Development of the New Generation Run-Flat Tire

The New Generation Run-Flat Tire

Author: Yasuo Mitarai – Sumitomo Rubber Industries Ltd., Japan

Presented to: International Tire Exhibition and Conference 9/22/2010

Sumitomo Rubber Industries Ltd. 2-1-1 Tsutsui-cho, Chuo-ku, Kobe 651-0071, Japan Abstract: Sumitomo Rubber Industries Ltd. (SRI), issued a press release of Dunlop's New

Generation Run-flat Tire in September, 2009.

Dunlop’s New Generation Run-Flat tire is composed of four unique new technologies.

The first is the CTT profile, the second is Aramid casing, the third is High thermal conductivity materials, and the last is a Dimple sidewall.

As a result, the new generation run-flat tire could claim reduced tire weight and a dramatic reduction in vertical stiffness. The result; excellent ride comfort, (equivalent to or better than normal tires), while maintaining the run-flat performance properties of the tire. Introduction: Before the New Generation Run-Flat tire is introduced, Dunlop’s history of Run-Flat technologies will first be reviewed.

In 1970, the Denovo run-flat system was developed and commercialized - the first commercial system in the world. From 1970, the Denovo2 run-flat tire and its sister TD tire were developed and fitted as OE to the Nissan 280ZX, Porsche 959 and several other European vehicles.

Then, in 1995 a sidewall reinforced type run-flat tire was developed which was called

Dunlop DSST.

This first generation of the self-supporting run-flat tire was the first that could be mounted on normal wheels.

In 2000, the second generation of self-supporting run-flat tires was developed and was known as CTT (“Combined Technology Tire”, since it also used features from Dunlop’s motorcycle technology)

Through the 3rd generation in 2003, SRI gave birth to the new fourth generation run-flat tire in 2009.

First Generation Run-Flat tire: For a better understanding of the new generation Run-Flat tire it’s important to review the features of the first Generation of Self-supporting Run-Flat tires:

The mechanism supporting load under zero inflation pressure is very simple - the sidewall reinforcement supports the vehicle weight.

The advantage is that DSST can be mounted on normal wheels and is compatible with a normal tire.

The disadvantages are that DSST is heavier in weight and has harder ride comfort than a normal tire due to the stiffness of the sidewall reinforcement components.

Features of the New Fourth Generation Run-Flat tire:

These disadvantages have been continuously improved over the preceding generations culminating finally in the development of the New Fourth Generation Run-Flat tire.

The features of the New Generation Run-flat tire can be defined primarily by 4 proprietary technologies.

4 Proprietary technologies

The first technology is the proven CTT Profile.

The second technology is the use of an Aramid Radial Casing material.

The third is the use of high thermal conductivity materials.

And the fourth technology is the use of Dimple Sidewall technology.

CTT Profile:

The CTT run-flat tire profile reduces the tire weight by approximately 10% and the vertical stiffness by 15%, compared with the first generation Run-Flat Tire.

The CTT profile is SRI’s original technology and called “The Combined Technology Tire” as it uses some technology from Dunlop motorcycle tires.

The new tire profile used in this tire is defined by an involute function.

The concept of the CTT run-flat tire is to separate regular tire performance properties from run-flat performance properties.

The round tread area assists with regular tire performance properties and the sidewall reinforcement area assures run-flat performance. Aramid Casing:

Research showed that to improve performance one of the main factors was the reduction of deformation to suppress heat generation when running deflated.

Therefore SRI worked to develop technology to increase the stiffness of the casing material and thus lower the heat generation.

An aramid casing has a stiffness that is 5 times that of a conventional rayon tire casing leading to a reduction in deformation and finally, suppression of heat generation in the reinforcement layer.

High Thermal Conductivity Materials:

Development of materials continued to achieve increased thermal conductivity to disperse heat from the reinforcement layer during run-flat driving.

This succeeded in shifting and dispersing heat by increasing the thermal conductivity in the reinforcement layer and sidewall rubber.

In particular, hardness was maintained and heat generation improved by compounding the material with a high thermal conductivity carbon fiber which is oriented in the circumferential direction.

The heat conductivity ratio was improved by 2.5 times for the sidewall reinforcement layer and by 1.5 times for the sidewall, when compared with the previous materials.

Dimple Sidewall:

This technology was developed after considering heat radiation from tires during deflated running.

After reviewing many shapes it was found that a circular shaped dimple easily disturbs air flow and is good for heat dispersion.

These dimples lowered the temperature by about 10 ºC at the tire sidewall surface and improved the run-flat durability.

Tire Performance of the New Generation Run-Flat Tire:

Through adopting these four technologies run-flat driving distance was increased by 2.3 times.

As a result, it was now possible to decrease the thickness of the sidewall reinforcement layer by 30% which still maintains a good level of run-flat performance but also allows a reduction in tire weight.

Thus, the New Generation Run-Flat tire has been further reduced in weight and vertical stiffness resulting in an excellent ride comfort level which is equivalent to or better than the normal tire.