1. Technical Field
The present technology relates to a pneumatic tire employing a variable pitch construction, the pneumatic tire having enhanced steering stability and uniformity.
2. Related Art
Pneumatic tires exist that have tread patterns in tread portions formed from vertical grooves provided in a circumferential direction and lateral grooves provided so as to intersect these vertical grooves. In such a pneumatic tire, by employing a variable pitch construction, wherein the lateral grooves are provided in the tire circumferential direction with a plurality of pitches, pitch noise generated in the tire circumferential direction is dispersed over a wide range of frequencies, leading to an improvement in noise properties.
For example, Japanese Unexamined Patent Application Publication No. 2004-210133 describes a pneumatic tire employing a variable pitch construction, wherein, in order to improve uniformity (poor uniformity in a pneumatic tire is a cause of vibration being generated in a steering wheel or a vehicle) a groove cross-sectional area of the lateral grooves is adjusted and a stiffness of a tread portion with respect to a tire radial direction is made uniform in the tire circumferential direction.
In Japanese Unexamined Patent Application Publication No. 2004-210133 described above, the stiffness of a tread portion is defined by an amount of vulcanized rubber pressed in during tire formation. Therefore, with the pneumatic tire described in Japanese Unexamined Patent Application Publication No. 2004-210133, the amount of vulcanized rubber pressed in is made uniform. As a result because the amount of vulcanized rubber pressed in is adjusted, there is a tendency for the volume of the lateral grooves to increase at areas of small pitch and the stiffness of land portions formed from the vertical grooves and lateral grooves in the tread portion to decrease. When a stiffness of land portions in a center region adjacent to a tire equatorial plane declines, there is a tendency for steering stability to decline.
In light of the foregoing, an object of the present technology is to provide a pneumatic tire in which steering stability can be improved while uniformity is maintained for a pneumatic tire employing a variable pitch construction.