When working with a hydraulic truck crane, you cannot rely on its tires to keep the vehicle and the load completely stable during the lifting operation. The truck employs four outriggers that act as balances and serve to keep the crane from leaning too much to one side or the other. However, it is a common mistake to assume that the weight of a load on a crane will be equally distributed across all four pads. You need to calculate the potential force that will be exerted on one pad before deciding whether or not it is safe to perform the lift.
Add the weight of the crane itself to the weight of the load you are attempting to lift to get the total weight that will be pushing down on the outrigger pads. It doesn't matter if you are using the metric or English standard systems.
Multiply the square of the radius of one of the outrigger pads by pi to obtain its surface area. The radius of the pad is equal to half of its diameter. Be sure to use the same system of measurement, metric or English standard, that you used in Step 1.
Divide the total weight calculated in Step 1 by the surface area calculated in Step 2 to obtain the total potential load that will be exerted on one of the outrigger pads, either in pounds or kilograms. If your crane is not rated to handle this amount or more, it is not safe to perform the lift.