In a tread pattern wherein the tread surface of a tire has a circumferential groove extending continuously in the circumferential direction, an elongated space is defined in a ground contact area of the tread surface between the circumferential groove and the road surface, having an open leading end and an open trailing end. Since the columnar resonance noise assumes a significant part in the total tire noise, it is an imminent task to suppress the columnar resonance noise or disperse the resonance frequency. Thus, there has been proposed a solution which provides a lateral groove, including an inclined groove, so as to extend in the tire width direction with its one end opened into the circumferential groove.
It is known that such a lateral groove is adapted to change the frequency of the columnar resonance noise, depending upon its configuration. Among others things, Patent Document 1 (WO 2002/078982 A1) describes that, when a lateral groove opening only into a circumferential groove has the other end that terminates in a land portion, the frequency of the columnar resonance noise caused by the circumferential groove is lowered.
Thus, the applicant previously proposed a technology as disclosed in Patent Document 2 (WO 2004/103737 A1), which improves the quietness of tires by elaborating the shape and structure of the lateral groove. This proposal provides a pneumatic tire capable of dispersing the frequency of the columnar resonance noise and lower the sound pressure level, by means of an arrangement wherein the tread surface is provided with two or more circumferential grooves continuously extending in the circumferential direction of the tire, and a plurality of lateral grooves, each having one end opened to at least one predetermined circumferential groove and the other end terminated in a land portion, are formed independently from the other lateral grooves opened into the other circumferential groove and a ground contact end of the tread. In other words, each lateral groove extends without crossing the other lateral grooves that can be opened into the other circumferential groove and/or the ground contact end of the tread, apart from the lateral grooves that extends into the same circumferential groove. The circumferential grooves and the lateral grooves have their respective widths determined such that their opposite groove walls do not contact each other under the tire posture wherein the tire is mounted onto an approved rim, filled with the maximum air pressure and loaded with a mass that corresponds to the maximum load capacity of the tire. The lateral grooves are arranged so that at least one lateral groove is always included completely in the ground contact surface of the tread. An extending length of a portion of each lateral groove in the ground contact surface, having a groove width of the lateral groove corresponding to not less than 30% of a groove width of the predetermined circumferential groove, is made not less than 40% of an extending length of the predetermined circumferential groove in the ground contact surface. Such a pneumatic tire makes it possible to disperse the frequency of the columnar resonance noise while simultaneously lowering the sound pressure level of the resonance noise.                Patent Document 1: WO 2002/078982 A1        Patent Document 2: WO 2004/103737 A1        