Motorcycle tires

This invention concerns a tire especially for motorcycles, having a textile carcass that comprises at least one pair of cord plies. Each ply has a plurality of cords. The cords are parallel to each other, crossed with those of the adjacent plies and are symmetrically inclined with respect to the circumferential direction, preferably at an angle between 50.degree. and 65.degree. to the midcircumferential plane, measured on the tire crown zone. The tire also has an annular reinforcing structure between the carcass and the tread, comprising at least one pair of textile cord strips, the cords of said strips being crossed with each other and symmetrically inclined with respect to the circumferential direction, at an angle comprised between 18.degree. and 25.degree., measured also on the crown of the tire.

BACKGROUND OF THE INVENTION 
The present invention is directed to tires for vehicle wheels, and more 
particularly to tires for motorcycles. 
These types of tires must have a very special structure for supporting 
conditions of usage that are quite different from those to which normal 
motor vehicle tires are subjected. It is enough, for example, to cite the 
fact that these tires must be capable of traveling at quite high camber 
angle, normally 40.degree.-45.degree., but even over 55.degree., as 
compared to the maximum values of 3.degree. or 4.degree. for usual motor 
vehicle tires. 
Therefore, this requirement involves, for those tires used on motorcycles, 
the need for having treads that are comparatively wider, or rather more 
enveloping, than the treads of motor vehicle tires, and with there being a 
pronounced curvature in the crown, i.e., a pronounced curvature of the 
tread at the shoulders that is contrary to what is found in other tires, 
whose treads are more flattened when built to have a reduction in the 
section-height/section-width ratio, commonly known as the H/C or aspect 
ratio. 
Moreover, a high stiffness is required in the sidewall for the purpose of 
supporting the vehicle during cornering with these high camber angles, and 
for conferring to the tire a greater directional capacity and a lateral 
stability during straightaway running at a high speed. 
All these difficulties are pushed to the extreme in the instance of 
motorcycle tires for racing on roads or tracts, where their performance is 
exploited to the maximum limit (camber angle up to 56.degree.), i.e., 
where the tires are always utilized at the threshold of the critical 
conditions of usage. 
For all these reasons, to date tires for motorcycles have only been able to 
utilize crossed-ply carcasses, i.e., with pairs of cord plies crossed 
together, at low angular values (20.degree.-30.degree.) with respect to 
the circumferential direction, since radial carcasses have proved to be 
absolutely unsuitable because of their excessive lateral instability in 
addition to the great flexibility of their sidewalls. 
SUMMARY OF THE INVENTION 
The applicant has now invented a new carcass structure that can be called 
"mixed" because, although not responding to the characteristics of the 
crossed-ply carcass, nor presenting the typical structure of radial 
carcasses, it nevertheless manages to combine all the advantages as 
regards the behavior of the radial carcasses and the structural advantages 
of the cross-ply carcasses, while sensibly improving the performances of 
this type of tire--particularly when utilized for sports or racing 
competitions. 
Hence, an important object of the present invention is a tire for 
motorcycle wheels, comprising a textile carcass, a tread band in the crown 
zone of said carcass, and having a deflection of a value between 0.20 and 
0.35. The tire has sidewalls and beds for anchoring of the tire on a 
corresponding mounting rim, with each bead comprising an annular 
reinforcing core circumferentially inextensible, said carcass comprising 
at least a pair of plies with their extremities turned up around said 
annular reinforcing core, and provided with cords disposed parallel to 
each other in each ply, and crossed with those of the adjacent plies, 
characterized by the fact that said cords are symmetrically inclined with 
respect to the midcircumferential plane at an angle generally between 
50.degree. and 65.degree., measured on the crown, and that a breaker 
structure is constructed between said carcass and the tread band, and that 
it comprises at least two strips made of textile cords that are parallel 
to one another in each strip and crossed with the cords of the adjacent 
strip. The strips are symmetrically inclined with respect to the 
circumferential direction at an angle between 18.degree. and 25.degree., 
measured on the crown. 
