The evaluation of commercial vehicle brake system balance is a complex analytical task. Tractor-trailer combinations frequently include different brake designs on different axles, which have widely varying characteristics. In addition, variations in brake parameters such as pressure, response times, linings, and heat transfer under various operating conditions add to the complexity of analyzing the brake system. This paper describes a mathematical model of the vehicle brake system and a program for a digital computer to solve the mathematical expressions. Using the computer to simulate dynamic brake system operation, current designs can be evaluated rapidly for effectiveness and possible improvement, and future designs can be analyzed prior to expensive prototype fabrication.