Factors Affecting Tyre Kilometerage

Pressure

It must be kept in mind that the pressures recommended by the manufacturer refer to a cold tyre, i.e. with an overage temperature of 20º C. An increase in pressure will result from heat generated by sidewall flexing, excessive brake use, abrasive road surfaces and carcass stress. The diagram, based on experimental data, illustrates the relationship between pressure and kilometerage. Also shown are the effects of a 20% alteration in normal pressure - a pressure increase will take 10% off tyre kilometerage, while a pressure decrease will decrease the life of the tyre by 15%. It is clear that damage results more from under-inflation than over-inflation.

Speed

Average driving speed affects the tyre the most. As heat inside the tyre increases, so the tyre itself becomes hotter and the effect is to add to a general weakening of the carcass. Such are the stresses on a carcass that to increase average driving speed from 70km/h to 110km/h will reduce the life of the tyre by half. For the record, tyre life is very greatly reduced by running at high speed on poor road surfaces.

Tyre load

The specified service load should never be exceeded. Excess load causes increased carcass flexing which in turn increases tyre temperature and consequently pressure. Experimental data shows that a 20% overload will reduce tyre life by 30%.

Temperature

External factors such as moisture and temperature have a recognized influence on tyre life. Running a tyre at a low temperature will greatly reduce the possibility of heat build-up and con-sequentially carcass stress. Contact with water will also lower tyre temperature.