PNEUMATIC TIRE

Abstract

Provided is a pneumatic tire having a sufficiently suppressed change in handling property and sufficiently improved durability. This pneumatic tire comprises a tread portion including a rubber layer, the rubber layer is formed of a rubber composition having 0.25 or less of a loss tangent (15° C. tanδ) measured under such conditions as 15° C., frequency 10 Hz, initial strain 5%, and dynamic strain rate 1%, the tread portion includes a plurality of rib-like land portions formed by circumferential grooves continuously extending in the circumferential direction, the tread portion has a ground contact surface partitioned, at the equatorial plane, such that one ground contact area Sa and the other ground contact area Sb satisfy a relationship of Sa>Sb, and (formula 1) and (formula 2) are satisfied where Wt (mm) is the cross sectional width of the tire, Dt (mm) is the outer diameter, and V (mm3) is a virtual volume being the volume of a space occupied by the tire when the tire is mounted on a standard rim and the internal pressure is 250 kPa.

1600≤(Dt.sup.2×ϕ/4)/Wt≤2827.4  (formula 1)

[(V+1.5×10.sup.7)/Wt]≤2.88×10.sup.5  (formula 2)

Claims

1. A pneumatic tire having a tread portion, wherein the rubber layer constituting the tread portion is formed by a rubber composition having a loss tangent (15° C.tanδ) of 0.25 or less measured under the conditions of 15° C., frequency 10 Hz, initial strain 5%, and dynamic strain rate 1%; a plurality of rib-shaped land portions are formed by circumferential grooves extending continuously in the circumferential direction, in the tread portion; when the ground contact surface of the tread portion is divided by the equatorial plane, and when one ground contact area is Sa and the other is Sb, Sa>Sb; and when the cross-sectional width of the tire is Wt (mm), the outer diameter is Dt (mm), and the volume of the space occupied by the tire is the virtual volume V (mm.sup.3), when the tire is installed on a standardized rim and the internal pressure is 250 kPa, the tire satisfies following (formula 1) and (formula 2):
1600≤(Dt.sup.2×π/4)/Wt≤2827.4  (formula 1)
[(V+1.5×10.sup.7)/Wt]≤2.88×10.sup.5  (formula 2).

2. The pneumatic tire according to claim 1, wherein the tire satisfies the following (formula 3),
[(V+2.0×10.sup.7)/Wt]≤2.88×10.sup.5  (formula 3).

3. The pneumatic tire according to claim 2, wherein the tire satisfies the following (formula 4),
[(V+2.5×10.sup.7)/Wt]≤2.88×10.sup.5  (formula 4).

4. The pneumatic tire according to claim 1, wherein the 15° C.tanδ is 0.20 or less.

5. The pneumatic tire according to claim 1, wherein when the outer diameter of the tire is Dt (mm) and the cross-sectional height of the tire is Ht (mm), when the tire is installed on a standardized rim and the internal pressure is 250 kPa, (Dt-2×Ht) is 470 (mm) or more.

6. The pneumatic tire according to claim 1, wherein the aspect ratio is 40% or more.

7. The pneumatic tire according to claim 6, wherein the aspect ratio is 45% or more.

8. The pneumatic tire according to claim 7, wherein the aspect ratio is 47.5% or more.

9. The pneumatic tire according to claim 1, wherein the tire satisfies 15° C.tanδ×Wt 50.

10. The pneumatic tire according to claim 9, wherein the tire satisfies 15° C.tanδ×Wt 40.

11. The pneumatic tire according to claim 10, wherein the tire satisfies 15° C.tanδ×Wt 30.

12. The pneumatic tire according to claim 1, wherein the tire satisfies Sb/Sa<0.8.

13. The pneumatic tire according to claim 12, wherein the tire satisfies Sb/Sa<0.75.

14. The pneumatic tire according to claim 13, wherein the tire satisfies Sb/Sa<0.7.

15. The pneumatic tire according to claim 1, wherein a plurality of circumferential grooves extending continuously in the tire circumferential direction are formed in the tread portion, and the total cross-sectional area of the plurality of circumferential grooves is 10 to 30% of the cross-sectional area of the tread portion.

