JPH04189603A - Pneumatic radial tire for cart - Google Patents

Abstract

PURPOSE:To improve abrasion and wear resistance by specifying crossing angle of each belt layer cord in relation to the equatorial plane of a tire, a constant load extension ratio of the belt layer cord and 300% modulus of the tread rubber and to improve road surface holding force by smoothing the deformation of the tire. CONSTITUTION:In a pneumatic tire for a cart with an outer diameter of 300mm or less and an aspect ratio of 0.5 or less, which is provided with a carcass 2 comprising a tread and at least one ply of organic fiber cords and a belt 3 containing two belt layers positioned while being mutually piled and comprising respective organic fiber cords extending in the direction crossing each other, a carcass ply cord is extended in the direction substantially perpendicular to the equatorial plane of a tire. In addition, the crossing angle of each belt layer cord in relation to the equatorial plane of the tire is made an angle in the range of 10 deg. to 30 deg., and constant load extension ratio of the belt layer cord in a production tire is specified to 4% or more. In addition, 300% modulus of tread rubber is specified to 20 to 45kgf/cm<2>.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a pneumatic radial tire for carts, and in particular, it provides improved wear resistance, improved steering characteristics, and , which brings about improvements in traction performance and braking performance.

(Prior Art) As conventional pneumatic tires for carts, even though radial tires having many excellent characteristics have become widely popular in recent years, bias tires have still been used.

This means that carts are ultra-light, high-speed vehicles that are extremely light in weight compared to normal passenger cars, and because they do not have a differential mechanism on the drive shaft, they are It is necessary to absorb the difference in rotation between the inside and outside tires in a turn by tire slipping.Therefore, when a radial tire with a general structure equipped with a belt is applied to a cart, The presence of the belt increases the rigidity of the tread surface, reducing the tire's ground contact and ultimately impairing steering stability.Furthermore, karts basically require not only a differential mechanism but also a suspension system. This is because machine setting becomes extremely difficult when using radial tires, whose handling performance is significantly different from bias tires, because the tires are not equipped with any equipment.

(Problem to be Solved by the Invention) However, bias tires generally do not deform as smoothly as radial tires when a vehicle turns, and their poor deformability makes it difficult to maneuver, especially when turning at high speeds. However, due to increased engine power and significant improvements in chassis design technology in recent years, karts are no longer satisfied with the maximum turning speed of bias tires. It's getting to the point where I can't do it anymore.

Furthermore, bias tires have the disadvantage of lower wear resistance than radial tires, which has diminished the original appeal of kart racing as a relatively inexpensive way to enjoy motor sports.

This invention was made to solve the problems of the prior art, and it is possible to make cart tires radial by selecting the shape and structure of the tire, and also by adjusting the materials and physical properties of the tire constituent materials within a predetermined range. As a result, the present invention provides a pneumatic radial tire for carts that has greatly improved turning limit speed and wear resistance.

(Means for Solving the Problems) The pneumatic radial tire for carts of the present invention has an outer diameter of 300 mrn or less and an aspect ratio of 0.5 or less, and at least -
each carcass ply cord of the carcass comprising plies extends in a direction substantially perpendicular to the tire equatorial plane;
In addition, the angle of intersection of each belt layer cord with the tire equatorial plane of a belt including two belt layers each consisting of organic fiber cords that are located inside and outside and overlapped and extend in mutually intersecting directions is 10° to 30°. The angle is within the range of, the constant load elongation rate of the belt layer cord of the product tire is 4% or more, and the 300% modulus of the tread rubber is 20 to 45 kgf/cm2, and more preferably, At least one of aliphatic polyamide cords and polyester cords is selected as the belt layer cord.

(Function) According to the present invention, by making the structure of the tire radial, various characteristics unique to the radial tire can be brought about, which can greatly improve the wear resistance. The tire deformation is made smoother to increase the road gripping force, and as a result, the turning limit speed can be increased.

In addition, by setting the outer diameter of the tire to 300 mm or less and the aspect ratio to 0.5 or less, appropriate side rigidity is achieved for the usable rim diameters (5 inches and 6 inches) specified for homologation. and maximize performance.

In other words, when the outer diameter of the tire exceeds 300 mm, the weight of the tire increases and the load on the engine increases, and when the aspect ratio exceeds 0.5, the weakness of side rigidity is accentuated and the roll of the machine is reduced. The amount becomes large, impairing the tire's ground contact.

Moreover, here, by using an organic fiber cord as the carcass ply cord, a larger ground contact area and appropriate ground contact pressure can be obtained due to the lower tread rigidity than when the carcass ply cord is a steel cord.

Then, the organic fiber cord is arranged in a direction substantially perpendicular to the tire equatorial plane, for example, from 90° to 70° with respect to the tire equatorial plane.
By extending in a direction forming an angle within a range of 5°,
It is possible to fully exhibit the characteristics unique to radial tires.

