The braking power of the spring brakes depends on:

The braking power of the spring brakes is indeed dependent on the service brakes being in proper adjustment. Spring brakes are designed to engage when air pressure in the system drops below a certain level, effectively applying the brakes until air pressure is restored. However, for spring brakes to function effectively, the service brakes must be correctly adjusted. If the service brakes are out of alignment or not functioning optimally, the spring brakes may not engage as intended or may not provide adequate braking force, greatly affecting the overall braking system's performance.

In contrast, while factors like the driver's reaction time, tire air pressure, and load weight may influence the overall braking effectiveness, they do not directly affect the braking power of the spring brakes themselves. The adjustment of the service brakes ensures that the system can operate efficiently, making this aspect crucial to the proper functioning of spring brakes during a stop.