Pneumatic tyre for two-wheeled vehicle

Abstract: A pneumatic tire for a two-wheeled vehicle having high lateral stiffness and exhibiting improved steering stability has a tread pattern defined in a tread portion (1) by numerous sets of combination lug groove patterns (3). In this tread portion, one set of the left and right sides of the lug groove patterns is reverse W-shaped as a whole in the tire rolling direction, each of mid bending points P on both sides of the reverse W-shape is arranged at the region of 20-80% of a tire tread half width TW from a tire central circumferential line EC, an angle ∝ of the lug groove component to a tire shoulder portion from the mid bending point P is 20-70° with respect to a tire equatorial plane E, and an angle β of the lug groove component to the tire central circumferential line EC from the bending point P is 20-70° with respect to the tire equatorial plane E.

Description: The present invention relates to a pneumatic tire for a two -wheeled vehicle (motorcycle), and particularly relates to a pneumatic tire for a two -wheeled vehicle capable of obtaining high lateral stiffness without requiring any tire structural change, material change and the like, and of exhibiting improved steering stability. In a conventional pneumatic tire for a two-wheeled vehicle, it is general to employ a measure for improving steering stability as much as possible under a specified tire size, and it is also general to improve the lateral stiffness of a tire. As an effective means for improving the lateral stiffness of a tire, for each kind of members for constructing a tire such as carcass ply, cord layers such as belt or breaker, bead filler effective for bead portion reinforcement and the like, it has been attempted to improve the material and the structure of these members, and to arrange additional reinforcing members. The aforesaid means certainly contributes to improvement of the lateral stiffness of a tire, but simultaneously encounters the problem that the lateral stiffness improvement by the change of material and structure increases the vertical spring constant of the tire with the result that the comfort against vibration is reversely affected. Moreover, the lateral stiffness improvement contingent to the addition of members is undesirable for not only an increase of the material cost but also an increase of the processing cost. Accordingly, an object of the invention is to provide a pneumatic tire for a two-wheeled vehicle capable of obtaining high lateral stiffness without requiring any structural change, material change and the like of a tire, and capable of exhibiting improved steering stability. It has been well-known that an increase of the ground-contact area of a load rolling tire at the tread surface is effective for the lateral stiffness improvement of a tire for a two -wheeled vehicle. As one means for increasing the ground-contact area, it is effective to decrease the flexural stiffness of a tread portion, but this tends to deteriorate the shearing stiffness of the tread portion within the ground- contact area, and further has a tendency to lower the flexural stiffness at a non-ground-contact area, and both these tendencies are disadvantageous to steering stability. The present inventors have therefore considered the tread pattern itself for increasing the ground-contact area without such disadvantage, and as a result accomplished the present invention. Attention is also drawn to the disclosures of JP-03-135802A and JP-08-142609A. JP-A-03-135 802, considered as closest prior art to the fire of claim 1, discloses a pneumatic motorcycle tire formed with lug groove patterns on the tread surface of a tread portion, wherein, on each of left and right sides with respect to the tire central circumferential line, each of said lug groove patterns has two mid bending points and each of the bending points forms V-shape grooves, wherein each of said lug groove patterns has a first lug groove component Go extending from a first mid bending point toward a tire shoulder portion, a second lug groove component Gi extending from the first mid bending point toward the tire central circumferential line, and a third lug groove component Gm extending from the second lug groove component at a second mid bending point toward the tire circumferenfial line, wherein each of the first mid bending points P is arranged at 75% of a tire tread half width TW from the tire central circumferential line EC, wherein the angle of the first lug groove component Go to a tire shoulder portion from the first mid bending point is 25 - 60° with respect to a tire equatorial plane, and wherein the angle of the second lug groove component Gi to the tire central circumferential line EC from the bending point P is 15-45° with respect to the tire equatorial plane E. The present invention provides a pneumatic motorcycle tire formed with lug groove patterns on the tread surface of a tread portion, wherein, on each of left and right sides with respect to a tire central circumferential line EC, each of said lug groove patterns has two mid bending points P,P' and each of the bending points P,P' forms reverse V-shape grooves with the tip of the V bring oriented in the tire rolling direction, wherein each of said lug groove patterns has a first lug groove component extending from a first mid bending point P toward a tire shoulder portion, a second lug groove component extending from said first mid bending point P toward the tire central circumferential line EC, and a third lug groove component extending from said second lug groove component