A high-precision steady state tire model is critical in the tire and vehicle matching research. For the moment, the popular Magic Formula model is an empirical model, which requires the pure and combined test data to identify the model parameters. Although MTS Flat-trac is an efficient tire test rig, the long test period and high test cost of a complete tire model tests for handling are yet to be solved. Therefore, it is necessary to explore a high accuracy method for predicting tire complex mechanical properties with as few test data as possible. In this study, a method for predicting tire combined slip characteristics from pure cornering and pure longitudinal test data has been investigated, and verified by comparing with the test data. Firstly, the prediction theory of UniTire model is introduced, and the formula for predicting combined slip characteristics based on constant friction coefficient is derived. Secondly, three different sizes of tires were tested for force and moment, and then the combined slip characteristics were predicted through the proposed method, and the prediction accuracy was calculated as well. Finally, the prediction accuracy was compared and analyzed among UniTire, Similarity and Combinator models, which further proved the validity of the prediction method proposed in this study.