Method of making tire with tire tread pitch bands

The tread of the tire of this invention is made using tread bands that have a variable pitch length. That is, the variable pitch length tread bands have a first pitch length on one axial side of the tread band and a second pitch length on the other axial side of the tread band. The transition between the first and second pitch lengths can be a gradual change across the tread band widthwise or a relatively abrupt change. The preferred tire has a tread band where the change in pitch length is widthwise within a groove of the tread. Tread bands of this invention have circumferential edges that mesh with each other such that one variable length tread band can be used with its smaller pitch length on one lateral side of the tread or rotated end to end and used with the smallest pitch length on the other lateral side of the tread of the tire. A method for producing a tread band having a change in the pitch length is also given in this invention. The result is a tire that effectively has twice the number of pitch lengths sequenced around the tire as there are separate tread bands. Reduced tread noise is achieved with a greater number of pitch lengths. Alternately stated, the tread of the tire of this invention has a reduced tread noise when using the same number of different tread bands. A single mold for providing a plurality of variable pitch length tread bands on the molded tire is also within the scope of this invention.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a pneumatic tire used for vehicles, and more 
particular to tread bands that reduce the noise generated on contact with 
a supporting surface. 
2. Discussion of the Art 
Noise and vibrations produced by the tread of a tire are the result of a 
number of different disturbances as the tire rolls in contact with a 
ground surface. The tire is made with a tread having elements to grip the 
ground surface and provide traction. Tread and tire elements vibrate and 
air disturbances exist upon impact with the ground surface creating pulses 
of air borne audio frequencies and vehicle vibrations. The interaction of 
all pulses creates what is referred to as tire noise. It has been the goal 
of many investigators to reduce the amplitude of tire noise peaks such 
that no objectionable audio and vehicle vibration problems exist. 
It is known in the art that the noise produced by the tread of a tire is 
modulated by selectively pitching and sequencing the load carrying 
elements. An array of load carrying elements is characterized by the 
relative pitch lengths of the various elements which are in the form of a 
tread band across the width of the tread. Each tread band has its own 
pitch length and is sequenced around the circumference of the tire with at 
least one other tread band having another pitch length. The greater the 
number of bands and the number of different pitch lengths the better 
distributed the noise can become over an audio frequency range. It is 
common to utilize random or sinusoidal sequencing of the respective bands 
of different pitch length in an attempt to modulate the tire noise peaks. 
A number of patents have disclosed tire treads that distribute the acoustic 
energy produced by the rotating tire uniformly over a wide frequency band. 
Methods for spreading the noise generated by sequencing the tread bands of 
a tire are detailed in U.S. Pat. Nos. 3,926,238; 4,178,199; 4,327,792; 
4,474,223; 4,598,748; and 5,240,054. Each of these patents disclose the 
importance of the relative pitch lengths and the sequencing of load 
supporting elements to achieve modulation of tire noise over a broad 
frequency spectrum. Once the load supporting elements are generally 
defined, it is well known how to change the overall size of a plurality of 
tread elements or bands and position them around the circumference of the 
tire to modulate tire noise. These patents provide background information 
for the generic tire noise problem. 
An increase in number of bands and the number of different pitch lengths 
allows the designer much more of an opportunity to modulate the tire 
noise. However, tire molds have become much more difficult to construct 
and the cost of such molds increases with the increasing number of 
different pitch lengths. That is, the fewer the number of different bands 
the less expensive the tire mold. U.S. Pat. No. 3,989,780 discloses some 
of the difficulties in using a variety of pitch lengths and sequencing 
tread bands in the tire mold building operation. This patent also 
discloses the desire to utilize a minimum number of pitch lengths, 
preferably two, for use in a tire tread to reduce cost. U.S. Pat. No. 
3,989,780 further discloses a method to select relative pitch lengths of a 
string of design elements (tread blocks) consisting of at least three 
elements of identical length, and modulating the noise spectrum 
distribution by varying the length and sequential positioning of said 
strings. The elements of this patent are tread blocks having the same 
shape but variations in their size only. This is a typical approach to 
noise modulation. 
The use of two separate circumferential sections of a tire tread, each with 
tread bands having their own separate pitch lengths and sequence, is 
disclosed in European Patents Applications (EP) 0,524,568 and 0,528,577. 