at a second mid bending point P' toward the tire shoulder portion, wherein each of the first mid bending points P is arranged within a region of 20-80% of a tire tread half width TW from the tire central circumferential line EC, wherein an angle α of the first lug groove component to a tire shoulder portion from the mid bending point P is 20-70° with respect to a tire equatorial plane E, and wherein an angle β of the second lug groove component to the tire central circumferential line EC from the bending point P is 20-70° with respect to the tire equatorial plane E. The pneumatic tire for a two-wheeled vehicle (motorcyle) according to the invention preferably has at least one circumferential groove formed in a tread central region and the circumferential groove arranged in the region from the tire central circumferential line EC to 35% of the tire tread half width TW. Moreover, a pitch DP of the lug groove is preferably 1/100 - 1/20 of the whole circumferential length. Furthermore, an offset amount OF for offsetting left and right patterns by symmetrizing the central circumferential line EC is preferably 0 - 1/20 of the whole circumferential length. Here, the central circumferential line EC means a crossing line between the tire equatorial plane E and the tread surface. The invention will be further described with reference to the accompanying drawings, wherein : Fig. 1 is a plan view of a tread pattern of a pneumatic tire for a two-wheeled vehicle according to the invention; and Fig. 2 is a left half cross section of the pneumatic tire for a two-wheeled vehicle according to the invention. Fig. 1 shows a tread surface 2 in a tread portion 1 of a pneumatic tire for a two-wheeled vehicle according to the invention, and the developed view should essentially show the tread surface 2 tapered from the center to both sides, but shows the whole of the tread surface 2 with the same length as that of the central circumferential length for convenience. Moreover, Fig. 2 is a cross section of the tire along the line X - X of Fig. 1, and the tire tread half width TW of the tread surface 2 shown in Fig. 1 means an arc length along the tread surface 2 from a central circumferential line EC to a tread surface 2 edge TE as shown in Fig. 2. In the pneumatic tire for a two- wheeled vehicle as a preferred embodiment of the invention shown in Fig. 1, numerous sets of lug groove patterns 3 are formed on the tread surface 2 of the tread portion 1. Each of the lug groove patterns 3 has two mid bending points P,P' each of which forms reverse V-shape grooves. Fig. 1 shows a developed plan view of the tire under such a condition that it is fitted to a two-wheeled vehicle and then observed from above, and the direction D indicates the tire rolling direction. Each of the mid bending points P should be arranged within a region of 20 - 80 %, preferably 35 - 65 %, of the tire tread half width TW from the central circumferential line EC. When this arrangement region is less than 20%, the cornering stability deteriorates due to tread surface stiffness excess of the shoulder portion against the central portion, while if the region exceeds 80%, the straight running stability deteriorates due to tread surface stiffness excess of the central portion against the shoulder portion. Moreover, an angle α of a lug groove component 3a from the above mid bending point P to the tire shoulder portion is 20 - 70° , preferably 40 - 60°, with respect to the tire equatorial plane E, and an angle β of a lug groove component 3b from the mid bending point P to the tire central circumferential line is 20 - 70° , preferably 25 - 45°, with respect to the tire equatorial plane E. The angle α is also preferably greater than the angle β. When these angles are less than 20° , the drainability during cornering deteriorates, while if the angles exceed 70 ° , the drainability during straight running deteriorates. Also, a lug groove component 3c extends from the lug groove component 3b at the mid bending point P' to the tire shoulder portion. A pitch DP of the lug groove pattern 3 is preferably 1 / 100 - 1 / 20 of the whole circumferential length for obtaining effects of the invention. Moreover, in order to improve comfort against vibration, the offset amount OF for offsetting (phase shifting) left and right patterns by symmetrizing the central circumferential line EC is preferably 0 -1/20 of the whole circumferential length. A width size of the lug groove is preferably 1/25 - 1/10 of the pitch DP. The pneumatic tire for a two-wheeled vehicle according to the invention is preferably formed with at least one circumferential groove 4 in a tread central region and the circumferential groove is arranged within a region of 35% of the tire tread half width TW from the tire central circumference EC. The provision of such circumferential groove lowers the stiffness of the ground-contact region and contributes to further improvement of the lateral stiffness based on ground - contact area improvement. The circumferential groove may be a zigzag groove or a straight groove, and further may be continuous or intermittent. Furthermore, the pneumatic tire for a two-wheeled vehicle according to the invention provided with the aforesaid tread patterns, as shown in Fig. 2, has a pair of sidewall portions 10 (only one is shown) connected by a tread portion and a pair of bead portions 11 (only one is shown), and is provided with a carcass 13 for reinforcing each of the above portions extended between bead cores 12 embeded in the bead portions 11. The carcass 13 may be either radial ply or bias ply; in the case