Passenger tire with low bead apex volume

A passenger radial tire which comprises a tread portion, a pair of axially spaced bead portions, a pair of sidewall portions extending therebetween, a pair of bead cores disposed one in each bead portion, and a carcass extending between the bead portions and turned up around the bead cores from the axially inside to the outside thereof to form two turned up portions and one main portion therebetween, wherein in at least the sidewall portions no bead apex exists to thereby the carcass turned up portions are located adjacently to the carcass main portion, and in each bead portion a bead reinforcement extending radially outwardly into the sidewall portion is disposed.

BACKGROUND OF THE INVENTION 
The present invention relates to a pneumatic tire, more particularly a 
radial ply tire in which a reduction in tire weight is achieved without 
sacrificing steering stability. 
On recent high-performance passenger cars, a low aspect ratio tire which is 
excellent in steering stability, grip performance and structural 
durability at a high speed is widely used. In particular, for a sports car 
in which high speed performance is of special importance, tires whose 
aspect ratio is less than 55% are now becoming used. In such a low aspect 
ratio tire, a weight reduction is further required to achieve a further 
improvement in car performance, e.g. running performance, low fuel 
consumption and the like. 
In a conventional pneumatic tires, as shown in FIG. 11, each bead portion 
is provided with a bead apex C between a carcass main portion A and a 
carcass turned up portion B in order to increase the bending rigidity of 
the bead portion and thereby improve the steering stability of the tire, 
the bead apex C is made of hard rubber and extends radially outwardly from 
the bead core into the sidewall portion over the radially outer edge of 
the rim flange. Thus, the bead apex has a considerable volume and weight. 
SUMMARY OF THE INVENTION 
It is therefore, an object of the present invention to provide a pneumatic 
tire in which, by decreasing the volume of the bead apex, the tire weight 
is decreased but without decreasing the bead rigidity and steering 
stability. According to one aspect of the present invention, a pneumatic 
tire comprises a tread portion, a pair of axially spaced bead portions, a 
pair of sidewall portions extending therebetween, a pair of bead cores 
disposed one in each bead portion, and a carcass extending between the 
bead portions and turned up around the bead cores from the axially inside 
to the outside thereof to form two turned up portions and one main portion 
therebetween, wherein, in at least the sidewall portions no bead apex 
exists and the carcass turned up portions are located adjacently to the 
carcass main portion, and in each bead portion a bead reinforcement 
extending radially outwardly into the sidewall portion is disposed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the figures, each of tire 1 has a tread portion 2, a pair of axially 
spaced bead portions 4, and a pair of sidewall portions 3 extending 
between the tread edges and the bead portions, and comprises a bead core 5 
disposed in each of the bead portions, a radial carcass 6 extending 
between the bead portions, a belt 12 disposed radially outside the carcass 
and inside a rubber tread, and at least one reinforcing layer 9 extending 
from each bead portion to the sidewall portion. In the Figures, each tire 
1 is shown mounted on its regular rim 10 and inflated to its normal inner 
pressure. 
The carcass 6 comprises at least one ply of radially arranged cords 
extending between the bead portions through the sidewall portions and the 
tread portion and turned up around the bead cores 5 from the axially 
inside to the outside thereof to form two turned up portion 6B and one 
main portion 6A therebetween. 
For the carcass cords, organic fiber cords, e.g. nylon, polyester, rayon 
and aromatic polyamide, or metal cords, or carbon fiber cords, or the like 
can be used. Preferably a light weight material cord is used. 
The carcass may include a ply which is turned up reversely around the bead 
cores from the axially outside to the inside thereof, and/or a ply which 
is not turned up around the bead cores. It is however, preferable to 
minimize the number of carcass plies for tire weight reduction. A 
reinforcing ply layer 9 is provided in each bead portion and sidewall 
portion and no or only a very small or short apex 8 is provided. These 
components provide the necessary lower sidewall stiffness in combination 
with the carcass turn up portion 6A and 6B. The carcass turnup height Hc, 
or the radial distance of the radially outer edge of the carcass turned up 
portion 6B from the bead base line BL, is set to be not less than 1/2 the 
tire section height Ht defined as the radial distance from the bead base 
line BL to the radially outermost point on the tread face. 
