JP4331338B2

JP4331338B2 - Pneumatic tire

Info

Publication number: JP4331338B2
Application number: JP21983699A
Authority: JP
Inventors: 金也森口; 幸司松山
Original assignee: Toyo Tire and Rubber Co Ltd
Current assignee: Toyo Tire Corp
Priority date: 1999-08-03
Filing date: 1999-08-03
Publication date: 2009-09-16
Anticipated expiration: 2019-08-03
Also published as: JP2001047819A

Description

【０００１】
【発明の属する技術分野】
本発明は、乗用車用空気入りタイヤ、特に扁平率が５５％以下のロードノイズが低減された空気入りタイヤに関する。
【０００２】
【従来技術】
自動車の高級化に伴って居住性の向上が強く要望されるようになり、特に扁平率が５５％以下の空気入りタイヤを装着し、高速で走行する機会が多い乗用車のロードノイズの低減が強く望まれている。主としてロードノイズは、路面の凹凸によりタイヤが振動し、この振動が車軸、サスペンションなどの伝播経路を通り、車室内で発生する周波数１００〜４００Ｈｚの騒音である。周波数１００〜２００Ｈｚのロードノイズについては、トレッド部のゴム厚みを大にする、カーカス剛性を小さくすることにより低減する方法が古くから講じられていた。しかし周波数が２００〜４００Ｈｚのロードノイズは上記方法によって低減できない。
【０００３】
一般に２００〜４００Ｈｚの周波数帯域のタイヤの振動は、両端がビードコアに係止されたカーカスプライのコードを共振させて両端を固定した絃のように定在波を作らせ、子午線方向に振動モードを形成していることは公知である。古くから繁用されている扁平率が６０％以上のタイヤは、ビード部のラジアル方向外側端部分とバットレスが定在波の腹になり、ベルト端と最大幅位置が節になると言われており、腹になる部分の質量分布を大きくして振動しにくくすれば、ロードノイズを小さくすることができる。このような考えに基づいてタイヤサイド部のタイヤ断面高さの１／５〜４／５の位置に密度がサイドゴムの１１０％以上である振動防止部材を設ける方法（特開平４−４３１０７）、サイドゴム表面の最大カーカス断面幅位置より半径方向外側に環状凸部を設ける方法（特開平９−１０９６２１）、サイドゴム表面の最大カーカス断面幅位置より半径方向内側に環状凸部を設ける方法（特開平９−１０９６２２）が提案された。発明者は、サイズ２１５／４５Ｒ１７のタイヤについて、特開平９−１０９６２１記載の方法でロードノイズの低減を試みたが、逆に増大し、限定された範囲でのみ有効な手段になることが分かった。
【０００４】
【発明が解決しょうとする課題】
扁平率が５５％以下の超扁平タイヤは、扁平率が６０％以上の古くから使用されていた繁用タイヤと比較して、トレッド部の幅が大きく、サイド部の子午線方向の幅が小さく、カーカスの最大幅位置の曲率半径が大きく、サイド部の幅に対してビード部が大きくなっていて断面形状が大きく異なる。振動の挙動も異なると予想され、振動モードの解析を行って次の知見を得た。すなわち、扁平率が５５％以下のタイヤの周波数約３５０Ｈｚ付近のタイヤ振動モードは、カーカスの最大幅位置からベルト端までの高さの約８０％の位置、所謂バットレス部及びトレッドの端からトレッド幅の約３０％タイヤ中心側に入った位置のそれぞれが定在波の節になり、トレッドの端からトレッド幅の約１０％入った位置、所謂トレッドショルダーとカーカスの最大幅位置付近が腹になるモード（以下、バットレス部とトレッドの端からトレッド幅の約３０％入った位置が定在波の節になり、トレッドショルダー及びカーカスの最大幅位置付近が腹になる振動モードを断面２次モードと言う）であり、扁平率が６０％以上のタイヤと節、腹が出現する位置が異なることが分かった。ロードノイズとの関係を確認するため、サイズ２１５／４５Ｒ１７のタイヤのサイド部の表面に幅８mm、厚み４mmのゴムテープをラジアル方向に位置を変えて環状に貼った試験タイヤを準備し、それぞれについて、図２にシステム図で示す測定装置を用いてタイヤトレッドセンター部に入力したときのタイヤサイド部のイナータンス（加速度応答／入力）を測定した。測定の結果テープを貼らないタイヤと比較して、バットレス部にテープを貼ったタイヤは２００〜４００Ｈｚの平均イナータンスが０．５ｄＢ大きくなり、カーカスの最大幅位置付近にテープを貼ったタイヤは１．６ｄＢ小さくなり、リムフランジ離反点からカーカスの最大幅位置高さまでの間にテープを貼ったタイヤは不変であることが分かった。