The two different segments across the tread width are separate and 
distinct from one another. This is possible when a clamshell type mold 
(mold half) is used which divides the tire circumferentially on a plane 
parallel to the midcircumferential plane. This solution is not feasible 
with a segmented mold, common in the industry. It is disclosed in EP 
0,528,577 that each base pitch can extend transversely over only a single 
circumferential section of the tire, being a single rib or combination of 
ribs. The construction of a mold to achieve this is not disclosed. The 
sequence of each half section can be rotated and modulated with the other 
half section of the tire tread to further reduce tire noise. This would 
require a large number of different tread bands in a segmented mold. 
European Patent Applications (EP) 0,542,493 also discloses the use of a 
plurality of base pitches or pitch lengths that may extend widthwise over 
a single circumferential section to include a circumferential rib or a 
combination of ribs. The base pitches are repeated to form the complete 
tread. No disclosure is given to define a method to combine the widthwise 
sections or how they may be achieved in a mold. 
The art teaches that using a larger number of tread bands will modulate the 
tread noise and spread the noise more uniformly over a band of 
frequencies. However, the need remains to achieve the modulation of tire 
tread noise with a plurality of pitch lengths in sequence 
circumferentially around the tire with a minimum number of different tread 
bands. Also, a method to achieve better modulation of tread noise with any 
selected sequencing technique and a given number of tread bands remains. 
SUMMARY OF THE INVENTION 
One object of the invention of the applicant is to formulate a method to 
use in modulating the noise magnitude as a function of the noise spectrum 
for tread features of a tire by utilizing a minimum number of different 
mold segments to form the tread portion of a tire. The relative size and 
orientation of tread bands are important considerations to achieve this 
objective. 
A further object of this invention is to teach one skilled in the art how 
to obtain a single tread band that can be used in two different 
orientations on the tread of a tire to reduce tire noise. 
The tire of this invention has a tread portion divided into a plurality of 
load carrying tread bands which extend widthwise across the tire and are 
sequenced circumferentially around the tire. The improvement of this 
invention is based on the individual shape, orientation and pitch lengths 
of the tread bands. The tire has at least one variable pitch length tread 
band having a first pitch length on one axial side and a second pitch 
length on the other axial side. The tread band is utilized both with the 
first pitch length positioned on one lateral side of the tread portion of 
the tire and, when rotated, the first pitch length is positioned on the 
other lateral side of the tread. The tread band is such that one 
circumferential edge of the variable pitch length band will mesh with the 
other circumferential edge of the variable pitch length band when rotated. 
Tires are cured in a mold to form the tread surface during the operation of 
making the tire. A parallel embodiment of this invention includes a single 
mold segment for a plurality of tread bands extending widthwise across a 
molded tire comprising a first pitch length on one axial side of the mold 
segment being greater than a second pitch length on the other axial side 
of the mold segment. The mold segment further comprises a circumferential 
edge which will mesh with the other circumferential edge of the mold 
segment when the mold segment is rotated end to end. The mold segment 
thereby providing a plurality of tread bands of the tire during the curing 
operation of making the tire. 
In a further embodiment of this invention, a method for producing a change 
in the pitch lengths of a plurality of load carrying tread bands 
circumferentially around a tread portion of a tire is given. This method 
achieves a modulated sequence of pitch lengths by a series of a minimum of 
seven steps. In step one, a minimum pitch length is selected along with a 
maximum pitch length for the tread using a ratio of the minimum pitch 
length to the maximum pitch length. In a second step, a first variable 
pitch length tread band is defined having the minimum pitch length on one 
axial side and a second pitch length on the other axial side. For the 
third step, a second variable pitch length tread band is defined having a 
third pitch length on one axial side and the maximum pitch length on the 
other axial side of the second tread band. The third pitch length is 
greater than the minimum pitch length but less than the second pitch 
length. The maximum pitch length is greater than the second pitch length. 
