A numerical methodology for designing observer feedback gains based on local linearization was proposed to make employing tire models with a higher accuracy and more complicated expressions become possible. The proposed methodology was implemented by discretization of the nonlinear system in the state space and calculation of the feedback gains at a certain given number of operating points using numerical approaches. The gains at discretized operating points were fitted to the expressions with respect to state variables to facilitate realtime observation and implementations. The effectiveness and parameter variation robustness of the proposed methodology were evaluated in a highfidelity vehicle dynamics simulation environment, and the simulation results show that the proposed methodology has a high estimation accuracy and good robustness.