【０００５】
本発明は、タイヤサイド部の形状を適正化することにより、重量が大きく増加することなく、周波数帯域２００〜４００Ｈｚのロードノイズが低減された扁平率５５％以下の空気入りタイヤを提供することを目的にしたものである。
【０００６】
【課題を解決するための手段】
２００〜４００Ｈｚ周波数帯域のタイヤ断面２次モードの腹になる位置のラジアル方向単位長さ当たりの質量を他の位置より大きくして慣性が大になるようにし、振動しても振幅が大きくならないようにすれば、路面の凹凸により振動の強制入力を受けても、タイヤが共振しにくくなるのでロードノイズが小さくなる。ロードノイズを低減するためにサイドゴムを部分的に重くしたことによりタイヤ重量が大になって燃費が悪化するのを、部分的に質量を変えてもロードノイズが変化しない位置のゴム厚みを小さくして腹になる位置の質量の増大を相殺または軽減して防止する。
【０００７】
すなわち本発明は、タイヤ周方向直角に多数のコードを配列したカーカスプライが１対のビードコアの間を跨がって断面馬蹄形のトロイド状をなし、該カーカスプライのクラウン部外側にベルトプライが配置し、該ベルトプライの外側をトレッドゴムで被覆し、カーカスプライのサイド部の外側をサイドゴムで被覆した扁平率が５５％以下のラジアル構造の空気入りタイヤにおいて、サイド部のタイヤ断面高さＬの３０％から４０％までの間に位置する範囲Ｉと４０％から７０％までの間に位置する範囲ＩＩを定め、範囲Ｉはカーカスプライ内に配列したコード外面からサイドゴム表面までの外面ゴム厚さをトレッド部ゴム厚さＴの０．２５〜０．４５倍にし、範囲ＩＩは外面ゴム厚さをトレッド部ゴム厚さの０．５０〜０．７５倍にするか、または／及び範囲ＩＩのサイドゴムを範囲Ｉより密度が大きいゴムで形成するか、または／及び範囲ＩＩのカーカスプライとサイドゴムとの間にスチールコードプライを配置して、外面ゴムのタイヤ内面の単位ペリフェリ長さ当たりの質量を範囲Ｉより大きくした空気入りタイヤである。
【０００８】
乗用車用タイヤのカーカスプライのサイド部に貼られるサイドゴムは、通常リムストリップに接着される部分とその近傍及びトレッドゴムに接着される部分とその近傍を除いて、厚みが全体にわたってほぼ一様になっている。サイドゴムの厚みは、縁石などとの接触によるカーカスプライの損傷、カーカスプライのコード配列の凹凸がサイドゴム表面に縞模様となって表れるサイド凹凸などの発生を防止するのに必要な厚み、重量、コストを勘案して経験的に決められ、一般的にトレッド幅の中心で測定したトレッド部ゴム厚みの約０．４倍程度にされる。範囲ＩＩは、サイドに出現する断面２次モードの腹を持ち、外面ゴム厚みをトレッド部ゴム厚みの０．５０〜０．７５倍にし、従来タイヤのサイド部外面ゴム厚みより厚くする。範囲ＩＩの外面ゴム厚みが０．５０倍より薄い場合はロードノイズ低減作用が小さく、０．７５倍より厚くしても厚みの増加に見合ったロードノイズ低減効果が奏されず、重量が増加するだけである。外面ゴム厚みを従来タイヤより厚くして振動しにくくした範囲ＩＩをタイヤ断面高さＬの４０％よりラジアル方向内側または７０％より外側に設けた場合、断面２次モードの腹になる位置が範囲ＩＩから乖離するためロードノイズ低減作用が生じない。尚、サイド部の外面ゴム厚みはカーカスプライのコード表面からサイドゴム表面までの厚みを指し、トレッド部ゴム厚みはベルトのコード被覆ゴムを含んだトレッド部のゴム厚みである。タイヤ断面高さは、ノミナルリム径を基準にしてそこからの離隔距離であって、リム組したタイヤの外径を測定し、外径からリムのノミナルリム径を減じた差に１／２を乗じて求めた値である。範囲Ｉ及び範囲ＩＩの高さはタイヤ断面高さと同様にノミナルリム径からの離間距離で表される。範囲Ｉは、サイドゴムが部分的に薄くなってもロードノイズの増減に影響せず、タイヤが縁石などに接触したときに損傷を受けにくい位置であるので、外面ゴム厚みを従来のサイド部より薄くすることができ、トレッド部ゴム厚みＴの０．２５〜０．４５倍にする。トレッド部ゴム厚さの０．２５倍より薄くなればサイド凹凸が発生しやすくなり、０．４５倍より厚くなればタイヤ重量が減少されない。
【０００９】
【発明の実施の形態】
