Seated posture inside a vehicle influences driver performance and control of a vehicle. Many vehicles do not properly allow for a natural seated posture for all drivers. Some vehicles are difficult to drive due to the fact that the driver is inadequately accommodated in the driver seat. For people of extreme stature, tall or short, and for people of extreme width, obese or pregnant populations, it can be difficult to safely operate a vehicle if there is not enough room in the cab or if some controls cannot be reached. This paper employs digital human models to study the effect of obesity on seated posture inside a vehicle. Eight digital human models, four non-obese and four obese, are subjected to reach tests inside a virtual vehicle cab. These tests are used to determine how obesity affects the clearance between the steering wheel and driver body and whether additional factors contribute to discomfort associated with obese people seated inside a vehicle. In order to model the obese subjects, factors such as increased waist circumference and limited joint range of motion due to obesity are included in the simulations. Also given is an indication of discomfort level through the output values of the multi-objective function in the optimization formulation. The benefit of using this method is that the human aspect of design can be included early in the design process, reducing or eliminating prototypes. If adjustments to the layout of the vehicle cab are needed the resulting postural differences can be quickly observed.