In this study the side airbag design for a large car was investigated. The assessment of the airbag efficacy was based on the TTI response of the SID. In general, large size cars have low TTI values to begin with due to their higher mass, stronger structure, and more spacing between the occupant and the door. The CALOPT optimization program was used to search the design space. We found that for this particular impact environment an airbag design with a high mass flow rate and a large vent resulted in the lowest TTI for the SID. The high mass flow rate enables the airbag to contact the dummy thorax early, which causes the dummy to begin to move away from the door before contact is established with the door. The large vent is necessary to avoid excessive force from the airbag during the dummy/airbag interaction. For the two inflators considered in this study it was found that the less aggressive inflator achieved a marginal reduction of 10% from the baseline TTI response. On the other hand, the more aggressive inflator achieved a reduction of 26% from the baseline TTI response. Compared to the over 40% TTI reduction reported in our previous studies for small size cars, side airbags seem less effective in a large size car than in a small size car for the impact condition and injury criteria considered in this study. Finally, it should be pointed out that a more complete assessment of side airbag efficacy should include responses of deflection-based injury criteria for the thorax, and utilize a more biofidelic test dummy model.