In FIG. 1, the tire 1 is a passenger tire having a low aspect ratio (tire 
section height/tire section width) of not more than 0.55 (55%). The tire 
size is P225/50R16, and two reinforcing layers 9A and 9B and a small size 
bead apex 8 are disposed in each bead portion. The belt 12 comprises a 
breaker 7 and a band 13 disposed over the belt both being in the tread 
portion. 
The small bead apex 8 is made of hard rubber having a JIS A hardness of 60 
to 90 degrees disposed radially outside the bead core 5 and between the 
carcass main portion 6A and the turned up portion 6B, and extending 
radially outwardly and tapering to provide a generally triangular cross 
section. 
The radial height Ha of the radially outer edge of the bead apex from the 
bead base line BL is set to be not more than the radial height Hf of the 
radially outer edge X1 of a flange 11 of the regular rim 10, whereby the 
bead apex rubber does not extend into the region radial outward of the 
above-mentioned outer edge X1 of the rim flange and so the bead apex 
volume is greatly decreased in comparison with that in the conventional 
tire. 
Further, the bead apex height Ha in this embodiment is less than 13% of the 
tire section height Ht. 
The reinforcing layer 9 comprises two reinforcing layers 9A and 9B disposed 
between the carcass main portion 6A and the turned up portion 6B; in this 
embodiment, the reinforcing layers 9A and 9B are high modulus cord 
reinforcing layers. Each layer 9A, 9B extends at least between two heights 
one being the rim flange height Hf and the other being a height Hs which 
is 0.25 times the tire section height Ht. Thus the layers may be extended 
between these heights or over a greater distance. In the first embodiment 
the radially outer edges of the reinforcing layers 9A and 9B are extended 
to heights H9au and H9bu, respectively, each of which is greater than 0.25 
times the tire section height Ht. 
The radially inner edges of the reinforcing layers 9A and 9B extend to 
heights H9ad and H9bd, respectively, each of which is smaller than the 
height Hf of the outer edge X1 of the rim flange 11 so that the layer 9A 
and 9B extend over a greater distance than the minimum specified of Hf to 
Hs. The radially inner edges are secured between the bead apex 8 and the 
carcass turned up portion 6B, and contact the radially outer face of the 
bead core 5. If the heights of the radially outer edges of the reinforcing 
layers are smaller than the minimum height Hs (=0.25 Ht), it becomes too 
difficult to maintain the required bead rigidity. When the height of the 
radially inner edges thereof are larger than the height Hf, there is no 
reinforcing layer in the most deflected part of the tire when loaded, that 
is, the part around the outer edge of the rim flange in which the amount 
of deformation is very large, and as a result, the bead rigidity is 
greatly decreased. 
More preferably, the inner edge of each reinforcing layer is located at a 
position radially inward of a boundary point FP which is the point where 
the tire side face comes into contact with the rim flange. 
Further, the height H9au, H9bu of the outer edge of each reinforcing layer 
is smaller than the radial height Hc of the carcass turned up portion to 
avoid stress concentration at the outer edge and to thereby reduce the 
chance of rubber separation failure. 
It is preferable that the outer edges of the reinforcing layers and the 
outer edge of the carcass turned up portion 6B are not aligned with each 
other. Therefore, in this embodiment, the height H9au of the axially inner 
reinforcing layer 9A is larger than that of the outer layer 9B. 
For the cords of the reinforcing layer, aromatic polyamide fiber cords are 
preferably used because of their light weight and high modulus of the same 
level as the steel cords. In passenger tires, the cord thickness or 
construction may be 1000d/2 to 1500d/3, the twist number is 20 to 55 
twist/5 cm, and the cord count is then 30 to 50/5 cm. 
The cords of each reinforcing layer are laid radially at an inclination 
angle of 15 to 75 degrees, more preferably 45 to 75 degrees, with respect 
to the radial direction of the tire, and the cords in each reinforcing 
layer cross the cords of the next layer, whereby the bead rigidity is 
effectively increased. 