16. The pneumatic tire according to claim 1, wherein a plurality of lateral grooves extending in the tire axial direction are formed in the tread portion, and the total volume of the plurality of lateral grooves is 2.0 to 5.0% of the volume of the tread portion.

17. The pneumatic tire according to claim 1, wherein when the outer diameter of the tire is Dt (mm) when the tire is installed on a standardized rim and the internal pressure is 250 kPa, the Dt is less than 685 (mm).

18. The pneumatic tire according to claim 1, wherein the cross-sectional width Wt (mm) is less than 205 mm.

19. The pneumatic tire according to claim 18, wherein the cross-sectional width Wt (mm) is less than 200 mm.

Description

EXAMPLES

[0220] Hereinafter, the present invention will be described in more specific with reference to Examples.

[Experiment 1]

[0221] In this experiment, 175 size tires were prepared and evaluated.

1. Manufacture of Rubber Compositions for Treads

[0222] First, a rubber composition for tread was produced.

(1) Compounding Material

[0223] First, each compounding material shown below was prepared.

(a) Rubber Component

(α-1) NR: TSR20

[0224] (α-2) SBR: Modified solution polymerization SBR produced according to the method described in the next paragraph. (Styrene content: 10% by mass, vinyl bond amount: 20% by mass, Mw: 250,000)
(α-3) BR: BR150 manufactured by Ube Kosan Co., Ltd.

[0225] The abovementioned SBR was produced according to the procedure shown below. First, cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene were charged into a nitrogen-substituted autoclave reactor. After adjusting the temperature of the contents of the reactor to 20° C., n-butyllithium was added to initiate polymerization. Polymerization was carried out under adiabatic conditions, and the maximum temperature reached 85° C. When the polymerization conversion reaches 99%, 1,3-butadiene was added, and then further polymerization was carried out for 5 minutes. Thereafter, N, N-bis(trimethylsilyl)-3-aminopropyltriethoxysilane was added as a modifying agent to carry out the reaction. After completion of the polymerization reaction, 2,6-di-tert-butyl-p-cresol was added. Then, the solvent was removed by steam stripping and dried by a heat roll adjusted to 110° C. to obtain the SBR.

(b) Compounding Materials Other than Rubber Components
(b-1) Carbon black: Diablack N.sub.220 manufactured by Mitsubishi Chemical Corporation
(b-2) Silica: Ultrasil VN3 manufactured by Evonik Co., Ltd. (BET specific surface area: 165 m.sup.2/g)
(b-3) Silane coupling agent: Si266 manufactured by Degussa Co., Ltd.

[0226] (Bis(3-triethoxysilylpropyl) disulfide)

(b-4) Oil: Process X-140 manufactured by Japan Energy Co., Ltd.
(b-5) Anti-aging agent: SA85 manufactured by Arizona Chemical Co., Ltd. (α-Methylstyrene resin)
(b-6) Zinc oxide: Zinc white No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd.
(b-7) Stearic acid: Stearic acid “TSUBAKI” manufactured by NOF CORPORATION
(b-8) Wax: Sunnoc wax manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
(b-9) Anti-aging agent-1: Nocrac 6C manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-Phenyl-N′(1,3-dimethylbutyl)-p-phenylenediamine)
(b-10) Crosslinking agent and vulcanization accelerator

[0227] Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

[0228] Vulcanization accelerator-1: Nocceler CZ-G (CBS) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (N-Cyclohexyl-2-benzothiazolyl sulphenamide)

[0229] Vulcanization accelerator-2: Nocceler D (DPG) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (1,3-Diphenylguanidine)

(2) Production of Rubber Composition

[0230] In accordance with the formulation shown in Table 1 and Table 2, materials other than sulfur and the vulcanization accelerator were kneaded under the conditions of 150° C. for 5 minutes using a Banbury mixer to obtain a kneaded product. Each compounding amount is a mass part.

