This paper presents a generalization of previous works developed by the authors in the field of the calculation and selection of slewing bearings, where a theoretical model for the estimation of the static load-carrying capacity of four-contact-point slewing bearings was obtained. Those previous works assumed that there was no preload in the balls; in the present work, the model has been improved in order to consider the effect of the preload, in such a way that it provides more realistic results because this type of bearings are preloaded in several applications to increase the stiffness and therefore the accuracy of the system. In parallel, and for comparison purposes, the finite element model built by the authors in previous works has been also adapted to include the preload in the balls. Both models, theoretical and FE, assess in complete agreement the increase of the stiffness with the preload level; the results show that the static load-carrying capacity does not vary appreciably with the usual values adopted for the preload. Copyright © 2013 John Wiley & Sons, Ltd.