ALTHOUGH many tire manufacturers are claiming that synthetic tires are better than natural rubber ones, Mr. Drew believes this is too much to expect. He feels that production of synthetic tires 85 to 90% as good as those made of natural rubber would be a scientific achievement of the first rank.
The reason for the limitations in the use of present-day synthetic material is that the material as certain deficiencies. The chief faults of GRS Government synthetic are:
It develops too much heat when flexed.
It loses extensibility when hot.
It has low fear resistance when hot.
The development of excessive heat in flexing is due to a high hysteresis loss, which is not critical in articles having a low flex or that are thin-walled, and therefore have a low angle of flex, but in heavy articles such as truck tires, it is one of the biggest deficiencies. Present high-speed trucks and buses tax natural rubber to its full extent, and any additional heat build-up creates more heat in the tire, which greatly reduces the strength of the cotton carcass. One way to alleviate the problem is to substitute rayon or nylon cord for the usual cotton.
Low tear resistance of the material when hot is also a factor that is causing a lot of trouble in test runs. When the tires are hot, they tend to cut and crack easily - these cuts and cracks having a bad tendency to grow.