According to a first embodiment of the invention, the carcass comprises 
only a pair of crossed plies, the cords of said crossed plies being 
respectively of synthetic fibers derived from cellulose in the axially 
innermost ply, and of aramid, i.e., aromatic polyamide, in the axially 
outermost ply, while the annular reinforcing structure made with strips of 
aramid cords comprises a further layer of longitudinally oriented 
polyamide cords that is disposed radially outwardly of said strips and 
having substantially the same width. 
In particular, quite conveniently, the synthetic fiber cords are of rayon, 
those of polyamide are of nylon, and those of aramid are of a material 
that is known on the market as KEVLAR, a registered DuPont trademark. The 
carcass cords are preferably symmetrically inclined with respect to the 
circumferential direction at an angle between 55.degree. and 60.degree.. 
According to a further preferred form, the carcass is provided with another 
reinforcing element for the beads, comprising a strip of textile cords 
flipped up (in a loop) around said annular reinforcing cord, said flipper 
presenting two legs of differing lengths, extending radially outwardly 
beyond the extremities of the turn ups of the carcass-plies, the cords of 
said strips in said legs being symmetrically inclined with respect to the 
radial direction at an angle of about 45.degree., that is, between about 
40.degree. and 50.degree.. 
Quite advantageously, the most extended leg of said flipper is at a radial 
height between 35% and 65% of the height of the tire sidewall. 
The tire structure, with or without said bead reinforcement, can be 
specialized as needed with the insertion of further reinforcing structural 
elements. 
According to a first variation of the invention, said structure comprises 
at least one further carcass ply provided with cords, preferably of 
polyamide, disposed radially and substantially extended from one side to 
the other of the tire. 
According to a further variation, each sidewall of said carcass has an 
additional layer of elastomeric material having an annular profile and a 
substantially lenticular cross-section which is inserted between said pair 
of crossed plies along the radially external portion of said sidewall, 
said layer presenting tapered extremities radially extended from the 
center to both its radial inner and outer ends, that is, towards the tire 
beads and towards the breaker structure. 
In any case, the present invention will be better comprehended with the aid 
of the following description and the attached figures, furnished solely by 
way of non-limiting example, in which:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, it can be noted that the tire of the invention substantially 
comprises a textile carcass 1, a tread band 2 disposed on the crown of 
said carcass, an annular reinforcing structure 3 between said tread band 
and said carcass, sidewalls 4, and tire beads 5 for anchoring said tire to 
its corresponding mounting rim. 
In particular, the tire beads 5 comprise an annular reinforcing core 6, 
that is generally metallic and usually known as a bead core, over which 
there is radially disposed an elastomeric material filler 7 having a high 
hardness. 
The carcass, in more detail, further comprises at least one pair of plies 8 
and 9 extending from one bead to the other and turned up around said bead 
cores 6, the radial height of the turnups of the plies being rather 
limited; generally, it does not go beyond the limit of the mounting rim 
flange, conveniently shown on the tire sidewall as a slightly raised ridge 
10 that serves also as a point of reference for correctly centering the 
tire on the mounting rim. 
The cords of said plies which are parallel to one another in each ply are 
crossed with the cords of the adjacent plies, and symmetrically inclined 
with respect to the tire's mid-plane m--m, according to an angle measured 
on the finished tire, having a rather high value of approximately 
60.degree., but comprised between 50.degree. and 65.degree., and 
preferably 55.degree. and 60.degree.. 
It is understood that these abovesaid angles are measured on the crown, 
astride the equatorial or mid-circumferential plane of the tire. 
As far as concerns the choice of material which is most suited for the 
cords of the carcass plies, attention must be paid to the fact that the 
rubberized fabric, out of which said plies are made, must possess a 
modulus that is not less than 200 Kg per linear millimeter of the fabric, 
the value of the modulus can be governed by an opportune choice of the 
type of cords as well as the density of the cords in the fabric, as 
oriented in the order of about 100 threads/dm. 
