What is meant by "brake lag" in an air brake system?

"Brake lag" refers specifically to the delay in air travel through the brake system after the driver initiates a braking action. When the driver presses the brake pedal, air must travel from the compressor through various components, such as hoses and valves, before it reaches the brake chambers. This journey can take a measurable amount of time, resulting in a slight delay between the application of the brake pedal and the actual engagement of the brakes on the wheels.

Understanding brake lag is critical for safe driving, especially in heavy vehicles like trucks and buses that utilize air brakes, as the delay can affect stopping distances and overall vehicle control. It emphasizes the importance of allowing for this lag when making decisions about stopping distance, particularly in emergency situations.