In this tire, the belt layer cord is also formed of organic fiber cord, and the belt layer cord has a constant load elongation rate (JISL10177.7) in the product tire.
By adjusting the amount of ground (according to The intersection angle of the cord with the tire equatorial plane is lO8~30°, more preferably 20°~30°.
Excellent grounding properties can also be ensured by setting it within the range of °.

That is, if the constant load elongation rate of the belt layer cord is less than 4%, the ground contact of the belt will be poor, and if it exceeds 13%, the hoop effect will decrease and the belt function will be impaired. Further, if the equatorial plane intersection angle of the belt layer cords is less than 10°, the belt rigidity becomes too high and the ground contact property is decreased, and if it exceeds 30°, the hoop effect decreases.

Furthermore, the 300% modulus of tread rubber (
JIS K63013 dumbbell method) 20 to 4
5 kg4/cm2, more preferably 20 to 35 kgf/
cm2, it is possible to provide an appropriate road grip force as a tread rubber for a cart.

Here, its 300% modulus is 20kgf/cm2
If it is less than 45 kgf/cm2, the abrasion resistance will decrease, and if it exceeds 45 kgf/cm2, it will not be possible to obtain excellent grip as a tire for racing cards.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a cross-sectional view in the tire width direction showing an embodiment of the present invention. In the figure, 1 indicates a pair of bead cores, and 2 indicates a carcass with both end portions folded back by the respective bead cores 1.

Further, 3 is a belt disposed on the outer circumferential side of the crown part of the carcass 2, and 4 is a belt disposed further on the outer circumferential side of the belt 3.
Continuous treads are shown in the side portions.

Here, the carcass 2 in this example consists of two carcass plies made of 840 d/2 nylon cord, and each carcass ply cord extends at an angle of 84° with respect to the tire equatorial plane. The belt 3 is formed of two belt layers made of 1500 d/2 polyester cord, and the belt layer cords of the inner and outer belt layers are extended in directions that intersect with each other, and the belt layers of each layer are The intersection angle of the layer cord with the tire equatorial plane is 25°.

Furthermore, in this example tire, the 300% modulus of the tread rubber constituting the tread 4 is 32 kgf/a.
m”.

Note that 5 in the figure indicates a bead epex disposed between the main body portion and the folded end portion of the carcass 2 on the outer peripheral side of the bead core I.

According to the radial tire configured as described above, as described above, the adaptability to karts can be greatly improved, the difficulty of machine setting can be effectively removed, and the tire on the inside side of the corner can be It is possible to absorb the rotation difference between the outer tire and the outer tire, and at the same time,
When applied to carts, radial tires can fully demonstrate their original functions, improve wear resistance, and significantly increase the turning speed limit.

[Comparative example]

A comparative test regarding steering characteristics, traction, and braking performance between the invention tire and the conventional tire will be described below.

The dimensions and other specifications of each tire used in the test are shown in the table below. When a racing cart (chassis: Birel engine: Barilla 100cc) equipped with these tires was run on the Sugo Circuit course, it was found that the invented tires were A kart equipped with this tire can run approximately 0.37 seconds faster in the best time and approximately 0.33 seconds faster in the average time than a kart equipped with conventional tires. Performance and brake performance are both
The feel evaluation far exceeded that of the latter cart. In this case, the wear resistance of the invented tire is about 30% that of the conventional tire.
exceeded.

And also, a racing cart (chassis; Yamaha engine: Yamaha 10) equipped with the tires shown in the table above.
When I ran the Haruna Circuit course with 0cc),
The kart equipped with the invented tires was able to travel approximately 0.19 seconds faster in the best time and approximately 0.14 seconds faster in the average time than the karts equipped with the conventional tires, as well as the steering characteristics and traction of the former kart. Both the characteristics and braking performance were significantly superior to those of the latter cart in the feeling evaluation, as in the previous test. In this case, the wear resistance of the invented tie is
This is an improvement of about 23% compared to conventional tires.

(Effects of the Invention) Thus, according to the present invention, the adaptability of the radial tire to carts can be significantly improved, and
Due to the unique characteristics of radial tires, both wear resistance and maximum turning speed can be greatly increased.

[Brief explanation of drawings]

FIG. 1 is a sectional view in the tire width direction showing an embodiment of the present invention.

Claims (1)

[Claims] 1. A carcass consisting of a tread, at least one ply of organic fiber cords, and two belt layers each consisting of organic fiber cords positioned overlapping each other and extending in mutually intersecting directions. Equipped with a belt and an outer diameter of 300m.
m or less, and has an aspect ratio of 0.5 or less, the carcass ply cord extends in a direction substantially perpendicular to the tire equatorial plane, and each belt layer cord has: The intersection angle with the tire equatorial plane is 10° to 30°.
The angle should be within the range of 20°, the constant load elongation rate of the belt layer cord in the product tire should be 4% or more, and the 300% modulus of the tread rubber should be 20 to 45 kgf/c.
Pneumatic radial tire for carts as m^2. 2. The pneumatic radial tire according to claim 1, wherein the belt layer cord is selected from at least one of polyamide cord and polyester cord.