A high-speed tire for use during both wet and drying road surface conditions is disclosed. The tread groove depth increases from a minimum depth near each tread edge to a maximum depth near the mid-circumferential plane. Each of an outer group of tread elements has a ground-contacting surface area equal to at least about two square inches, and the net-to-gross ratio of the tread central zone is not greater than about 65 percent. Transverse grooves extend from the mid-circumferential plane to a tread edge at an angle relative to the mid-circumferential plane which is greater than about 75 degrees at the respective tread edge and which is less than about 40 degrees at the mid-circumferential plane. The widths of circumferential grooves progressively decrease as their respective distances from the mid-circumferential plane increase.

The foregoing abstract is not to be taken as limiting the invention of this 
application, and in order to understand the full nature and extent of the 
technical disclosure of this application, reference must be made to the 
accompanying drawings and the following detailed description. 
This invention relates to tires, and more particularly, high-speed tires 
such as racing tires. 
A normal racing tire for use on dry track surfaces is slick; that is, it 
has no tread pattern whatsoever except for very small wear indicator 
depressions in the tread surface. A racing tire employing a tread pattern 
which has wide, deep, closely spaced grooves throughout the width and 
circumference of the tread has been employed during periods of time in 
road racing when it is raining or the track is wet, since it is necessary 
during such periods to remove rapidly from between the tire and the track 
surface the large quantities of water being accumulated as the tire goes 
through the footprint so as to prevent skidding or hydroplaning and to 
afford sufficient traction. Road racing is a type of racing which includes 
many combinations of left and right turns and which normally takes place 
in varied weather conditions. Since the tread elements of such a tire have 
a large height and a small surface area, they tend to squirm or otherwise 
distort especially in the shoulder regions and thereby generate heat as 
the tire travels through the footprint especially during periods of 
continuous cornering. During a period of time while the tire is contacting 
a wet track surface, the water being evacuated keeps the tread elements 
sufficiently cool so that the tire tread is generally not damaged. 
However, during periods of time when the track is dry or drying, there may 
be insufficient cooling of the tread elements during high-speed use of a 
tire with such a tread, especially during periods of continuous cornering, 
resulting in blistering of the tread elements, especially in the shouler 
regions of the tire. 
For these reasons, it has been considered necessary in the past to provide 
two types of tires for road racing during overcast weather conditions 
wherein the track surface is wet and may begin drying or is dry and may 
become wet during a race. One type of tire would be used when the track is 
wet and the other type would be used when the track is dry or drying. 
However, the time required to change tires after a rain or when a rain 
begins may be crucial to the outcome of a race. It is therefore desirable 
to provide a racing tire which has sufficient water evacuation capacity 
for use on a wet track but which will also not be damaged due to 
blistering of the tread elements during cornering when the track is dry or 
drying. 
It is an object of the present invention to provide such a tire. Other 
objects of this invention will become apparent hereinafter. 
To acquaint persons skilled in the arts most closely related to the present 
invention, certain preferred embodiments thereof illustrating a best mode 
now contemplated for putting the invention into practice are described 
herein by and with reference to the annexed drawings forming a part of the 
specification. The embodiments shown and described herein are illustrative 
and as will become apparent to those skilled in these arts can be modified 
in numerous ways within the spirit and scope of the invention defined in 
the claims hereof.

There is shown in FIG. 1 a tire 10 which is a toroidal-shaped composite 
structure provided with a pair of conventional, circular, inextensible 
beads 12 from which extend respectively a pair of sidewalls 14. The 
sidewalls 14 terminate at the edges of a crown portion 16 which extends 
circumferentially of the tire 10 and which includes a tread 18 outwardly 
thereof. The tire 10 includes a conventional carcass 20 which may be of 
one or more plies of either radial or bias tire cord fabric extending 
between the beads 12 for reinforcement of the tire 10. One or more belts 
or breakers 22 may be provided between the carcass 20 and the tread 18. 
