(1) Providing grip in both wet and dry conditions (2) Improving driving stability (3) Preventing or reducing aquaplaning (4) Assuring adequate wear and irregular wear resistance and (5) Having an attractive appearance

The relationship between the pattern design and the tire's performance is mentioned below.

Nowadays, Toyo Tires uses super computer analysis to help our designers to better understand the detail of the dynamic contact area, which could not have been previously seen, and therefore allowing more freedom to the designer.

This innovative approach enables us to define specific performance targets, and then design a tread pattern to meet the required performance levels.

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PCR tires are used under many various conditions and are required to perform well in all of them. There are currently many types of PCR tires and they can be basically classified into three categories.

• General Use PCR ? Standard Tire, in a word
• PCR with excellent driving performance ? High Performance(HP), Ultra HP(UHP) Tire
• PCR for Winter Weather ? Winter tire including Lamellen Tire and Studless Tire

STANDARD

UHP

WINTER

A tire is constructed of many types of rubber and cords. Moreover, each tire type has many differences in design factors such as pattern, construction and material.

The difference in design factors which have a major influence on the characteristics of each type of tire is explained.

1. Tread Rubber
2. Tread Pattern
3. Tire Construction

The below explanation is the general method of tire design. In practice, there are many different cases on actual tire.

1. Tread Rubber

STANDARD UHP STUDLESS Hardness Criterion Softer More Soft Heat Generation Criterion Higher Higher Wear Resistance Criterion worse worse Hysteresis Loss* Criterion Higher Higher

*When rubber is repeatedly deforming and recovering, it has some difference between providing and giving back energy. Generally, this is called 'Hysteresis Loss'.

In the case of UHP tires, softer and higher heat generating tread rubber is necessary to provide improved grip on dry and wet surfaces. In case of STANDARD tires, better wear resistance and low hysteresis loss is for longer wear life and low fuel consumption. In case of studless, the tread rubber is softer than UHP. But the purpose of using softer rubber is different from UHP. It is to provide a better grip on ice surfaces.

2. Tread Pattern

STANDARD UHP STUDLESS   Void Ratio Criterion Smaller Slightly Smaller Uni- directional Not Apply Mostly Apply Sometime Apply Block Size Criterion Bigger Slightly Bigger Sipe Density Criterion less more

In case of UHP, uni-directional patterns are mostly applied since this design provides better water drainage. This allows for improved wet performance without making the void ratio big (this provides a larger contact area). Smaller void ratio is better for dry grip.

In case of studless, the pattern with many sipes is designed for obtaining better traction on ice surfaces.

3. Tire Construction

STANDARD UHP STUDLESS Side Stiffness *1 Criterion Stiffer Equivalent Tread Radius Criterion Larger Equivalent or Slightly Larger Cap Ply Basically Not Apply*2 Mostly Apply Not Apply Tread Depth Criterion Shallower Deeper Belt Width Criterion Wider Equivalent

*1 In this time, stiffer side means designing high turn up ply and/or bead filler.
*2 Sometimes it applies as occasional demands.

In case of UHP, a stiffer sidewall is designed to provide for better handling stability. The wider belt and cap ply is for high speed durability.

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1. Introduction

A tire has to fulfill many performance requirements. Some of these are dry/wet handling, ride, comfort, noise, rolling resistance, wear, etc..

One of the design criteria that affects tire performance is the tire contact patch. Contact patch is changed by a combination of tire profile and construction.

• Factors contributing to tire profile: tread width, tread crown radius, etc.
• Factors contributing to tire construction : belt material, belt angle, presence of cap/edge ply, etc.

The relationship between the tire profile, especially tread crown radius and contact patch, will be reviewed below.

2. Tire Performance - Contact Patch Shape

The tire's contact patch contributes to a tire's performance in the following manner.(See Fig. 1)

• Bigger Center Area: Better Straight Stability and Handling Response
• Bigger Shoulder Area: Better Cornering Performance

A tire designer has to decide tread width and crown radius according to the tire's required performance.

3. Contact Patch Shape - Crown Radius

• Smaller Crown Radius (see Fig. 2): Longer Center Length, Narrower Contact Width ( In this case, center area's contact pressure is higher than shoulder area's.)
• Bigger Crown Radius (see Fig. 2): Longer Shoulder Length, Wider Contact Width ( In this case, shoulder area's contact pressure is higher than center area's.)

For example, it is presumed that there are 2 contact shapes from different Crown radius.

Tire Size : 195/65R15 ( Tires have the same construction.)

• Tire A: Crown radius = R360mm.
• Tire B: Crown radius = R620mm.

While Tire A's contact patch is oval in shape, Tire B's contact patch is rectangular.

Table 1. Dimentions of Contact Patch

Tread Radius [mm] Center Length [mm] Shoulder Length [mm] Contact Width [mm] Contact Area [mm²] Tire A 360 148 111 130 168 Tire B 620 128 126 136 170

4. Crown Radius - Tire Performance

Fig. 4 shows comparison data in cornering power between Tire A (smaller crown radius) and Tire B (bigger crown radius). Tire B has higher cornering power than tire A, this means a larger crown radius tire has better cornering performance than a smaller crown radius tire. An UHP tire which requires High Cornering Performance usually adopts larger (flatter) crown radius. The bigger crown radius makes a contact patch close to a rectangle shape, and provides higher cornering performance. When a much larger crown radius is used to obtain higher cornering performance, the contact patch will become butterfly shaped. (Fig. 5) In this case, other tire performance criteria will be reduced. For example, longer shoulder length may contribute to excessive shoulder wear.

5. Conclusion

The table below shows the relationship between Crown Radius and Contact Patch. This verifies that the contact patch is an important item for tire performance.

Note: In the previous case, the tread shape with one constant radius is shown. In the case of a constant crown radius the contact patch shape change, while cornering, will not be smooth. Therefore, to provide a smooth cornering transition, we usually utilize two or three crown radii on the same tire. This provides uniform distribution of contact pressure and leads to an even contact shape as well as smooth cornering.

Table 2. Comparison Table of Tread Radius

Center Length Shoulder Length Contact Patch Straight Stability Limit of Tire Grip Wear Tread Radius Bigger Rectangle Shape Shoulde Wear Tread Radius Smaller Oval Shape Center Wear

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