JPH02151502A - Motocross tire - Google Patents

Abstract

PURPOSE:To improve cornering grip characteristic by specifying the radii of the central and outer side portions of a tread surface, and specifying the ratio between both radii. CONSTITUTION:A plurality of blocks are formed on the ground contact surface of a tire by forming a plurality of grooves 10 on the tread surface 9. In this case, a central part M formed with an arc having its center on a tire equator surface C and with the radius R1 of 20-30mm is provided on the tread surface 9. Outer side portions N formed with an arc continuous to both tire axis direction edges Ma of the central portion M and having the radius R2 of 90-100mm are also provided. The radio R2/R1 between the radius R1 of the central portion M and the radius R2 of the outer side portion N is set to 3-5. Thus the cornering grip characteristic and stability are improved to be specifically suited for the front tire for motocross.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a motocross tire that can improve cornering grip performance by regulating the radius of curvature of the tread surface in the cross-sectional direction.

[Conventional technology]

Motocross races for motorcycles are usually held on a course with a lap length of 1.5 to 2.0 am, but the course includes various corners such as hairpins, roundabouts, 5-shaped corners, snaking corners, and high-speed corners. It has parts. The outcome of the race will be determined by how fast you can navigate these corners. In addition, it is known that the grip performance of the front tires greatly affects cornering performance in races, and grip of the front tires is always required during all cornering such as entering, turning, and exiting each corner.

[Problem to be solved by the invention]

For front tires like this for motocross,
Conventionally, tread surface patterns, tread surface shapes,
Although consideration has been given to tire rigidity, tread rubber properties, etc., these measures may not be sufficient on motocross courses where course conditions are inherently unstable.

For example, it was insufficient to deal with changes in the course over time due to changes in weather, i.e., changes in the road surface from dry to medium to wet and from wet to medium to dry, as well as changes in condition between each position, so improvements were made. There is a strong demand for

On the other hand, tires manufactured for conventional motocross are
For example, in the case of tires of tire size to be mounted on rims of 20 to 22 inches, as shown in Fig. 4, the radius r1 of the center portion of the tread surface a is approximately 45 mm, and the outer edge portions C on both sides of the tread surface a have a radius r1 of approximately 45 mm. It was formed into a nearly circular shape with a radius of approximately 60 square meters and a ratio r 2 / rl of both radii of 1.5 or less.

The reason for adopting a radius ratio r 2 / r 1 that is close to a circle as shown in Figure 2 is that it is considered to be optimal for obtaining the total performance of straight running performance and cornering performance, and therefore,
In the past, in order to improve cornering and grip performance, various studies have been made on the shape of blocks on the tread surface, their arrangement, and the rubber performance of the tread rubber, but improvements in the above items are limited to improving cornering grip performance. It was observed.

As a result of intensive research aimed at solving the above-mentioned problems, the inventor has developed a radius that can change the ground contact area by changing the camber angle by setting a new ratio of the diameters of both hands on the tread surface. They discovered that by changing the ground contact area, it is possible to exceed the limits of conventional cornering and grip performance.

According to the present invention, the radius of the central portion of the tread surface and the outer f, ! The object of the present invention is to provide a motocross tire that can improve cornering grip based on the ratio of the radius of the part to the radius of greater than 3 and less than or equal to 5.

[Means for solving problems]

In order to achieve the above object, the motocross tire of the present invention has grooves formed on the tread surface, which extend from the inner side of the trend section to the sidewall section, are folded back at the bead core of the bead section, and extend from 30° to 40° in the circumferential direction. a cross-ply carcass with carcass cords intersecting and tilting at an angle of 65°; and the tread portion has a Shore A hardness of 65
The total area of the grooves (SC;) with respect to the total tread surface area (SC;)
A front tire for motocross is mounted on a rim with a ratio ST/SO of 70 to 85% and a rim diameter of 20 to 22 inches, the tread surface having a tire equator center and a radius (R1 ) is 20-30III[lI
A central portion consisting of a circular arc and an inner edge smoothly extending to both edges in the tire axial direction of the central portion and having a radius (R2) of 90 to
100 m and includes an outer portion whose outer edge extends to the tread end, and the ratio R2/R1 of the radius (R1) (R2) is greater than 3 and less than 5.

[Effect]

As mentioned above, the motocross tire 1 has R2/R, which is the ratio of the radius R1 of the central part of the tread surface to the outer part R2.
Since 1 is set to be 3 or more and 5 or less, when the camber angle becomes small as shown by the solid line in FIG. 3, a ground contact area proportional to the angle can be obtained.

Further, when the camber angle is large, a constant ground contact area can be obtained regardless of the camber angle.

Therefore, compared to the conventional system where the ground contact area is constant regardless of the camber angle as shown by the broken line in Fig. 3, when the camber angle is small, that is, when driving in a straight line or on a gentle curve,
The ground contact area is small, so straight-line running performance can be further improved, and the camber angle is large, that is, when running on a sharp curve, the ground contact pressure is greater than that of the conventional one, so that grip performance can be improved.

〔Example〕

An embodiment of the present invention will be described below based on the drawings.

