The Rolling Resistance, Wear and Traction Properties of Tread Compounds

Abstract The paper gives a brief survey of the state of friction and abrasion research with a view of the possibility to use laboratory methods for the development of new compounds with optimal traction and abrasion properties. It shows that viscoelasticity plays a decisive role in friction and in this way measurements of the dynamic properties give a good indication of the possibilities for good traction properties. However, friction is still a good deal more complex than the modulus or loss factor curves. It takes in different frequency ranges and temperatures in the contact area so that a direct laboratory measurement of these properties is still very desirable. If the speed and temperature correspond to the log a T v values experienced in practice and the laboratory track structure and texture is not too far removed from that of road surfaces, the correlation with road tests is high. To simulate the structure and texture of road surfaces with durable laboratory surfaces, a combination of two surfaces may be necessary. Abrasion is not only influenced by the strength properties of the rubber but also by oxidation and thermal degradation. To give these processes the correct weight in the laboratory, the testing conditions have to be mild and a combination of several conditions is necessary in order to demonstrate the complexity of interactions, which can lead to ranking reversals. Energy dissipation, speed, and abrasive surface structure and texture are identified as prime variables to achieve a high correlation with road wear. Since viscoelasticity, encompassing not only polymer but also filler, oil-extension, curing and other compound additives, plays a major role in both friction and wear, the rolling resistance of the compound is always effected and has to be taken into account. Modern polymerization methods and new filler concepts make it possible to change the viscoelastic properties in such detail that high friction and—to the degree to which strength contributes to wear—high wear resistance can be combined with low rolling resistance. This development has certainly not reached its climax yet. Exciting times lie ahead for tire compounders, polymer- and filler chemists alike.