Patent Publication Number: US-2023141597-A1

Title: Heavy duty pneumatic tire

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority on Japanese Patent Application No. 2021-183309 filed on Nov. 10, 2021, the entire content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to heavy duty pneumatic tires. 
     BACKGROUND ART 
     From the viewpoint of drainage performance, the tread of a heavy duty pneumatic tire (hereinafter, tire) has at least three circumferential grooves. Among the circumferential grooves of the tread, the circumferential groove located on each outer side in the axial direction is a shoulder circumferential groove. 
     A belt and a band are disposed between the tread and a carcass. The belt includes a plurality of belt plies aligned in the radial direction. Each belt ply includes a large number of belt cords aligned with each other. The belt cords are normally steel cords. The band includes a spirally wound band cord. The band cord is a steel cord or a cord formed from an organic fiber such as nylon fiber. The stiffness of a tread portion is controlled by adjusting the configuration of the belt or the band (For example, PATENT LITERATURE 1 below). 
     CITATION LIST 
     Patent Literature 
     
         
         PATENT LITERATURE 1: Japanese Laid-Open Patent Publication No. 9-105084 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     A tire in a running state undergoes repeated deformation and restoration. This causes the shape of the tire to change. The ground-contact shape of the tire changes, so that uneven wear resistance of the tire may deteriorate. 
     In a running state of the tire, a tread end portion of the tire moves actively. The portion of the tread where the circumferential grooves are disposed has a lower stiffness than the portion of the tread where no circumferential groove is disposed. Some low-flatness tires having an aspect ratio of 65% or less have wide tread surfaces. Each shoulder circumferential groove in such a tire is located more outward in the axial direction than that in a high-flatness tire. In the low-flatness tire, a shape change is large around the shoulder circumferential groove. To suppress a shape change, the tire may use a full band including a spirally wound band cord. 
     The band cord included in the full band substantially extends in the circumferential direction. A force acts on the full band of the tire in a running state so as to spread from the inner side toward the outer side in the radial direction. This force increases the tension of the band cord. 
     The tire bends when coming into contact with a road surface. This causes the force acting on the full band to decrease, and thus the tension of the band cord decreases. When the tire becomes separated from the road surface and restores, the force acting on the full band increases, and thus the tension of the band cord increases. The band cord of the tire in a running state undergoes repeated fluctuation of the tension. A break may occur in the band cord depending on the degree of fluctuation of the tension. When the band cord breaks, the holding force of the band decreases. In this case, the full band may not be able to contribute to suppression of a shape change. 
     An edge band is disposed over the end of the full band to suppress the fluctuation of the tension of the band cord in the full band. In this case, the edge band exerts a force on the full band, thus causing an inner portion of the edge band in the radial direction to have strain easily. Depending on the degree of strain, peeling of the cord from the rubber, that is, belt edge loose may occur in an end portion of the belt. 
     The present invention has been made in view of the above circumstances. An object of the present invention is to provide a heavy duty pneumatic tire that can achieve suppression of a shape change due to running while reducing the risk of occurrence of a break of the band cord and belt edge loose. 
     Solution to Problem 
     A heavy duty pneumatic tire according to one aspect of the present invention has a nominal aspect ratio of 65% or less. The heavy duty pneumatic tire includes a tread having a tread surface that comes into contact with a road surface, a pair of sidewalls connected to an end of the tread and located radially inward of the tread, a pair of beads being a first bead and a second bead that are located radially inward of the sidewalls, a carcass located inward of the tread and the pair of sidewalls and extending between the first bead and the second bead, and a reinforcing layer located between the tread and the carcass. The tread has at least three circumferential grooves. Among the at least three circumferential grooves, a circumferential groove located on each outer side in the axial direction is a shoulder circumferential groove. The reinforcing layer includes a band including a spirally wound band cord, and a belt including a large number of belt cords aligned with each other. The band includes a full band and a pair of edge bands located radially outward of an end of the full band. The end of the full band is located axially outward of the shoulder circumferential groove. The belt includes a first belt ply, a second belt ply located radially outward of the first belt ply, and a third belt ply located radially outward of the second belt ply. The third belt ply is located radially inward of the pair of edge bands. A distance between each edge band and the full band or the third belt ply is not less than 2.2 mm and not greater than 4.0 mm. A ratio of a tire thickness at an end of the tread surface to a tire thickness at an equator plane is not less than 1.2 and not greater than 2.0. 
     Preferably, in the heavy duty pneumatic tire, the edge band has an outer end located axially inward of an end of the third belt ply. A distance in the axial direction from the outer end of the edge band to the end of the third belt ply is not less than 8 mm. 
     Preferably, in the heavy duty pneumatic tire, the reinforcing layer includes a buffer layer formed from a crosslinked rubber. The buffer layer is located between the pair of edge bands and the full band or the third belt ply. 
     Preferably, in the heavy duty pneumatic tire, a ratio of a stress of the buffer layer at 200% elongation to a loss tangent of the buffer layer at 70° C. is not less than 75. 
     Preferably, in the heavy duty pneumatic tire, the buffer layer includes a pair of narrow buffer layers opposed to each other with the equator plane between the narrow buffer layers. 
     Preferably, in the heavy duty pneumatic tire, the full band is located between the second belt ply and the third belt ply. A direction in which the belt cords included in the second belt ply are inclined is opposite to a direction in which the belt cords included in the third belt ply are inclined. 
     Advantageous Effects of the Invention 
     The present invention provides a heavy duty pneumatic tire that can achieve suppression of a shape change due to running while reducing the risk of occurrence of a break of the band cord and belt edge loose. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a cross-sectional view illustrating a part of a heavy duty pneumatic tire according to an embodiment of the present invention. 
         FIG.  2    is a schematic diagram illustrating the configuration of a reinforcing layer according to an embodiment of the present invention. 
         FIG.  3    is an enlarged cross-sectional view illustrating a part of the tire shown in  FIG.  1   . 
         FIG.  4    is an enlarged cross-sectional view of the reinforcing layer, showing a modification of the reinforcing layer. 
         FIG.  5    is an enlarged cross-sectional view of the reinforcing layer, showing another modification of the reinforcing layer. 
     
    
    