2. Tire manufacturinga Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded at 80° C. for 5 minutes using an open roll to obtain a tread rubber composition. A tread is formed using the obtained tread rubber composition, bonded together with other tire members to form an unvulcanized tire, which is then press-vulcanized for 10 minutes under the condition of 170° C. to produce each test tire having a size of 175 type (Example 1-1 to Example 1-5 and Comparative Example 1-1 to Comparative Example 1-5).

[0231] In each test tire, the above-mentioned (L.sub.80/L.sub.0) was 0.5, the total cross-sectional area of the circumferential groove was 22% of the cross-sectional area of the tread portion, and the total volume of the lateral grooves including the lateral grooves having the groove width/groove depth of 0.65 was set to 3.5% of the volume of the tread portion.

3. Parameter Calculation

[0232] After that, the outer diameter Dt (mm), the cross-sectional width Wt (mm), the cross-sectional height Ht (mm), the Sb/Sa, and the aspect ratio (%) of each test tire were obtained, and the virtual volume V (mm.sup.3) was obtained. At the same time, a rubber test piece for viscoelasticity measurement was produced by cutting out from the rubber layer of the tread portion of each test tire in a length 20 mm×width 4 mm×thickness 2 mm so that the tire circumferential direction was the long side. For each rubber test piece, tan δ (15° C.tan δ) was measured under the conditions of 15° C., frequency 10 Hz, initial strain 5%, and dynamic strain 1% using an Eplexor series manufactured by GABO Co., Ltd. The thickness direction of the sample was the tire radial direction. The results are shown in Tables 1 and 2.

[0233] In addition, Sa and Sb can be obtained as follows. That is, the tire is installed on the standardized rim, the standardized internal pressure is applied, the tread surface is painted with black ink, the standardized load is applied and the tread surface is pressed against the thick paper (camber angle is 0°) so that the black ink is transferred to the paper. Specifically, the tire is rotated by 72° in the circumferential direction and, using five thick papers, the ink is transferred each at five places to obtain a transferred image. As a result, it can be considered that the shape of the ground contact surface over the entire circumference of the tire is obtained.

[0234] Then, when transfer images of the five thick papers are divided by the equatorial plane, Sa is obtained by totaling the areas of one of the contact areas (the part excluding grooves and sipes, that is, the inked area); and Sb is obtained by totaling the areas of the other contact area (the portion excluding the groove and the sipe, that is, the inked area).

[0235] Then, (Dt−2×Ht), (Dt.sup.2×π/4)/Wt, (V+1.5×10.sup.7)/Wt, (V+2.0×10.sup.7)/Wt, (V+2.5×10.sup.7)Wt, and 15° C.tan δ×Wt were determined. The results are shown in Tables 1 and 2.

4. Performance Evaluation Test

(1) Evaluation of Handling Performance

[0236] After mounting each test tire on all wheels of the vehicle (domestic FF vehicle, displacement 2000 cc) and filling it with air so that the internal pressure became 250 kPa, the driver sensually inspected the change in handling characteristics on a five-point scale from 1 (feeling a significant change) to 5 (feeling almost no change) when driving at the speed of 40 km/h and 120 km/h on the test course on the dry road surface. Then, the total score of the evaluation by 20 drivers was calculated.

[0237] Next, the result in Comparative Example 1-5 was set to 100 and the evaluation was indexed based on the following formula to evaluate the handling characteristics. The larger the value, the better the handling characteristics.

=[(Result of test tire)/(Result of Comparative Example1-5)]×100

(2) Evaluation of Durability Performance

[0238] After mounting each test tire on all wheels of the vehicle (domestic FF vehicle, displacement 2000 cc) and filling it with air so that the internal pressure becomes 250 kPa, a driving 10 laps at a speed of 50 km/h, followed by climbing onto the unevenness provided on the road surface at a speed of 80 km/h was repeated on the test course on a dry road surface in an overloaded state. Thereafter, the lap was performed again at a speed of 50 km/h and then the speed was gradually increased to measure the speed at the time when the driver felt an abnormality.

[0239] Next, the result in Comparative Example 1-5 was set as 100, and the durability performance was relatively evaluated by indexing based on the following formula. The larger the value, the better the durability.