本発明の一実施形態を図面に基づいて説明する。図１は、リムに着座した本発明の空気入りタイヤの左半分の断面図である。リム２に着座した空気入りタイヤ１は、多数のコードがタイヤ周方向に対し直角に配列したコード層の両面をゴム被覆したカーカスプライ３が一対のビードコア６の間を跨がって端をビードコア６に係止した断面馬蹄形のトロイド状の形状を有し、カーカスプライ３のクラウン部外側にベルトプライの２層でなるベルト４を布設し、その外側とカーカスプライのクラウン部のベルトが包囲していない部分をトレッドゴム５で被覆し、カーカスプライのサイド部の外側をサイドゴム７で被覆してなる。サイド部のタイヤ断面高さＬの３０％から４０％高さの間に位置して環状の溝をなす範囲Ｉ８を設け、タイヤ断面高さＬの４０％から７０％高さの間に位置して環状突起をなす範囲ＩＩ９を設ける。範囲Ｉの外面ゴム厚みｔ1 はトレッド部ゴム厚みＴの０．２５〜０．４５倍にされ、範囲ＩＩの外面ゴム厚みｔ2はトレッド部ゴム厚みＴの０．
５０〜０．７５倍にされる。範囲ＩＩは環状突起にされるのが好ましいが、環を部分的に切断した形状の突起にされてもよい。範囲ＩＩの外面を形成するゴムに残余部分を形成するゴムより密度が高くされたものを用いることができる。また、スチールコード層をカーカスプライとサイドゴムの間に配置して外面ゴムのタイヤ内面の単位ペリフェリ長さ当たりの質量を大きくすることもできる。
【００１０】
【実施例】
範囲Ｉ及び範囲ＩＩの外面ゴムを表１に示したトレッド部ゴム厚みに対する比で表した厚みにしてサイズ２１５／４５Ｒ１７のラジアル構造の空気入りタイヤを試作した。試作タイヤの重量を測定した。測定結果を表１に従来タイヤを１００とした指数で示した。次いで下記に示す方法でトレッド加振時のサイドウオール応答の２００〜４００Ｈｚのパーシャルレベルを測定した。測定結果を表１に従来タイヤを基準にしてそれに対する振動伝達率の増減で示した。値が小さい程好ましい。（値が負の場合は、絶対値が大きいほど好ましい）
【００１１】
【表１】

【００１２】
トレッド加振時のサイドウオール応答のレベル測定方法：
図２にシステム図が示される試験装置の加振器をゴムで吊られた被試験タイヤのトレッドセンターに当てて周波数を１０００Ｈｚまで増加しながらラジアル方向に加振し、タイヤサイド部のインナータンスを計測した。
【００１３】
最大断面幅位置よりラジアル方向内側でタイヤサイド部に環状突起を設けてロードノイズを小さくした構造の従来タイヤと比較して、実施例タイヤはいずれも振動伝達率が減少し、範囲ＩＩのゴム厚みが大きくなるほど振動伝達率の減少が大きくなる。実施例１、２、３、比較例１の対比から範囲Ｉのゴム厚みの変化の振動伝達率に及ぼす影響は小さいことが分かる。従来タイヤと範囲Ｉのゴム厚みを同じにし、範囲ＩＩのゴム厚みを大にした比較例１は振動伝達率が大きく低下するが、タイヤ重量が増加するので好ましくない。
【００１４】
【発明の効果】
本発明は、扁平率が５５％以下の空気入りタイヤの断面２次モードの振動の腹になる位置、言い換えればタイヤサイド部上のタイヤ断面高さの４０％から７０％の間にある位置に設けた範囲ＩＩのタイヤ内面の単位ペリフェリ長さ当たりの質量を大きくすることにより、ロードノイズが低減するとともに、タイヤ内面の単位ペリフェリ長さ当りの質量が変化してもロードノイズの増減に殆ど影響せず、しかも縁石などに接触しても外傷を受けにくいタイヤ断面高さの３０〜４０％に位置する範囲Ｉの外面ゴム厚みを薄くすることにより、タイヤ性能が損われることなく、範囲ＩＩのタイヤ内面の単位ペリフェリ長さ当たりの質量を大きくしたためのタイヤ重量の増加が相殺、または少なくされて燃費の悪化が防止される効果を有する。
【図面の簡単な説明】
【図１】図１は、リムに着座した本発明の空気入りタイヤの左半分の断面図である。
【図２】図２は、振動伝達率を測定する装置のシステム図である。
【符号の説明】
１空気入りタイヤ
２リム
３カーカスプライ
４ベルト
５トレッドゴム
６ビードコア
７サイドゴム
８範囲Ｉ
９範囲ＩＩ
Ｔトレッド部ゴム厚み
Ｌタイヤ断面高さ
ｔ1 範囲Ｉの外面ゴム厚み
ｔ2 範囲ＩＩの外面ゴム厚み[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic tire for a passenger car, and more particularly to a pneumatic tire with reduced road noise with a flatness ratio of 55% or less.
[0002]
[Prior art]
