Ensuring the safety of passengers is one of the prime challenges for vehicle design engineers. The braking system is the most important safety feature incorporated in a vehicle. Most of the commercial vehicles such as trucks, buses, etc., are equipped with an air brake system. The air brake system is sensitive to maintenance and needs to be monitored regularly to ensure its proper functioning. Current monitoring methods of air brake systems are predominantly manual in nature and can be performed only when the vehicle is stationary. One of the most important parameters that are critical for the proper functioning of an air brake system is the push rod stroke. The push rod stroke is related to the clearance between the brake pad/shoe and the brake drum and hence is indicative of brake wear. The objective of this research work is to study the mechanical subsystem of the air brake system and develop a mathematical model for the same. This model will correlate the push rod stroke and the clearance between the brake pad/shoe and the brake drum. This model will ultimately be useful for providing a warning in case of excessive brake wear and helpful in avoiding a degradation in the performance of the brake system thus increasing the safety of the vehicle. This model will also be useful for studying the response of a commercial vehicle during braking. An experimental setup has been developed and data collected from the same are used to corroborate this mathematical model. © Copyright 2009 SAE International.