     DETAILED DESCRIPTION 
     The following will describe in detail the present invention based on preferred embodiments with appropriate reference to the drawings. 
     In the present disclosure, a state where a tire is mounted on a normal rim, the internal pressure of the tire is adjusted to a normal internal pressure, and no load is applied to the tire is referred to as a normal state. 
     Unless otherwise specified herein, the dimensions and angles of each component of the tire are measured in the normal state. 
     The dimension and the angle of each component in a meridian cross-section of the tire, which cannot be measured with the tire fitted on the normal rim, are measured in a cross-section of the tire obtained by cutting the tire along a plane including a rotation axis, with the distance between right and left beads being made equal to the distance between the beads in the tire fitted to the normal rim. 
     The normal rim means a rim specified in a standard on which the tire is based. The “standard rim” in the JATMA standard, the “Design Rim” in the TRA standard, and the “Measuring Rim” in the ETRTO standard are normal rims. 
     The normal internal pressure means an internal pressure specified in the standard on which the tire is based. The “highest air pressure” in the JATMA standard, the “maximum value” recited in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and the “INFLATION PRESSURE” in the ETRTO standard are normal internal pressures. 
     A normal load means a load specified in the standard on which the tire is based. The “maximum load capacity” in the JATMA standard, the “maximum value” recited in the “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, and the “LOAD CAPACITY” in the ETRTO standard are normal loads. 
     In the present disclosure, the “nominal aspect ratio” is the “nominal aspect ratio” included in “tyre designation” specified in JIS D4202 “Automobile tyres-Designation and dimensions”. 
     In the present disclosure, a tread portion of the tire is a portion of the tire that comes into contact with the road surface. A bead portion is a portion of the tire that is fitted to a rim. A side portion is a portion of the tire that extends between the tread portion and the bead portion. The tire includes a tread portion, a pair of bead portions, and a pair of side portions. These portions are portions of the tire. 
     In the present disclosure, the number of cords included per 5 cm width of a tire element, including cords aligned with each other, is represented as the density of the cords included in this element (unit: ends/5 cm). Unless otherwise specified herein, the density of each cord is obtained in a cross-section of the element obtained by cutting the tire along a plane perpendicular with respect to the longitudinal direction of the cord. 
     In the present disclosure, a crosslinked rubber is a molded product of a rubber composition obtained by pressurizing and heating the rubber composition. The rubber composition is an uncrosslinked rubber obtained by mixing a base rubber and chemicals in a kneader such as a Banbury mixer. The crosslinked rubber is also referred to as vulcanized rubber, and the rubber composition is also referred to as unvulcanized rubber. 
     Examples of the base rubber include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and isobutylene-isoprene-rubber (IIR). Examples of the chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oils, fillers such as zinc oxide, lubricants such as stearic acid, antioxidants, processing aids, sulfur, and vulcanization accelerators. A base rubber and chemicals are selected as appropriate and the content of each selected chemical is determined as appropriate in accordance with the specification of each element formed from a rubber composition, such as the tread and the sidewalls. 
     In the present disclosure, the loss tangent (also referred to as tan δ) at a temperature of 70° C., of an element formed from a crosslinked rubber among elements of the tire, is measured in accordance with the regulation of JIS K6394 with a viscoelastic spectrometer (“VES” made by Iwamoto Seisakusho Co., Ltd.) under the following conditions. 
     Initial strain=10% 
     Dynamic strain=2% 
     Frequency=10 Hz 
     Variation mode=Tensile 
     In this measurement, a test piece is sampled from the tire. If no test piece can be sampled from the tire, a test piece is sampled from a sheet-shaped crosslinked rubber (hereinafter, also referred to as rubber sheet) obtained by pressurizing and heating, at a temperature of 170° C. for 12 minutes, a rubber composition used to form an element to be measured. 
     In the present disclosure, the stress at 200% elongation, of an element formed from a crosslinked rubber among elements of the tire, is measured in accordance with the regulation of JIS K6251 (Measurement for determination of tensile stress at a given elongation). Stress at 200% elongation is also referred to as 200% modulus. 
       FIG.  1    shows a part of a heavy duty pneumatic tire  2  (hereinafter, simply “tire  2 ”) according to an embodiment of the present invention. The tire  2  is mounted to a vehicle such as a truck and a bus. The nominal aspect ratio of the tire  2  is 65% or less. In other words, the tire  2  has a nominal aspect ratio of 65% or less. The tire  2  is a low-flatness tire. 
       FIG.  1    shows a part of a cross-section (hereinafter, meridian cross-section) of the tire  2  cut along a plane including the rotation axis of the tire  2 . In  FIG.  1   , the right-left direction is the axial direction of the tire  2 , the up-down direction is the radial direction of the tire  2 . The direction perpendicular to the plane of the drawing sheet of  FIG.  1    is a circumferential direction of the tire  2 . A dashed and single-dotted line CL represents an equator plane of the tire  2 . 
     The tire  2  includes a tread  4 , a pair of sidewalls  6 , a pair of beads  8 , a pair of chafers  10 , a carcass  12 , a pair of cushion layers  14 , an inner liner  16 , a pair of steel fillers  18 , and a reinforcing layer  20 . 
     The tread  4  comes into contact with a road surface at an outer surface of the tread  4 . The outer surface is a tread surface  22 . The tread  4  has the tread surface  22  that comes into contact with the road surface. In  FIG.  1   , reference sign PC represents the point of intersection of the tread surface  22  and the equator plane. The point of intersection PC is also referred to as an equator of the tire  2 . 
     In  FIG.  1   , reference character PE represents an end of the tread surface  22 . A double-headed arrow WT represents the width of the tread surface  22 . The width WT of the tread surface  22  is the distance in the axial direction from a first end PE of the tread surface  22  to a second end PE of the tread surface  22 . 
     In the tire  2 , when the ends PE of the tread surface  22  are unidentifiable in appearance, each end PE of the tread surface  22  is defined by a position on the tread surface  22  that corresponds to the outer end in the axial direction of a ground-contact surface obtained when the normal load is applied to the tire  2  in the normal state and the tire  2  is brought into contact with a flat surface at a camber angle of 0°. 
     The tread  4  includes a base portion  24  and a cap portion  26  located radially outward of the base portion  24 . The base portion  24  is formed from a crosslinked rubber having low generation properties. The cap portion  26  is formed from a crosslinked rubber for which wear resistance and grip performance are taken into consideration. As shown in  FIG.  1   , the base portion  24  covers the entirety of the reinforcing layer  20 . The cap portion  26  covers the entirety of the base portion  24 . 
     In the tire  2 , the tread  4  has at least three circumferential grooves  28 . The tread  4  of the tire  2  shown in  FIG.  1    has four circumferential grooves  28 . These circumferential grooves  28  are aligned in the axial direction and continuously extend in the circumferential direction. 
     Among the four circumferential grooves  28  of the tread  4 , the circumferential groove  28  located on each outer side in the axial direction is a shoulder circumferential groove  28   s . The circumferential groove  28  located inward of the shoulder circumferential groove  28   s  in the axial direction is a middle circumferential groove  28   m . In the tire  2 , the four circumferential grooves  28  include a pair of middle circumferential grooves  28   m  and a pair of shoulder circumferential grooves  28   s.    
     In the tire  2 , from the viewpoint of contribution to drainage performance and traction performance, the width in the axial direction of the middle circumferential groove  28   m  is preferably not less than 2% and not greater than 10% of the width WT of the tread surface  22 . The depth of the middle circumferential groove  28   m  is preferably not less than 13 mm and not greater than 25 mm. The width in the axial direction of the shoulder circumferential groove  28   s  is preferably not less than 1% and not greater than 7% of the width WT of the tread surface  22 . The depth of the shoulder circumferential groove  28   s  is preferably not less than 13 mm and not greater than 25 mm. 