Along with the upgrading of automobiles, there is a strong demand for improved comfort. Especially, pneumatic tires with a flatness ratio of 55% or less are installed, and there is a strong reduction in road noise for passenger cars that often run at high speeds. It is desired. The road noise is mainly a noise with a frequency of 100 to 400 Hz that is generated in the passenger compartment by the vibration of the tire caused by the unevenness of the road surface, and the vibration passing through the propagation path such as the axle and suspension. For road noise with a frequency of 100 to 200 Hz, a method of reducing the carcass rigidity by increasing the rubber thickness of the tread portion has long been taken. However, road noise having a frequency of 200 to 400 Hz cannot be reduced by the above method.
[0003]
In general, the vibration of a tire with a frequency band of 200 to 400 Hz is caused by resonating a carcass ply cord locked at both ends with a bead core to create a standing wave like a ridge with both ends fixed, and a vibration mode in the meridian direction. It is known that it is formed. For tires with a flatness ratio of 60% or more that have been used for a long time, it is said that the radially outer edge of the bead and the buttress are the antinodes of the standing wave, and the belt edge and maximum width position become nodes. The road noise can be reduced by increasing the mass distribution of the belly portion to make it difficult to vibrate. Based on such an idea, a method of providing a vibration preventing member having a density of 110% or more of the side rubber at a position of 1/5 to 4/5 of the tire cross section height of the tire side portion (Japanese Patent Laid-Open No. 4-43107), side rubber A method of providing an annular convex portion radially outward from the position of the maximum carcass cross-sectional width on the surface (Japanese Patent Laid-Open No. 9-109621), and a method of providing an annular convex portion radially inward from the position of the maximum carcass cross-sectional width of the side rubber surface 109622) was proposed. The inventor tried to reduce road noise for the tire of size 215 / 45R17 by the method described in JP-A-9-109621. However, the inventor increased it and found that it became an effective means only in a limited range. .
