FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION LOWROLLINGRESISTANCETIRE
APPLICANT
CEAT LIMITED
An Indian Company
RPG HOUSE, 463, Dr. Annie Besant Road,
Worli, Mumbai 400 030, India.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to pneumatic tires with low rolling resistance. Particularly, it relates to pneumatic radial tires having improved profile that reduces rolling resistance.
BACKGROUND OF THE INVENTION
Performance of a tire can be majorly measured based on three parameters. They are rolling resistance, traction and wear resistance. The set of these three parameters are referred as magic triangle in the tire industry. Manufacture of tires with superior quality require alignment of all the three parameters within the allowable ranges.
A pneumatic tire has a profile extends from the shoulder which connects with the tread portion to the sidewall region. It has a higher contribution in the reduction of rolling resistance. In the prior art, curvature radius of tire is reduced in order to reduce contact area of the tire and rubber thickness disposed on the shoulder area of tire is reduced in order to reduce weight of the tire. However, the said changes may lead to small contact area of tread region and sub-optimal braking performance of tire.
In other literature, contact area of the tread region is increased to improve the braking performance. However, such change is liable to increase weight of the tire in turn it increases high rolling resistance of tire.
Therefore, there is a need in the art to construct profile for pneumatic tires with low rolling resistance and optimal breaking performance.
SUMMARY OF THE INVENTION
This summary is provided to introduce concepts related to a pneumatic tire with low rolling resistance that indicate data representative of constructing improved

profile of pneumatic tires. The concepts are further described below in the detailed description. This summary is not intended to identify essential features of the claimed invention nor is it intended for use in determining or limiting the scope of the claimed invention.
The present invention relates to pneumatic tires with improved profile that provide pneumatic tires with low rolling resistance, high breaking performance, improved ride and handling properties.
In an aspect, tread portion of pneumatic tire having tread width in the range of 70% to 80% of nominal tire section width SW when tire is mounted on a measuring rim and inflated to a standard pressure but loaded with no tire load, a pair of sidewall portions having arcs and contains a pair of bead portions having bead core, a profile from shoulder to sidewall includes: a shoulder profile connecting the tread and buttress, a buttress profile connecting to shoulder profile and sidewall, a carcass extending from a bead core through the tread and sidewall portions, a steel belt positioned between tread portion and carcass, a tire section centerline passing from the center of tread portion, the reference height of the tire section intersecting with tire centerline.
Referring to FIG. 1, the tire has a tread potion “1”, shoulder potion “2” and sidewall “5”. The tread portion “1” comprises a top profile having different tread radii herein referred as TR1 and TR2, and bottom profile having different tread radii herein referred as IR1 & IR2.
In another aspect, tire with modified profile is proposed in which top radii TR1 & TR2 and bottom radii IR1 & IR2 were increased in order to reduce the rolling resistance of the tire without compromising ride comfort and handling properties of the tire. Reducing the mass of the tread in the shoulder region “S”, designing the contact patch in a square shape also result uniform distribution of weight over

the contact patch and reduction in the stresses in contact patch region which in turn results in the reducing the rolling resistance.
The detailed description is described with reference to the accompanying figures. It should be noted that the description and the figures are merely examples of the present invention and not meant to represent the invention itself.
FIG. 1 shows a cross sectional view of pneumatic radial tires for passenger vehicles, as per an implementation of the present invention;
FIG. 2 shows a contact patch of tire, as per an implementation of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
DEFINITIONS
In describing the invention, the afore-mentioned terminology will be used in accordance with the definitions set forth below. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein.
As used herein, each of the following terms has the meaning associated with it in this section. Specific and preferred values listed below for individual process parameters, substituents, and ranges are for illustration only; they do not exclude other defined values or other values falling within the preferred defined ranges. All publications mentioned herein are incorporated by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.

As used herein, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise.
The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.
When the term “about” is used in describing a value or an endpoint of a range, the disclosure should be understood to include either the specific value or end-point referred to.
As used herein, the terms “comprises”, “comprising”, “includes”, “including”, “containing”, “characterized by”, “having” or any other variation thereof, are intended to cover a non-exclusive inclusion.
Embodiments of the present invention is explained with reference to the accompanying drawings.
In an embodiment, a pneumatic radial tire is described in FIG. 1 which is a cross section of the pneumatic radial tire for a passenger vehicle.
Radial tire describes a pneumatic tire structure in which the ply cords extend to the beads and are laid substantially at 90 degrees to the centerline of the tread, the carcass being stabilized by an essentially in-extensible circumferential steel belt.
FIG .1 represents a pneumatic tire cross section including a tire axis C/L, tire section reference height RH and nominal rim diameter D under a standard state. Here, the standard state is arrived for tire when the tire is mounted on measuring rim and the said tire is inflated to a standard pressure with no tire load.

