It is well known that as the weight of some automobile subsystems is reduced, there is the potential for further reduction in total weight. In preparing an estimate of automobile fuel economy in the post-1985 period, it became necessary to estimate approximate overall weight propagation factors suitable for such an analysis. The derivation of the factors is based on separating total automobile weight into weight sensitive and weight insensitive parts, and developing regression equations for the weight sensitive part. The data used to develop the regression equations were taken from the literature on weight propagation, and from National Highway Traffic Safety Administration (NHTSA) sponsored vehicle teardown studies. Two factors were determined, one for a totally new vehicle, and another for upgrading an existing design.