Inflation Dynamics

Earthmoving tyres are designed to carry a specific load at a specific inflation pressure when mounted on a specific width rim. When these conditions are met, the deflection of the tyre carcass is in the optimum range and maximum tyre performance can be expected. If the combinations of these design dynamics are altered for any reason, tyre performance is reduced.

Inflation pressures should be checked Daily. Recommended inflation pressures based on total load on tyres should be used. For accurate inflation, use a special low-pressure gauge with 10 kPa graduations. Gauges should be checked occasionally for accuracy. Always use sealing valve caps to prevent loss of air.

A special inflation gauge is available for testing tyres filled with water or calcium chloride solutions. (If a stainless steel gauge has not been utilised, be sure to wash out the gauge with clear water after using on tyres filled with calcium chloride.)

To determine the true operating pressure for a liquid filled tyre. the valve should be at the top of the tyre. Tyres filled with water or air-and-water should be tested when the tyres are cold, since the pressure rises somewhat as the fluid increases in temperature. A tyre that has sufficient pressure when it is hot may be under-inflated when it cools down.

Tyre overload and inflation

Tyre overload or under-inflation have the same effect of over-deflecting the tyre. Under such conditions the tread on the tyre will wear rapidly and unevenly, particularly in the shoulder area. Radial cracking in the upper sidewall area will be a problem.

With under-inflated drive tyres in high torque applications, sidewall buckles will develop, leading to carcass breaks in the sidewall.

While an under-inflated drive tyre may pull better in some soil conditions, this is not generally true and not worth the high risk of tyre damage that such an operation invites.

Over inflation

Over-inflation results in an under-deflected tyre carcass. The tread is more rounded, concentrating tread wear in the centreline area. Traction is reduced in high torque service because ground contact of the tread shoulder area is reduced and the harder carcass - with reduced flexing characteristics - does not work as efficiently.

In addition, the tightly stretched over-inflated carcass is more subject to weather checking and impact break damage.

More tyres go out of service prematurely from under-inflation than for any other reason.

Continuous buckling or folding causes cord separation and a series of breaks in the sidewall area. It also causes a series of cracks at the edges of the bars. Sometimes the cracks may extend into the sidewall. Inflation pressure checks are particularly important on hydro-inflated tyres because the air volume is relatively small, and any air loss results in a much greater decrease in pressure than when the tyre is inflated with air only.