     As described above, the tread  4  has at least three circumferential grooves  28 . This allows the tread  4  to have at least four land portions  30 . The tread  4  of the tire  2  shown in  FIG.  1    has four circumferential grooves  28  and thus has five land portions  30 . These land portions  30  are aligned in the axial direction and continuously extend in the circumferential direction. 
     Among the five land portions  30  of the tread  4 , the land portion  30  located on each outer side in the axial direction is a shoulder land portion  30   s . Each shoulder land portion  30   s  includes an end PE of the tread surface  22 . The land portions  30  located inward of the shoulder land portions  30   s  in the axial direction are middle land portions  30   m . The land portion  30  located inward of the middle land portions  30   m  in the axial direction is a center land portion  30   c . In the tire  2 , the five land portions  30  include the center land portion  30   c , a pair of middle land portions  30   m , and a pair of shoulder land portions  30   s.    
     In the tire  2 , the width in the axial direction of the center land portion  30   c  is not less than 10% and not greater than 18% of the width WT of the tread surface  22 . The width in the axial direction of each middle land portion  30   m  is not less than 10% and not greater than 18% of the width WT of the tread surface  22 . The width in the axial direction of each shoulder land portion  30   s  is not less than 15% and not greater than 25% of the width WT of the tread surface  22 . The width in the axial direction of each land portion  30  is represented as the width in the axial direction of the top surface of the land portion  30  that forms a part of the tread surface  22 . 
     In the tire  2 , the land portion  30  located at the center in the axial direction among the land portions  30  of the tread  4 , that is, the center land portion  30   c  is located on the equator plane. The tire  2  includes the tread  4  having the land portion  30  on the equator plane. The tread  4  may have the circumferential groove  28  on the equator plane. 
     Each sidewall  6  is connected to an end of the tread  4 . The sidewall  6  extends radially inward from the end of the tread  4 . The sidewall  6  is located radially inward of the tread  4 . The sidewall  6  is formed from a crosslinked rubber. 
     Each bead  8  is located radially inward of the sidewall  6 . The bead  8  includes a core  32  and an apex  34 . 
     The core  32  extends in the circumferential direction. The core  32  includes a wound steel wire. The core  32  has a substantially hexagonal cross-sectional shape. 
     The apex  34  is located radially outward of the core  32 . The apex  34  includes an inner apex  34   u  and an outer apex  34   s . The inner apex  34   u  extends radially outward from the core  32 . The outer apex  34   s  is located radially outward of the inner apex  34   u . The inner apex  34   u  is formed from a hard crosslinked rubber. The outer apex  34   s  is formed from a crosslinked rubber that is more flexible than the inner  34   u.    
     Each chafer  10  is located axially outward of the bead  8 . The chafer  10  is located radially inward of the sidewall  6 . The chafer  10  comes into contact with a rim (not shown). The chafer  10  is formed from a crosslinked rubber for which wear resistance is taken into consideration 
     The carcass  12  is located inward of the tread  4 , the pair of sidewalls  6 , and the pair of chafers  10 . The carcass  12  extends between a first bead  8  and a second bead  8 . 
     The carcass  12  includes at least one carcass ply  36 . The carcass  12  of the tire  2  is composed of one carcass ply  36 . The carcass  36  is turned up around each core  32  from the inner side toward the outer side in the axial direction. The carcass ply  36  includes a ply body  36   a  that extends from a first core  32  to a second core  32 , and a pair of turned-up portions  36   b  that are connected to the ply body  36   a  and turned up around the respective cores  32  from the inner side toward the outer side in the axial direction. 
     The carcass ply  36  includes a large number of carcass cords aligned with each other, which are not shown. These carcass cords are covered with a topping rubber. Each carcass cord intersects the equator plane. In the tire  2 , an angle (hereinafter, intersection angle of the carcass cord) of the carcass cords relative to the equator plane is not less than 70° and not greater than 90° The carcass  12  has a radial structure. The carcass cords of the tire  2  are steel cords. 
     Each cushion layer  14  is located between the reinforcing layer  20  and the carcass  12  (specifically, the carcass ply body  36   a  of the carcass ply  36 ), at an end  20   e  of the reinforcing layer  20 . The cushion layer  14  has an inner end  14   ue  located axially inward of the end  20   e  of the reinforcing layer  20 . The cushion layer  14  has an outer end  14   se  located axially outward of the end  20   e  of the reinforcing layer  20 . The cushion layer  14  is formed from a soft crosslinked rubber. 
     The inner liner  16  is located inward of the carcass  12 . The inner liner  16  is joined to the inner surface of the carcass  12  with an insulation (not shown) between the inner liner  16  and the inner surface. The inner liner  16  constitutes the inner surface of the tire  2 . The inner liner  16  is formed from a crosslinked rubber having a high air blocking property. The inner liner  16  retains the internal pressure of the tire  2 . 
     Each steel filler  18  is located at a bead portion B. The steel filler  18  is turned up around the core  32  from the inner side toward the outer side in the axial direction along the carcass ply  36 . The steel filler  18  includes a large number of filler cords aligned with each other, which are not shown. The filler cords are steel cords. 
     The reinforcing layer  20  is located radially inward of the tread  4 . The reinforcing layer  20  is located between the tread  4  and the carcass  12 . The reinforcing layer  20  includes a band  38  and a belt  40 . 
     The band  38  includes a full band  42  and a pair of edge bands  44 . 
     The full band  42  is disposed such that both ends  42   e  thereof are opposed to each other across the equator plane. The end  42   e  of the full band  42  is located axially inward of an end  40   e  of the belt  40 . 
     In  FIG.  1   , a double-headed arrow WF represents the width in the axial direction of the full band  42 . The width WF in the axial direction of the full band  42  is represented as the distance in the axial direction from a first end  42   e  of the full band  42  to a second end  42   e  of the full band  42 . 
     In the tire  2 , from the viewpoint of ensuring the stiffness of the tread portion T, a ratio (WF/WT) of the width WF in the axial direction of the full band  42  to the width WT of the tread surface  22  is preferably not less than 0.70 and not greater than 0.80. 
     The pair of edge bands  44  are spaced apart from each other in the axial direction with the equator plane between the edge bands  44 . Each edge band  44  is located between the tread  4  and the full band  42 . The edge band  44  is located radially outward of the end  42   e  of the full band  42 . The edge band  44  has an inner end  44   ue  located axially inward of the end  42   e  of the full band  42 . The edge band  44  has an outer end  44   se  located axially outward of the end  42   e  of the full band  42 . The edge band  44  overlaps the end  42   e  of the full band  42  in the radial direction. 
     In the tire  2 , the position of the outer end  44   se  of the edge band  44  may coincide with the position of the end  42   e  of the full band  42  in the axial direction. In this case as well, the edge band  44  is located radially outward of the end  42   e  of the full band  42  and overlaps the end  42   e  of the full band  42  in the radial direction. 
     The belt  40  includes at least three belt plies  46  aligned in the radial direction. Each belt ply  46  is disposed such that both ends  46   e  thereof are opposed to each other across the equator plane. 
     The belt  40  includes a first belt ply  46 A, a second belt ply  46 B, a third belt ply  46 C, and a fourth belt ply  46 D. 
     The first belt ply  46 A is the innermost belt ply  46  in the radial direction among the four belt plies  46  constituting the belt  40 . In the tire  2 , the first belt ply  46 A is layered on the carcass  12 , inward of the tread  4 . 
     The second belt ply  46 B is located radially outward of the first belt ply  46 A. The third belt ply  46 C is located radially outward of the second belt ply  46 B. The fourth belt ply  46 D is located radially outward of the third belt ply  46 C. In the tire  2 , the fourth belt ply  46 D is the outermost belt ply  46  in the radial direction among the four belt plies  46  constituting the belt  40 . 
     In the tire  2 , the fourth belt ply  46 D is located between the pair of edge bands  44 . The third belt ply  46 C is located radially inward of the pair of edge bands  44 . The pair of edge bands  44  are located radially outward of the first belt ply  46 A, the second belt ply  46 B, and the third belt ply  46 C. 