Further, the bead portion in this embodiment is provided with an additional 
bead reinforcing layer 14 made of organic fiber cords, preferably aromatic 
polyamide fiber cords. This reinforcing layer 14 is positioned around the 
bead cores to extend from the axially inner side to the outer side of the 
bead portion. The radial height Hg of the radially outer edge of the 
axially outward portion thereof is larger than the rim flange height Hf. 
The belt 12 is composed of a breaker 7 comprising at least two crossed 
plies 7A and 7B disposed on the radially outside of the carcass, and a 
band 13 disposed radially outside the breaker. 
For the breaker cords, aromatic polyamide cords are used to achieve minimum 
tire weight while providing the required hoop effect for the tread 
portion. 
On the other hand, in an aromatic polyamide cord, the strength and rigidity 
against bending deformation is low in comparison with steel cords. As a 
result, road grip performance, tread wear life and noise performance are 
liable to be impaired, and a breaker edge failure is also liable to be 
caused. In order to avoid those problems, the above-mentioned band 13 is 
disposed radially outside the breaker 7. 
The band 13 may be, as shown in FIG. 2, formed by winding a ribbon of 
rubber around the breaker spirally and continuously in the circumferential 
direction of the tire. In the ribbon of rubber, a nylon cord or 2 to 15 
parallel nylon cords are embedded in the longitudinal direction thereof. 
In tread shoulder regions SH, the axially adjacent windings are overlapped 
with each other by about a half of the ribbon width, but not overlapped in 
a tread crown region CR, whereby the hoop effect of the band 13 becomes 
larger in the shoulder regions than the crown region, and the rigidity 
thereof is also increased which can compensate for lack of the rigidity of 
the aromatic polyamide breaker at its edge portions. 
In the band 13, therefore, the or each nylon cord is laid at almost zero 
angle or a small angle with respect to the circumferential direction of 
the tire, that is, laid in parallel with the tire circumferential 
direction of the tire. On the other hand, the cords of each breaker ply 
are laid at an inclination angle of 10 to 30 degrees with respect to the 
circumferential direction of the tire so as to cross the cords of the next 
breaker ply. Therefore, the cords of the breaker and band form a 
triangulated structure. 
FIG. 3 shows another embodiment of the present invention, in which no bead 
apex at all is disposed in the bead portions 4. In this embodiment, the 
tire size is 185/60R14, and the carcass 6 is turned up around the bead 
cores 5 from the axially inside to the outside thereof. Each turned up 
portion 6B thereof is bent abruptly to extend along the radially outer 
surface 5a of the bead core, and then extend radially outwardly along the 
axially outer surface of the reinforcing layer 9 and the carcass main 
portion 6A. The radially inner edges of the reinforcing layers 9A and 9B 
are extended to the outer surface 5a of the bead core to contact thereto. 
Test tires of size P225/50R16 having specifications given in Table 1 were 
prepared and tested for spring constant, steering stability, ride comfort 
and tire noise. The test results are also shown in Table 1. 
In the tests, the lateral spring constant was defined as a lateral force 
(100 kgf) divided by the amount of deformation (mm) of the tire caused by 
the lateral force, when the tire was mounted on its regular rim and 
inflated to its regular pressure. The longitudinal spring constant was 
defined as a variation (100 kgf) of the longitudinal force divided by the 
variation of the amount of deformation (mm) of the tire when the 
longitudinal force is increased to 450 kgf from 350 kgf. 
The steering stability, ride comfort and tire noise were evaluated in five 
ranks by a test driver, using a 3000 cc passenger car running at speeds 
between 100 km/h and 240 km/h. The larger the point, the better the 
result. 
The tire weights of Examples 1 and 2 according to the present invention 
were lighter than Reference tires 1 and 2 while the other tire performance 
factors were improved or maintained. 
FIG. 4 shows another embodiment of the present invention, in which two 
reinforcing layers 9A and 9B are disposed axially outside the carcass 
turned up portion 6B therealong. 
