The effectiveness of computer simulation modeling for product development support is evidenced by its wide-spread usage. For example, finite element analysis (FEA), has been found indispensable for reducing product development cycle time and cost as well as enhancing product quality. Along with other pertinent information, accurately defined loads are necessary for conducting effective FEA for product design optimizations. FEA results using rough estimated loads often do not provide a good basis for design improvement. A better approach is to define loads through system simulation modeling. The development of such a model involves the synthesis of a wide range of product design knowledge along with a systematic process for model correlation. As the technology becomes matured, there is a strong drive to make the process more efficient by integrating the different types of simulation techniques. Two examples are given in this paper. The first one is the prediction of fatigue life of powertrain components for product sizing and structure optimization. Here the load spectrum and stress is defined by vehicle system simulation and component structure models. In the second example, several models are used to design an off-highway vehicle transmission housing in order to reduce noise. These models include gear tooth contact, shaft bearing system dynamics, FFT analysis, FEA structural dynamics, and acoustic analysis. Simulation modeling technology integration is a team project. Management issues, as well as technical issues, need to be addressed for its success. Some management issues are building a cross-functional team, selecting compatible software and hardware, streamlining and validating the process, and experience captivity.