Manufacturers' Published Gradeability Specifications
The manufacturers' gradeability specifications which are published in specifications sheets and sales literature are engineering specifications which are a measure of the mechanical efficiency of the power train components under ideal conditions and often have nothing to do with safe forklift truck operation or how a user can expect the vehicle to perform under normal operating conditons.
Maximum gradeability is often a calculated value based on the efficiency of transfer of power from the engine or drive motor(s) to the drive wheels, and assumes a maximum coefficent of friction between the drive tires and the travel surface.
It is not unusual to see published gradeability for engine and electric powered trucks to be between 20% and 40%.
Trucks loaded to capacity have the higher gradeability numbers.
However, very few trucks could climb or descend grades as steep as 20% to 40% safely in normal operating conditiions.
A grade that exceeds 10% should be considered hazardous and should not be attempted unless surface conditions are ideal and the operator is experienced. We do not recommend using lift trucks on any grade that exceeds 15%.
The danger is that, on slopes or ramps that exceed 15% of grade, there is a greater likelihood that when ascending or descending, the unit may break traction and start wheel spinning when going up or sliding when going down.
Once a truck starts to slide, there is a very high possibility that it will not slide down the hill in a straight line and in a good laterally level condition. In many or most cases, during a slide, the truck will slide sideways and if this happens, there is a very high probability of a lateral tipover.
In order to insure safe operation and avoid the possibility of a lateral tip over accident, do not attempt to travel on any surface that has a grade that is greater than 15%, and follow the rules for direction of travel on ramps and sloped surfaces for your vehicle. Specific rules are in place for forklift trucks (Powered Industrial Trucks) when they must travel on ramps or sloped surfaces. Consult the operator's manual for the vehicle and your safety training provider for these important operating procedures.
Remember, the manufacturers' published gradeability specifications should be considered to be engineering specifications or laboratory results based on ideal conditions representing drive train efficiency and NOT actual vehicle performance in usual or customary conditions found in most user applications. They are engineering specifications which have very little or nothing to do with safe operation in normal conditions found in the workplace.