This work reports the different steps of a frequency decomposition method applied for fatigue lifetime assessment. The studied loadings are multiaxial time series measured at the vehicle wheel. The proposed decomposition presupposes that the loading results from both dynamic vehicle effects at low frequencies (Driven Road loadings) and random loads at high frequencies (Random Road loadings). This signal partition has two assets for fatigue purposes. First, the spectral methods can be applied to the Random effects. Two spectral damage formulations are tested in this paper. Then, the Driven Road loadings, related to the vehicle manoeuvre, enables to implement the Rainflow counting method on only one time series instead of the initial set of six per wheel, or twelve per axle. The implemented approach illustrated on a braking manoeuvre is validated, comparing the damage summation of the Random and Driven Road loadings with the one based on the usual Rainflow counting method applied to the overall time series.