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Downshifting before starting down a hill and before entering a curve is essential for maintaining control and stability of the vehicle. When approaching a hill, downshifting helps to use engine braking, which reduces reliance on the brake system and prevents overheating and potential brake failure. This technique also keeps the vehicle at a safe speed, allowing for better control when descending.

Similarly, when entering a curve, downshifting lowers your speed, allowing for smoother handling of the turn. It helps in maintaining traction and balance, particularly in a large vehicle, which might be less agile than smaller cars. This practice enhances safety by ensuring you have the right gear to accelerate post-curve without a sudden need to downshift, which could lead to loss of control.

This strategy is part of safe driving practices that are critical for managing the unique characteristics of heavy vehicles and their handling on various terrains.