[0004]
[Problems to be solved by the invention]
The super flat tire with an aspect ratio of 55% or less has a larger tread width and a smaller width in the meridian direction of the side portion than a conventional tire with an aspect ratio of 60% or more, The radius of curvature at the maximum width position of the carcass is large, the bead portion is larger than the width of the side portion, and the cross-sectional shape is greatly different. The vibration behavior is also expected to be different, and the following knowledge was obtained by analyzing the vibration mode. That is, a tire vibration mode with a flatness ratio of 55% or less of a tire having a frequency of about 350 Hz is approximately 80% of the height from the maximum width position of the carcass to the belt end, the so-called buttress portion and the tread width from the tread edge. Approximately 30% of the tires are located at the center of the tire, each of which is a standing wave node, where the tread width is approximately 10% from the end of the tread, the so-called tread shoulder and carcass near the maximum width position. Mode (hereinafter referred to as vibration mode in which the position where approximately 30% of the tread width enters from the end of the buttress and the tread becomes a node of the standing wave, and the vicinity of the maximum width position of the tread shoulder and the carcass becomes the antinode. It was found that tires having a flatness ratio of 60% or more and positions where nodes and bellies appear are different. In order to confirm the relationship with road noise, we prepared test tires with rubber tapes of 8mm width and 4mm thickness on the surface of the side part of tires of size 215 / 45R17, and affixed in an annular shape in the radial direction. The inertance (acceleration response / input) of the tire side portion when it was input to the tire tread center portion was measured using the measuring device shown in the system diagram of FIG. As a result of the measurement, the tire with the tape applied to the buttress portion has an average inertance of 200 to 400 Hz increased by 0.5 dB, and the tire with the tape applied near the maximum width position of the carcass is 1. It became smaller by 6 dB, and it was found that the tire with the tape applied between the rim flange separation point and the maximum width position height of the carcass was unchanged.
[0005]
The present invention provides a pneumatic tire having a flatness ratio of 55% or less in which road noise is reduced in a frequency band of 200 to 400 Hz without significantly increasing weight by optimizing the shape of the tire side portion. It is intended.
[0006]
[Means for Solving the Problems]
The mass per unit length in the radial direction of the position that becomes the antinode of the tire cross-section secondary mode in the 200 to 400 Hz frequency band is made larger than other positions so as to increase the inertia, so that the amplitude does not increase even if it vibrates. In this case, even if a forced input of vibration is received due to road surface irregularities, the tire is less likely to resonate and road noise is reduced. In order to reduce road noise, the weight of the tires increases due to partial weighting of the side rubber, and the fuel consumption deteriorates.The rubber thickness at the position where the road noise does not change even if the mass is partially changed is reduced. To prevent or reduce the increase in mass at the stomach position.
[0007]
That is, according to the present invention, a carcass ply in which a large number of cords are arranged at right angles to the tire circumferential direction forms a toroidal shape with a horseshoe cross section across a pair of bead cores, and a belt ply is disposed outside the crown portion of the carcass ply In a pneumatic tire having a radial structure with a flatness ratio of 55% or less, in which the outer side of the belt ply is covered with tread rubber and the outer side of the side part of the carcass ply is covered with side rubber, the tire cross-section height L of the side part is A range I located between 30% and 40% and a range II located between 40% and 70% are defined. The range I is the thickness of the outer rubber from the outer surface of the cord arranged in the carcass ply to the side rubber surface. Is 0.25 to 0.45 times the tread rubber thickness T, and range II is to make the outer rubber thickness 0.50 to 0.75 times the tread rubber thickness Alternatively, the side rubber in the range II is formed of a rubber having a density higher than that in the range I, or / and the steel cord ply is disposed between the carcass ply and the side rubber in the range II, so that the unit peripheral of the tire inner surface of the outer rubber is arranged. This is a pneumatic tire having a mass per length larger than the range I.