     In the tire  2 , the second belt ply  46 B has the largest width in the axial direction, and the fourth belt ply  46 D has the smallest width in the axial direction. The first belt ply  46 A and the third belt ply  46 C may have the same width in the axial direction. Alternatively, the first belt ply  46 A may have a slightly larger width in the axial direction than the third belt ply  46 C. 
     The end  40   e  of the belt  40  of the tire  2  is represented as the end  46   e  of the belt ply  46  having the largest width in the axial direction among the plurality of belt plies  46  constituting the belt  40 . In the belt  40  of the tire  2 , the second belt ply  46 B has the largest width in the axial direction as described above. The end  40   e  of the belt  40  of the tire  2  is represented as an end  46 Be of the second belt ply  46 B. The end  40   e  of the belt  40  is also the end  20   e  of the reinforcing layer  20 . 
     As shown in  FIG.  1   , the first belt ply  46 A has an end  46 Ae located axially outward of the shoulder circumferential groove  28   s . The second belt ply  46 B has an end  46 Be also located axially outward of the shoulder circumferential groove  28   s . The third belt ply  46 C has an end  46 Ce also located axially outward of the shoulder circumferential groove  28   s . The fourth belt ply  46 D has an end  46 De also located axially outward of the shoulder circumferential groove  28   s . In the tire  2 , the end  46 De of the fourth belt ply  46 D may be located axially inward of the circumferential groove  28   s.    
     As shown in  FIG.  1   , the end  46 Ae of the first belt ply  46 A is located axially outward of the end  42   e  of the full band  42 . The end  46 Be of the second belt ply  46 B is also located axially outward of the end  42   e  of the full band  42 . The end  46 Ce of the third belt ply  46 C is also located axially outward of the end  42   e  of the full band  42 . In the tire  2 , the first belt ply  46 A, the second belt ply  46 B, and the third belt ply  46 C each have a width in the axial direction larger than the width WF in the axial direction of the full band  42 . 
     In  FIG.  1   , a double-headed arrow W 1  represents the width in the axial direction of the first belt ply  46 A. A double-headed arrow W 2  represents the width in the axial direction of the second belt ply  46 B. A double-headed arrow W 3  represents the width in the axial direction of the third belt ply  46 C. A double-headed arrow W 4  represents the width in the axial direction of the fourth belt ply  46 D. The width in the axial direction of each belt ply  46  is represented as the width in the axial direction from a first end  46   e  of the belt ply  46  to a second end  46   e  of the belt ply  46 . 
     In the tire  2 , from the viewpoint of ensuring stiffness of the tread portion T, a ratio (W 1 /WT) of the width W 1  in the axial direction of the first belt ply  46 A to the width WT of the tread surface  22  is preferably not less than 0.80 and preferably not greater than 0.90. A ratio (W 2 /WT) of the width W 2  in the axial direction of the second belt ply  46 B to the width WT of the tread surface  22  is preferably not less than 0.85 and preferably not greater than 0.95. A ratio (W 3 /WT) of the width W 3  in the axial direction of the third belt ply  46 C to the width WT of the tread surface  22  is preferably not less than 0.80 and preferably not greater than 0.90. The width W 4  in the axial direction of the fourth belt ply  46 D is set as appropriate in accordance with the specifications of the tire  2 . 
       FIG.  2    shows the configuration of the reinforcing layer  20 . In  FIG.  2   , the right-left direction is the axial direction of the tire  2 , and the up-down direction is the circumferential direction of the tire  2 . The direction perpendicular to the plane of the drawing sheet of  FIG.  2    is the radial direction of the tire  2 . The front side of the drawing sheet of  FIG.  2    is the outer side in the radial direction, and the back side of the drawing sheet is the inner side in the radial direction. 
     As shown in  FIG.  2   , the full band  42  and the edge bands  44  that constitute the band  38  each include a spirally wound band cord  48 . In  FIG.  2   , the band cords  48  are represented by solid lines for the convenience of description, but are covered with a topping rubber  50 . 
     In the tire  2 , the band cords  48  are steel cords or cords formed from an organic fiber (hereinafter, organic fiber cords). When the band cords  48  are organic fiber cords, the organic fiber may be, for example, nylon fibers, polyester fibers, rayon fibers, and aramid fibers. In the tire  2 , the same cord or different cords may be used as a band cord  48 F of the full band  42  and band cords  48 E of the edge bands  44 . The band cords  48  used for the full band  42  and the edge bands  44  are determined according to the specifications of the tire  2 . 
     As described above, the full band  42  includes the spirally wound band cord  48 F. The full band  42  has a jointless structure. In the full band  42 , an angle of the band cord  48 F relative to the circumferential direction is preferably not greater than 5° and more preferably not greater than 2°. The band cord  48 F extends substantially in the circumferential direction. 
     The density of the band cord  48 F in the full band  42  is not less than 20 ends/5 cm and not greater than 35 ends/5 cm. The density of the band cord  48 F is represented as the number of cross-sections of the band cord  48 F included per 5 cm width of the full band  42  in a cross-section of the full band  42  included in the meridian cross-section. 
     As described above, the edge band  44  includes the spirally wound band cord  48 E. The edge band  44  has a jointless structure. In the edge band  44 , an angle of the band cord  48 E relative to the circumferential direction is preferably not greater than 5° and more preferably not greater than 2°. The band cord  48 E of the edge band  44  extends substantially in the circumferential direction. 
     The density of the band cord  48 E in the edge band  44  is not less than 20 ends/5 cm and not greater than 35 ends/5 cm. The density of the band cord  48 E is represented as the number of cross-sections of the band cord  48 E included per 5 cm width of the edge band  44  in a cross-section of the edge band  44  along a plane perpendicular to the direction in which the band cord  48 E extends. 
     As shown in  FIG.  2   , each belt ply  46  constituting the belt  40  includes a large number of belt cords  52  aligned with each other. In  FIG.  2   , the belt cords  52  are represented by solid lines for the convenience of description, but are covered with a topping rubber  54 . 
     The belt cords  52  of the tire  2  are steel cords. The density of the belt cords  52  in each belt ply  46  is not less than 15 ends/5 cm and not greater than 30 ends/5 cm. 
     The belt cords  52  in each belt ply  46  are inclined relative to the circumferential direction. 
     The direction in which the belt cords  52  included in the first belt ply  46 A are inclined (hereinafter, the inclination direction of first belt cords  52 A) is identical to the direction in which the belt cords  52  included in the second belt ply  46 B are inclined (hereinafter, the inclination direction of second belt cords  52 B). 
     The inclination direction of the second belt cords  52 B is opposite to the direction in which the belt cords  52  included in the third belt ply  46 C are inclined (hereinafter, the inclination direction of third belt cords  52 C). 
     The inclination direction of the third belt cords  52 C is identical to the direction in which the belt cords  52  included in the fourth belt ply  46 D are inclined (hereinafter, the inclination direction of fourth belt cords  52 D). 
     In the tire  2 , the belt  40  is configured such that the second belt cords  52 B and the third belt cords  52 C cross each other. The belt  40  contributes to stabilization of the ground-contact shape of the tire. The inclination direction of the first belt cords  52 A may be opposite to the inclination direction of the second belt cords  52 B. The inclination direction of the third belt cords  52 C may be opposite to the inclination direction of the fourth belt cords  52 D. 
     In  FIG.  2   , an angle θ 1  is an angle (hereinafter, inclination angle θ 1  of the first belt cords  52 A) of the belt cords  52  included in the first belt ply  46 A relative to the equator plane. An angle θ 2  is an angle (hereinafter, inclination angle θ 2  of the second belt cords  52 B) of the belt cords  52  included in the second belt ply  46 B relative to the equator plane. An angle θ 3  is an angle (hereinafter, inclination angle θ 3  of the third belt cords  52 C) of the belt cords  52  included in the third belt ply  46 C relative to the equator plane. An angle θ 4  is an angle (hereinafter, inclination angle θ 4  of the fourth belt cords  52 D) of the belt cords  52  included in the fourth belt ply  46 D relative to the equator plane. 
     In the tire  2 , the inclination angle θ 1  of the first belt cords  52 A, the inclination angle θ 2  of the second belt cords  52 B, the inclination angle θ 3  of the third belt cords  52 C, and the inclination angle θ 4  of the fourth belt cords  52 D are preferably not less than 10° and preferably not greater than 60°. 
