with the nominal operating load, to rotate against a road wheel mounted with a vertical axis of rotation and rotating at a speed in the range from 150 km/h to 0 km/h. The road wheel carries on its radially outer surface a bar of parallelepipedal shape of predetermined dimensions which forms the obstacle, The tire is fitted on a fixed dynamometer hub which measures the excitation (force at the hub) that the obstacle produces on the tire. 
   The test yielded the three-dimensional diagrams of the amplitude of the force as a function of speed and frequency. Areas which could be characterized by ranges of speed and frequency were selected from these diagrams and the root mean square value of amplitude (expressed in kg) which forms a parameter predicting the plastic comfort characteristics of the tire was calculated for each of these areas. 
   
     
       
             
           
             
             
             
             
           
             
           
             
             
             
             
           
         
             
                 
             
           
           
             
               a) Asymmetric tyre 
             
           
        
         
             
                 
               Root mean square value 
               Invention 
               C 1   
             
             
                 
                 
             
             
                 
               Radial 
               45 
               48 
             
             
                 
               Longitudinal 
               53 
               62 
             
             
                 
                 
             
           
        
         
             
               b) Directional tyre 
             
           
        
         
             
                 
               Root mean square value 
               Invention 
               C 2   
             
             
                 
                 
             
             
                 
               Radial 
               44 
               50 
             
             
                 
               Longitudinal 
               51 
               61 
             
             
                 
                 
             
           
        
       
     
   
   The range of measurement of the root mean square value in the radial direction of the tire was from 20 Hz to 40 Hz with a speed decreasing from 120 km/h to 10 km/h. 
   The range of measurement of the root mean square value in the longitudinal direction of the tire was from 60 Hz to 140 Hz with a speed decreasing from 120 km/h to 10 km/h. 
   In the obstacle test, the assessment expressed by the test driver in the evaluation of the plastic comfort improved as the root mean square value, such as that of the tires according to the invention, decreased. 
   Straight-Line Aquaplaning Test. 
   The test was conducted on a straight section of smooth asphalt of predetermined length with a film of water of predetermined constant depth which was automatically restored whenever the test vehicle passed through it. In a first step, the speed (km/h) at which the tires started to lose adhesion was measured (V 1 ); in a second step, the speed (km/h) at which there was total loss of adhesion was measured (V 2 ). 
   
     
       
             
           
             
             
             
             
             
           
             
           
             
             
             
             
             
           
         
             
                 
             
           
           
             
               a) Asymmetric tyre 
             
           
        
         
             
                 
                 
               Invention 
               PZero 
               C 1   
             
             
                 
                 
             
             
                 
               V1 
               86.5 
               83 
               86 
             
             
                 
               V2 
               90.5 
               87 
               90.5 
             
             
                 
                 
             
           
        
         
             
               b) Directional tyre 
             
           
        
         
             
                 
                 
               Invention 
                 
               C 2   
             
             
                 
                 
             
             
                 
               V1 
               87 
                 
               87.5 
             
             
                 
               V2 
               92.5 
                 
               91 
             
             
                 
                 
             
           
        
       
     
   
   Cornering Aquaplaning Test. 
   The test was conducted on a section of route with smooth and dry asphalt on a bend of constant radius having a predetermined length and having, in a final section, an area of predetermined length covered with a film of water of predetermined thickness. 
   During the test, the maximum centrifugal acceleration and the maximum speed of the vehicle corresponding to complete aquaplaning were measured. The table shows the values of acceleration and speed expressed as a percentage, the value for the reference tire (PZero) being set at 100 in each case. 
   
     
       
             
           
             
             
             
             
             
           
             
           
             
             
             
             
             
           
         
             
                 
             
           
           
             
               a) Asymmetric tyre 
             
           
        
         
             
                 
                 
               Invention 
               PZero 
               C 1   
             
             
                 
                 
             
             
                 
               Max. acceleration 
               109 
               100 
               113 
             
             
                 
               Max. speed 
               106 
               100 
               105 
             
             
                 
                 
             
           
        
         
             
               b) Directional tyre 
             
           
        
         
             
                 
                 
               Invention 
               PZero 
               C 2   
             
             
                 
                 
             
             
                 
               Max. acceleration 
               122 
               100 
               111 
             
             
                 
               Max. speed 
               110 
               100 
               106 
             
             
                 
                 
             
           
        
       
     
   
   Noise Test. 
   Tests were conducted in a chamber acoustically insulated from the exterior (semi-anechoic chamber) with a Porsche car, as specified above, fitted first with new tires according to the invention and then with new commercial comparison tires. 
     FIGS. 7 and 8  show the graphs of noise inside the vehicle (dB(A)) as a function of the decreasing speed from 180 to 20 km/h, for a front left-hand tire and a rear left-hand tire respectively. More particularly, the curve A relates to the commercial comparison tire and the curve B relates to the tire according to the invention. 
   Noise tests on the road were carried out on the same vehicle fitted with the aforesaid new tires, and the results were expressed according to the subjective evaluation of the test driver. The evaluation of the tires according to the invention and the commercial comparison ones was 7, where the limit of acceptability of new tires is 6. 
   The noise test on the road was repeated, only for the vehicle fitted with the tires according to the invention, at successive mileage intervals, with the following results:
         after 3,240 km, the noise level was 6.5;   after 6,840 km, the noise level was 6;   after 10,800 km, the noise level was 6.       

   At this point the tires were returned to the semi-anechoic chamber, where the noise values shown by curves C of  FIGS. 7 and 8  were measured. 
   The data confirm that the tire according to the invention, in spite of degradation, maintains a noise level equal to the threshold of acceptability of new tires, even after 10,800 km of use. 
   During this period of use, it was also found that the wear, particularly on the shoulders, was considerably reduced: the tire was found to be practically free of signs of premature and uneven wear, specifically of the “saw tooth” wear phenomenon type. 
   In particular, the measurements of tread wear were carried out at the same time as the noise tests and the results are shown in the attached graphs ( FIG. 9 ) which represent the profile of the blocks, along an axial sequence of meridian planes, reconstructed by a laser beam. The measurements shown in  FIG. 9  were made after 10,800 km of use of the 225/40 ZR 18 tire. The first two profiles relate to the blocks of the right-hand shoulder, the profiles of the third to the sixth relate to the blocks of the central rows, and the last two profiles relate to the blocks of the left-hand shoulder. 
   Each graph shows a portion of the circumferential extension of the tire where it will be noted that the decrease of the height of the blocks due to wear takes place in a practically uniform way on the periphery of each block and in all of the blocks.