High perimeter tread element

An improved pneumatic tire having a tread portion comprising of plurality of independent projections. Each independent projection has a configuration such that the perimeter of the projection is substantially greater than the diameter of a circle which circumscribes the projection.

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 in the following detailed description. 
BACKGROUND OF THE INVENTION 
The present invention relates to a pneumatic tire, and more particularly to 
a pneumatic tire for use in all seasons. A pneumatic tire designed for use 
in all seasons involves a trade-off between tire performance 
characteristics. For example, a pneumatic tire having good ice and snow 
traction generally has poor dry road traction and is usually much noisier 
than a tire designed to be used on dry road in the warmer seasons. 
Applicants have discovered a tread pattern for a pneumatic tire which has 
acceptable ice and snow traction performance characteristics while at the 
same time having acceptable levels of performance for use on dry roads, 
thereby enabling the tire to be used in all seasons. 
SUMMARY OF THE INVENTION 
The present invention is directed to a pneumatic tire having a tread 
portion comprising a plurality of independent projections. Each 
independent projection has a configuration such that the perimeter of the 
projection is substantially greater than the diameter of a circle which 
circumscribes the projection. Preferably, the perimeter of each projection 
is at least five times the mean diameter of the circle which circumscribes 
the projection. There is provided in the tread portion a sufficient number 
of projections so that total perimetric length of projections divided by 
the total tread surface area is at least about 3.5 lineal inches per 
square inch.

DETAILED DESCRIPTION OF THE DRAWINGS 
With reference to FIGS. 1 and 2, there is illustrated a pneumatic tire 10 
having a ground engaging portion 12 which extends circumferentially about 
the radially outer surface of the tire 10. The tread portion 12 comprises 
a plurality of independent projections 14 placed circumferentially about 
the tread portion 12 and spaced from each other so as to provide plurality 
of grooves 16 between adjacent projections 14. The grooves 16 have a 
cross-sectional width sufficiently large so that the grooves 16 do not 
close up at the tread contact surface when in the footprint of the tire, 
thereby providing water channeling passages in the tread portion. 
The tire 10 generally comprises a pair of sidewall portions 24 which extend 
from each of the lateral ends of said tread portion 12 radially inward 
terminating in a pair of bead portions 25 respectively. A cord reinforced 
carcass ply structure 26 extends from bead portion to bead portion. 
Preferably, the cords of the ply layers of the carcass structure 26 form 
an angle with respect to the mid-circumferential plane CP of the tire from 
about 75.degree. to about 90.degree. . 
The projections 14 generally have a central portion 18 and a plurality of 
limbs or projections 20 which extend outward from the central portion. 
Preferably, the projections 14 have a symmetrical configuration and the 
limbs 20 have substantially the same overall configuration. However, the 
projection may be assymetrical as illustrated in FIG. 3 or may take many 
other shapes and configurations not illustrated. The projections 14 have a 
configuration such that the perimeter P of the projection as viewed in a 
plane perpendicular to the tread surface, is substantially greater than 
its circumscribing circle as illustrated in FIG. 2. Generally, the 
perimeter P is at least five times the diameter D of the circumscribing 
circle, preferably the perimeter P is about six times that of diameter D 
and less than or equal to eight times the diameter D. In the particular 
embodiment illustrated the perimeter is approximately 5.67 times that of 
the circumscribed circle. In the embodiment illustrated, the independent 
projections 14 have an overall crystalline configuration, the limbs 20 
being separated from each other by a cut-out portions 22. The cut-out 
portion 22 is to be distinguished from slits, blades or sipes normally 
found in the tread elements. The cut-out portions 22 are sufficiently 
large such that when in the footprint of the tire, the adjacent limbs 20 
do not close up at the tread surface. For the purposes of this invention, 
the perimeter of any given element is the actual physical lineal distance 
measured about the element as viewed in the plane perpendicular to the 
tread surface excluding any blades or sipes that may extend into the 
projection. 
The tread portion 12 is provided with sufficient number of projections 14 
such that the average perimetric length of projections per square inch of 
tread surface area is at least 3.5 lineal inches per square inch of tread 
for the entire configuration of the tire, in the particular embodiment 
illustrated the average perimetric length of projection per square inch of 
tread portion is 4.25 inches per square inch. This assures a minimum 
number of biting edges in the tread portion for traction. 
The tread width TW is at least sixty percent of the section diameter SD and 
in the particular embodiment illustrated the tread width is approximately 
sixty five percent of the section diameter SD. For the purposes of this 
invention, the tread width TW is the axial distance across the tread 
portion as measured from the footprint of the tire inflated to design 
inflation pressure and at rated load. The section diameter SD is the 
maximum axial distance measured parallel to the rotational axis of the 
tire measured from the axially outer surfaces of the tire exclusive of any 
indica or other markings. The aspect ratio of the tire, that is, the 
section height SH divided by the section diameter SD, ranges generally 
from about 60 to 85 and in the particular embodiment illustrated is about 
75. 
While certain representative embodiments and details have been shown for 
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. For 
example, referring to FIG. 3, there is illustrated a modified shape of the 
independent projection.