     From the viewpoint of effectively restraining movement of the tread portion T and obtaining a ground-contact surface that is stable in shape and whose shape change is small, the inclination angle θ 1  of the first belt cords  52 A is preferably not less than 40° and preferably not greater than 60°. The inclination angle θ 2  of the second belt cords  52 B is preferably not less than 150 and preferably not greater than 30°. The inclination angle θ 2  of the second belt cords  52 B is further preferably not greater than 20°. The inclination angle θ 3  of the third belt cords  52 C is more preferably not less than 15° and more preferably not greater than 30°. The inclination angle θ 3  of the third belt cords  52 C is further preferably not greater than 20°. The inclination angle θ 4  of the fourth belt cords  52 D is more preferably not less than 15° and more preferably not greater than 50°. 
       FIG.  3    shows a part of the cross-section of the tire  2  shown in  FIG.  1   .  FIG.  3    shows the tread portion T of the tire  2 . 
     In the tire  2 , each of the end  46 Be of the second belt ply  46 B and the end  46 Ce of the third belt ply  46 C is covered with a rubber layer  56 . Two rubber layers  56  are further disposed between the end  46 Be of the second belt ply  46 B and the end  46 Ce of the third belt ply  46 C, each of which is covered with the rubber layer  56 . In the tire  2 , an edge member  58  including four rubber layers  56  is disposed between the end  46 Be of the second belt ply  46 B and the end  46 Ce of the third belt ply  46 C. The edge member  58  is formed from a crosslinked rubber. The edge member  58  contributes to maintaining the interval between the end  46 Be of the second belt ply  46 B and the end  46 Ce of the third belt ply  46 C. In the tire  2 , a change due to running in the positional relationship between the end  46 Be of the second belt ply  46 B and the end  46 Ce of the third belt ply  46 C is suppressed. The edge member  58  is a part of the reinforcing layer  20 . The reinforcing layer  20  of the tire  2  includes a pair of edge members  58  in addition to the band  38  and the belt  40 . 
     In the tire  2 , the full band  42  is disposed such that both ends  42   e  thereof are opposed to each other across the equator plane, as described above. The full band  42  extends in the axial direction from the equator plane toward each of the ends  42   e . Additionally, in the tire  2 , the edge band  44  is located outward of the end  42   e  of the full band  42  in the radial direction. 
     Although the tire  2  is a low-flatness tire, the full band  42  and the pair of edge bands  44  effectively suppress deformation of the tread portion T. A change of the shape of the tire  2 , for example, a change of the contour (hereinafter, also referred to as case line) of the carcass  12 , is suppressed, so that a change of the ground-contact shape of the tire  2  is suppressed. 
     As describe above, the band cord  48 F included in the full band  42  extends substantially in the circumferential direction. A force acts on the full band  42  of the tire  2  in a running state so as to spread from the inner side toward the outer side in the radial direction. This force increases the tension of the band cord  48 F. 
     A tire bends when coming into contact with a road surface. This causes the force acting on the full band of the tire to decrease, and thus the tension of the band cord decreases. When the tire becomes separated from the road surface and recovers, the force acting on the full band increases, and thus the tension of the band cord increases. The band cord of the tire in a running state undergoes repeated fluctuation in tension. A break may occur in the band cord depending on the degree of fluctuation of the tension. When the band cord breaks, the holding force of the band decreases. In this case, the full band may not be able to contribute to suppression of a shape change. 
     In the tire  2 , the edge band  44  holds the end  42   e  of the full band  42 . Fluctuation of the tension of the band cord  48 F included in the full band  42  is suppressed, so that occurrence of a break of the band cord  48 F caused by the fluctuation is suppressed. The full band  42  of the tire  2  can stably exhibit the function of suppressing a shape change. The edge band  44  is narrower than the full band  42 . Tension fluctuation as in the full band  42  is thus less likely to occur in the band cord  48 E of the edge band  44 . A break is thus less likely to occur in the band cord  48 E of the edge band  44 . 
     As shown in, for example,  FIG.  3   , in the tire  2 , the full band  42  is disposed between the second belt ply  46 B and the third belt ply  46 C, which are wider than the full band  42 . The second belt ply  46 B and the third belt ply  46 C reduce the force acting on the full band  42 . In particular, the belt cord  52  included in the second belt ply  46 B and the belt cord  52  included in the third belt ply  46 C have a crossing relationship, thus effectively reducing the force acting on the full band  42 . Fluctuation of the tension of the band cord  48  included in the full band  42  is suppressed, so that occurrence of a break of the band cord  48  caused by the fluctuation of the tension is suppressed. The full band  42  of the tire  2  can stably exhibit the function of suppressing a shape change. From this viewpoint, it is preferred that among the first belt ply  46 A, the second belt ply  46 B, and the third belt ply  46 C each included in the belt  40 , the second belt ply  46 B and the third belt ply  46 C are wider than the full band  42  and that the full band  42  is located between the second belt ply  46 B and the third belt ply  46 C. In this case, the direction in which the belt cords  52  included in the second belt ply  46 B are inclined is preferably opposite to the direction in which the belt cords included in the third belt ply  46 C are inclined. 
     In the tire  2 , the edge band  44  is disposed outward of the end  42   e  of the full band  42  to suppress the fluctuation in tension of the band cord  48  of the full band  42  and to prevent a break of the band cord  48 . The edge band  44  exerts a force on the full band  42 . The inner portion of the edge band  44  in the radial direction is thus in a situation where strain is likely to occur. 
     As describe above, the full band  42  is located between the second belt ply  46 B and the third belt ply  46 C. In other words, the third belt ply  46 C is located between the edge band  44  and the full band  42 . The third belt ply  46 C includes the belt cord  52 . Thus, when the edge band  44  is close to the third belt ply  46 C, strain may concentrate in the radial inner portion of the edge band  44 , and belt edge loose caused by the strain may occur. In contrast, when the edge band  44  is distant from the third belt ply  46 C, a portion between the edge band  44  and the third belt ply  46 C has a huge volume. In this case, belt edge loose caused by heat generation may occur because rubbers tend to generate heat when deformed. 
     In  FIG.  3   , a length indicated by a double-headed arrow Y is the distance between the edge band  44  and the third belt ply  46 C. 
     The distance Y is represented as the distance (code-to-code distance) between the band cord  48 E included in the edge band  44  at the outer end  44   se  of the edge band  44  and the third belt cord  52 C included in the third belt ply  46 C. The distance Y represents the thickness of a rubber element located between the band cord  48 E and the third belt cord  52 C. When the outer end  44   se  of the edge band  44  is located axially outward of the end  46 Ce of the third belt ply  46 C, the distance Y is represented as the distance, at the end  46 Ce of the third belt ply  46 C, between the band cord  48 E and the third belt cord  52 C. 
     In the tire  2 , the distance Y between the edge band  44  and the third belt ply  46 C is not less than 2.2 mm and not greater than 4.0 mm. 
     The distance Y is not less than 2.2 mm, thus suppressing occurrence of strain caused by the force exerted by the edge band  44 . In the tire  2 , occurrence of belt edge loose caused by strain is suppressed. From this viewpoint, the distance Y is preferably not less than 3.0 mm. The distance Y is not greater than 4.0 mm, thus allowing the portion between the edge band  44  and the third belt ply  46 C to have an appropriate volume. Heat generation is reduced, so that occurrence of belt edge loose caused by the heat generation is suppressed. From this viewpoint, the distance Y is preferably not greater than 3.5 mm. 
     In  FIG.  3   , a solid line EL is a line normal to the outer surface of the carcass  12  and passing through the end PE of the tread surface  22 . The line normal to the outer surface of the carcass  12  is hereinafter also referred to as “normal line”. The solid line EL is hereinafter also referred to as “normal line EL”. A double-headed arrow E represents the thickness of the tire  2  (hereinafter, tire thickness E) measured along the normal line EL of the carcass  12 . The normal line EL passes through the portion of the tire  2  where the shoulder land portion  30   s  are disposed. The tire thickness E is the thickness of the tire  2  at the end PE of the tread surface  22 . 
