Commercial vehicle brake simulations must include non-linear and/or transient conditions. But to the user they must also be competitive tools. One simulation which appears to adequately model these conditions is discussed from a user's point of view where economic restraints place additional burden on the simulation beyond just modeling vehicle performance. The aspects of input definition, verification, confidence in results and acceptance criteria are considered as they affect the definition of whether the simulation “works” or not. Recommendations are made which should lead to a more commercially useful tool. The basic factors defined are applicable to other vehicle simulations.