Quite conveniently, moreover, the cords of the said plies are chosen from 
diverse materials, depending upon the position of the plies in the 
structure. More precisely speaking, the cords of the axially inner ply 8 
are made out of a synthetic fiber derived from cellulose, for example, of 
rayon, while those of the axially outer ply 9 are made of aromatic 
polyamide or aramid, better known under the name KEVLAR, a registered 
DuPont trademark. 
The annular structure 3 in the crown of said carcass comprises a pair of 
strips 12 and 13 whose width is substantially equal to the width of the 
tread, and whose profile is progressively spaced away from the profile of 
the carcass plies towards the axial outer extremities of said structure, 
thus defining a "V"-shaped areas 22 under the axial outer ends of the 
structure 3. From now on in this text, structure 3 shall be referred to as 
the "belt" structure. The belt is symmetrical about the 
mid-circumferential plane m--m in all embodiments. 
Preferably, the sidewall 4 has its radially outer portion extending into 
the area 22 between carcass and belt, thus creating an efficacious 
supporting action for the belt extremities. The cords of said strips 12 
and 13, which are textile and preferably made of aromatic polyamide, i.e., 
of the already-mentioned KEVLAR, are parallel to one another in each strip 
12 and 13, crossed with the cords of the adjacent strips and symmetrically 
inclined, preferably at an angle of 22.degree., but lying between 
18.degree. and 25.degree., with respect to the equatorial plane of the 
tire. 
These angles are intended to be measured on the tire crown, astride the 
equatorial plane thereof. 
According to a particular preferred embodiment, as seen in FIG. 2a, a 
further layer 14 is disposed radially outwardly and overlaps crossed-cord 
strips 12 and 13. Layer 14 is substantially as wide as the underlying 
layers (the variations in width are on the order of about the usual 
staggering between the edges of superimposed layers), and comprises 
textile cords disposed longitudinally at 0.degree., i.e., parallel to the 
equatorial plane of the tire. 
The cords of said layer at 0.degree. are preferably of polyamide, for 
example, of nylon. 
As an alternative to the above-said layer 14, other variations are also 
possible; for example, the layer 14 of cords at 0.degree. could also be 
substantially wider than the underlying strips of crossed cords and their 
extremities, i.e., those portions 20 exceeding the width of the underlying 
belt structure, may be turned-up axially towards the center of the tire on 
both axial ends of layer 14. 
However, it is not necessary for the folded edge of these turnups to 
coincide with the edges of the underlying strips 12 and 13, since they can 
terminate either axially outwardly or axially inwardly with respect to the 
edges of strips 12 and 13. 
According to another embodiment, as shown in FIG. 2b, the central portion 
of said layer 14 may be omitted so that the radial outer layer of the belt 
structure has only one winding 17, single or in several radially 
overlapping layers 171,172, disposed on each extremity of the pair of 
inclined cord strips. Preferably, the winding 17 is in the form of 
doubled-over strips 24, as shown in FIG. 2b, each having an axial width of 
about 20-30% of the axial width of the belt. The winding 17 may be made of 
a continuous filament wound circumferentially about the tire in 
side-by-side coils or may be made of a calandered multifilament strip, as 
is known in the tire art. 
It is clear that, owing to the effect of the longitudinal orientation of 
the cords in the finished tire, the turnups of outer layer 17 which 
radially overlap the belt axial outer extremities can be considered, in 
the finished tire, to be the zones of a single layer in which the cords at 
0.degree. are disposed so as to have a greater density at the axial edges 
than at the center of said layer. 
As already mentioned at the beginning of the present description, the 
motorcycle tire of the instant invention is particularly intended to 
present a tread that is comparatively much more enveloping than the tread 
of motorcar tires, and has a pronounced curvature in the crown; in other 
words, it has rounded shoulders. 