In the fourth step, both circumferential edges of both the first and the 
second variable pitch length tread bands are profiled to be the same. This 
makes the four edges compatible so that they will mesh with one another 
regardless of the axial end to end orientation of the first and second 
tread bands. The fifth step is to incorporate the first and second tread 
bands with profiled edges to form the tread of the tire. The first and 
second tread bands are both orientated with a smallest pitch on one axial 
side of the tread as well as an orientation with the smallest pitch length 
on the other axial side of the tread of the tire. In the sixth step, the 
first and second tread bands in both orientations are sequenced 
circumferentially around the tread in a predetermined order to form a 
tread surface of the tire for contact with a supporting surface for the 
tire. Finally, the seventh step provides for modulating and changing the 
selected pitch lengths and the sequence in step one and step six to 
achieve a reduced noise level from the tire when rolling in contact with 
the supporting surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A typical tread for a tire is illustrated in FIG. 1. This tire 20 has a 
tread with four tread bands of different pitch lengths A-D. A tread band 
has a length across the axial width of the tire equal to the tread width 
TW of the tire. The tread width TW is that portion of the tire in contact 
with the supporting surface when the tire is mounted, inflated and loaded 
according to tire standards in the industry. These standards are defined 
by the Tire and Rim Association, Inc. (T&RA) of Copley, Ohio. The limits 
of the tread width TW is shown by the dashed lines 22 in FIG. 1. The two 
circumferential edges 24 of each tread band defines its limit 
circumferentially around the tread of the tire. The four tread bands are 
shown separated from one another to illustrate that there are four 
different pitch lengths A through D. In fact, each tread band would 
interface with another tread band at a circumferential edge 24. The number 
and position of each tread band of different pitch length are selected 
according to a sequence criteria to give a low noise level as the tread 
contacts the supporting surface. Numerous techniques to provide proper 
sequence criteria are known in the industry. It is further known that a 
greater number of different pitch lengths can provide lower noise levels. 
However, the greater the number of tread bands the higher the 
manufacturing costs for the tire 20. The constant pitch length tread bands 
illustrated in FIG. 1 are typical in the art and give one pitch length for 
one tread band. The scope of this invention includes the use of variable 
pitch length tread bands to achieve the effect of a larger number of pitch 
lengths with a limited number of different tread bands. 
Tire noise can best be studied by investigating the frequency of contact 
between a tire tread feature and the supporting surface. The more frequent 
the contact the higher the frequency of the tire and vehicle vibrations 
which produce noise. To investigate this in more detail, refer to the 
illustrations of FIGS. 2 and 3. A schematic side view of a tire tread 14 
in contact with a supporting surface 90 is illustrated in Fig. 2. The 
tread 14 has one radius R when free to expand and another radius RR when 
rolling about its axis of rotation A in contact with the ground 90. The 
tire tread deforms radially at the leading edge 16 as well as at the 
trailing edge 17 of contact with the supporting surface. The result of 
these deformations and the flat contact portion 18 are such that the 
circumferential length of the tire's tread is not changed due to its 
contact with the supporting surface. This circumferential length is equal 
to 2 R and is herein referred to as the development length L of the tire 
tread 14. 
The speed V of the tire is represented by its angular velocity W expressed 
in cycles per second. Consider a single surface feature 12 repeated around 
the tread 14 with a constant spacing distance P between each adjacent pair 
of features 12. There are L/P features around the development length of 
the tire. This is referred to as the spectrum S=L/P associated with 
feature 12. The frequency Hz of the impact of feature 12 with the 
supporting surface is given by W.times.L/P and is expressed as cycles per 
second. If there is only one feature 12 on the tire the magnitude M of the 
contact is defined as unity (1.0). This is illustrated in FIG. 3 where the 
magnitude M is plotted against spectrum S and shows only one vertical bar 
having a magnitude of one. 
When the tread contains more than one feature or the features are not 
equally spaced, they begin to share frequencies with each other and the 
magnitude at any one spectrum is less than one. This is illustrated by 
considering one tread feature having a length A1 and another tread feature 
having a larger length B2, as shown in FIG. 2. There are two spectrum 
values; one at S1=L/A1 and another at S2=L/B2. Obviously both features 
cannot be placed continuously around the development length L at the same 
time. Therefore, they share space on the tread with each other and no 
single magnitude as large as 1.0 can exists. There are other spectral 
values that also have a magnitude, such as that associated with the 
average PA of A1 and B2. The illustration of FIG. 4 shows a typical 
magnitude vs. spectrum plot for a tread 14 having two features of 
different length sharing its development length L. Many other spectrum 
values will also exist with only two features when such features are 
randomly placed to share space on the tread 14. A broken line 15 in FIG. 4 
illustrates a typical maximum magnitude limit for all specrtum values that 
likely exist. A tire having lower noise level will have a magnitude vs. 
spectrum with a broken line 15 with less magnitude variation over the 
spectrum associated with frequencies SxW in an audible range of about 200 
to about 2000 cycles per second. This concept is used to evaluate the 
tread features of this invention. 