[0008]
Side rubber that is affixed to the side part of the carcass ply of a passenger car tire is generally uniform throughout the thickness, except for the part that adheres to the rim strip and its vicinity and the part that adheres to the tread rubber and its vicinity. ing. The thickness of the side rubber is the thickness, weight, and cost required to prevent carcass ply damage due to contact with curbstones, etc., and side irregularities that appear as stripes on the side rubber surface. Is determined empirically, and is generally about 0.4 times the rubber thickness of the tread portion measured at the center of the tread width. Range II has a bellows of a secondary mode of cross-section that appears on the side, and the outer rubber thickness is 0.50 to 0.75 times the tread rubber thickness, which is thicker than the outer rubber thickness of the conventional tire. When the outer surface rubber thickness in the range II is thinner than 0.50 times, the road noise reduction action is small, and even if thicker than 0.75 times, the road noise reduction effect corresponding to the increase in thickness is not achieved, and the weight increases. Only. When the range II in which the outer rubber thickness is thicker than that of the conventional tire and is less likely to vibrate is provided radially inward of the tire cross-section height L or outside of 70%, the position where the antinode in the secondary cross-section mode is in the range Since it deviates from II, the road noise reduction effect does not occur. The outer surface rubber thickness of the side portion refers to the thickness from the cord surface of the carcass ply to the side rubber surface, and the tread portion rubber thickness is the rubber thickness of the tread portion including the belt cord covering rubber. The tire cross-section height is the distance from the nominal rim diameter as a reference. Measure the outer diameter of the rim-assembled tire and multiply by 1/2 the difference between the outer diameter and the nominal rim diameter. This is the calculated value. The heights of the range I and the range II are represented by the separation distance from the nominal rim diameter in the same manner as the tire cross-section height. Range I does not affect the increase or decrease in road noise even if the side rubber is partially thinner, and is less susceptible to damage when the tire contacts a curb, etc., so the outer rubber thickness is thinner than the conventional side part. The tread rubber thickness T is 0.25 to 0.45 times. If the thickness of the tread rubber is less than 0.25 times, side irregularities are likely to occur, and if the thickness is more than 0.45 times, the tire weight is not reduced.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the left half of the pneumatic tire of the present invention seated on a rim. The pneumatic tire 1 seated on the rim 2 has a carcass ply 3 in which a plurality of cords are arranged at right angles to the tire circumferential direction and covered with rubber on both sides of a cord layer. 6 has a toroidal shape with a horseshoe cross section locked to 6, and a belt 4 consisting of two layers of belt plies is provided outside the crown portion of the carcass ply 3, and the belt and the crown portion of the carcass ply are surrounded by the belt 4. The part which is not covered is covered with the tread rubber 5, and the outside of the side part of the carcass ply is covered with the side rubber 7. An annular groove I8 is provided between 30% and 40% of the tire cross-section height L of the side portion, and located between 40% and 70% of the tire cross-section height L. A range II9 forming an annular protrusion is provided. The outer surface rubber thickness t1 in the range I is 0.25 to 0.45 times the tread rubber thickness T, and the outer rubber thickness t2 in the range II is 0.
50-0.75 times. The range II is preferably a circular protrusion, but may be a protrusion having a shape obtained by partially cutting the ring. A rubber having a higher density than the rubber forming the remaining portion can be used as the rubber forming the outer surface of the range II. In addition, the steel cord layer can be disposed between the carcass ply and the side rubber to increase the mass per unit peripheral length of the tire inner surface of the outer rubber.
