In general, the FIALA tire model is valid on smooth roads only.  Furthermore it does not produce accurate results in full vehicles undergoing events that include zero velocity (parking), transients, high camber values, or combined slip (braking/acceleration during cornering).  It can be used as a first approximation, or when accurate tire Magic Formula coefficients are not available, because the FIALA tire property file coefficients can be modified manually and do not require fitting routines of test data.

References

Ref[1] - Fiala, E. (1954): Seitenkräfte am rollenden Luftreifen. VDI Zeitschrift, 96, 1954.

Ref [2] - Pacejka, Hans, B., Tire and Vehicle Dynamics.