In particular, said curvature is expressed here as a value of the 
deflection "f", i.e., the h/.lambda. ratio, where h represents the radial 
height of the belt that generally coincides with that of the tread, and 
.lambda. represents the maximum width of the tread, as illustrated in FIG. 
1. For the tires of the invention, the value of "f" is generally comprised 
between 0.20 and 0.35. 
The tire just described can be greatly specialized with the addition of 
further structural elements. According to a first variation, as shown in 
the sidewalls of the tire of FIGS. 2a, 2b and 3, in an axially inner 
position to said bundle of crossed-cord plies there is disposed at least 
one further ply 11, extending from one sidewall to the other sidewall of 
the tire, the cords of which are made of polyamid for convenience sake, 
for example, of nylon. These cords are disposed radially, i.e., oriented 
at 90.degree. with respect to the said mid-circumferential plane m--m of 
the tire. 
When present, said ply is not turned up around the bead cores, but, 
preferably, it will extend from bead heel to bead heel, terminating 
adjacent the radially outermost extremity of said bead cores. 
Also in FIGS. 2a and 2b, there is illustrated a second preferred variation 
of the tire of FIG. 1. 
In said variation, between the plies 8 and 9 of crossed cords in the 
radially outer portion of the sidewall, there is an annular elastomeric 
material profile 15, having a lenticular cross-section, with its radial 
inner and outer extremities tapered, extending radially towards the bead 
heels and towards the belt extremity. The thickness of said profile is 
preferably between one to six times the thickness of the carcass plies. 
And so, also, the hardness of the elastomeric material out of which the 
profile is made can vary within ample limits, for example, between 
40.degree. and 90.degree. of Shore-A hardness. 
The advantages of this profile 15 are multiple. Among these, as the chief 
advantages, there is a greater stiffness conferred to the sidewall 
without, however, compromising its flexibility and riding comfort; this 
results in the maintenance, even under tedious conditions of use, of an 
optimal profile for the carcass plies, so reducing the strains and 
wearing-out of the cords in the said plies, and the increased capacity of 
the tire to be self-supporting. 
It must also be stressed that the usage of said profile in the tires of the 
invention has been made possible only after the adoption of a 
well-defined, limited and critical field of variability for the angles of 
the crossed cords in the carcass plies and, precisely, in the previously 
cited range. In fact, in the tires of the state of the art, the insertion 
of this profile 15 between the carcass plies 8 and 9 would cause 
distortions in the geometry of the cords and unbalanced systems of strains 
in the plies, owing to the effects of the reciprocal de-coupling between 
said plies due to the thickness of the profile, with generating ruinous 
effects in the tire behavior during use. 
FIG. 3 illustrates, also in cross-section, another embodiment of the tire 
of the invention that proves to be particularly advantageous whenever the 
tire is utilized for sports and racing events, and especially for public 
events. 
It can be noted that, for such usage, the radially outer profile of the 
tread has also been conveniently modified with respect to the version 
normally used, i.e., it is shaped to have a sharp corner at its 
extremities, for allowing the driver, before he actually loses control of 
the vehicle itself, to appreciate the fact that the angle of inclination 
of the vehicle, i.e., the camber angle, has reached the maximum value 
admissible. 
Apart from the above-said modifications, in this further variation, the 
tire bead has been conveniently stiffened through the means of a loop 16, 
made of a strip of aromatic polyamid cords, for convenience sake of 
KEVLAR, wound around said bead core and said filler. 
The two legs 161 and 162 of the loop 16 are of differing lengths, so as to 
have their ends located at two diverse heights along the radial height of 
the sidewall and, however, at a height that is greater than that of the 
turnups of the carcass plies 8 and 9. Moreover, the cords of the strip of 
loop 16, as disposed in the two legs 161 and 162, are symmetrically 
inclined with respect to the radial direction, at an angle of about 
45.degree., that is, comprised between 40.degree. and 50.degree.. 
