Pneumatic tyres release 10-15 kPa of air pressure every month requires regular topping up. Vehicles run with improper tyre pressure has been identified as one of the primary factors which leads into major and catastrophic road accidents due to puncture and explosion. The main aim of this research work is to design a pressure chamber for an Automatic Tyre Inflating System (ATIS) to replenish the pressure loss of a pneumatic tyre. In this paper, a model has been developed to mathematically derive the critical amount of required pressurized air for ATIS intermediary chamber design. Finite element analysis was also performed onto the designed chamber considering critical engineering elements to ensure safe operation with the pressure of 8449kPa. ATIS is postulated to automatically replenish adequate amount of pressurised air into the tyre when the tyre pressure drops 10% below the desired pressure. Thus, the air loss from the tyre can be continuously compensated for 12 months to have them running with safe pressure at all time without having human intervention to inflate them.