What happens during downshifting when climbing a hill?

When a vehicle is climbing a hill and downshifting occurs, the transmission shifts to a lower gear, which increases the engine's power output. This process is essential because climbing an incline requires more torque to overcome gravitational forces. By downshifting, the engine can operate at a higher RPM, allowing it to produce more power and maintain momentum.

This technique ensures that the engine remains within its optimal power band, which is crucial for effective performance under load. As the transmission engages a lower gear, the vehicle becomes more capable of handling the incline, making it easier to ascend without losing speed.

The other choices do not accurately describe the effects of downshifting. For instance, increased resistance would not aid in climbing, and a sharp decrease in engine RPM would negatively impact power delivery. Additionally, stalling is typically a result of engine failure to produce enough torque, which downshifting could help prevent in such situations.