In this embodiment, the tire size is 185/60R14. The radial heights H9ad and 
H9bd of the radially inner edges of the reinforcing layers 9A and 9B are 
set smaller than the height Hf of the outer edge X1 of the flange 11 of 
the rim 10. The radial heights H9au and H9bu of the radially outer edges 
of the reinforcing layers are larger than the height Hs which is 0.25 
times the tire section height Ht. Therefore, the axially outer face of the 
carcass turned up portion 6B is again covered between more than the height 
Hf and the height Hs. Further, the heights H9au and H9bu are preferably 
smaller than the height Hc of the carcass turned up portion. 
Between the carcass main portion 6A and each carcass turned up portion 6B, 
a hard rubber bead apex 8 is disposed in the same manner as the tire in 
FIG. 1. The height Ha of the bead apex 8 is less than the height Hf so 
that no bead apex rubber exists in the region radially outward of radially 
outer edge X1 of the rim flange 11. 
The cords of each reinforcing layer are arranged generally radially at an 
inclination angle of 15 to 75 degrees, more preferably, 45 to 75 degrees 
to the radial direction of the tire so as to cross the cords of the 
adjacent reinforcing layer. In FIG. 4, the belt 12 comprises a breaker 7 
comprising only two crossed aromatic polyamide cord plies. However, it is 
possible to dispose the above-mentioned band 13 radially outside thereof. 
FIG. 5 shows a modification of the bead portion of the tire in FIG. 4, 
wherein the bead apex 8 is completely eliminated. The carcass 6 is turned 
up around the bead cores 5 from the axially inside to the outside thereof. 
Each turned up portion 6B is bent abruptly to contact the radially outer 
face 5a of the bead core 5, and then extends radially outwardly while 
contacting with the carcass main portion 6A. The inner edge of each 
reinforcing layer is extended to the bent part of the carcass turned up 
portion 6B to contact thereto. 
FIG. 6 shows another embodiment of the present invention, which is very 
similar to or the almost same as the tire shown in FIG. 4 excepting the 
position of the axially inner reinforcing layer 9A. In this embodiment, 
the axially inner reinforcing layer 9A is disposed between the carcass 
main portion 6A and each turned up portion 6B. The radially inner edge 
thereof is secured between the bead apex 8 and the carcass turned up 
portion. The axially outer reinforcing layer 9B is disposed axially 
outside the carcass turned up portion. 
FIG. 7 shows a modification of the bead portion of the tire in FIG. 6, 
wherein the bead apex 8 is completely eliminated. 
FIG. 8 shows still another embodiment of the present invention, in which 
two reinforcing layers 9A and 9B are disposed axially inside the carcass 
main portion. In this embodiment, the radial heights H9ad and H9bd of the 
radially inner edges of the reinforcing layers are set smaller than the 
above-mentioned height Hf of the rim flange 11. The radial heights H9au 
and H9bu of the outer edges thereof are larger than the height Hs which is 
0.25 times the tire section height Ht. Further, the height H9ad of the 
axially inner layer 9A is smaller than the height H9bd of the axially 
outer layer 9B, and the height H9au of the axially inner layer 9A is 
smaller than the height H9bu of the axially outer layer 9B. 
Between the carcass main portion 6A and each carcass turned up portion 6B, 
a hard rubber bead apex 8 is disposed in the same manner as the tire in 
FIG. 1. The height Ha of the bead apex 8 is smaller than the height Hf, 
whereby no bead apex rubber exists in the region radially outward of 
radially outer edge X1 of the rim flange 11. 
FIG. 9 shows another embodiment of the present invention, which is very 
similar to or almost same as the tire shown in FIG. 8 except for the 
position of the axially outer reinforcing layer 9B. In this embodiment, 
the axially outer reinforcing layer 9B is disposed between the carcass 
main portion 6A and each turned up portion 6B. The radially inner edge 
thereof is secured between the bead apex 8 and the carcass turned up 
portion. The axially inner reinforcing layer 9A is disposed axially inside 
the carcass main portion therealong. 
FIG. 10 shows a modification of the bead portion of the tire in FIG. 9, 
wherein the bead apex 8 is completely eliminated. 