     In  FIG.  3   , a double-headed arrow D represents the thickness (hereinafter, tire thickness D) of the tire  2  measured along a line normal to the carcass  12  and passing through the equator PC, that is, along the equator plane. The tire thickness D is the thickness of the tire  2  at the equator plane. 
     In the tire  2 , the thickness measured along the line normal to the carcass  12  is greatest at the normal line EL of the carcass  12  passing through the end PE of the tread surface  22 . In the tire  2 , the portion where the shoulder land portion  30   s  is disposed is the thickest portion. An end  20   e  portion of the reinforcing layer  20  is located at the thickest portion. The thickest portion is a portion that moves actively during running and thus becomes hot easily. If the thickest portion has a large volume, belt edge loose caused by heat generation may occur. 
     In the tire  2 , a ratio (ED) of the tire thickness E at the end PE of the tread surface  22  to the tire thickness D at the equator plane is not less than 1.2 and not greater than 2.0. The ratio (E/D) is not greater than 2.0, thus allowing the portion where the shoulder land portion  30   s  is disposed to have an appropriate volume. Heat generation is reduced, so that occurrence of belt edge loose caused by this heat generation is suppressed. From this viewpoint, the ratio (E/D) is preferably not greater than 1.8. 
     The ratio (E/D) is not less than 1.2, thus allowing the tread surface  22  to have an appropriate profile. Occurrence of a bias in the contact pressure distribution is prevented, so that occurrence of uneven wear is suppressed. The effect of the shape-change suppression function of the full band  42  is thus fully achieved. From this viewpoint, the ratio (E/D) is preferably not less than 1.5. 
     In the tire  2 , the end  42   e  of the full band  42  is located axially outward of the shoulder circumferential groove  28   s , the pair of edge bands  44  are located radially outward of the end  42   e  of the full band  42 , the third belt ply  46 C is located radially inward of the pair of edge bands  44 , the distance Y between the edge band  44  and the third belt ply  46 C is not less than 2.2 mm and not greater than 4.0 mm, and the ratio (E/D) of the tire thickness E at the end PE of the tread surface  22  to the tire thickness D at the equator plane is not less than 1.2 and not greater than 2.0. 
     In the tire  2 , occurrence of a break of the band cords  48  and belt edge loose, which may occur when the full band  42  is used to suppress a shape change due to running, is suppressed. The tire  2  achieves suppression of a shape change due to running while reducing the risk of occurrence of a break of the band cords  48  and belt edge loose. The tire  2  has a ground-contact surface that is stable in shape and whose shape change is small, thus improving a variety of performance, such as uneven wear resistance and steering stability. 
     In the tire  2 , the outer end  44   se  of the edge band  44  is located axially inward of the end  46 Ce of the third belt ply  46 C. In  FIG.  3   , a double-headed arrow BE represents the distance in the axial direction from the outer end  44   se  of the edge band  44  to the end  46 Ce of the third belt ply  46 C. 
     In the tire  2 , the distance BE in the axial direction is preferably not less than 8 mm. This configuration allows the outer end  44   se  of the edge band  44  to be disposed at an appropriate distance from the end  46 Ce of the third belt ply  46 C. This prevents concentration of strain in the end  46 Ce of the third belt ply  46 C and the outer end  44   se  of the edge band  44 . In the tire  2 , the risk of occurrence of belt edge loose is effectively reduced. From this viewpoint, the distance BE in the axial direction is more preferably not less than 10 mm. 
     In the tire  2 , the position of the outer end  44   se  of the edge band  44  with respect to the end  42   e  of the full band  42  is determined taking into consideration the holding of the full band  42 . Thus, no preferable upper limit of the distance BE in the axial direction is set. 
     In the tire  2 , the distance Y between the edge band  44  and the third belt ply  46 C is controlled, as described above. To control the distance Y, the reinforcing layer  20  of the tire  2  includes a buffer layer  60  formed from a crosslinked rubber, between the edge band  44  and the third belt ply  46 C. 
     The buffer layer  60  has a sheet shape and thus contributes to precise control of the distance Y. In the tire  2 , the distance Y is an appropriate distance, thus effectively reducing the risk of occurrence of belt edge loose caused by strain as well as the risk of occurrence of belt edge loose caused by heat generation. The buffer layer  60  contributes to reduction of the risk of occurrence of belt edge loose. From this viewpoint, it is preferred that the reinforcing layer  20  includes the buffer layer  60  formed from a crosslinked rubber and that the buffer layer  60  is located between the pair of edge bands  44  and the third belt ply  46 C in the radial direction. In the tire  2 , the thickness of the buffer layer  60  is set as appropriate taking the distance Y into consideration. 
     As shown in  FIG.  3   , the buffer layer  60  of the tire  2  includes a pair of narrow buffer layers  62  disposed with the equator plane between the narrow buffer layers  62 . Each of the narrow buffer layers  62  is located immediately below the corresponding edge band  44 . 
     In the tire  2 , the position of the outer end  62   se  of the narrow buffer layer  62  coincides with the position of the outer end  46 Ce of the third belt ply  46 C in the axial direction. In the axial direction, the position of the outer end  62   se  of the narrow buffer layer  62  may coincide with the position of the outer end  44   se  of the edge band  44 . The outer end  62   se  of the narrow buffer layer  62  may be located between the outer end  46 Ce of the third belt ply  46 C and the outer end  44   se  of the edge band  44 . The position of the outer end  62   se  of the narrow buffer layer  62  is adjusted as appropriate between the outer end  44   se  of the edge band  44  and the end  46 Ce of the third belt ply  46 C, taking into consideration actions of the edge band  44 . 
     As shown in  FIG.  4   , in the tire  2 , the buffer layer  60  may include a wide buffer layer  64  having both ends  64   e  opposed to each other across the equator plane. In this case, the tire  2  has fewer elements than the tire  2  in which the buffer layer  60  includes the pair of narrow buffer layers  62 . A reinforcing layer  20   a  shown in  FIG.  4    contributes to improvement of the productivity. 
     The higher the stress M of the buffer layer  60  at 200% elongation, the less likely the buffer layer  60  has strain. The smaller the loss tangent T of the buffer layer  60  at 70°, the less likely the buffer layer  60  generates heat. 
     In the tire  2 , a ratio (M/T) of the stress M of the buffer layer  60  at 200% elongation to the loss tangent T at 70° C. is preferably not less than 75. This configuration allows the buffer layer  60  to be less likely to have strain and generate heat. The buffer layer  60  effectively contributes to reduction of the risk of occurrence of belt edge loose. From this viewpoint, the ratio (M/T) is more preferably not less than 80 and further preferably not less than 100. From the viewpoint of suppressing occurrence of belt edge loose, the greater the ratio (M/T), the better. Thus, no preferable upper limit of the ratio is set. The ratio (M/T) is calculated with the unit of the stress M at 200% elongation being megapascal (MPa). 
     In the tire  2 , from the viewpoint that the buffer layer  60  having an appropriate stiffness is formed, the stress M of the buffer layer  60  at 200% elongation is preferably not less than 11 MPa. From the viewpoint that the difference in stiffness between the buffer layer  60  and another rubber element located around the buffer layer  60  is appropriately maintained and that occurrence of damage due to the difference in stiffness is suppressed, the stress M at 200% elongation is preferably not greater than 15 MPa. 
     In the tire  2 , the end  42   e  of the full band  42  is located outward of the shoulder circumferential groove  28   s  in the axial direction, as described above. 
     In  FIG.  3   , a double-headed arrow SF represents the direction in the axial direction from the shoulder circumferential groove  28   s , specifically from the outer edge of the shoulder circumferential groove  28   s  to the end  42   e  of the full band  42 . A double-headed arrow WS represents the width in the axial direction of the shoulder land portion  30   s . The width WS in the axial direction is represented as the distance in the axial direction from the inner end of the top surface of the shoulder land portion  30   s  (i.e., the outer edge of the shoulder circumferential groove  28   s ) to the outer end of this top surface (in the tire  2 , the end PE of the tread surface  22 ). 