The tire 10 is a racing tire whose tread 18 is constructed, as best shown 
in FIG. 2 and as will be described in detail hereinafter, for use in both 
wet and drying track conditions. The term "racing tire" is defined, for 
the purposes of this specification and the claims, as a tire designed for 
racing at speeds in excess of 100 miles per hour (160 km. per hour). 
As shown in FIG. 2, the tread 18 is provided with a plurality of tread 
elements 24 which are separated by a network of grooves 26. In order to 
provide sufficient traction during periods of rain or periods when the 
track is wet, the tread 18 is provided over a substantial portion thereof 
with grooves which are sufficiently deep, wide, and closely spaced to 
remove the water entering the tread contact patch. However, such a tread 
pattern provided throughout the width of the tread 18 may result in 
blistering of tread elements in the shouler regions of a tire especially 
while cornering at high speeds during dry or drying conditions. Therefore, 
the tread elements in the shoulder regions are provided with a combination 
of larger surface area, less height, and a shape which will provide 
sufficient stability to prevent blistering due to squirm of the tread 
elements as the tire travels through the footprint. In other words, a tire 
for use in road races in both wet and drying track conditions should have 
a large void volume for evacuation of water in the central region and 
tread elements which have high stability to prevent blistering in the 
shoulder areas. 
In order to provide such a tire, in accordance with one aspect of this 
invention, the groove network 26 has a minimum depth within a distance 
from each tread edge equal to 20 percent of the tread width which minimum 
depth is less than about 0.15 inches (0.38 cm). The tread edges are 
determined by the axially outermost points of a tire which touch the 
ground as the tire travels through its footprint when mounted on a vehicle 
under rated pressure and load. The term "axially", as used herein, refers 
to a direction parallel to a tire's rotational axis. A 
"mid-circumferential plane" is defined herein as a plane which is 
perpendicular to the rotational axis of a tire and which lies midway 
between the tread edges. The mid-circumferential plane of tire 10 is 
illustrated at 28 in the drawings. The tread width is determined from the 
tire's footprint at the widest points thereof. Groove network depth is 
measured in a direction perpendicular to the tire's rotational axis and is 
illustrated at 30 in FIG. 3. In accordance with a preferred embodiment of 
this invention, the groove network depth within a distance of 20 percent 
of the tread width from each tread edge is equal to less than 0.10 inch 
(0.25 cm). This embodiment is meant to encompass a groove network depth 
within 20 percent of tread width from each tread edge which is equal to 
zero; that is, the absence of grooves within 20 percent of tread width 
from each tread edge. 
In order to provide sufficient groove depth for water evacuation in the 
center regions of the tread during periods of use on a wet track, the 
groove network has a maximum depth within a distance of 10 percent of the 
tread width from both sides of the mid-circumferential plane 28 which 
maximum depth is preferably equal to at least the lesser of 0.20 inches 
(0.51 cm) and 2.5 percent of the tread width. 
The groove network depth preferably progressively increases as the groove 
network 26 extends in a direction across the tread from each tread edge to 
the mid-circumferential plane as best shown in FIG. 3. By the term 
"progressively increases" as applied to the groove network depth is meant 
an overall pattern of increase in groove network depth such as in 
incremental stages of in a geometric progression so that as each 
transverse groove of the groove network extends across the tread toward 
the mid-circumferential plane 28, the groove depth generally increases, 
and each circumferential groove is generally shallower than other 
circumferential grooves spaced closer to the mid-circumferential plane but 
deeper than other circumferential grooves spaced further from the 
mid-circumferential plane. 
Of course, the groove network depth "progressively increases" as long as 
there is an overall pattern of increase in groove network depth even 
though there may be an occasional decrease in groove network depth as the 
groove network 26 extends in a direction across the tread from each tread 
edge to the mid-circumferential plane. 
In accordance with another aspect of this invention those tread elements 
such as those shown at 32, which are disposed at least partially within a 
distance of 20 percent of the tread width from a respective tread edge 
(hereinafter referred to as the "outer group of tread elements") each have 
a ground-contacting surface area equal to at least about 2 square inches 
to aid in providing sufficient stability of the tread elements 32 so that 
blistering due to squirm of the tread elements in the shoulder regions 
does not occur while cornering at high speeds in dry or drying conditions. 