According to a preferred variation, the radially more extended leg, which 
can be the one 161 in the axially innermost position, as in FIG. 3, but 
could also be the one 162 in the axially outer position has its extremity 
at a radial height k which lies between 65% and 35% of the radial height 
of the tire sidewall, and preferably, where possible, it overlaps by a 
distance of not less than the usual staggering, usually 5 mm, the radially 
inner extremity of the annular profile 15. 
The term "height of the sidewall" is intended to mean the radial height H 
of the portion between the base heel (line r in FIG. 1) and the belt 
extremity (see FIG. 3). 
In any case, it must be observed that the variations just described, both 
the one relative to the radial ply 11 and the one regarding the annular 
profile 15, and so also the one relative to the loop 16, are not expressly 
connected to any specific usage, for example, sports, but they are 
accessory characteristics, in relation to FIG. 1, which can exist either 
independently one from the other or even coexist, as in the case 
illustrated in FIG. 3. 
The tire of the invention has shown itself to have a notable series of 
advantages with respect to the known tires of the state of the art, that 
is those having a crossed-ply carcass. 
In particular, it possesses a greater lateral stability that eliminates the 
well-known "oscillations" of the vehicle rounding a curve, a greater 
circumferential stiffness which allows for the transmission of greater 
acceleration and deceleration torques, a greater shear stiffness which 
allows, among other things, for traveling in curves with camber angles 
having a higher value than those normally utilized, and hence with less 
drift, with all the road-gripping advantages and also a greater driving 
precision than is usual, even at high speeds. 
The reason it has been possible to achieve such results are not to be 
attributed certainly to one characteristic rather than to another, but the 
applicant believes, without wishing by this to in any way limit what 
concerns the invention, that they are due to the sum total of 
circumstances that are linked together. In particular, the use of angles, 
which are very high for the pair of crossed cord plies and comprised in a 
well-defined range of values, has allowed for the said plies to work 
disjointedly between themselves in an orthotropal manner, and not with the 
need for having any reciprocal connection, as would be the case if the 
angle of inclination for the cords, with respect to the 
mid-circumferential plane of the tire, had a value less than that of the 
above-defined range of critical limits. 
On the contrary, it has already been stated that, but for those angles 
having values higher than the critical limit, the tire would manifest the 
unacceptable phenomenon of having lateral instability during straightaway 
running. 
As already mentioned, this de-coupling has permitted the usage of diverse 
materials for the cords of said plies, for example, already known rayon 
and KEVLAR cords, as well as inserting an elastomeric material profile 15 
between plies 8 and 9. All these provisions are not realizable with the 
usual crossed-ply tires of the state of the art, because they would suffer 
a decrease in their qualitative behavior characteristics. 
So also the high value of the angle of said crossed plies allows probably 
for the annular reinforcing structure, placed in the carcass crown, to 
carry on to a maximum degree its positive effect, so that the tire of the 
invention has proved to sum up both the structural excellence of the tires 
having a crossed-ply carcass as well as the behavior qualities of the 
radial structures, with obviating the respective defects which, on the 
contrary, are connected with the known tires and which are even an 
impediment for adopting the purely radial structures in this type of tire. 
In particular, when used for public sports on race tracks, the tire of the 
invention has permitted using higher straightaway speed and a greater 
acceleration and deceleration during curving with high camber values, and 
thus obtaining a time-saving in the order of about a half-second every 
kilometer travelled. 
An aspect that is of less importance, but not negligible, is that all of 
the above-said advantages have been obtained without sacrificing the 
riding comfort with respect to the known tires, and such a characteristic 
is quite desirable for long traveling on normal roads and with tire 
structures that are lighter with respect to the usual structures. 
It has to be understood that the present description is solely by way of 
non-limiting example, the scope of protection being defined by the 
following claims.