[0240] Durability

=[(Result of test tire)/(Result of Comparative Example1-5)]1×100

(3) Comprehensive Evaluation

[0241] The evaluation results of (1) and (2) above were totaled to obtain a comprehensive evaluation.

(4) Evaluation Result

[0242] The results of each evaluation are shown in Tables 1 and 2.

TABLE-US-00001 TABLE 1 Example No. 1-1 1-2 1-3 1-4 1-5 SIZE 175/40R21 175/40R21 175/40R21 175/50R20 175/60R19 (Formulation) NR 20 20 20 20 20 SBR 30 30 30 30 30 BR 50 50 50 50 50 Carboneplexor 5 5 5 5 5 Silica 120 100 80 120 120 Silane coupling agent 4.5 4.5 4.5 4.5 4.5 Oil 60 30 5 60 60 Zinc oxide 3 3 3 3 3 Stearic acid 3 3 3 3 3 Anti-aging agent 2 2 2 2 2 Wax 2 2 2 2 2 Sulfur 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 accelerator-1 Vulcanization 1 1 1 1 1 accelerator-2 (Parameter) 15° C. tanδ 0.19 0.16 0.13 0.19 0.19 Sb/Sa 0.91 0.82 0.68 0.91 0.91 Dt(mm) 672 673 674 684 693 V(mm.sup.3) 23225099 23279803 23332669 29988186 34384955 Wt(mm) 177 176 175 182 177 Ht(mm) 69 70 70 88 105 Dt-2 × Ht(mm) 533 533 533 508 483 (Dt.sup.2 × π/4)/Wt 2004 2021 2039 2019 2131 (V + 1.5 × 10.sup.7)/Wt 215961 217499 219044 247188 279011 (V + 2.0 × 10.sup.7)/Wt 244210 245908 247615 274660 307260 (V + 2.5 × 10.sup.7)/Wt 272458 274317 276187 302133 335508 Aspect ratio (%) 39 40 40 48 59 15° C. tanδ × Wt 33.63 28.16 22.75 34.58 33.63 (Evaluation result) Handling characteristics 112 115 119 113 117 Durability 117 121 127 114 111 Comprehensive evaluation 229 236 246 227 228

TABLE-US-00002 TABLE 2 Comparative example No. 1-1 1-2 1-3 1-4 1-5 SIZE 175/80R14 175/60R19 175/80R14 175/80R14 175/80R14 (Formulation) NR 20 20 20 20 20 SBR 30 30 30 30 30 BR 50 50 50 50 50 Carbon 5 5 5 5 5 Silica 150 150 120 100 80 Silane coupling agent 4.5 4.5 4.5 4.5 4.5 Oil 110 110 60 30 5 Zinc oxide 3 3 3 3 3 Stearic acid 3 3 3 3 3 Anti-aging agent 2 2 2 2 2 Wax 2 2 2 2 2 Sulfur 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 accelerator-1 Vulcanization 1 1 1 1 1 accelerator-2 (Parameter) 15° C.tanδ 0.26 0.26 0.19 0.16 0.13 Sb/Sa 1 1 0.91 0.82 0.68 Dt(mm) 636 693 635 637 636 V(mm.sup.3) 38652508 34384955 38041064 38610099 38870883 Wt(mm) 177 177 175 176 178 Ht(mm) 140 105 140 141 140 Dt-2 × Ht(mm) 356 483 356 356 356 (Dt.sup.2 × π/4)/Wt 1795 2131 1810 1811 1785 (V + 1.5 × 10.sup.7)/Wt 303122 279011 303092 304603 302645 (V + 2.0 × 10.sup.7)/Wt 331370 307260 331663 333012 330735 (V + 2.5 × 10.sup.7)/Wt 359619 335508 360235 361421 358825 Aspect ratio (%) 79 59 80 80 79 15° C. tanδ × Wt 46.02 46.02 33.25 28.16 23.14 (Evaluation result) Handling characteristics 91 97 95 98 100 Durability 90 95 97 98 100 Comprehensive evaluation 181 192 192 196 200

[Experiment 2]

[0243] In this experiment, 195 size tires were prepared and evaluated.

