Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
1999-01-07
2001-08-21
Maki, Steven D. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S209170, C152S209280, C152S454000, C152S531000
Reexamination Certificate
active
06276415
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a pneumatic radial tire for motorcycle, and more particularly to a pneumatic radial tire for use in a front wheel of a motorcycle simultaneously establishing excellent durability and steering stability by a proper combination of a tread pattern and a belt structure.
2. Description of Related Art
This type of the conventional tire comprises a belt containing cords extended substantially in a circumferential direction of a tread and has a directional tread pattern defined by main slant grooves each having an acute-side inclination angle of not less than 45° with respect to the circumferential direction of the tread and extending from a tread center up to a tread shoulder region. The tread pattern has main slant grooves
1
,
2
convexly curing toward a rotating direction of the tire on both sides of a tread center C which are arranged symmetrically with respect to the tread center C as shown in FIG.
1
.
In such a tire and hence such a tread pattern, there is a problem that shimmy is liable to be particularly caused in a front wheel tire due to a fact that the bending rigidity of the tread is high in a meridional section of the tire. Also, circumferential components of the main slant grooves
1
,
2
are less, so that there are problems that drainage performance on wet road, resistance to lateral slipping and the like are low and a high gripping force on wet road surface can not be developed.
On the contrary, if it is intended to adjust the bending rigidity of the tread by arranging circumferential grooves continuing straightforward in the circumferential direction of the tread on a ground contact region of the tread in addition to the main slant grooves
1
,
2
, the drainage performance on wet road can be enhanced while controlling the occurrence of shimmy. However, since the cords in the belt substantially extend in the circumferential direction of the tread, the bending resistance at the bottom of the circumferential groove becomes small and hence there is a problem that cracking at the groove bottom is created at a relatively premature stage.
As partly and collectively shown in
FIG. 2
, therefore, there are proposed patterns in one wherein circumferential zigzag grooves
3
continuously extending zigzag in the circumferential direction of the tread are arranged on the ground contact region of the tread in addition to the main slant grooves
1
,
2
. In another pattern slant sub-grooves
4
or
5
are arranged to extend straightforward and intersect with the main slant groove
1
,
2
or open to the main slant grooves
1
,
2
. In another pattern slant sub-grooves
6
extend straightforward between the main slant grooves
1
,
2
so as not to communicate therewith and have a large inclination angle &agr; of more than 30° with respect to the circumferential direction of the tread.
According to these patterns, the control of shimmy and the improvement of drainage performance on wet road are generally attained owing to the presence of the circumferential zigzag groove
3
, or slant sub-groove
4
,
5
or
6
.
However, when the circumferential zigzag groove
3
is arranged to continuously extend in the circumferential direction of the tread, there is an improving effect as compared with the straight groove, but the rigidity is lowered too much to degrade the stability and the steering property.
When the slant sub-grooves
4
,
5
are arranged to intersect with or open to the slant main grooves
1
,
2
, the rigidity is lower than that of the circumferential zigzag groove
3
and the stability and the steering property are further degraded.
Even in both cases, the occurrence of cracking at the bottom of the zigzag groove
3
or the sub-groove
4
or
5
can not sufficiently be prevented.
When the slant sub-grooves
6
having an inclination angle &agr; of more than 30° with respect to the circumferential direction of the tread are arranged between the slant main grooves
1
,
2
, the drainage performance on a wet road can not be improved to an expected extent. Also, the component of the sub-groove
6
in the circumferential direction of the tread is less and the length of groove edge in the circumferential direction of the tread is short, so that there is a problem that the resistance to lateral slipping in the tire can not be enhanced to an expected extent.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to solve the aforementioned problems of the conventional technique and to provide a pneumatic radial tire for a motorcycle which prevents the occurrence of shimmy and sufficiently enhances the resistance to lateral slipping to improve the steering stability on wet road surface while ensuring the excellent drainage performance on wet road and effectively prevents the occurrence of cracking at the groove bottom to advantageously enhance the tread durability.
It is another object of the invention to provide a pneumatic radial tire for a motorcycle capable of enhancing a rigidity balance at meridional section of the tire to further effectively prevent the occurrence of cracking at the groove bottom and realize the bending rigidity of the tread effective for reducing cornering power to a handle shimmy and balancing a quick handling in the application of a camber angle and a linearity in a change of steering force required therefor by an adequate combination of tread pattern and belt structure.
According to the invention, there is the provision of a pneumatic radial tire for motorcycle comprising a belt containing cords extended substantially in a circumferential direction of a tread and having a directional tread pattern defined by main slant grooves each having an acute-side inclination angle of not less than 45° with respect to the circumferential direction of the tread and extending from a tread center or a vicinity thereof up to a tread shoulder region and a slant sub-groove extending between the slant main grooves and having an acute-side inclination angle with respect to the circumferential direction of the tread smaller than that of the slant main groove, in which a groove width of the slant main groove is within a range of 3-15% of a periphery length between both ends of the tread when the tire is mounted onto a standard rim and inflated with an air pressure corresponding to 80% of a maximum air pressure with no loading; a main portion of the slant sub-groove having at least one of a width and a depth larger than that of the other portion is terminated so as not to open into the slant main groove; the main portion has an acute-side inclination angle of 0-30° with respect to the circumferential direction of the tread, a groove width narrower than that of the slant main groove, a length in the circumferential direction of the tread corresponding to 30-80% of an arranging pitch of the slant main groove, and a depth corresponding to 50-100% of a depth of the slant main groove.
In the invention, the slant sub-groove may be disposed on a center of the tread, in which the slant sub-groove is extended between two pairs of slant main grooves, each pair of which communicating with each other at the tread center.
Moreover, the term “main portion of the slant sub-groove” used herein means a width-wider portion or a depth-deeper portion when the slant sub-groove has at least one of narrow-wide groove width and shallow-deep groove depth. When both the groove width and the groove depth are constant, the whole of the slant sub-groove is a main portion.
When a portion having a narrow groove width and a deep groove depth and a portion having a wide groove width and a shallow groove depth are mixed together in the one slant sub-groove, the main portion means the portion having a deep groove depth. On the other hand, when a plurality of portions having a wide groove width or a deep groove depth are existent in the one slant sub-groove, these plural portions correspond to the main portion of the slant sub-groove, in which the length of the main portion is a total length of these plural portions.
Bridgestone Corporation
Maki Steven D.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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