In this study, a Schulze Ring Shear Tester and the Discrete Element Method (DEM) are employed to investigate the effect of polydispersity on the binary shear flows. Both experimental results and DEM simulations show that the pre-shear stresses are greater for binary blends than for monodispersed particles. The flowability of these mixtures is strongly affected by the solid fraction, with minimal flow function values correlating to maximum packing fraction. However, minimum flow function values are not observed at the same packing fractions where the maximum pre-shear stress occurs. The powder friction has a slightly higher contribution to powder strength than powder adhesion, and the frictional component follows the same trend as shear stress with mixture composition. Using DEM, it is demonstrated that the addition of small adhesive particles reduces the averaged angular velocity of the larger particles, which makes a contribution to the larger shear stress for binary blends.