Gradeability

Gradeability refers to a vehicle’s ability to ascend inclined slopes while under load. In automotive and heavy equipment contexts, it is typically defined as the maximum grade (expressed as a percentage) that the vehicle can maintain at a prescribed speed in a specified gear, given engine torque, transmission, wheel radius, and vehicle weight.

The calculation of gradeability follows a simple energy-balance idea. At a steady climb, the required tractive force is the weight on grade (W) multiplied by the grade (W × grade). The available tractive force at the driven wheels is F = (torque × gear_ratio × efficiency) / wheel_radius. Gradeability (%) is often expressed as (F / W) × 100. This is a simplified model that neglects factors such as rolling resistance, aerodynamic drag, and variations in torque with RPM, but it captures the essential relationship between available traction and load.

Several factors influence gradeability. Engine torque curve and maximum power, transmission and final-drive ratios, and wheel radius determine how much force can be delivered at the wheels. Vehicle weight, payload, and rolling resistance affect the load to be overcome. Tire grip, road surface conditions, and braking requirements also play roles, particularly at higher speeds or with heavier loads.

Applications and limitations. Gradeability is used to assess tractors, trucks, forklifts, and construction machinery for suitability on planned routes and workloads. Because gradeability depends on speed, gear, and traction, it is not a fixed property and must be specified for the intended operating conditions.