The carcass 6 is turned up around the bead cores 5 from the axially inside 
to the outside thereof. Each turned up portion 6B is bent abruptly to 
contact with the radially outer face 5a of the bead core 5, and then 
extends radially outwardly while contacting with the axially outer surface 
of the reinforcing layer 9B. The inner edge of the axially outer 
reinforcing layer 9B is extended to the outer face 5a of the bead core to 
contact thereto. 
In the embodiments shown in FIGS. 3-10, for the cords of the reinforcing 
layers, organic fiber cords, e.g. nylon, polyester and the like, and metal 
cords, e.g. steel can be used. However, aromatic polyamide fiber cords 
having a modulus of the same level as the steel cords but a lighter weight 
are preferably used. When aromatic polyamide cords are used, the cord 
thickness and construction are 720d/2 to 3000d/2, the twist number is 20 
to 70/10 cm, and the cord count is 25 to 45/5 cm. 
Test tires of size 185/60R14 having the specifications given in Table 2 
were prepared and tested for spring constant, lane change stability, yaw 
convergence, cornering G on asphalt. The test results are also shown in 
Table 2. 
The lane change stability and yaw convergence were evaluated in five ranks 
by a test driver. The larger the point, the better the result. The lane 
change stability is the stability when a quick lane change was made during 
straight running at a speed of 100 km/h, and the yaw convergence is the 
convergence of the yaw caused by the above-mentioned quick lane change. 
The cornering G on asphalt was calculated from the maximum cornering speed 
marked by the test vehicle during cornering on a dry asphalt road at a 
radius of 50 meters and the lateral force on the vehicle at the maximum 
cornering speed. 
The weights of the Example tires according to the present invention were 
lighter than the Reference tires while the other tire performance factors 
were improved or maintained. 
Between the adjacent plies, e.g. between the carcass main portion and the 
turned up portion, between the carcass ply and the reinforcing layer, a 
thin rubber layer (not shown) whose thickness is less than 3 mm, 
preferably less than 2 mm may be disposed to mitigate shearing stress 
between the respective layers. Further, In each bead portion, three 
reinforcing layers can be disposed, in which the axially inner layer is 
disposed axially inside the carcass main portion, the axially outer layer 
is disposed axially outside the carcass turned up portion, and the middle 
layer is disposed between the carcass main portion and the turned up 
portion. 
As described above, in tires according to the present invention, the bead 
apex does not exist in the flexing sidewall regions or more specifically 
does not extend into the region radially outward of the radially outer 
edge of the rim flange. Also the reinforcing layers are provided which 
extend from each bead portion into the sidewall portions. Thus the tire 
weight is reduced without sacrificing the steering stability, and the fuel 
consumption performance can be improved. 
Further, when aromatic polyamide cords are used for the belt reinforcement, 
the tire weight can be further decreased. 
TABLE 1 
__________________________________________________________________________ 
Ex. 1 Ex. 2 Ref. 1 Ref. 2 
__________________________________________________________________________ 
Tire size P225/50R16 
P225/50R16 
P225/50R16 
P225/50R16 
Carcass 1 ply 1 ply 1 ply 1 ply 
Cord polyester 
polyester 
polyester 
polyester 
1500d/2 
1500d/2 
1500d/2 
1500d/2 
Breaker aromatic 
aromatic 
steel polyamide 
Cord polyamide 
polyamide 
1X5/0.25/35e 
1500d/2 
1500d/2 
1500d/2 
Cord angle (deg) 
20 20 24 20 
Band 0 0 0 0 
Cord angle (deg) 
Reinforcing layer 
2 plies 
2 plies 
1 ply 1 ply 
Cord aromatic 
aromatic 
steel steel 
polyamide 
polyamide 
1500d/2 
1500d/2 
Ht (mm) 114 114 114 114 
Hc (mm) 70 70 70 70 
Hc/Ht (%) 61.4 61.4 61.4 61.4 
H9au (mm) 63 63 50 50 
H9bu (mm) 58 58 -- -- 
H9au/Ht 55.2 55.2 43.8 43.8 
Ha (mm) 12 -- 33 33 
Ha/Ht (%) 10.5 -- 28.9 28.9 
Hf (mm) 17.5 17.5 17.5 17.5 
TEST RESULTS 
Tire weight (kg) 
10.0 9.8 10.9 10.5 
Spring constant 
Lateral (kgf/mm) 
14.0 13.8 14.3 14.0 
Longitudinal 
22.1 22.0 22.3 22.1 
(kgf/mm) 
Steering stability *1 
3 3 3 2.9 
Ride comfort *1 
3.1 3.1 3 3 
Noise *1 3 3 3 2.9 
__________________________________________________________________________ 
*1) evaluated in five ranks, wherein the standard is 3. 
