TURIN, Italy-Tire noise and rolling resistance were the twin themes of the TyreTech '95 conference, held last October in Turin. Symposium organizers also tried to give some new perspectives on the industry via a road research engineer and a couple of vehicle engineers who described their views of tire development.
The overwhelming message of the conference was that while rolling resistance continues to be a very important factor, noise reduction also will be a critical element in tire design in coming years. In rolling resistance, a number of papers made it clear that silica-based tread compounds are not the only way of reducing rolling resistance.
Tire makers are now talking about ``low hysteresis compounding'' for all the rubber compounds used in a tire. (Hysteresis is the tendency of a material to absorb or release slowly the energy put into it.) Furthermore, there is now a good understanding of how and where rolling resistance is generated.
This has given new impetus to the search for design ideas to minimize rolling resistance, from tire construction through design and compounding.
Nevertheless, at least two speakers pointed out that an efficient driving style will do more to save fuel than any amount of technology in the tire.
Bruno Cena, from automaker Fiat's technical center in Turin, said the current generation of low rolling resistance tires is very good for long, straight runs, but less beneficial at saving fuel when driving at the speed limit on winding roads, or when the driver makes many tight, low-speed turns.
Frank Philpot of Goodyear's Luxembourg Technical Center listed a number of ways of reducing fuel consumption by 2 percent, including a speed reduction of about 2 mph, or reducing the number of times a car stops from about 55 mph, as at traffic lights. Another way is reducing rolling resistance by 10 percent.
Tires traditionally have been developed by trial and error, he said, but it is now vital to be able to access the experience built up over the years. For this reason, he said data retrieval systems in tire making are more important now than they have ever been.
He also said finite element modeling of tire behavior is invaluable in developing new tires with low rolling resistance, or for optimizing other properties.
The tread area still dissipates the most energy, Mr. Philpot said, and hysteresis cannot be eliminated completely from this area, because most tires rely on some degree of hysteresis to create wet grip. However, he said that work on other parts of the tire is not wasted. The apex, for example, dissipates the most energy per unit volume.
One example of the analysis of tire elements to improve rolling resistance was given by Tatsuhiko Kanegawa of Bridgestone Corp., who presented the tire maker's Grand Unified Theory of the Tire (GUTT). It follows previous carcass shape theories developed by other Bridgestone engineers.
The concept relies on some serious number crunching by a new Bridgestone computer.
In one analysis the engineers sought to maximize tension in the reinforcement fibers closest to the bead, in order to reduce rolling resistance. The resulting profile was unexpected because it did not follow a ``natural'' contour.
This new profile shape, together with other developments-including new types of carbon black and bead geometry-are currently being used in production tires sold in Japan.
Bridgestone claims its LL carbon black is longer than it is wide, with an aspect ratio of about 1.5:1. Critics say the shape is broken down during mixing and handling, offering no benefits over ordinary carbon.
Presenting an alternative view on tire development-especially from the noise point of view-was Guy Descornet of Belgium's Road Research Institute.
He highlighted the importance that ``megatexture''-which refers to road surface irregularities-has on tire noise and overall wear.
Large megatexture features in roads are bad, he con-cluded, because they result in increases in rolling resistance, vibrations, tire noise and noise within vehicles.