     In the tire  2 , a ratio (SF/WS) of the distance SF in the axial direction from the shoulder circumferential groove  28   s  to the end  42   e  of the full band  42  to the width WS in the axial direction of the shoulder land portion  30   s  is preferably not greater than 50%. This configuration allows the end  42   e  of the full band  42  to be disposed distant from an end portion of the tread  4  that actively moves in a running state. Fluctuation of the tension of the band cord  48  is suppressed, so that occurrence of a break of the band cord  48  is suppressed in the tire  2 . The full band  42  of the tire  2  contributes to suppression of a shape change. From this viewpoint, the ratio (SF/WS) is more preferably not greater than 35% and further preferably not greater than 25%. 
     When the ratio (SF/WS) is set to be not less than 10%, the end  42   e  of the full band  42  is located at an appropriate distance from the shoulder circumferential groove  28   s , specifically from the bottom of the shoulder circumferential groove  28   s . In the tire  2 , occurrence of damage starting from the bottom of the shoulder circumferential groove  28   s  is suppressed. The width of the full band  42  is ensured, thus allowing the full band  42  to contribute to suppression of a shape change of the tire  2 . From this viewpoint, the ratio (SF/WS) is more preferably not less than 15%. 
     In the tire  2 , the inner end  44   ue  of the edge band  44  is located inward of the end  42   e  of the full band  42  in the axial direction, as described above. In  FIG.  3   , a length indicated by reference sign We is the distance in the axial direction from the end  42   e  of the full band  42  to the inner end  44   ue  of the edge band  44 . 
     In the tire  2 , the distance We in the axial direction from the end  42   e  of the full band  42  to the inner end  44   ue  of the edge band  44  is preferably not less than 10 mm. This configuration allows the edge band  44  to effectively hold the end  42   e  of the full band  42 . Fluctuation of the tension of the band cord  48  included in the full band  42  is suppressed, so that occurrence of a break of the band cord  48  due to the fluctuation of the tension is suppressed. The full band  42  of the tire  2  can more stably exhibit the function of suppressing a shape change. From this viewpoint, the distance We in the axial direction is preferably not less than 20 mm. From the viewpoint that the influence of the edge band  44  on the mass of the tire  2  is reduced, the distance We in the axial direction is preferably not greater than 50 mm. 
     In the tire  2 , the position of the inner end  44   ue  of the edge band  44  is determined in consideration of involvement in occurrence of damage starting from the bottom of the shoulder circumferential groove  28   s . From the viewpoint of effectively suppressing occurrence of damage starting from the bottom of the shoulder circumferential groove  28   s , in the axial direction, the inner end  44   ue  of the edge band  44  is preferably located outward of the bottom of the shoulder circumferential groove  28   s  and is more preferably located further outward of the shoulder circumferential groove  28   s . In the tire  2 , the inner end  44   ue  of the edge band  44  may be located inward of the bottom of the shoulder circumferential groove  28   s  in the axial direction. In this case, the inner end  44   ue  of the edge band  44  is more preferably located further inward of the shoulder circumferential groove  28   s  in the axial direction. 
       FIG.  5    shows a modification of the reinforcing layer  20 . A reinforcing layer  20   b  has substantially the same configuration as the reinforcing layer  20  shown in  FIG.  3   , except for the exclusion of the fourth belt ply  46 D and the change of the position of the full band  42 . The same elements as those of the reinforcing layer  20  shown in  FIG.  3    are designated by the same reference signs, and the description thereof is omitted. 
     In the reinforcing layer  20   b , the entirety of the band  38  is located radially outward of the belt  40 . In the reinforcing layer  20   b , the full band  42  is disposed radially outward of the third belt ply  46 C, whereas in the reinforcing layer  20  shown in  FIG.  3   , the full band  42  is disposed between the third belt ply  46 C and the second belt ply  46 B. The pair of narrow buffer layers  62  constituting the buffer layer  60  are located between the pair of edge bands  44  and the full band  42 . 
     In the reinforcing layer  20   b  as well, the buffer layer  60  contributes to control of the distance Y. In the reinforcing layer  20   b , the distance Y is the distance between the edge band  44  and the full band  42 . As shown in  FIG.  5   , the distance Y in the reinforcing layer  20   b  is represented as the distance between the band cord  48 E included in the edge band  44  at the outer end  44   se  of the edge band  44  and the band cord  48 F included in the full band  42 . When the edge band  44  is configured such that the full band  42  is turned up at the end  60   e  of the buffer layer  60 , the distance Y is represented as the distance between the band cord  48 E included in the edge band  44  and the band cord  48 F included in the full band  42 , which is obtained at an end of a portion of the buffer layer  60  that has a uniform thickness. When the outer end  44   se  of the edge band  44  is located axially outward of the end  42   e  of the full band  42 , the distance Y is represented as the distance, at the end  42   e  of the full band  42 , between the band cord  48 E and the band cord  48 F. 
     In the reinforcing layer  20   b  as well, the distance Y is preferably not less than 2.2 mm and not greater than 4.0 mm, preferably not less than 3.0 mm, and preferably not greater than 3.5 mm. This configuration allows the distance Y to be an appropriate distance. The risk of occurrence of belt edge loose caused by strain as well as the risk of occurrence of belt edge loose caused by heat generation is thus effectively reduced in the tire  2 . 
     As is obvious from the above description, the present invention provides the heavy duty pneumatic tire  2  that can achieve suppression of a shape change due to running while reducing the risk of occurrence of a break of the band cord and belt edge loose. The present invention exhibits a noticeable effect in the low-flatness heavy duty tire  2  having a nominal aspect ratio of 65% or less. 
     EXAMPLES 
     The following will further describe the present invention by way of, for example, Examples, but the scope of the present invention should not be limited to these Examples. 
     Example 1 
     A heavy duty pneumatic tire (tire size=355/50R22.5) having the basic structure shown in  FIGS.  1  to  3    and having the specifications shown in Table 1 below was obtained. 
     The band in Example 1 includes a full band and a pair of edge bands. 
     The full band is disposed between the second belt ply and the third belt ply. 
     The end of the full band is located axially outward of the shoulder circumferential groove. This is represented as “Y” in the cell for “FB” in Table 1. 
     The pair of edge bands are disposed radially outward of the end of the full band. The end of the full band is covered by the edge band. This is represented as “Y” in the cell for “EB” in Table 1. 
     The distance Y between the edge band and the third belt ply, the distance BE in the axial direction from the outer end of the edge band to the end of the third belt ply, the ratio (E/D) of the tire thickness E at the end of the tread surface to the tire thickness D at the equator plane, and the ratio (M/T) of the stress M of the buffer layer at 200% elongation to the loss tangent T at 70° C. were set as shown in Table 1 below. The buffer layer in Example 1 includes a pair of narrow buffer layers. 
     Examples 2 to 7 and Comparative Examples 1 to 4 
     Tires of Examples 2 to 7 and Comparative Examples 1 to 4 were obtained in the same manner as Example 1, except that the distance Y, the distance BE, the ratio (E/D), and the ratio (M/T) were set as shown in Tables 1 and 2 below. 
     In Comparative Example 1, the end of the full band is located axially inward of the shoulder circumferential groove. This is represented as “N” in the cell for “FB” in Table 1. 
     In Comparative Example 2, the outer end of the edge band is located axially inward of the end of the full band. The edge band is not disposed radially outward of the end of this full band. This is represented as “N” in the cell for “EB” in Table 1. 
     [Profile Change] 
     A test tire was fitted onto a rim (11.75×22.5) and inflated with air to adjust the internal pressure of the tire to a normal internal pressure. The tire was caused to run on a drum tester at a speed of 80 km/h for 1000 km, and a profile of the case line on the inner side of the shoulder circumferential groove was obtained. The profile of the case line was compared with the profile of the case line before running to confirm a change in profile before and after running. The results are represented as indexes according to the following ratings in Tables 1 and 2 below. A higher value represents that a change in profile is suppressed. In the running test, a normal load was applied to the tire. In this evaluation, not less than 95 is allowable. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Change amount 
                 Index 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0.0 mm to 0.5 mm 
                 100 
               