In the figure, the motocross tire l of the present invention has a bead core 2.
The tire includes a bead portion 3 through which the tire passes, a sidewall portion 4 extending outward in the radial direction of the tire along the bead portion 3, and a tread portion 5 connecting the outer ends of the sidewall portion 4.

The motocross tire 1 also includes a carcass 6 which passes from the tread portion 5 through the sidewall portion 4 and is folded around the bead core 2 of the bead portion 3 from the inside to the outside in the axial direction of the tire.
A belt layer 12 is provided within the radially outer tread portion 5 of the carcass 6.

Further, the motocross tire 1 is mounted on the rim seat part F of a rim H in which the lower surface 3a of the bead part 3 has an outer diameter of 20 to 22 inches.

The carcass 6 is made of cross ply having a carcass cord inclined at an angle of 30° to 40° in the tire circumferential direction.

Further, the tread portion 5 is provided with a thick rubber portion 7 on the outside of the belt II 12, and the rubber portion 7 has a hardness of 6.
It is formed using rubber of 5@ to 80@.

The tread portion 5 has a plurality of blocks 15 raised from its outward facing surface as shown in FIG.
A plurality of grooves 10- extending in the circumferential direction and the axial direction of the tire are formed between the grooves 5 and 5.

Further, by enveloping the outer peripheral surface of each block 15, 15, a tread surface 9, which becomes the ground contact surface of the tire, is formed.

The tread surface 9 has a ratio ST/SG of the total area ST of the grooves 10 to the total tread surface area SG of 70 to 8.
The block 15 is set within a range of 5%.

As described above, in the present invention, the groove area of the grooves 10 on the tread surface 9 is set to be larger than the land area which is the sum of the areas of the outer surfaces of each block.

The tread surface 9 has a central portion M having a center on the tire equator C plane and consisting of a circular arc with a radius R1 of 20 to 30 mm, and inner edges Na on both sides Ma in the tire axial direction of the central portion M.
, Na are smoothly connected and are formed by outer portions N and N consisting of circular arcs with radius R2. Further, an outer edge Nb of the outer portion N extends to the tread end P. Also, the central portion M
R2/ which is the ratio of radius R■ of
R1 is set to be greater than 3 and less than or equal to 5. The radius ratio R
If 2/R1 is less than 3, the cornering grip performance will deteriorate, and if R2/R1 is 5 or more, the ground contact area will increase or decrease sensitively to changes in the camber angle, resulting in a lack of running stability.

〔Concrete example〕

Exhaust JI 125 cc motocross car tire has a tire size of 80/1 according to the present invention on the front.
00-21 and tires with the specifications shown in Table 1, standard tires of 100/90/19 were installed on the rear of the same vehicle, and five test drivers tested the actual car under the conditions shown in Table 2. A test was conducted. Evaluation,
The average value of the driver's feeling evaluation was converted into an index, and the results are shown in Table 1. For comparison, a prototype with conventional specifications was also manufactured and tested in the same manner. It was found that the grips and stability of the examples were higher than those of the comparative examples, and therefore the lap times were also improved.

〔Effect of the invention〕

As described above, in the motocross tire of the present invention, the radii of the central part of the tread surface and the outer part are restricted, and the radius ratio R2/R1 of the outer part and the central part is greater than 3 and 5.
As the tire has the following properties, the lap time in races can be improved by improving cornering grip and stability, and it can be suitably used as a front tire for motocross.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing one embodiment of the present invention, Fig. 2 is a developed view showing its tread surface, Fig. 3 is a graph showing the relationship between camber angle and ground contact area, and Fig. 4 is a conventional FIG. 2 is a cross-sectional view showing the technique. 2--bead core, 3--bead part, 4--sidewall part, 5-) red part, 6- carcass, 7--rubber part, 9--tread surface, 1
0.-groove, C-.tire equator, H-.all, M
- Central part, Ma... - Side edge, N - Outer part, N
a: Inner edge, Nb: Outer edge, P: Tread edge, R1: Radius, R2: Radius, SG: Total tread surface area, ST: Total area of grooves.

Claims (1)

[Claims] 1. A cross-ply carcass cord that extends from the inside of the tread section with grooves on the tread surface, passes through the sidewall section, is folded back at the bead core of the bead section, and crosses and tilts at an angle of 30° to 40° in the circumferential direction. The tread portion includes a carcass, and the tread portion has a Shore A hardness of 65° to
It has a rubber part formed using 80° rubber and has a total area (ST) of the grooves relative to the total tread surface area (SG).
The ratio ST/SG is 70-85%, and the rim diameter is 20-85%.
A front tire for motocross mounted on a 22-inch rim, wherein the tread surface has a central portion consisting of an arc having a center at the tire equator and a radius (R1) of 20 to 30 mm, and a central portion in the axial direction of the tire. It includes an outer portion where the inner edges are smoothly continuous on both sides and the radius (R2) is 90 to 100 mm, and the outer edge extends to the tread end, and the ratio R2/R1 of the radii (R1) and (R2).
Motocross tires with a value greater than 3 and less than 5.