Liquid droplets impinging onto heated and dry unheated surfaces have been the subject of experimental and numerical investigations in various fields. Experimental studies have not provided sufficient quantitative data for the proper validation of numerical studies. Moreover, experimental efforts have focused on droplets impinging onto unheated surfaces rather than heated surfaces, for which reports are very scarce. This study investigated two marginally distinct regimes of droplet-surface interactions: droplets impacting onto a sapphire glass surface that was unheated or heated above the Leidenfrost temperature with moderate Weber numbers. Radial spreading velocities were measured with a high spatiotemporal resolution inside the expanding liquid lamella by using time-resolved particle image velocimetry (PIV). The obtained data were analyzed to compare the two cases and obtain insights about the existing mechanisms. The differences in spreading mechanisms were analyzed by using the radial velocity profiles. The profiles demonstrated similar characteristics and had linear and nonlinear parts simultaneously. The nonlinearity in the outermost radial positions originated from vortical upward flow motions. For the impacts on the heated surface, the maximum nondimensional spreading velocity detected was less than that on the unheated surface. For both cases, the velocity profiles in the inner radial positions showed good agreement with quasi-one-dimensional theory.