What critical vehicle factor is important for effective downhill braking?

Effective downhill braking is particularly dependent on the selection of the appropriate transmission gear for engine braking. When descending a hill, utilizing engine braking allows the driver to control the vehicle's speed more effectively by engaging the engine's resistance to assist in slowing down the vehicle. This type of braking relies on the engine's compression to reduce speed, helping to avoid overheating and excessive wear on the vehicle's brake system.

While proper steering alignment, tire pressure levels, and air brake system checks are all important factors in vehicle safety and performance, they do not directly contribute to the critical aspect of controlling speed during a downhill descent. Correct gear selection plays a pivotal role in managing the vehicle's momentum on inclines, making it central to the effectiveness of downhill braking.