[0244] After producing the test tires of Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-5 shown in Tables 3 and 4 in the same manner as in Experiment 1, each parameter was calculated by performing the same procedure. Then, in the same manner, a performance evaluation test was conducted and evaluated. In this experiment, the result in Comparative Example 2-5 was set as 100 for evaluation. The results of each evaluation are shown in Tables 3 and 4.

TABLE-US-00003 TABLE 3 Example No. 2-1 2-2 2-3 2-4 2-5 SIZE 195/40R20 195/40R20 195/40R20 195/50R19 195/60R18 (Formulation) NR 20 20 20 20 20 SBR 30 30 30 30 30 BR 50 50 50 50 50 Carbon 5 5 5 5 5 Silica 120 100 80 120 120 Silane coupling agent 4.5 4.5 4.5 4.5 4.5 Oil 60 30 5 60 60 Zinc oxide 3 3 3 3 3 Stearic acid 3 3 3 3 3 Anti-aging agent 2 2 2 2 2 Wax 2 2 2 2 2 Sulfur 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 accelerator-1 Vulcanization 1 1 1 1 1 accelerator-2 (Parameter) 15° C. tanδ 0.19 0.16 0.13 0.19 0.19 Sb/Sa 0.91 0.82 0.68 0.91 0.91 Dt(mm) 664 664 664 679 691 V(mm.sup.3) 28719183 28719183 28719183 36015050 42378735 Wt(mm) 200 200 200 201 201 (Dt.sup.2 × π/4)/Wt 1731 1731 1731 1801 1866 Ht(mm) 78 78 78 98 117 Dt-2 × Ht(mm) 508 508 508 483 457 (V + 1.5 × 10.sup.7)/Wt 218596 218596 218596 253806 285466 (V + 2.0 × 10.sup.7)/Wt 243596 243596 243596 278682 310342 (V + 2.5 × 10.sup.7)/Wt 268596 268596 268596 303557 335218 Aspect ratio (%) 39 39 39 49 58 15° C. tanδ × Wt 38.00 32.00 26.00 38.19 38 (Evaluation result) Handling characteristics 109 111 115 110 113 Durability 116 117 121 109 106 Comprehensive evaluation 225 228 236 219 219

TABLE-US-00004 TABLE 4 Comparative example No. 2-1 2-2 2-3 2-4 2-5 SIZE 175/80R14 175/60R19 175/80R14 175/80R14 175/80R14 (Formulation) NR 20 20 20 20 20 SBR 30 30 30 30 30 BR 50 50 50 50 50 Carbon 5 5 5 5 5 Silica 150 150 120 100 80 Silane coupling agent 4.5 4.5 4.5 4.5 4.5 Oil 110 110 60 30 5 Zinc oxide 3 3 3 3 3 Stearic acid 3 3 3 3 3 Anti-aging agent 2 2 2 2 2 Wax 2 2 2 2 2 Sulfur 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 accelerator-1 Vulcanization 1 1 1 1 1 accelerator-2 (Parameter) 15° C. tanδ 0.26 0.26 0.19 0.16 0.13 Sb/Sa 1 1 0.91 0.82 0.68 Dt(mm) 686 664 686 686 686 V(mm.sup.3) 44856521 28719183 44856521 44856521 44856521 Wt(mm) 201 200 201 201 201 (Dt.sup.2 × π/4)/Wt 1839 1731 1839 1839 1839 Ht(mm) 127 78 127 127 127 Dt-2 × Ht(mm) 432 508 432 432 432 (V + 1.5 × 10.sup.7)/Wt 297794 218596 297794 297794 297794 (V + 2.0 × 10.sup.7)/Wt 322669 243596 322669 322669 322669 (V + 2.5 × 10.sup.7)/Wt 347545 268596 347545 347545 347545 Aspect ratio (%) 63 39 63 63 63 15° C. tanδ × Wt 52.26 52.00 38.19 32.16 26.13 (Evaluation result) Handling characteristics 91 97 96 98 100 Durability 90 95 98 99 100 Comprehensive evaluation 181 192 194 197 200

[Experiment 3]

[0245] In this experiment, 225 size tires were prepared and evaluated.