of the radial ply, a belt 14 is provided around the circumference of the carcass 13, and in the case of the bias ply, a breaker 14 is provided around the circumference of the carcass 13 or can be omitted as constructed as in the prior art. It is preferable that the belt 14 is at least one ply of textile cord. This invention will be further described with reference to the following Example and Comparative Example. As an Example and a Comparative. Example, there were manufactured bias ply tires (size 110/70R17) for a two-wheeled vehicle (motorcycle) comprising a carcass having a 2 ply construction of 6, 6-nylon cords of 1260D/2 and a breaker consisting of two complex layers of 1260D/2 nylon fiber cord. In the manufactured tire of the Example, as shown in Fig. 1, numerous sets of lug groove patterns 3 were formed on the tread surface 2 of the tread portion 1. Each of mid bending points P on both sides was arranged within a region of almost 50% of the tire tread half width TW. Moreover, the angle α of the groove component 3a to the tire shoulder portion from the mid bending point P was 50° with respect to the tire equatorial plane E, and the angle β of the lug groove component 3b to the tire central circumferential line EC from the mid bending point P was 35° with respect to the tire equatorial plane E. Moreover, the pitch DP of the lug groove pattern 3 was 1 / 40 of the whole circumferential length, and the offset amount OF was 1/80 of the whole circumferential length. In the tread central zone was continuously formed one circumferential zigzag groove within the region of 10% of the tire tread half width TW from the tire central circumferential line EC. On the other hand, in the manufactured tire of the Comparative Example, the reverse V-shaped grooves used in the above Example were inverted in the tire rolling direction, to provide V-shaped grooves in the tire rolling condition. On the tires of Example and Comparative Example, camber thrusts (CTH) to each camber (CA) angle were evaluated. Test conditions are as follows. To the tire to be tested was applied a load 110 kgf in the camber (CA) direction, the tire was run by pressing to a drum tester, the camber angle was changed from 0° to 45° , and camber thrusts (CTH) generated in the tire were measured. The evaluation was indicated with an index on the basis of the tire of Comparative Example as 100. The larger the numerical values, the better the results. The obtained results are shown in the following Table 1. As explained above, in the pneumatic tire for a two-wheeled vehicle according to the invention, high lateral stiffness is obtained without requiring any tire structural change, material change and the like by forming a predetermined lug groove pattern on a tread, and excellent steering stability is exhibited.

Claims: A pneumatic motorcycle tire formed with lug groove patterns (3) on the tread surface (2) of a tread portion (1), wherein, on each of left and right sides with respect to a tire central circumferential line EC, each of said lug groove patterns has two mid bending points P,P' and each of the bending points P,P' forms reverse V-shape grooves with the tip of the V being oriented in the tire rolling direction, wherein each of said lug groove patterns has a first lug groove component (3a) extending from a first mid bending point P toward a tire shoulder portion, a second lug groove component (3b) extending from said first mid bending point P toward the tire central circumferential line EC, and a third lug groove component (3c) extending from said second lug groove component (3b) at a second mid bending point P' toward the tire shoulder portion, wherein each of the first mid bending points P is arranged within a region of 20-80% of a tire tread half width TW from the tire central circumferential line EC, wherein an angle α of the first lug groove component (3a) to a tire shoulder portion from the mid bending point P is 20-70° with respect to a tire equatorial plane E, and wherein an angle β of the second lug groove component (3b) to the tire central circumferential line EC from the first mid bending point P is 20-70° with respect to the tire equatorial plane E. A pneumatic tire as claimed in claim 1, characterized in that said angle a is 40-60° and said angle β is 25-45° with respect to the tire equatorial plane E, and the angle α is greater than the angle β. A pneumatic tire as claimed in claim 1 or 2, characterized in that at least one circumferential groove (4) is formed at a tread central region, and the circumferential groove is arranged in a region from the tire central circumferential line EC to 35% of the tire tread half width TW. A pneumatic tire as claimed in claim 3, characterized in that said circumferential groove (4) is a zigzag circumferential groove. A pneumatic tire as claimed in any of claims 1 to 4, characterized in that a pitch DP of said lug groove pattern (3) is 1/100-1/20 of the whole circumferential length. A pneumatic tire as claimed in any of claims 1 to 5, characterized in that an offset amount OF for offsetting left and right patterns by symmetrizing the central circumferential line EC is 0-1/20 of the whole circumferential length. A pneumatic tire as claimed in any of claims 1 to 6, characterized in that each of the first mid-bending points P is arranged within a region of 35-65% of the tire tread half width TW from the tire circumferential line EC.

Inventors: NAKAGAWA HIDEMITSU, SUMIDA TAKASHI, NAKAGAWA, HIDEMITSU, SUMIDA, TAKASHI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1998
Main classification: B60C11
IPC codes: B60C11