The measuring rim is a wheel rim officially approved or recommended for the tire by standard ITTAC. The standard pressure is the “Inflation Pressure” in ITTAC and the maximum pressure given in the “Tire Load Limits at various Cold Inflation Pressures” table in ITTAC or the similar standard. In case of passenger car tires, the standard pressure is defined as 180 kPa by ITTAC.
As shown in FIG. 1, the pneumatic tire in accordance with the present embodiment comprises: a tread portion 1; a pair of sidewall portions 5 each of which extends from the end of tread portion to axially inwards; a pair of bead portions 6 which seats on the wheel rim and connects to the sidewall portion each of which has a bead core 6a; the shoulder portion 2, buttress portion 3 connects the tread portion and sidewall portion. The pneumatic tire, as illustrated here is for passenger car applications having aspect ratio 80 and tread width not extending more than 70-80% of nominal section width of tire.
The tread is the part of the tire which comes in contact with the ground and through which the driving, braking and cornering forces are transmitted. The tread width TW is the width of tread portion measured under the standard condition, as the linear distance between the tread edges. The tread edges are the outermost edges of the tread portion contact patch contacting the ground without any camber angle at standard condition and specified load. The specified load is maximum load capacity as per ITTAC load – inflation table.
In the tire section including the tire axis under the standard condition, the tread portion 1 comprises a tread width TW (mm) varies from 70% to 80% of the overall tire a section width SW (mm).
In the tire section, the axial distance measured over the maximum sidewall elevation including engravings or protective ribs under standard state and when measured on inflation pressure is termed as overall tire section width SW. The section width SW is the dimensions at which tire section achieves the maximum

width under standard state and when measured on inflation pressure and is represented as centerline in the given FIG. 1.
In the tire section, section height is half the difference between overall diameter OD and nominal rim diameter D. The rim diameter D is the dimensions of rim diameter as defined in the ITTAC for given tire size on which the tire fits during mounting.
In the tire section, aspect ratio is the hundredth times section height divided by section width. In the tire section, the axial distance between rim diameter and overall width centerline is termed as reference height RH and for this case it is preferably in the range of 45-55 % of the section height.
In the tire section, skid depth is the maximum axial depth of tread groove measured as distance between tread topmost surface and bottommost surface.
The tire includes a decoupling groove which is an arc 3b having radius of curvature connecting the buttress line 3a and sidewall upper radius USR. The shape of decoupling groove reduces the rubber mass from shoulder region 3 and also disconnects tread 1 and sidewall region 5.
The tire includes: a carcass 4 extending between bead cores 6a through the tread portion 1, sidewall portions 5 and shoulder portion 3; and belt package 10 disposed radially outside the carcass in the tread portion 2. The carcass 4 is made up of at least one carcass ply which is composed of rubberized carcass cords arranged at an angle in the range of 85-90 degrees with respect to tire centerline CL. Carcass is made up of polyester, nylon, rayon, aramid and similar material. The current embodiment illustrated here is made up of polyester.
The belt package 7 comprises, two belt plies 7a & 7b laid at an angle from 20-30 degrees with respect to tire centerline CL and criss-cross to each other to ensure

rigidity of the tread portion is firmly maintained. The belt package 7 has further a layer of organic cover cord 7c which is made up of at least one organic ply placed above belt 7b; which is composed of rubberized cords arranged at an angle in the range of 0-5 degrees with respect to tire centerline CL. Cover cord is made up of polyester, nylon, rayon, aramid and similar material having low elastic modulus. The cover belt 7c prevents the lifting of tire carcass at high speed running and hence improves the high speed durability of the tire.
The tire also includes: a tire shoulder profile 3 between the tread portion 1 and sidewall portion 5 which further include a shoulder profile 7a which is an arc having curvature from 15-35 mm; a sidewall profile defining at least one radius having which is an arc having its center inside the sidewall portion and lying on RH. A buttress profile which is made up of line which is connecting shoulder radius 7a and sidewall radius USR.
The tread top portion 11 is constituted by two radii TR1 & TR2; TR1 is an arc having curvature from 2.5-4.5 times the value of nominal section width having its center inside tread portion, on the tire centerline CL and cord straight length from 20-40 % of TW; TR2 is an arc tangent to TR1 at starting end having curvature from 0.2-0.5 times the value of TR1 and tangent to Shoulder radius TR3 at the end.
Moreover, referring to FIG. 1, the tire bottom profile 12 starts from the centreline CL region and extends to shoulder region is improved to include: IR1 is an arc having curvature from 4.0-8.0 times the value of nominal section width having its center inside tread portion and on the tire centerline CL and cord straight length from 20-40 % of TW and placed at the distance equivalent to skid depth N; IR2 is an arc tangent to IR1 at starting end having curvature from 0.2-0.5 times the value of TR1 and tangent to shoulder inside radius IR3 at the end.

