Colloidal suspensions exhibit a transition from shear-thinning to shear-thickening behavior as the shear rate increases. Despite all the experimental and computational studies, an understanding of the structure of suspensions in different flow regimes remains controversial. In this work, a dissipative particle dynamics model was employed to perform a comprehensive study of the rheological and morphological behaviors of monodisperse and bimodal suspensions over a wide range of shear rates. The interplay between rheology and structure indicates that hydroclusters are formed in the shear-thickening regime, whereas interparticle interaction is responsible for the shear-thinning response at low stresses. The effect of particle size, ratio, and combination in bimodal systems have also been investigated and quantitative agreement with existing experimental data was found. Thus, it was possible for the first time to perform a comprehensive study on different aspects of the bimodal dispersions and correlate the macroscopic behavior with the microstructure in different flow regimes.