[0010]
【Example】
A pneumatic tire having a radial structure of size 215 / 45R17 was manufactured by setting the outer surface rubber in the range I and range II to a thickness represented by the ratio to the thickness of the tread rubber shown in Table 1. The weight of the prototype tire was measured. The measurement results are shown in Table 1 as an index with the conventional tire as 100. Next, the partial level of 200 to 400 Hz of the side wall response during tread vibration was measured by the method described below. The measurement results are shown in Table 1 in terms of increase / decrease of vibration transmissibility relative to the conventional tire. A smaller value is preferable. (If the value is negative, the larger the absolute value, the better)
[0011]
[Table 1]

[0012]
Sidewall response level measurement method during tread excitation:
The test equipment shown in the system diagram in FIG. 2 is applied to the tread center of a tire to be tested suspended by rubber, and the frequency is increased up to 1000 Hz. Measured.
[0013]
Compared to a conventional tire having a structure in which an annular protrusion is provided in the tire side portion radially inward from the maximum cross-sectional width position to reduce road noise, all of the tires of the examples have a reduced vibration transmissibility, and the rubber thickness in the range II The greater the is, the greater the reduction in vibration transmissibility. From the comparison of Examples 1, 2, 3 and Comparative Example 1, it can be seen that the influence of the change in rubber thickness in range I on the vibration transmissibility is small. In Comparative Example 1 in which the rubber thickness in the range I is the same as that of the conventional tire and the rubber thickness in the range II is increased, the vibration transmissibility is greatly decreased, but the tire weight is not preferable.
[0014]
【The invention's effect】
The present invention is located at a position where it becomes an antinode of vibration of a secondary cross section mode of a pneumatic tire having a flatness ratio of 55% or less, in other words, at a position between 40% and 70% of the tire cross section height on the tire side portion. By increasing the mass per unit peripheral length on the inner surface of the tire in the range II provided, road noise is reduced, and even if the mass per unit peripheral length on the inner surface of the tire changes, there is almost no effect on the increase or decrease in road noise. In addition, by reducing the thickness of the outer surface rubber in the range I located at 30 to 40% of the tire cross-section height which is not easily damaged even if it comes into contact with the curbstone, etc., the tire performance is not impaired. The increase in the weight of the tire due to an increase in the mass per unit peripheral length of the tire inner surface is offset or reduced, thereby preventing the deterioration of fuel consumption.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of the left half of a pneumatic tire of the present invention seated on a rim.
FIG. 2 is a system diagram of an apparatus for measuring vibration transmissibility.
[Explanation of symbols]
1 Pneumatic tire 2 Rim 3 Carcass ply 4 Belt 5 Tread rubber 6 Bead core 7 Side rubber 8 Range I
9 Range II
T Tread rubber thickness L Tire cross section height t1 Range I outer rubber thickness t2 Range II outer rubber thickness

Claims

A carcass ply in which a large number of cords are arranged at right angles to the tire circumferential direction straddles between a pair of bead cores in a toroidal manner, a belt ply is disposed on the outer side of the crown of the carcass ply, and the outer side of the belt ply is made of tread rubber. In a pneumatic tire having a radial structure with a flatness ratio of 55% or less, in which the outer side of the side part of the carcass ply is covered with side rubber, the side part is located between 30% and 40% of the tire cross-section height L A pneumatic tire characterized in that a range II located between 40% and 70% is defined as a range I, and the mass per unit peripheral length of the tire inner surface of the outer rubber of the range II is larger than the range I.

The outer surface rubber thickness in the range I is 0.25 to 0.45 times the tread rubber thickness T, and the outer rubber thickness in the range II is 0.50 to 0.75 of the tread rubber thickness.
The pneumatic tire according to claim 1, which is doubled.

The pneumatic tire according to claim 1, wherein the range II is a side rubber having a density higher than that of the range I.

The pneumatic tire according to claim 1, 2, or 3, wherein a steel cord ply is disposed between the carcass ply and the side rubber in range II.