The sidewall end Z is linear distance between belt-2 6a end and end of sidewall component 4 which defines the sidewall ending on the shoulder region below belt. Preferably, the sidewall end Z is in the range of 10-15mm for 80 aspect ratio tires.
In the tire section, the drop of belt is controlled by tread bottom radius drop SD as 100 times the of tread width TW at distance X from tread width end TW, which is controlled by combination of change of radii in tread top surface TR1, TR2 and tread bottom surface IR3, IR4 and its length L1 & L2. Preferably, the tread bottom radius drop SD is in the range of 2.5 mm -3.5 mm. The distance X from tread width end TW at which the SD is measured is preferably in the range of 4-6 mm.
For a given pneumatic tire, contact patch is the portion of the tire that is in actual contact with the ground when the tire is mounted on standard rim with specified internal pressure and at rated load. The contact patch size, shape and pressure distribution within the contact patch are important for the rolling resistance, rider comfort & handling characteristics of the tire & vehicle.
The contact patch shape is defined as the squareness of the contact patch which is defined in FIG. 2. The contact patch squareness is defined as ratio of contact patch length at shoulder LS to contact patch length at center LC. Furthermore, the contact patch length at shoulder at LS is measured at 80 % of contact patch width CW point on the overall contact patch length.
In order to reduce rolling resistance of the tire, the rubber thickness at tread and shoulder region may also be reduced so as to reduce weight of the tire. Contact patch of the tire is also constructed to be more squarer (0.70 > LS/LC < 1) in terms of area so as to distributed uniform pressure and reduce fatigue from the flexing of the sidewall portion 3.
The bottom profile of the tire constituted by larger inner radii IR1 & IR2. This bottom profile reduces the contact pressure on the shoulder region that tends to

reduce and the shape of the contact patch becomes squarer. Moreover, the rubber thickness at shoulder region reduces due to larger value of inner radius IR2 which reduces the weight of the rubber at tread area. The larger IR1 & IR2 also reduces the deflection in the tread region as the belt will be flatter in the tread region in running condition.
Moreover, the tread width is set 70-80% of nominal section width which ensures that the ground contact width is not less than 70% which ensures that breaking & handling performance is not adversely affected. The buttress region 7b is made up of straight line in place of curvature which reduces weight of rubber in buttress region and reduces the rolling resistance.
The buttress profile is having a decoupling groove on an outer surface of the tire which improves the flexibility of the sidewall portion 3 when tire is loaded and running on road. This will result into higher deformation in sidewall as compared to tread during the running condition and reduces the deformation in tread region. The influence of the deformation in the tread portion 2 against the rolling resistance is greater than that of the sidewall portion 3.
Therefore, the embodiment of tire section discussed here in accordance with the present invention has comparatively small deformation in the tread portion 2, the rolling resistance is also decreased.
When the tread width TW is less than 70% to the nominal section width SW, the contact width and ground contact area tends to decrease which reduce the breaking and handling performance. When the tread width is more than 80% to the nominal section width SW, the rubber weight in the tread region tends to be high which increases the rolling resistance. Preferably, the tread width TW is in the range of 70-80% to the nominal section width SW for balanced performance of rolling resistance, handling and ride comfort.
When the shoulder radius TR3 for high aspect ratio tire 80 is greater than 25, it reduces the rolling resistance but also reduces the mass which deteriorates wear

performance during cornering. The lower radius of curvature of TR3 smaller than 15 mm increases the rolling resistance and higher heat generation at shoulder will not father help to improve wear performance. Preferably, the radius of curvature TR3 of shoulder profile is in the range of 15-30 mm for 80 aspect ratio.
When the reference height RH of the tire is more than 55% to section height SH, it increases the LSR which will deteriorate the ride comfort. When the reference height RH of the tire is less than 55% to section height SH it increases the rubber gauge at the shoulder region which deteriorate the rolling resistance. Preferably, the reference height RH of the tire section during standard condition is in the range of 45-55 % to the section height for tire 1.
The present invention described in the present application is more specifically described and explained by means of following design iterations. It is also evident that the present invention is not limited to these examples or design iterations.
Comparison test:
Pneumatic tires for passenger categories of size 165/80R14 having the same construction and rubber compound of FIG. 1 except for details shown in Table 1 below were validated. The test method adopted is mentioned below:

