Patent Application
20230339269
The present invention relates to motorcycle tires (hereinafter also referred to as simply “tires”), and more particularly, to motorcycle tires having improved water draining capacity and achieving both excellent dry and wet performance.
There have conventionally been proposed motorcycle tires having a tread pattern in which many tilted grooves are arranged to ensure driving stability on dry and wet ground. For example, Patent Document 1 proposes a tread pattern that enables improvement of wear resistance, steering stability, and ride quality in a balanced manner.
Specifically, in a motorcycle tire having a tread with a designated rotational direction, the tread includes a plurality of tilted main grooves that extend outward in the tire axis direction from the center area to the outside of the tread edges, and a plurality of tilted sub grooves that extend outward in the tire axis direction from the middle areas to the shoulder areas. The tilted main grooves and the tilted sub grooves are each provided with a gradually narrowing terminal portion with the groove width gradually decreasing toward the first grounding side in the rotational direction, in which the straight line connecting, in the shortest distance, the end of the gradually narrowing terminal portion in a tilted main groove on later grounding side in the rotational direction and the end of the gradually narrowing terminal portion in a tilted sub groove on the first grounding side in the rotational direction is 85 to 90° relative to the tire circumferential direction.
However, Patent Document 1 has not conducted any investigation on the water draining capacity of the tire, as well as demonstrated insufficient performance of the tire on wet ground. This problem is especially pronounced in weather-susceptible tires, such as touring and scooter tires.
Accordingly, an object of the present invention is to provide a motorcycle tire that has improved water draining capacity and is excellent in both dry and wet performance.
In order to solve the above problems, the present inventor has intensively studied to find that the problems can be solved by making a main groove formed in a tread a predetermined shape, thereby completing the present invention.
The motorcycle tire of the present invention is a motorcycle tire including an annularly formed tread,
In the tire of a preferred embodiment of the present invention, the at least one main groove becomes shallower outward in a tread width direction. In the tire of another preferred embodiment of the present invention, the at least one main groove has three or more widened portions enlarged outward in the groove width direction and has at least one section where the extending length along the groove wall between the tops of adjacent widened portions is 0.3 to 50% longer than the length of the virtual straight line connecting the tops of the adjacent widened portions.
Preferably, in the tire of the present invention, the at least one main groove extends from a center area to a shoulder area. Preferably, in addition, in the tire of the present invention, the angles of the groove wall on the first grounding side in the rotational direction and of the groove wall on the later grounding side in the rotational direction are ±20° relative to the perpendicular direction at the bottom of the at least one main groove. Preferably, in addition, in the tire of the present invention, the number of the widened portions is 20 or less. Preferably, in addition, in the tire of the present invention, the at least one main groove is provided with a ridge in the bottom of the widened portion. Here, the center area refers to an area in the tread to be in contact with the ground when a motorcycle is run with the tire inflated to normal internal pressure and loaded with a normal load, while the shoulder area refers to an area on either side of the center area of the tread.
According to the present invention, a motorcycle tire having improved water draining capacity and achieving both excellent dry and wet performance can be provided.
Now, the motorcycle tire of the present invention will be described in detail with reference to the drawings. The tire of the present invention has an annularly formed tread.
The tire 10 or 20 of the present invention has a tread 11 or 21 with main grooves 12 or 22. At least one of the groove wall on the first grounding side in the rotational direction and the groove wall on the later grounding side in the rotational direction of at least one main groove of the main grooves 12 or 22 in the tire 10 or 20 of the present invention has two or more, preferably three or more, widened portions enlarged outward in the groove width direction (hereinafter also referred to as “main grooves 12a or 22a having two or more widened portions”).
In the embodiment shown in
In this way, the tire 10 or 20 of the present invention can achieve improved water draining capacity by providing at least one of the groove wall 12A or 22A on the first grounding side in the rotational direction and the groove walls 12B or 22B on the later grounding side in the rotational direction of at least one of the main grooves 12 with two or more widened portions. When driving on a wet ground, the tire allows water to be temporarily contained in the widened portions and compressed upon ground contact, thereby draining the water toward the shoulder area like a pump. In other words, water entering into a main groove 12a or 22a having two or more widened portions moves along the main groove 12a or 22a having two or more widened portions, and is drained along the extension lines of the groove wall 12A or 22A on the first grounding side in the rotational direction and the groove wall 12B or 22B on the later grounding side in the rotational direction, which results in improved water draining capacity as compared with a main groove 12 that linearly drains water.