The features on a tread of a tire that contact the supporting surface can 
be considered as individual blocks, grooves in the tire tread or the tread 
band as a whole having many blocks and grooves. The four tread bands of 
FIG. 1 have four pitch lengths A-D which are also considered as 
independent tread features. A key concept of this invention is that only 
two tread bands can be used to achieve four pitch lengths. 
In one embodiment of this invention (using two tread bands) the bands 40,42 
of FIG. 5 are each shaped to have a variable pitch length. The maximum and 
minimum pitch lengths, B2 and A1 respectively, are chosen to avoid having 
tread features which are not appropriate for wear rate or stiffness 
performance; i.e. having a preferred minimum pitch length A1 of at least 
1.0 percent and a preferred maximum pitch length B2 of not more than 2.5 
percent of the development length L. The smallest tread band 40 has a 
second pitch length B1 at one lateral end 261 in addition to the minimum 
pitch length A1 at the other lateral end 281. The largest tread band 42 
has a third pitch length A2 at one lateral end 282 in addition to the 
maximum pitch length B2 at the other lateral end 262. The maximum pitch 
length B2 is chosen to avoid having tread features with high stiffness 
values and the minimum pitch length A1 is chosen to avoid having tread 
features with low stiffness values. A preferred ratio of the minimum pitch 
length A1 to the maximum pitch length B2 is in a range of about 0.50 to 
about 0.75. The third pitch length A2 is selected to be greater than the 
minimum pitch length A1 but less than the second pitch length B1. 
The circumferential edges 41,43 of the two tread bands 40,42 are designed 
to mesh with each other regardless of the end to end orientation of the 
tread bands. That is, the smaller tread band 40 can be positioned to have 
end 281 colinear with either end 262 of the larger tread band 42 or end 
261 of another smaller tread band 40 which is rotated end to end. The 
ability of having circumferential edges 41 and 43 which mesh depends on 
these edges being symmetrical about the midcircumferential plane M and 
each edge having the same profile. Changes in the pitch length of the 
tread bands 40,42 can vary from abrupt changes such as 30 and 32 to 
gradual changes such as 31 and 33, as illustrated in FIG. 5. Gradual 
changes can be from a first transition point 4,5 on one axial side to a 
second transition point 6,7 on the other axial side. The magnitude of the 
change C1 in pitch length on both sides of either tread block is the same. 
That is, B1-A1=B2-A2=2.times.C1. The transition points 4-7 can be located 
at any distance S from the end of the tread band to provide a long 
transition length T or a relatively short transition length T. The 
preferred transition length is such that the transition occurs in a groove 
of the tire tread pattern. 
Tread features within a tread band are also rotated end to end when the 
tread band is used in both orientations. Tread features 60,61 within a 
tread band which are symmetrical are repeated on both lateral halves of 
the tire in the same angular position. Tread features 62,63 within a tread 
band which are asymmetrical are repeated as asymmetrical when the tread 
band is rotated. However, the effect of rotating the tread bands helps to 
make asymmetrical tread features more symmetrical for the overall tread 
pattern. Two smaller tread bands 40,40 with one rotated to mesh with the 
other will give tread feature 60 spaced a distance of P1+P2 from 
symmetrical tread feature 61. If another tread band 40 is added to these 
two, the new tread feature 60 is now at a different distance from tread 
feature 61; when P1 is not equal to P2. This fact further helps to 
modulate the tread noise. 
The transition in pitch length from a shorter pitch length A to a longer 
pitch length B can be stepped as illustrated in the plan view of a tread 
band 46 shown in FIG. 6. Tread features have been omitted to help 
illustrate the features of the invention. This tread band 46 has four step 
changes in pitch length. These may correspond with the circumferential 
grooves in a five rib tire tread pattern. The step magnitude is 
symmetrical with respect to a midcircumferential plane M being one 
distance C3 for the two internal steps and a second distance C2 for the 
two lateral steps. The tread band 46 meshes with itself at circumferential 
edges 47 when rotated end to end. This tread band 46 is combined with a 
larger tread band 48 as illustrated in the plan view of FIG. 7. The larger 
tread band 48 has a shorter pitch length C on one end and a longer pitch 
length D on the other end. The ratio of the minimum pitch length A to the 
maximum pitch length D is once again in the range of about 0.50 to about 
0.75. Two smaller tread bands 46 are meshed at circumferential edges 47 
with two larger tread bands 48 in FIG. 7. The actual tread of a tire would 
have a predetermined number of each of the tread bands 46,48 arranged in a 
predetermined manner to modulate the tread noise. It is noted that the 
pitch ratio (i.e. A/D at the lateral ends 26,28) varies across this tread 
band arrangement. In fact, there are only two pitch lengths in the central 
segment of the tread. This may allow one to select a relatively small 
pitch ratio A/D for the most lateral segments of the tread without 
influencing tread wear. Such a selection would help modulate the noise 
produced by the lateral ribs of the tire tread pattern. The preferred 
tread band step arrangement continues to be a single large step made 
within a groove of the tire tread pattern. 