Table 1 : Tire Cavity Design Parameter & Results
Tire Size 165/80R14
Ratios V1 V2 V3 V4
TW/SW % 74 74 74 74
TR1/SW 2.5 2.8 3.2 3.6
TR2/TR1 0.4 0.4 0.25 0.25
L1/TW 0.25 0.25 0.25 0.25
IR1/SW 2.00 2.4 2.8 3.2
IR2/IR1 0.81 0.62 0.45 0.22

RH 53 53 53 53
X 5 5 5 5
TR3 20 20 20 20
IR3 25 25 25 25
Comparison Test
Contact Patch Squareness 0.84 0.86 0.88 0.92
RRC 10.55 10.18 10.27 9.88
Ride Comfort 6.75 6.75 6.75 6.75
Handling 6.75 6.75 6.75 6.75
Rolling Resistance test:
The test tire was mounted on a wheel rim of 4.5 x 14.0 J with the internal pressure of 210 kPa, and the rolling resistance coefficient was measured as per rolling resistance test ISO 28580. The results are shown by rolling resistance coefficient value, where lower the value better the rolling resistance is.
Ride Comfort Test:
The tires were mounted on wheel rims of 4.50 x 14.0 J with the internal pressure of 210 kPa, and fitted in test vehicle, the test engineer drove the vehicle on a test track and evaluated the ride comfort by subject feeling by test engineer as per the rating criteria defined in the test protocol. The results are shown in Table 1 by the index, where the larger the index, better the ride comfort is.
Handling Test:
The test vehicle mentioned above was driven on the test track for handling and braking test as per the speed and manoeuvring conditions defined in the Handling test. The handling test is subject feeling by the test engineer as per the rating criteria defined in the test protocol. As per The results are shown in Table 1 by the index, where the larger the index, better the handling performance is.

From the test results, it was confirmed that lower rolling resistance was achieved using the optimized tire profile contour without comprising ride comfort and handling performance of example tires in accordance present invention. The present invention effectively improved the rolling resistance of the tire.
The present invention described in the present application is more specifically described and explained by means of following design iterations. It is also evident that the present invention is not limited to these examples or design iterations.
Although examples for the present disclosure have been described in language specific to structural features and/or methods, it should be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed and explained as examples of the present disclosure.

We claim:
1. A pneumatic tire comprising:
a tread portion;
a pair of sidewall portions;
a pair of bead portions each having a bead core;
a carcass extending between bead cores through the tread portion, sidewall portion and shoulder portions;
a belt disposed radially outside the carcass in the tread portion wherein the tread portion having tread width TW of 70% to 80% of nominal section width SW; and
radius of curvature of the shoulder profile is in a range from 15-35 mm; containing at least one radius whose center of curvature inside the sidewall and a buttress profile connecting between the shoulder profile and the sidewall profile.
2. The tire as claimed in claim 1, where in tread width (in mm) is between TW is 70% to 80% of nominal SW.
3. The tire as claimed in claim 2, where in the radius of curvature of the shoulder profile is in the range of 15-35 mm.
4. The tire as claimed in claim 2, where in the sidewall profile having at least one radius whose center of curvature is inside the sidewall.
5. The tire as claimed in claim 1, wherein the tread portion having top profile comprising two radii of curvature TR1 and TR2; where in radius of curvature of TR1 is 2.5-4.5 times the value of nominal section width SW; wherein the nominal section width having cord length 20-40% of section width SW and radius of curvature of TR1 is 0.2-0.5 times of radius of curvature of TR2.

6. The tire as claimed in claim 1, wherein the tread profile having bottom profile comprising two radii of curvature IR1 and IR2; where in IR1 is an arc having curvature from 4.0-8.0 times the value of nominal section width; IR2 is an arc tangent to IR1 having curvature from 0.2-0.5 times the value of IR1.
7. The tire as claimed in claim 1, where in the reference height of tire RH is preferably in the range of 45-55% of the section height.
8. The tire as claimed in claim 1, wherein the drop of bottom radius (SD in mm) is 2.5-3.5 % of Tread width TW.