TABLE 2 
__________________________________________________________________________ 
Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 
__________________________________________________________________________ 
Tire size 185/60R14 
185/60R14 
185/60R14 
185/60R14 
185/60R14 
185/60R14 
Carcass cord polyester 
polyester 
polyester 
polyester 
polyester 
polyester 
Bead construction 
FIG. 1 FIG. 1 FIG. 4 FIG. 5 FIG. 6 FIG. 7 
Reinforcing layer 
2 plies 
2 plies 
2 plies 
2 plies 
2 plies 
2 plies 
Cord aromatic 
steel aromatic 
aromatic 
aromatic 
aromatic 
polyamide polyamide 
polyamide 
polyamide 
polyamide 
Cord angle (deg) *1 
+30 & -30 
+30 & -30 
+30 & -30 
+30 & -30 
+30 & -30 
+30 & -30 
Ht (mm) 110 110 110 110 110 110 
Hc (mm) 65 65 65 65 65 65 
Hc/Ht (%) 59 59 59 59 59 59 
H9au (mm) 55 50 55 55 55 55 
H9bu (mm) 50 45 50 50 50 50 
H9au/Ht (%) 50 45 50 50 50 50 
Ha (mm) 16 16 16 -- 16 -- 
Hf (mm) 18 18 18 18 18 18 
TEST RESULTS 
Tire weight *2 
96 98 96 95 96 95 
Lateral spring constant *2 
99 103 98 97 100 99 
Cornering asphalt G *2 
98 104 99 98 101 99 
Lane change stability *3 
3.0 3.5 3.0 2.9 3.1 3.0 
Yaw convergence *3 
3.0 3.5 3.0 2.9 3.1 3.0 
__________________________________________________________________________ 
Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ref. 
__________________________________________________________________________ 
Tire size 185/60R14 
185/60R14 
185/60R14 
185/60R14 
185/60R14 
Carcass cord polyester 
polyester 
polyester 
polyester 
polyester 
Bead construction FIG. 8 .div. FIG. 8 
FIG. 9 FIG. 10 
FIG. 11 
Reinforcing layer 2 plies 
2 plies 
2 plies 
2 plies 
-- 
Cord aromatic 
aromatic 
aromatic 
aromatic 
polyamide 
polyamide 
polyamide 
polyamide 
Cord angle (deg) *1 +30 & -30 
+30 & -30 
+30 & -30 
+30 & -30 
-- 
Ht (mm) 110 110 110 110 110 
Hc (mm) 65 65 65 65 65 
Hc/Ht (%) 59 59 59 59 59 
H9au (mm) 50 50 50 50 -- 
H9bu (mm) 55 55 55 55 -- 
H9au/Ht (%) 45 45 45 45 -- 
Ha (mm) 16 -- 16 -- 42 
Hf (mm) 18 18 18 18 18 
TEST RESULTS 
Tire weight *2 96 95 96 95 100 
Lateral spring constant *2 
104 99 102 98 100 
Cornering asphalt G *2 
102 100 102 99 100 
Lane change stability *3 
3.3 3.0 3.1 3.0 3.0 
Yaw convergence *3 3.3 3.0 3.1 3.0 3.0 
__________________________________________________________________________ 
*1) The angles of the axially inner layer & outer layer with respect to 
the radial direction. 
*2) The results are indicated by an index based on the assumption that 
Ref. = 100. 
In Tire weight, the smaller is better. In Lateral spring constant and 
Cornering asphalt G, the larger index is better. 
*3) evaluated in five ranks, wherein the standard is 3.