A further embodiment of this invention is a method for producing a change 
in the pitch lengths of load carrying tread bands. The tread bands are 
placed adjacent to each other circumferentially around the tire's outer 
surface and contain tread pattern elements in relief that contact a 
supporting surface. The location or sequencing of tread bands of different 
size can help provide a low noise level as the tread of the tire contacts 
the supporting surface. The invention allows one to use a single tread 
band that effectively yields two pitch length changes. The steps used to 
achieve the advantages of this invention are described herein. 
A minimum pitch length is selected to keep the tread elements from becoming 
too small. A minimum pitch is preferably not less than about 1.0 percent 
of the development length L as previously defined. To keep the larger 
tread elements from being much larger than the smaller tread elements and 
producing an uneaven wear problem, a preferred ratio of the smallest pitch 
length to the largest pitch length is in the range of about 0.50 to 0.75. 
Selecting this ratio a maximum pitch length is obtained having previously 
selected the minimum pitch length. Furthermore, the largest pitch length 
is preferably no more than 2.5 percent of the development length L. The 
average pitch length is the average of the minimum and maximum values 
selected. A first variable pitch length tread band is selected having the 
minimum pitch length at one axial end and a second pitch length at the 
other axial end of the tread band. A second variable pitch length tread 
band is selected having the maximum pitch length on one axial end and a 
third pitch length at the other axial end. Pitch lengths are measured 
parallel to a midcircumferential plane of the tire. The preferred third 
pitch length is selected to be greater than the minimum pitch length but 
less than the second pitch length. The second pitch length is less than 
the maximum pitch length. 
Treads of a tire are formed during the moulding operation in making a tire. 
The mould is a negative imprint of the relief features forming the 
exterior configuration of the tread, shoulder areas and sidewalls on a 
surface that generally conforms to the outer surface of the cured tire. 
Integral with having a tire with variable pitch tread bands is the making 
of a number of molds that achieve these bands in a cured tire. The ability 
to make only a minimum number of molds reduces the cost of manufacturing 
the tire. The structural features of a mold segment are parallel with 
those of a tread band which results from the mold, and are within the 
scope of this invention. For example, one of the tread mold segments looks 
like one of the tread bands of FIG. 10. However, the grooves become 
projections from the flat surfaces of the tread blocks. The total mold 
further extends beyond the tread band's lateral edges 26 and 28 (FIG. 7) 
to the bead area. The mold segment referred to herein is that portion 
extending across the tread width TW (FIG. 1). 
The method includes profiling the circumferential edges of each tread band 
such that they all mesh with each other. It is necessary that there is an 
equal number of tread bands that are oriented with the smaller pitch 
length on one axial side and tread bands that are orientated with their 
larger pitch length located on the same axial side of the tread. Each 
tread band must be adjacent to a tread band place that has been rotated as 
shown in FIG. 7. The profiled edges 47 must be anti-symmetrical with 
respect to a radial plane R perpendicular to the midcircumferential plane 
(see FIG. 6). That is, on one axial side a first edge will be on one side 
of the radial plane R and on the other axial side the first edge will be 
on the other side of the radial plane R. In addition, a second edge will 
have the same relationship from side to side and will have edges 
converging with the first edge on one axial side and diverging with the 
first edge on the other axial side. This makes the edges compatible and 
mesh with one another regardless of the end to end orientation of the 
tread bands. The same or similar geometric relationships exist if tread 
bands, or portions thereof, are positioned diagonally across the tread 
width TW to make an acute angle with respect to the midcircumferential 
plane M. 