[0246] After producing the test tires of Examples 3-1 to 3-5 and Comparative Examples 3-1 to 3-5 shown in Tables 5 and 6 in the same manner as in Experiment 1, each parameter was calculated by performing the same procedure. Then, in the same manner, a performance evaluation test was conducted and evaluated. In this experiment, the result in Comparative Example 3-5 was set as 100 for evaluation. The results of each evaluation are shown in Tables 5 and 6.

TABLE-US-00005 TABLE 5 Example No. 3-1 3-2 3-3 3-4 3-5 SIZE 225/35R22 225/35R22 225/35R22 225/50R20 225/40R21 (Formulation) NR 20 20 20 20 20 SBR 30 30 30 30 30 BR 50 50 50 50 50 Carbon 5 5 5 5 5 Silica 120 100 80 120 120 Silane coupling agent 4.5 4.5 4.5 4.5 4.5 Oil 60 30 5 60 60 Zinc oxide 3 3 3 3 3 Stearic acid 3 3 3 3 3 Anti-aging agent 2 2 2 2 2 Wax 2 2 2 2 2 Sulfur 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 accelerator-1 Vulcanization 1 1 1 1 1 accelerator-2 (Parameter) 15° C. tanδ 0.19 0.16 0.13 0.19 0.19 Sb/Sa 0.91 0.82 0.68 0.91 0.91 Dt(mm) 717 715 718 735 712 V(mm.sup.3) 36459171 35629276 36878037 51856443 40005129 Wt(mm) 230 228 231 234 229 Ht(mm) 79 78 80 114 89 Dt-2 × Ht(mm) 559 559 559 508 533 (Dt.sup.2 × π/4)/Wt 1755 1761 1753 1813 1739 (V + 1.5 × 10.sup.7)/Wt 223736 222058 224580 285711 240197 (V + 2.0 × 10.sup.7)/Wt 245475 243988 246225 307079 262031 (V + 2.5 × 10.sup.7)/Wt 267214 265918 267870 328446 283865 Aspect ratio (%) 34 34 34 49 39 15° C. tanδ × Wt 43.70 36.48 30.03 44.46 43.51 (Evaluation result) Handling characteristics 107 109 112 108 110 Durability 112 115 119 107 105 Comprehensive evaluation 219 224 231 215 215

TABLE-US-00006 TABLE 6 Comparative example No. 3-1 3-2 3-3 3-4 3-5 SIZE 225/60R20 225/50R20 225/60R20 225/60R20 225/60R20 (Formulation) NR 20 20 20 20 20 SBR 30 30 30 30 30 BR 50 50 50 50 50 Carbon 5 5 5 5 5 Silica 150 150 120 100 80 Silane coupling agent 4.5 4.5 4.5 4.5 4.5 Oil 110 110 60 30 5 Zinc oxide 3 3 3 3 3 Stearic acid 3 3 3 3 3 Anti-aging agent 2 2 2 2 2 Wax 2 2 2 2 2 Sulfur 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 accelerator-1 Vulcanization 1 1 1 1 1 accelerator-2 (Parameter) 15° C. tanδ 0.26 0.26 0.19 0.16 0.13 Sb/Sa 1 1 0.91 0.82 0.68 Dt(mm) 778 734 778 778 778 V(mm.sup.3) 62176957 50925101 62176957 61904251 62722369 Wt(mm) 228 231 228 227 230 Ht(mm) 135 113 135 135 135 Dt-2 × Ht(mm) 508 508 508 508 508 (Dt.sup.2 × π/4)/Wt 2085 1832 2085 2094 2067 (V + 1.5 × 10.sup.7)/Wt 338495 285390 338495 338785 337923 (V + 2.0 × 10.sup.7)/Wt 360425 307035 360425 360812 359662 (V + 2.5 × 10.sup.7)/Wt 382355 328680 382355 382838 381402 Aspect ratio (%) 59 49 59 59 59 15° C. tanδ × Wt 59.28 60.06 43.32 36.32 29.90 (Evaluation result) Handling characteristics 91 97 97 99 100 Durability 90 95 98 99 100 Comprehensive evaluation 181 192 195 198 200

[Summary of Experiments 1 to 3]

[0247] From the results of Experiments 1 to 3 (Tables 1 to 6), for tires of any size, 175 size, 195 size, 225 size, it turns out that pneumatic tires in which not only the rolling resistance is reduced, but also the change in handling characteristics at low-speed running and high-speed running is sufficiently suppressed, and the durability is also sufficiently improved, when Sa>Sb (Sb/Sa<1) and the above (formula 1) and (formula 2) is satisfied, can be provided.