               
                   
                 0.6 mm to 1.0 mm 
                 95 
               
               
                   
                 1.1 mm to 1.5 mm 
                 90 
               
               
                   
                 1.6 mm to 2.0 mm 
                 85 
               
               
                   
                 2.1 mm to 2.5 mm 
                 80 
               
               
                   
                   
               
            
           
         
       
     
     [Uneven Wear Resistance] 
     A test tire was fitted onto a rim (11.75×22.5) and inflated with air to adjust the internal pressure of the tire to a normal internal pressure. The tire was mounted to the drive shaft of a test vehicle (tractor head). The test vehicle was caused to tow a trailer loaded with luggage and to run on a test course including an asphalt road surface. The difference in amount of wear between the shoulder land portion and the middle land portion of the test tire was calculated when the wear ratio of the tire reached 30% in terms of mass. The result is represented as an index with the result of Example 1 being regarded as 100, in Tables 1 and 2 below. A higher value represents that the difference in amount of wear is smaller and the uneven wear resistance is higher. In this evaluation, not less than 95 is allowable. 
     [JLB Break Resistance] 
     Each tire for which the above-described evaluation had been made for uneven wear resistance was inspected by sialography or X-ray to confirm the presence or absence of internal damage. When internal damage was confirmed, the tire was disassembled to confirm whether this internal damage was a break of the band cord of the full band. The results are shown in Tables 1 and 2 below according to the following ratings. In this evaluation, the rating D is unallowable, and the other ratings are allowable. 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 Case where no broken portion is observed in the band cord 
                 A 
               
               
                 Case where one broken portion is observed in the band cord 
                 B 
               
               
                 Case where two broken portions are observed in the band cord 
                 C 
               
               
                 Case where three or more broken portions are observed in the  
                 D 
               
               
                 band cord 
               
               
                   
               
            
           
         
       
     
     [BEL Resistance] 
     The test tire was fitted onto a rim (11.75×22.5) and inflated with air to adjust the internal pressure of the tire to a normal internal pressure. The tire was caused to run on a drum tester at a speed of 100 km/h with a load 1.4 times the normal load being applied to the tire, and the time to occurrence of belt edge loose (BEL) was measured. The result is represented as an index with the result of Example 1 being regarded as 100, in Tables 1 and 2 below. In this evaluation, not less than 80 is allowable. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Comparative 
                 Comparative 
                 Comparative 
                 Comparative 
                   
                   
               
               
                   
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
                 Example 1 
                 Example 2 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 FB 
                 N 
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
               
               
                 EB 
                 Y 
                 N 
                 Y 
                 Y 
                 Y 
                 Y 
               
               
                 Y [mm] 
                 3.0 
                 3.0 
                 1.5 
                 2.2 
                 3.2 
                 2.2 
               
               
                 BE [mm] 
                 8 
                 — 
                 8 
                 10 
                 15 
                 5 
               
               
                 E/D [—] 
                 1.2 
                 1.2 
                 1.2 
                 0.5 
                 1.7 
                 2.0 
               
               
                 M/T 
                 80 
                 80 
                 100 
                 100 
                 160 
                 100 
               
               
                 Profile 
                 85 
                 100 
                 100 
                 90 
                 100 
                 95 
               
               
                 change 
               
               
                 Uneven 
                 85 
                 95 
                 90 
                 80 
                 100 
                 95 
               
               
                 wear 
               
               
                 resistance 
               
               
                 JLB break 
                 B 
                 C 
                 B 
                 B 
                 A 
                 B 
               
               
                 resistance 
               
               
                 BEL 
                 70 
                 70 
                 70 
                 80 
                 100 
                 80 
               
               
                 resistance 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Example  
                 Example  
                 Example  
                 Example  
                 Example  
               
               
                   
                 3 
                 4 
                 5 
                 6 
                 7 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 FB 
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
               
               
                 EB 
                 Y 
                 Y 
                 Y 
                 Y 
                 Y 
               
               
                 Y [mm] 
                 2.2 
                 2.2 
                 2.2 
                 4.0 
                 3.2 
               
               
                 BE [mm] 
                 10 
                 10 
                 10 
                 8 
                 8 
               
               
                 E/D [−] 
                 2.0 
                 2.0 
                 1.2 
                 2.0 
                 1.5 
               
               
                 M/T 
                 50 
                 80 
                 80 
                 100 
                 100 
               
               
                 Profile change 
                 95 
                 95 
                 95 
                 95 
                 100 
               
               
                 Unevenwear 
                 95 
                 95 
                 95 
                 95 
                 100 
               
               
                 resistance 
                   
                   
                   
                   
                   
               
               
                 JLB break resistance 
                 B 
                 B 
                 B 
                 A 
                 A 
               
               
                 BEL resistance 
                 80 
                 90 
                 90 
                 90 
                 90 
               
               
                   
               
            
           
         
       
     
     In Examples, suppression of a shape change due to running is achieved while the risk of occurrence of a break of the band cord and belt edge loose is reduced, as shown in Tables 1 and 2. From the evaluation results, the advantages of the present invention are clear. 
     INDUSTRIAL APPLICABILITY 
     The above-described technology for achieving suppression of a shape change due to running while reducing the risk of occurrence of a break of the band cord and belt edge loose can be applied to various tires. 
     REFERENCE SIGNS LIST 
     
         
         
           
               2  tire 
               4  tread 
               6  sidewall 
               8  bead 
               12  carcass 
               20  reinforcing layer 
               22  tread surface 
               28   s  shoulder circumferential groove 
               38  band 
               40  belt 
               42  full band 
               44  edge band 
               46 ,  46 A,  46 B,  46 C,  46 D belt ply 
               48  band cord 
               52  belt cord 
               60  buffer layer 
               62  narrow buffer layer 
               64  wide buffer layer