On the other hand, in order to provide sufficient void in the central 
region of the tread for water evacuation during driving at high speeds in 
wet track conditions, a central zone of the tread 18 which extends over 
the width of the tread 18 from the mid-circumferential plane 28 toward 
each tread edge a distance of 10 percent of the tread width (for a total 
width of the central zone equal to 20 percent of tread width) has a 
net-to-gross ratio which is not greater than about 65 percent. By 
"net-to-gross ratio" is meant the ratio of the total ground-contacting 
surface area of the tread elements or portions of tread elements in the 
central zone to the product of the width of the central zone and the 
circumference of the tread at the mid-circumferential plane 28. 
In accordance with another aspect of this invention, the groove network 26 
includes circumferential grooves 34 the widths of which progressively 
decrease as their respective distances from the mid-circumferential plane 
28 increase from a greater width at the mid-circumferential plane 28 to a 
lesser width at or near each tread edge in order to provide a maximum 
amount of void in the central area of the tread for water evacuation and 
to provide a maximum tread element surface area for maximum stability of 
the tread elements in the shoulder regions for prevention of blistering 
while cornering at high speeds during dry or drying track conditions. 
Circumferential groove width is illustrated at 36 in FIG. 3 and is 
measured in a direction perpendicular to a wall of a groove at the 
ground-engaging surface of the tread. In accordance with a preferred 
embodiment of this invention, the width of the circumferential groove 38 
nearest the mid-circumferential plane 28 is at least 40 percent greater 
than the width of the circumferential groove 40 nearest each tread edge. 
In addition to the size and height, it is also preferable for providing 
greatest stability to the tread elements in the outer group of tread 
elements that they have certain shapes. For example, if they have sharp 
corners such as are found in triangular-shaped elements or if they are 
excessively long as compared to their width, their stability may be 
decreased markedly. Therefore, in accordance with a preferred embodiment 
of this invention, each of the outer group of tread elements has a width 
which is at least 90 percent of the length thereof. In accordance with 
another preferred embodiment of this invention, the ground-contacting 
surface of each of the outer group of tread elements is substantially 
rectangular in shape. 
In accordance with another aspect of this invention, the groove network 26 
is provided with transverse grooves 42 as well as circumferential grooves 
34 for more efficient evacuation of water from the footprint. It is 
believed that a more efficient evacuation of water from the tread 
footprint can be achieved if it is evacuated via a path along which it 
would naturally otherwise flow. Therefore, it is preferable that each of 
the transverse grooves 42 extend from the mid-circumferential plane 28 to 
a tread edge at an angle relative to the mid-circumferential plane 28 at 
the respective tread edge which is greater than about 75 degrees as shown 
at 44 in FIG. 2, and each transverse groove 42 further preferably extends 
at an angle relative to and at the mid-circumferential plane 28 which is 
less than about 40 degrees as shown at 46 in FIG. 2, the angle at which 
each transverse groove 42 extends relative to the mid-circumferential 
plane 28 progressively decreasing as the transverse groove 42 extends 
across the tread from each tread edge to the mid-circumferential plane 28 
as clearly shown in FIG. 2. All of these transverse grooves 42 preferably 
extend from the mid-circumferential plane 28 in the same circumferential 
direction as illustrated at 48 in FIG. 2 to direct the water as much as 
possible in its direction of natural flow. Such a tire may be called a 
"directional tire" and is mounted on a vehicle such that the portion of 
each transverse groove 42 at the mid-circumferential plane 28 will enter 
the footprint first as the tire goes through the footprint. 
In addition to racing tires, this invention may also be useful in other 
types of tires such as wherein it is important to evacuate water from the 
tread contact patch during wet conditions while also preventing the tread 
elements in the shoulder regions from blistering during high-speed driving 
under dry or drying road surface conditions. 
While certain representative embodiments and details have been shown for 
the purpose of illustrating the invention, it will be apparent to those 
skilled in the art that various changes and modifications may be made 
therein without departing from the spirit or scope of the invention.