Main grooves 12a and 12b having two or more widened portions have a larger amount (length) of edges than linear main grooves, allowing more edges to be in contact with the ground, which results in improvement of the grip performance, braking performance, and traction performance. Preferably, the tires 10 and 20 of the present invention have a structure comprising at least one section where the extending length along the groove wall between the tops of adjacent widened portions is 0.3 to 50% longer than the length of the virtual straight line connecting the tops of the adjacent widened portions. Preferably, for example, at least one main groove has three or more widened portions enlarged outward in the groove width direction and has at least one section where the extending length along the groove wall between the tops of adjacent widened portions is 0.3 to 50% longer than the length of the virtual straight line connecting the tops of the adjacent widened portions.
In the embodiment shown in
It is noted that, although the tires 10 and 20 of the present invention, as shown in
Preferably, main grooves 12a or 22a having two or more widened portions in the tire 10 or 20 of the present invention become shallow outward in the tread width direction.
The depth of a main groove 12a or 22a having two or more widened portions in the tire 10 or 20 of the present invention may gradually decrease outward in the tread width direction, or may stepwisely become shallow outward in the tread width direction. The tire 10 or 20 of the present invention may also have main grooves 12b or 22b other than the main grooves 12a or 22a having two or more widened portions, which main grooves 12b or 22b may also have such a structure that the groove bottom becomes shallow outward in the tread width direction. In this case, all the main grooves 12b or 22b other than the main grooves 12a or 22a having two or more widened portions may become shallow outward in the tread width direction, or only some of the main grooves 12b or 22b may become shallow outward in the tread width direction.
The positions of the main grooves 12a and 12b having two or more widened portions in the tire 10 or 20 of the present invention are not particularly restricted. The main grooves 12a and 12b may be positioned only in the center area or the shoulder areas. Preferably, as shown, the main grooves 12a or 22a having two or more widened portions extend from the center area to the shoulder areas. This structure can further improve the water draining capacity during straight driving and cambering.
In the embodiment shown in
Preferably, the angles of the groove wall 12A or 22A on the first grounding side in the rotational direction and the groove wall 12B or 22B on the later grounding side in the rotational direction in a main groove having two or more widened portions in the tire 10 or 20 of the present invention are ±20° relative to the perpendicular direction at the bottom of the main groove having two or more widened portions. Formation of the groove walls of the main grooves 12a or 22a having two or more widened portions in a nearly perpendicular state allows for appropriate rigidity of the tread 11 or 21, resulting in improvement of the braking performance and the traction performance.
Preferably, in addition, the number of widened portions of a main groove 12a or 22a having two or more widened portions in the tire 10 or 20 of the present invention is 20 or less. This is because a larger number of widened portions may contrarily impair the water draining capacity of main grooves. The number of widened portions is more preferably 10 or less, and still more preferably 5 or less.
Preferably, in addition, the main grooves 12a or 22a having two or more widened portions in the tire 10 or 20 of the present invention are provided with ridges in the bottoms of the widened portions. As shown in
The height of a ridge 13 or 23 is not particularly limited as long as it is less than the depth of the main groove 12a or 22a having two or more widened portions, and is preferably 90% or less of the depth of the main groove 12a or 22a having two or more widened portions. Preferably, in addition, the extending length of a ridge 13 or 23 is 30 to 50% of that of the widened portion. It is noted that ridges 13 or 23 may be provided in all or only some of widened portions present in the main grooves 12a or 22a having two or more widened portions. In addition, the ridges 13 or 23 may be provided in all or only some of the main grooves 12a or 22a having two or more widened portions present in the tread 11 or 21.
Preferably, as shown in the figures, the tire 10 or 20 of the present invention includes the main grooves 12a or 22a having two or more widened portions, such that the numbers of the widened portions in the groove wall 12A or 22A on the first grounding side in the rotational direction and in the groove wall 12B or 22B on the later grounding side in the rotational direction are equal; such that the widened portions in the groove wall 12A or 22A on the first grounding side in the rotational direction and the widened portions in the groove wall 12B or 22B on the later grounding side in the rotational direction are positioned to be coupled with each other; and such that the thus-formed widened portions are provided with the ridges 13 or 23 in their groove bottoms. Similarly, in this case, all or some widened portions may be provided with the ridges 13 or 23 in their groove bottoms.
