Pneumatic brake system is widely used in heavy truck, medium and heavy buses for its great superiority and braking performance over other brake systems. Pneumatic brake system consists of various valves such as Dual Brake Valve (DBV), Quick release Valve (QRV), Relay Valve (RV), Brake chambers. Dynamics of each valve is playing a crucial role in overall dynamic performance of the braking system. However, it is very difficult to find the contribution of each valve and pipe diameters in overall braking performance. Hence, it is very difficult to arrive a best combination for targeted braking performance as it is not possible to evaluate all combination on the actual vehicle. Hence, it is very important to have a mathematical model to optimize and evaluate the overall braking performance in early design phase.The present study is focusing on the mathematical model of a pneumatic brake circuit. The present model can be used in the design stage to finalize and optimize the Pneumatic brake system specifications. The vehicle level mathematical model has been created after validating component level model of each valves and system level model of brake system. The objective was to minimize cost as well as maximize the braking performance requirement as per IS11852 subjected to constraint such as pipe diameter, and difference between rise rate of pressure in the front and rear brake chambers. The results predicted by mathematical model was in very good correlation with the experimental results. Hence, the present mathematical model is used to freeze the braking system specification in the design phase itself.