If a vehicle drives over a gradient, a force of resistance acts on the vehicle, the force of climbing resistance. The weight force Fz resolves itself into the following components:
Component in the normal direction: FZ·cos αst
Component parallel to the gradient: FZ·sin αst

At small angles:sin αst ≈ p
Force of climbing resistance: Fst = FZ·sin αst≈ FZ·p