Pitch sequence

The present invention relates to a tire having a tread comprising at least 33 repeating design cycles placed continuously about the circumference of the tire wherein the design cycles have a total of three different cycle lengths including a short length (S), a medium length (M) and a long length (L) wherein the pitch sequence is MSSSLMMSMLLMLLLMSMSSSMSLLLMMMSSSS.

BACKGROUND OF THE INVENTION 
The present invention relates to tire treads, and more specifically relates 
to tire treads in which the length of repeating design cycles or pitches 
are modulated in order to reduce lug impact frequency when the tire rolls 
on a hard surface. In the past, tire treads for tires used with large 
equipment have been designed by using repeating design cycles extending 
circumferentially about the periphery of the tire. In most such tire 
treads, a single design cycle or pitch is repeated. However, some prior 
designers have proposed using different number of design cycles or pitches 
on the tire tread circumference. 
SUMMARY OF THE INVENTION 
Experience has shown that the preceding prior proposal results in 
undesirable lug impact frequency. Lug impact frequency is a phenomenon of 
the pitching of the tire and the speed of the vehicle resulting in a 
vibration or surging in the vertical and horizontal directions. This 
vibrating or surging is known in the industry as tread lug-induced 
vibration. The inventor has discovered that it is possible to selectively 
reduce the impact frequency by using a randomized sequence of pitches or 
design cycles on the tire. According to the preferred practice of the 
invention, a 33 random pitched sequence is used to provide a tread pattern 
having a complimentary Fourier spectra, such that the total energy 
generated by the rolling tire is spread as uniformly as possible over the 
frequency spectrum.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a portion of an exemplary tire 10 having a tread with an outer 
surface 11 with lug tread elements 13. Exemplary tread design cycles, such 
as 12-22 extend around the circumference of the tire. The design cycles 
are defined with respect to being perpendicular to the axis of rotation of 
the tire. According to the preferred practice of the invention, 33 pitches 
are used. Three different pitch lengths are used having the ratio 9:10:11. 
When the letters S, M and L are used to designate the small, medium and 
large pitch lengths, the pitch sequence is as follows: 
MSSSLMMSMLLMLLLMSMSSSMSLLLMMMSSSS, 
where S, M and L are the small, medium and large pitch lengths, 
respectively. A preferred tire of the present invention is 16.00 R25, 
wherein the length of the small pitch is 127.99 mm, the length of the 
medium pitch is 142.21 mm and the length of the long pitch is 156.44 mm. 
Those skilled in the art will appreciate that the foregoing sequence is 
chosen to have a desirable Fourier spectra. That is, the total vibrational 
energy is spread as uniformly as possible over the frequency spectrum when 
the tire is rotated over a road surface. 
It is possible to predict the frequency spectrum that will be generated by 
the sequences of the tire. Those skilled in the art recognize that 
computer programs capable of such prediction are available and in use. By 
using the computer program to predict the frequency spectrum, the total 
sound energy is spread as uniformly as possible over the frequency 
spectrum. 
Those skilled in the art will recognize that the embodiments described 
herein may be modified and altered without departing from the true spirit 
and scope of the invention as defined in the appended claims.