The first and second tread bands are incorporated to form the tread of the 
tire. The relative position and orientation of the first and second bands 
are sequenced to circumferentially cover the tire and form the surface of 
the tire that contacts the supporting surface. Numerous techniques for 
sequencing the tread bands are known in the art and discussed in the 
background. Those techniques formulated for four different pitch lengths 
are appropriate for the two tread bands discussed herein. Once the noise 
level of the tire is measured the pitch lengths and sequencing can be 
modulated to optimize the noise level for different surfaces and/or 
operating conditions of the vehicle. 
This invention is not limited to two variable pitch tread bands, as the 
scope of this invention applies to any number of variable pitch length 
tread bands. One variable pitch length tread band may be appropriate for 
some applications where tire noise is not a critical performance criteria. 
Two variable pitch length tread bands are preferred for most passenger car 
tires. The scope of this invention also includes the use of constant pitch 
length tread bands simultaneously along with those having a variable pitch 
length. The respective edges of the tread bands must be such that all 
tread bands mesh with each other. 
EXAMPLE 
A comparison between the tire noise level using prior art constant pitch 
length tread bands and those of this invention using variable pitch length 
tread bands is made using magnitude vs. spectrum graphs as previously 
described. A plan view showing two constant pitch length tread bands for a 
tire tread pattern is illustrated in FIG. 8. A magnitude vs. spectrum 
graph for an optimized tread, using the tread bands of FIG. 8, is shown in 
Fig.11. A plan view showing four constant pitch length tread bands for the 
same tire tread pattern is illustrated in FIG. 9. A magnitude vs. spectrum 
graph for an optimized tread, using the tread bands of FIG. 9, is shown in 
FIG. 12. Finally, a plan view showing the use of two variable width tread 
bands to make a total of four tread bands according to the invention for 
the same tire tread pattern is illustrated in FIG. 10. A magnitude vs. 
spectrum graph for the optimized tread, using the tread bands of FIG. 10, 
is shown in FIG. 13. The optimization technique used in each of these 
three cases was the same. Results show a definite reduction in the noise 
magnitude for the tires having four tread bands (FIGS. 12 and 13). These 
two cases also show little difference in noise magnitude using a total of 
four tread bands. The two variable pitch length tread bands perform as 
well as the prior art four constant pitch length tread bands. 
A significant reduction in the noise level is anticipated with the use of 
four variable pitch length tread bands in lieu of four constant pitch 
length tread bands (FIG. 9). With each of the four variable pitch length 
tread bands used both with their smallest pitch length on one lateral side 
of the tread of the tire as well as on the other lateral side of the tread 
(rotated), the tread noise level can approach that of a tire having eight 
(8) constant pitch length tread bands. That is, with the same number of 
different tread bands being manufactured, a reduction in the noise can be 
achieved using variable pitch length tread bands. By sequencing these 
eight tread bands (four in one orientation and four rotated end to end) 
around the tire's tread, lower magnitudes would be achieved than those 
shown in FIG. 12 for the four constant pitch length tread bands. 
A further evaluation was performed for a mounted, inflated and loaded tire 
in contact with a supporting surface. A significant portion of the noise 
is generated as the tread of the tire goes into and comes out of contact 
with the supporting surface. During tire rolling, the impact of tread 
features with the supporting surface at a leading edge of contact may be 
different than impact of tread features at a trailing edge of contact. 
FIGS. 14A and 15A show the magnitude vs. spectrum for the leading edge of 
contact where FIGS. 14B and 15B are for the trailing edge of contact. The 
tire having the tread bands of FIG. 8 are shown in FIG. 14A and 14B and 
the tire having the tread bands of FIG. 10 are shown in FIG. 15A and 15B. 
The noise level of the tire having tread bands according to the invention 
(FIG. 10) is obviously much lower. That is, the magnitude vs. spectrum 
graph at the leading edge of the tire of this invention (FIG. 10), shown 
in FIG. 15A, illustrates magnitudes much less than those for the two 
constant pitch length tread bands (FIG. 8), shown in FIG. 14A. The same 
conclusions can be made where the magnitude vs. spectrum graph at the 
trailing edge (FIG. 15B) for the tire having the tread bands of this 
invention (FIG. 10) illustrates magnitudes much less than those at the 
trailing edge (FIG. 14B) of the tire having two constant pitch length 
tread bands (FIG. 8). The overall noise level is commonly represented by 
the total impact engery given in deciBells (dB). The overall noise level 
of the tire of this invention was more than two (2) dB lower than the 
prior art tire; as indicated by the dB values shown on FIG. 14A vs. FIG. 
15A as well as those shown on FIG. 14B vs. FIG. 15B.