[0248] Then, it turns out that, by satisfying each of the requirements specified in claim 2 and thereafter, a tire having further improved change in handling characteristics at low-speed running and high-speed running and durability can be provided.

[0249] On the other hand, when either (formula 1) or (formula 2) is not satisfied, the change in handling characteristics at low-speed running and high-speed running is not sufficiently small, and the durability is not sufficiently improved.

[Experiment 4]

[0250] Next, three types of tires (Examples 4-1 to 4-3) in which the relationship between the virtual volume V and the cross-sectional width Wt did not differ significantly were produced with the same composition and evaluated in the same manner. Here, in addition to the above-mentioned evaluation of handling characteristics and durability performance, fuel efficiency was also evaluated.

[0251] Specifically, each test tire was mounted to all wheels of the vehicle (domestic FF vehicle, displacement 2000 cc), filled with air so that the internal pressure became 250 kPa, and then driven on the test course on the dry road surface at a speed of 100 km/h. After making a 10 km lap, the accelerator was released, and the distance from when the accelerator was turned off until the vehicle stopped was measured, as the rolling resistance of each test tire.

[0252] Next, taking the result in Example 4-3 as 100, and the results were indexed based on the following formula to relatively evaluate the fuel efficiency. The larger the value, the longer the distance from the timing when the accelerator is turned off until the vehicle stops, and the smaller the rolling resistance in the steady state, showing excellent fuel efficiency.

Fuel efficiency=[(Result of test tire)/(Result of Example4-3)]×100

[0253] Then, as in Experiments 1 to 3, the evaluation results were totaled to make a comprehensive evaluation. The results of each evaluation are shown in Table 7.

TABLE-US-00007 TABLE 7 Example No. 4-1 4-2 4-3 SIZE 175/55R18 195/50R19 225/45R20 (Formulation) NR 20 20 20 SBR 30 30 30 BR 50 50 50 Carbon 5 5 5 Silica 90 90 90 Silane coupling agent 4.5 4.5 4.5 Oil 15 15 15 Zinc oxide 3 3 3 Stearic acid 3 3 3 Anti-aging agent 2 2 2 Wax 2 2 2 Sulfur 1.5 1.5 1. 5 Vulcanization 2 2 2 accelerator-1 Vulcanization 1 1 1 accelerator-2 (Parameter) 15° C. tanδ 0.14 0.14 0.14 Sb/Sa 0.73 0.73 0.73 Dt(mm) 650 677 709 V(mm.sup.3) 30681323 35409871 43419514 Wt(mm) 183 200 226 Ht(mm) 96 97 101 Dt-2 × Ht(mm) 457 483 508 (Dt.sup.2 × π/4)/Wt 1813 1800 1747 (V + 1.5 × 10.sup.7)/Wt 249625 252049 258493 (V + 2.0 × 10.sup.7)/Wt 276947 277049 280617 (V + 2.5 × 10.sup.7)/Wt 304270 302049 302741 Aspect ratio (%) 53 49 44 15° C. tanδ × Wt 25.62 28.00 31.64 Handling characteristics 107 104 100 Durability 104 102 100 Fuel efficiency 111 106 100 Comprehensive evaluation 322 312 300

[0254] Table 7 shows that, when there is no large difference in the relationship between the virtual volume V and the cross-sectional width Wt, all the handling characteristics, durability performance and fuel efficiency are improved, as the cross-sectional width Wt becomes smaller as from less than 205 mm to less than 200 mm, and as the aspect ratio increases. That is, it can be seen a remarkable effect is exhibited.

[0255] Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above embodiments within the same and equal range as the present invention.