The structure of the tread 11 or 21 in the tire 10 or 20 of the present invention is not particularly restricted as long as at least one main groove has two or more widened portions. For example, such a structure is preferable that at least one main groove becomes shallow outward in the tread width direction; and/or that at least one main groove has three of more widened portions enlarged outward in the groove width direction and has at least one section where the extending length along the groove wall between the tops of adjacent widened portions is 0.3 to 50% longer than the length of the virtual straight line connecting the tops of the adjacent widened portions. For the other structures, known structures can be used.
As shown, in addition to the main grooves 12a or 22a having two or more widened portions, the main grooves 12b or 22b not having two or more widened portions may be provided. The shape of the main grooves 12b or 22b not having two or more widened portions can be linear as in the embodiments shown in
In the embodiment shown in
In addition, the tire 10 or 20 of the present invention may be provided with a shallow groove, depending on the purpose, that is shallower and narrower than the main grooves 12 or 22, for example, with a groove depth of 0.1 to 2.0 mm and a groove width of 0.5 to 2.0 mm. Again, no particular restriction is imposed on the shape of the shallow groove.
The tire 10 or 20 of the present invention may be provided with circumferential main grooves extending in the tire circumferential direction. However, in motorcycles that turn by tilting the tire, main grooves provided from the center toward the shoulders can more efficiently promote water draining. When the tire 10 or 20 of the present invention has a spiral belt layer as an outermost reinforcing layer in which reinforcing cords exist in the substantially tire circumferential direction, circumferential main grooves provided in the center area may cause cracks in the groove bottom along the reinforcing cord layer. Therefore, in such a structure, any circumferential main grooves should not be provided in the center area.
For the configurations other than the tread 11 or 21, the tire 10 or 20 of the present invention can employ any known structures. As shown in
In addition, the tires shown in the figures are provided with a belt 18 or 28 composed of at least one (two in the illustrated embodiment) belt layers on the outer side of the carcass 16 or 26 in the tire radial direction. The belt cord in the belt layer 18 or 28 can be any known extensible and highly elastic cords, and can be selected as appropriate from, for example, organic fibers such as aromatic polyamides (Aramid, e.g., trade-named Kevlar, from DuPont de Nemours, Inc.), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), rayon, and nylon; and those made of materials such as steel, glass fibers, and carbon fibers. Such a belt 18 or 28 may be composed of two or more tilted belt layers arranged such that the directions of the cords in the layers intersect with each other, or may one or more spiral belt layer with the direction of the cord being substantially tire circumferential.
The tire 10 or 20 of the present invention can be applied to both tires with a radial structure and a bias structure. The tire 10 or 20 of the present invention is a motorcycle tire achieving both excellent dry and wet performance and can be particularly preferably applied to tires for motorcycles that are often affected by the weather.
Now, the motorcycle tire of the present invention will be described in more detail with reference to examples.
A front tire with the tread pattern shown in
Tires were prepared in the same manner as in Example except that all main grooves were linear. Similar to Example described above, they were mounted on a motorcycle as front and rear wheels.
Reference example shows estimated values on the assumption that main grooves with the groove wall on the first grounding side in the rotational direction and the groove wall on the later grounding side in the rotational direction each having two widened portions were arranged from the center portion to the shoulder portions, based on the results obtained from the main grooves that have two widened portions and are provided in the shoulder portions shown in
The grip performance and straight-line acceleration performance (hydroplaning performance) on wet ground of the front and rear tires were evaluated based on the rider's impression. The obtained results were calculated by setting those from Comparative Example as an index value of 100. The critical behavior, traction performance during acceleration, and braking performance of the rear tire in a middle-to-low speed range were also evaluated based on the rider's impression. The obtained results were calculated by setting those from Comparative Example as an index value of 100. The straight-line acceleration performance (hydroplaning performance) was evaluated by performing driving with acceleration on wet ground, and measuring the motorcycle driving speed and number of tire revolution, considering the speed at which the number of tire revolution increased (at the time when the driving tire went into a skid causing the peripheral speed of the tire to exceed the motorcycle driving speed) as the hydroplaning occurrence speed.
Table 1 shows that the tire of the present invention has improved water draining capacity and can exert both excellent dry and wet performance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-173192 | Sep 2019 | JP | national |
| 2019-173193 | Sep 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/034574 | 9/11/2020 | WO |
